Salish Sucker (Catostomus sp. cf. catostomus): COSEWIC assessment and status report 2024

Official title: COSEWIC assessment and status report on the Salish Sucker (Catostomus sp. cf. catostomus) in Canada

Committee on the status of Endangered Wildlife in Canada (COSEWIC)

Endangered

2024

COSEWIC assessment summary

Assessment summary - May 2024

Common name

Salish Sucker

Scientific name

Catostomus sp. cf. catostomus

Status

Endangered

Reason for designation

This small fish has a restricted range in southwestern British Columbia. It is susceptible to continuing decline in amount and quality of habitat due to reduced stream flow, pollution, and decreasing oxygen content of the water as a result of increased stream temperature and high nutrient loading. These threats are expected to worsen due to climate change-induced extreme heat and drought events. Moreover, invasive species that prey upon this fish or modify its habitat are also contributing to population declines. Ongoing declines in several streams, in spite of habitat restoration efforts, and projected future declines resulted in the change in status. If these threats cannot be mitigated, they could lead to the extirpation of this species.

Occurrence

British Columbia

Status history

Designated Endangered in April 1986. Status re-examined and confirmed in November 2002. Status re-examined and designated Threatened in November 2012. Status re-examined and designated Endangered in May 2024.

COSEWIC executive summary

Salish Sucker

Catostomus sp. cf. catostomus

Wildlife species description and significance

Salish Sucker is a genetically distinct dwarf form of Longnose Sucker (Catostomus catostomus). It is a member of a unique fish community that survived continental glaciation in an ice-free refuge in Washington State and is of scientific interest in the study of evolution and glacial history.

Aboriginal (Indigenous) traditional knowledge

All species are significant and are interconnected and interrelated. There is no species-specific Aboriginal Traditional Knowledge (ATK) in the report other than the Halq'emeylem name for Salish Sucker, Skwímeth, which translates as “many red markings.”

Distribution

Salish Sucker are documented from the Fraser, Nooksack, and Little Campbell drainages in the Lower Fraser River Valley of British Columbia and from an additional 6 watersheds in western Washington State. Within Canada, 15 subpopulations in 13 watersheds are documented.

Habitat

In British Columbia, Salish Sucker are found in small lowland streams and sloughs, especially headwater marshes and beaver ponds. Adults and yearlings prefer large pools or ponds (> 50 m length) deeper than 70 cm with abundant logs/stumps or aquatic vegetation for cover. They typically spawn in flowing shallow water (up to 50 cm/s) over gravel or cobble bottoms. First-summer juveniles prefer shallower pools and ponds with abundant cover. In winter, Salish Sucker seek quiet water with deep cover and may move more than 1.7 km off the main channel into tributaries and ditches that are dry in summer.

Biology

Salish Sucker live for up to 5 years and mature at 2 years, with generation time estimated at 3 years. The species spawns between April and early July, and the small, adhesive eggs are broadcast over gravel or cobble and fertilized in the water. No nest is constructed. An average female contains about 3,000 eggs and may spawn twice per year, maturing one ovary at a time.

They are most active around dawn and dusk. Summer home range averages approximately 175 m of channel, but fish may undertake longer migrations of more than 1 km to access spawning sites. During the day, they typically retreat to resting sites, often in thick vegetation off the main channel. They tend to return to the same resting site on successive days. Salish Sucker eat a variety of aquatic invertebrates. Salish Sucker are active at temperatures as low as 7^oC but are most active between 12^oC and 20^oC. They are rarely found in water warmer than 20^oC. They are captured less frequently where water contains less than 4 mg/L dissolved oxygen, and growth is reduced at levels lower than 3 mg/L.

The combination of small body size, rapid maturation, and high number of eggs relative to body size facilitates rapid population growth, quick positive response to habitat enhancement, and rapid recovery from occasional population losses.

Population sizes and trends

Individual subpopulations range in size from well below 100 adults to the low thousands. Most subpopulations have been estimated once or twice using mark-recapture methods, but for several subpopulations, too few fish have been caught to allow a quantitative estimate. The total Canadian population is currently estimated to be between 4,200 and 11,600 adults, but it is unlikely to exceed 6,700.

Salish Sucker abundance in Canada has declined by an estimated 34%–46% over the past decade. One subpopulation, Agassiz Slough, has likely been extirpated, and several more (Sqemélwelh Creek, Mountain Slough, Hope Slough) are believed to be very close to extirpation. Several other subpopulations, in Bertrand Creek, Salmon River, and Pepin Creek, have undergone extreme declines (> 75%) over the same period. Historical (20th century) declines associated with the draining of Sumas Lake, construction of dikes, channelizing of streams, and draining of wetlands were likely much larger even than these recent declines in terms of number of individuals.

Threats

The overall threat level to Salish Sucker is considered Very high. The most pressing threats are pollution, primarily from agricultural nutrients, and habitat drying during drought exacerbated by climate change. Toxic substances in stormwater impact habitats in urban areas and in areas adjacent to major roads. Annual dredging for flood control on agricultural lands affects a large portion of occupied habitat, reducing habitat complexity and sometimes spawning riffles. Additional authorized and illegal modifications to habitat occur annually. Gravel mining occurs in three watersheds, elevating the risk of large-scale sediment releases into habitat, as has occurred several times historically. The hundreds of road and rail crossings on occupied habitat present an ongoing threat of spills. Invasive aquatic and riparian plants degrade key habitats, while several introduced fish and amphibian species may elevate predation risk.

Protection, status, and recovery activities

Salish Sucker is listed as Threatened under Schedule 1 of the federal Species at Risk Act (SARA), which protects individuals and critical habitat identified in the SARA recovery strategy. Approximately 42.1 of 196.5 km of habitat identified as critical under SARA flows through protected areas held by the federal, provincial, or municipal governments. The remainder is on private lands. Salish Sucker is Red-listed in British Columbia. The species was assigned a global conservation status of Critically Imperilled (G1) by NatureServe, along with a national status of Imperilled (N2) in both the U.S. and Canada. It is ranked as ranked as Critically Imperilled (S1) in both British Columbia and Washington State. The American Fisheries Society lists Salish Sucker as Endangered. The International Union for the Conservation of Nature (IUCN) Red List does not currently include Salish Sucker. It was listed as Endangered in 1990 and 1994, but not subsequently. Recovery activities include ongoing population monitoring, surveys for undocumented subpopulations, habitat mapping, research on hypoxia impacts, and development and monitoring of numerous habitat enhancement projects.

Technical summary

Catostomus sp. cf. catostomus

Salish Sucker

Meunier de Salish

Skwímeth (Halq'emeylem)

Range of occurrence in Canada: British Columbia

Demographic information:

Generation time (usually average age of parents in the population)

Approximately 3 years

Based on IUCN method

Is there an [observed, estimated, inferred, or projected] continuing decline in number of mature individuals?

Yes

Estimated based on catch per unit effort (CPUE) and mark-recapture data.

[Observed, estimated, or projected] percent of continuing decline in total number of mature individuals within 3 years [or 1 generation; whichever is longer up to a maximum of 100 years]

Unknown

Significant decline in some subpopulations, but data not available over this time frame.

Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations, whichever is longer up to a maximum of 100 years]

Unknown

Significant decline in some subpopulations, but data not available over this time frame.

[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last 10 years [or 3 generations; whichever is longer]

34%–46% reduction over last 10 years

Estimated from changes in mark-recapture Abundance estimates and catch per unit effort available from 9 of 15 subpopulations using an abundance-weighted change method (45.8%) and IUCN method (34.3%) that standardized declines to a 10-year period (see Table 6).

[Projected, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations, up to a maximum of 100 years]

>50% reduction over next 10 years

Inferred based on worsening primary threats, although with high uncertainty due to non-linearity of main threat impacts.

[Observed, estimated, inferred, projected, or suspected] percent [reduction or increase] in total number of mature individuals over any period [10 years, or 3 generations; whichever is longer, up to a maximum of 100 years], including both the past and the future.

>50% reduction over a 10 year-period including past and future

Estimated. Rate of decline has increased rapidly over time (non-linear) in response to hypoxia and temperature tolerance limits being exceeded.

Are the causes of the decline clearly reversible?

Perhaps

The primary threat is agricultural nutrient loading, which may be mitigated by changes in legislation/policy. The main watershed in which this species is located (Fraser) is surrounded by significant urban and agricultural development, making such reversals challenging. Climate change impacts could be mitigated by habitat restoration (primarily riparian) and maintenance of minimum in-stream flows.

Are the causes of the decline clearly understood?

Yes

Severe hypoxia driven by agricultural nutrient loading and habitat dewatering in severe drought are dominant causes.

Are the causes of the decline clearly ceased?

No

Current policy allows for continued increases to nutrient loading. Climate change driven drought and heat are expected to worsen.

Are there extreme fluctuations in number of mature individuals

No

Extreme declines have occurred in multiple watersheds, but these are due to anthropogenic impacts. High recruitment years have also (rarely) been observed following habitat restoration, but in general, recovery of numbers following a crash has not occurred.

Extent and occupancy information:

Estimated extent of occurrence (EOO)

1,401 km²

Calculated based on minimum convex polygon around known occurrences in extant subpopulations.

Index of area of occupancy (IAO), reported as 2x2-km grid value

252 km²

Reduced from 260 km² in 2012 status report due to apparent extirpation from Agassiz Slough and parts of Bertrand and Salmon River. Calculated using 2 x 2 km grid but, given that this includes large areas with no evidence of Salish Sucker and stream habitats are typically only a few metres wide, actual area of occupancy is highly unlikely to exceed 1 km².

Is the population “severely fragmented”, that is, is >50% of individuals or >50% of the total area “occupied” (as a proxy for number of individuals) in habitat patches that are both (a) smaller than required to support a viable subpopulation, and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse?

1. No
2. No

Number of “locations”

One per occupied watershed (13 – Agassiz)

12

Main threats are nutrient pollution/hypoxia, habitat dewatering, and heat acting at the watershed level. Although climate change-induced events could potentially act simultaneously on multiple watersheds, even neighbouring watersheds often differ in ways that affect their vulnerability to threats.

Is there an [observed, inferred, or projected] continuing decline in extent of occurrence?

No

Extent of occurrence unaffected by suspected extirpation.

Is there an [observed, inferred, or projected] continuing decline in index of area of occupancy?

Yes

Inferred extirpation in Agassiz Slough and portions of Bertrand Creek and Salmon River.

Is there an [observed, inferred, or projected] continuing decline in number of subpopulations?

Yes

Inferred extirpation from Agassiz Slough.

Is there an [observed, inferred, or projected] continuing decline in number of “locations”?

Yes

Inferred extirpation from Agassiz Slough.

Is there an [observed, inferred, or projected] continuing decline in [area, extent and/or quality] of habitat?

Yes

Yes, worsening water quality across range (Rosenfeld et al. 2021)

Are there extreme fluctuations in number of subpopulations?

No

Are there extreme fluctuations in number of “locations”?

No

Are there extreme fluctuations in extent of occurrence?

No

Are there extreme fluctuations in index of area of occupancy?

No

Number of mature individuals (by subpopulation):

Quantitative analysis:

Is the probability of extinction in the wild at least 20% within 20 years [or 5 generations], or 10% within 100 years]

Unknown

Analysis not conducted

Threats:

Was a threats calculator completed for this species?

Yes (Appendix 3)

Overall assigned threat impact: Very high (2023)

Key threats were identified as:

1. Pollution (IUCN 9) – high impact
2. Climate Change and Severe Weather (IUCN 11) – high impact
3. Natural System Modifications (IUCN 7) – high impact
4. Invasive and Other Problematic Species and Genes (IUCN 8) – high impact
5. Energy Production and Mining (IUCN 3) – low impact
6. Transportation and Service Corridors (IUCN 4) – low impact

What limiting factors are relevant?

• None. Salish Sucker has a naturally high intrinsic rate of population growth and is well adapted to recover from severe episodic declines in abundance if habitat conditions improve. Ongoing declines are a function of increasing threat severity, not intrinsic limiting factors.

Rescue effect (from outside Canada):

Status of outside population(s) most likely to provide immigrants to Canada.

Unknown

Only subpopulations in Pepin, Fishtrap, and Bertrand creeks are connected to waterways outside Canada. Their status in Washington is unknown.

Is immigration known or possible?

Yes

Salish Sucker occurs at the USA border regularly in Pepin Creek, and occasionally in Fishtrap Creek and Cave Creek.

Would immigrants be adapted to survive in Canada?

Yes

Same subpopulations

Is there sufficient habitat for immigrants in Canada?

No

Habitat degradation is driving declines in Canada.

Are conditions deteriorating in Canada?

Yes

Worsening landscape-scale hypoxia is occurring in these watersheds (Rosenfeld et al. 2021).

Are conditions for the source (that is, outside) population deteriorating?

Yes

Washington portion of the population are downstream of Canadian ones and subject to the same threats. Cross-border nutrient pollution in these streams has been a political issue for several decades.

Is the Canadian population considered to be a sink?

No

No evidence of higher abundance in USA or significant immigration into Canada.

Is rescue from outside Canada likely, such that it could lead to a change in status?

No

No evidence of higher abundance in USA or significant immigration into Canada.

Wildlife species with sensitive occurrence data (general caution for consideration):

Could release of certain occurrence data result in increased harm to the Wildlife Species or its habitat?

No

COSEWIC status history

Designated Endangered in April 1986. Status re-examined and confirmed in November 2002. Status re-examined and designated Threatened in November 2012. Status re-examined and designated Endangered in May 2024.

Status and reasons for designation:

Status

Endangered

Alpha-numeric codes

A3bce+4bce

Reason for change in status

I.i; I.ii; II.ix; II.xi; IV.iii; IV.vii

Reasons for designation

This small fish has a restricted range in southwestern British Columbia. It is susceptible to continuing decline in amount and quality of habitat due to reduced stream flow, pollution, and decreasing oxygen content of the water as a result of increased stream temperature and high nutrient loading. These threats are expected to worsen due to climate change-induced extreme heat and drought events. Moreover, invasive species that prey upon this fish or modify its habitat are also contributing to population declines. Ongoing declines in several streams, in spite of habitat restoration efforts, and projected future declines resulted in the change in status. If these threats cannot be mitigated, they could lead to the extirpation of this species.

Applicability of criteria:

A: Decline in total number of mature individuals:

Meets Endangered, A3bce+4bce

Future decline is inferred at > 50% (A3bce), based on worsening primary threats, and decline spanning past and future is estimated at > 50% (A4bce). Meets Threatened, A2bce. Decline in number of mature individuals over the past three generations (10 years) estimated conservatively at 34%, based on declines in mark-recapture Abundance estimates and catch per unit effort, decline in quality of habitat, and effects of introduced taxa and pollutants (A2bce).

B: Small range and decline or fluctuation

Not applicable

The EOO (1,401 km²) and IAO (252 km²) are below thresholds for Endangered, and the population is experiencing an observed and projected decline in IAO, extent and quality of habitat, number of locations, and number of mature individuals. However, the number of locations (12) exceeds the threshold for Threatened, and it is neither severely fragmented nor subject to extreme fluctuations.

C: Small and declining number of mature individuals

Not applicable

Estimated number of mature individuals (4,216 to 11,620) exceeds the threshold for Endangered, but comes close to meeting the threshold for Threatened (10,000).

D: Very small or restricted population

Not applicable

Estimate of 4,216 to 11,620 mature individuals is above thresholds for D1, and IAO (252 km²) does not meet the threshold for Threatened, D2. Although actual area of occupancy is likely < 1 km², the number of locations is 12, and the species is likely not prone to a substantial decline from effects of human activities or stochastic events within 1 to 2 generations.

E: Quantitative analysis

Not applicable

Analysis not conducted.

Preface

Since the last status report on Salish Sucker was published (COSEWIC 2012), one previously unknown subpopulation has been discovered, in Sqemélwelh Creek on Chawathil First Nation Reserve Land. Mark-recapture Abundance estimates have been attempted for all subpopulations, and estimates from one or more years since 2012 have been completed for 12 of 15 subpopulations (Pearson unpubl. data). Catastrophic declines in abundance have been documented in several subpopulations due to reach-scale dewatering and/or extreme hypoxia events (Bertrand Creek mainstem, Salmon River, Sqemélwelh Creek), and one subpopulation is believed extirpated (Agassiz Slough).

Research has been published on the extent, severity, and impacts of hypoxia on Salish Sucker (Rosenfeld et al. 2021; Zinn et al. 2021; Ramirez 2022). These studies show that over 40% of identified critical habitat is hypoxic (dissolved oxygen < 4 mg/L) by late summer. Hypoxia is driven by elevated stream temperatures, reduced stream flow, and high nutrient pollution (eutrophication), but it is significantly reduced by shade from riparian forest. A high-level assessment of cumulative impacts on habitat has been published (Boyd et al. 2022). An assay for Salish Sucker environmental DNA (eDNA) was developed at the University of Victoria in 2021, but it has yet to be field tested (Helbing pers. comm. 2023).

A number of recovery documents have also been published, including the Recovery Potential Assessment for the Salish Sucker in Canada (Fisheries and Oceans Canada 2015; Pearson 2015a). Critical habitat has been protected by a ministerial Order in Council (2019). The recovery strategy was amended based on new information, which included reducing abundance targets and adding areas of critical habitat to Little Campbell River, Chilliwack Delta, Salmon River, and Bertrand Creek watersheds (Fisheries and Oceans Canada 2020). The action plan for the Nooksack Dace and the Salish Sucker was published (Fisheries and Oceans Canada 2017) and amended (Fisheries and Oceans Canada 2020b), and a report on the progress of recovery strategy and action plan implementation was published (Fisheries and Oceans Canada 2022). Guidelines for the capture, handling, scientific study, and salvage of Salish Sucker were updated (Pearson 2015b).

COSEWIC history

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (2024)

Wildlife Species

A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.

Extinct (X)

A wildlife species that no longer exists.

Extirpated (XT)

A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A wildlife species facing imminent extirpation or extinction.

Threatened (T)

A wildlife species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^*

A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.

Not at Risk (NAR)^**

A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.

Data Deficient (DD)^***

A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.

^* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.
^** Formerly described as “Not In Any Category”, or “No Designation Required.”
^*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994. Definition of the (DD) category revised in 2006.

The Canadian Wildlife Service, Environment and Climate Change Canada, provides full administrative and financial support to the COSEWIC Secretariat.

Wildlife species description and significance

Name and classification

Current classification:

Class: Actinopterygii

Order: Cypriniformes

Family: Catostomidae

Genus: Catostomus

Species: Catostomus sp. cf. catostomus

Common names:

English: Salish Sucker (Schultz 1947)

French: Meunier de Salish (McPhail 2007)

Indigenous (Halq'emeylem): Skwímeth (Victor pers. comm. 2019)

Synonyms and notes:

The Halq'emeylem name, Skwímeth, translates as “many red markings” (Victor pers. comm. 2019). Salish Sucker was first described for western science by Schultz (1947) from a Lake Cushman, Washington, specimen. Uncertainty remains around its taxonomic status. Although it is clearly a form of Longnose Sucker (C. catostomus) that is both genetically and morphologically distinguishable from other “western” and “eastern” Longnose Suckers found in Canada (McPhail and Taylor 1999), the geographic ranges of other forms of “western” Longnose Sucker and Salish Sucker do not overlap.

Description of wildlife species

Adult Salish Suckers are dark green, mottled with black on the back, and dirty white on the belly, and they develop a broad, red lateral stripe during the spawning season (Figure 1). The stripe is particularly vivid in males, which also develop callus-like tubercles on the anal fin during the spawning season. Scales are small, as is the mouth, which is located on the underside of the head (McPhail 2007). Males are smaller than females as adults. Very few males exceed 200 mm in length (maximum 206 mm), and they may be sexually mature at slightly less than 100 mm. The largest female captured in Canada was 287 mm, although only 10% of females exceed 200 mm (Pearson and Healey 2003). Body size is widely variable among C. catostomus populations, and dwarfism is relatively common (Scott and Crossman 1973; McPhail 2007; Lepage 2014). Salish Sucker body size is among the smallest reported for C. catostomus forms (Pearson and Healey 2003; LePage 2014). The sexes may be separated by the shape of the anal fin (Figure 2). Juveniles are more silvery and uniform in colouration, with first-year fish having a more pronounced terminal mouth (Pearson pers. obs.).

Figure 1. A male Salish Sucker (142 mm fork length, 37.2 g; May 20, 1999, Pepin Creek, BC, UTM 10U 541247 5430169).

Figure 2. Male Salish Sucker (top) have a larger, fan-shaped anal fin which develops abundant tubercles during the spawning season. Females (below) have distinctly thickened anterior rays and a more rectilinear shape.

Salish Sucker are readily distinguished from Largescale Sucker (C. macrocheilus), with which they sometimes occur, by their smaller body size, more numerous scales, and fewer dorsal fin rays (Table 1; McPhail and Taylor 1999).

Designatable units

Salish Sucker is recognized as an evolutionarily significant unit (McPhail and Taylor 1999) and warrants recognition as a Designatable Unit (DU) within C. catostomus, in accordance with the COSEWIC guidelines for recognizing DUs (COSEWIC 2020). Within British Columbia, it occupies three independent drainages: the lower Fraser River, the Nooksack River, and the Little Campbell River. Dispersal between the Fraser and Nooksack drainages is possible via occasional highwater connections between headwaters (Pearson 2004a; see Habitat trends below). Although there is some evidence of genetic distinction between these groups (different mtDNA haplotypes at the ND2 gene; McPhail and Taylor 1999), it is not sufficient to justify treating them as separate DUs within Salish Sucker, in accordance with the COSEWIC guidelines (COSEWIC 2020).

Evidence for discreteness

Salish Sucker differs, and is diagnosable from other western C. sp. cf. catostomus populations (McPhail 1987), by adult body size (Pearson and Healey 2003), morphology, and molecular genetic characteristics. McPhail and Taylor (1999) sequenced PCR-amplified mitochondrial DNA fragments of the cytochrome b gene (360 bp) and the NADH subunit 2 (ND2) gene (510 bp) from 45 Salish Sucker across eight localities in British Columbia and western Washington, and from 94 Longnose Sucker representing 24 localities from western Alaska to Quebec. They showed that Salish Sucker is distinguished from other Longnose Sucker by a single unique haplotype at the cytochrome b gene and by two unique haplotypes at the ND2 gene. Thus, it satisfies criterion D1 in terms of discreteness (that is, with evidence of heritable traits and markers that clearly distinguish it from other western C. sp. cf. catostomus populations).

Evidence for evolutionary significance

Available evidence suggests that before the Illinoian glaciation (200,000 years ago), C. catostomus was distributed across North America and into Siberia, as it is today. The range was subsequently fragmented by glaciation, re-formed at least partly during the Sangamon interglacial period, then re-fragmented during the most recent (Wisconsinan) glaciation (McPhail and Taylor 1999). The present distribution indicates that the populations survived in four ice-free refugia during the Wisconsinan glaciation: the Bering, the Great Plains (Mississippi-Missouri system), the Pacific Ocean, and the Chehalis (in western Washington State), from which Salish Sucker emerged (McPhail 2007). This complex history of fragmentation and isolation produced geographically structured evolutionary divergences among populations. Catostomus sp. cf. catostomus is quite variable in form and a number of subspecies have been recognized historically (Scott and Crossman 1973). McPhail (2007) reported that three morphological types of Longnose Sucker occur in British Columbia: a typical large-bodied form (sexual maturity at > 300 mm), geographically scattered “dwarf” populations, which may or may not be genetically distinct, and the genetically and morphologically distinct Salish Sucker. As a distinct lineage originating in a separate Pleistocene glacial refugium, it satisfies criterion S1 for significance.

As a result of the discovery of the Sqemélwelh Creek subpopulation at Chawathil, Salish Sucker are separated from the most downstream vouchered record of the Columbia form of C. catostomus (Fraser River 1.9 km west of Hope,1959, Beaty Biodiversity Museum) by less than 10 km of Fraser River channel. However, the two forms clearly differ with respect to life history and habitat associations. The Columbia form matures at 5 to 7 years and can survive up to 19 years, while Salish Sucker matures at 2 years and lives a maximum of 5 to 6 years (McPhail 2007). The Columbia form is primarily associated with cold-water rivers and lakes, while Salish Sucker in British Columbia are predominantly found in slow-moving headwater streams, wetlands, and beaver ponds (McPhail 2007). Salish Sucker is considered a unique element in the evolutionary history of the Longnose Sucker, satisfying criterion S2 in terms of significance. The selective regime of Salish Sucker has given rise to local adaptations that could not be practically reconstituted if lost.

Special significance

Salish Sucker is a member of the “Chehalis fauna,” a unique fish community that survived continental glaciation in an ice-free refuge in Washington State (McPhail 1967 2007). It is of considerable scientific interest in the study of zoogeography and evolution (McPhail and Carveth 1993; McPhail 2007; Lepage 2014). The suckers (Catostomidae) are a diverse family of fishes (at least 76 species), many of which are at risk. As a group, they suffer from the perceptions that they are “trash” fish, tolerant of poor habitat conditions, and a predatory threat to eggs and juveniles of economically important species, although available data do not support these perceptions (Cooke et al. 2005).

Aboriginal (Indigenous) knowledge

Aboriginal Traditional Knowledge (ATK) is relationship-based. It involves information on ecological relationships between humans and their environment, including characteristics of species, habitats, and locations. Laws and protocols for human relationships with the environment are passed on through teachings and stories, and Indigenous languages, and they can be based on long-term observations. Place names provide information about harvesting areas, ecological processes, spiritual significance, or the products of harvest. ATK can identify life history characteristics of a species or distinct differences between similar species.

Cultural significance to Indigenous peoples

There is no species-specific ATK in the report other than the Halq'emeylem name. However, Skwímeth (Salish Sucker) is important to Indigenous Peoples who recognize the interrelationships of all species within the ecosystem.

Distribution

Global range

Longnose Sucker is one of the most widely distributed fishes in North America, occurring from Labrador south to Maryland, west through Pennsylvania, northern Minnesota, northern Colorado, and Washington State, and north to the Arctic Ocean and Alaska. It also occurs in several eastern Siberian drainages (Scott and Crossman 1973; McPhail 2007). Salish Sucker occupy the lower Fraser River Valley in British Columbia and seven drainages in northwestern Washington State (Figure 3). Additional undocumented subpopulations may occur in both Canada and the United States.

Figure 3. The global range of Salish Sucker is restricted to northern Washington State and the lower Fraser River Valley in southwestern British Columbia (adapted from McPhail 1987; McPhail and Taylor 1999; Molly Hallock, Washington Dept. Fish and Game, unpubl. data; COSEWIC 2012).

Canadian range

The current Canadian range of Salish Sucker comprises about 5.9% (1,401 km²) of the 23,912 km² global extent of occurrence. It is known from 13 watersheds in Canada, all in the lower Fraser River Valley of British Columbia (Table 2; Figures 4, 5, 6, 7, and 8). The entire range is within the Coastal Western Hemlock Biogeoclimatic Zone in streams flowing primarily through private lands.

Historical changes in the Canadian range are poorly documented, but significant reductions have certainly occurred over the past 150 years. The presence of Salish Sucker in Salwein Creek and Hopedale Slough suggests that it occupied Sumas Lake (Figure 6), into which these waterways flowed prior to drainage of the lake in the 1920s (Woods 2001). The lake’s mix of marsh and shallow open water and its small, gravel-bottomed tributary streams would have provided excellent habitat. Anecdotal evidence also suggests the historical presence of Salish Sucker in a headwater wetland of Cave Creek (Bertrand Creek tributary) prior to its drainage in the 1960s (Pearson 1998). Drainage of headwater wetlands was common, and agricultural and urban development transformed the Fraser Valley landscape. Longnose Sucker was recorded, but not retained, from Davis Lake (Table 3; Figure 4) when it was poisoned with rotenone in 1963 (FIDQ 2022). The subpopulation in the Little Campbell River was believed extirpated (Pearson 2004; McPhail 2007), as were subpopulations in Salwein Creek, Howe’s Creek (Bertrand Tributary), and the lower Salmon River (Inglis et al. 1992), but the species’ presence has since been reconfirmed in these areas (Pearson 2004). The Agassiz Slough subpopulation appears to have been recently extirpated. No Salish Sucker were captured in extensive sampling there in 2021, 2022, and 2023. Approximately 80% of the slough’s length was dewatered during the extreme droughts of 2022 and 2023 (Pearson unpubl. data).

Figure 4. Fifteen subpopulations of Salish Sucker have been documented in Canada: the Little Campbell River (A, 2020), the Salmon River (B, 2022), Bertrand Creek (contains 3 subpopulations; C, 2021), Pepin Creek (D, 2022), Fishtrap Creek (E, 2019), Salwein Creek (F, 2023), Hopedale Slough (G, 2022), Chilliwack Delta (H, 2023), Hope Slough/Elk Creek (I, 2018), Mountain Slough (J, 2016), Miami Creek (K, 2023), Agassiz Slough (L, 2014), and Sqemélwelh Creek (M, 2023) (COSEWIC 2012).

Figure 5. Western watersheds of the Salish Sucker range in Canada showing identified critical habitat (Fisheries and Oceans Canada 2020), known spawning riffles, barriers, and linkages between watersheds. The three Bertrand Watershed subpopulations are numbered: 1) Cave Creek; 2) Perry Homestead Creek; and 3) Howe’s Creek/Bertrand mainstems.

Figure 6. Central watersheds of the Salish Sucker range in Canada showing identified critical habitat (Fisheries and Oceans 2020), spawning riffles, barriers, and linkages between watersheds.

Figure 7. Eastern watersheds of the Salish Sucker range in Canada showing identified critical habitat (Fisheries and Oceans 2020), spawning riffles, barriers, and linkages between watersheds.

Figure 8. Sqemélwelh Creek at Chawathil Reserve 4, the most eastern watershed known to contain Salish Sucker in Canada, showing occupied habitat, spawning riffles, and barriers.

Salish Sucker has been known to western science in Canada since the 1950s. Most early work (1960s to 1980s) was conducted by McPhail (1987). He documented subpopulations in the Little Campbell River, the Nooksack River tributaries (Bertrand, Pepin, and Fishtrap creeks), and Salwein Creek. Considerable effort has been expended to locate additional subpopulations since then (Appendix 1). In 1992, 117 sites in 34 watersheds were sampled using minnow traps and electrofishing, but no additional subpopulations were found (Inglis et al. 1992). Pearson (2004) sampled 429 sites in 45 watersheds in 2000 using large funnel traps (Feddes traps). He found previously unknown subpopulations in Miami Creek, Agassiz Slough, and Hopedale Slough. Further sampling between 2001 and 2006 concentrating on adjacent watersheds documented subpopulations in Mountain Slough, Hope Slough/Elk Creek, and the former Chilliwack River Delta. Historical records of purported “Longnose Sucker” (without supporting physical evidence) are concentrated in the Pitt River watershed downstream of Pitt Lake (Table 3, Figure 4). The Lower Pitt and Alouette rivers, along with Davis Lake, Chilliwack Lake, Hatzic Lake tributaries, Stave Lake tributaries, and Nicomen Slough and tributaries were surveyed in 2016 and 2017, but no additional subpopulations were found. In 2018, Pearson (unpubl. data) identified a subpopulation while conducting sampling for salmonids in Sqemélwelh Creek at Chawathil First Nation near Hope. Additional surveys in the few other potentially suitable water bodies in the Hope area were completed in 2023, but they found no Salish Sucker. A habitat enhancement project carried out by Fisheries and Oceans Canada (DFO) and a local stewardship group in 2019 connected Salwein Creek to Peach Creek, a small stream with wetlands confined between the Vedder River and a set-back dike. Two Salish Sucker were captured on the Peach Creek side in 2020 (Pearson unpubl. data).

Most potentially occupied water bodies in the Fraser Valley have now been sampled at least once for Salish Sucker using appropriate targeted methods (Appendix 1). However, additional undocumented subpopulations may exist, because Salish Sucker have proven difficult to detect when at very low densities and have been mistakenly thought extirpated from watersheds in the past (McPhail 1987; Pearson 2004).

Population structure and variability

Twelve of the 15 Salish Sucker subpopulations occur within separate tributaries of a major river (Fraser or Nooksack) or in a small river that enters the ocean independently (Little Campbell). The Bertrand Creek watershed contains three subpopulations each occupying a separate tributary or the upper mainstem and separated by more than 5 km of unsuitable habitat with no occurrence records. Salwein Creek and Hopedale Slough are tributaries on opposite banks of the Vedder River, which is shallow, rocky, and swift. The Vedder River is more than 120 m wide, and Salwein Creek enters it approximately 750 m downstream of Hopedale Slough. As Salish Sucker are unlikely to move between these habitats regularly, they are considered distinct subpopulations.

ND2 haplotypes separate Salish Sucker from other forms of western Longnose Sucker. One of these haplotypes is unique to Pepin Creek (Nooksack drainage), while the other was found in the two Fraser River subpopulations and four Washington State subpopulations examined (McPhail and Taylor 1999).

Extent of occurrence and area of occupancy

Current EOO:

Extent of occurrence (EOO) within Canada is 1,401 km², calculated using a minimum convex polygon that encompasses known records in all occupied watersheds (Figure 9) and excluding Washington occurrences. The decrease from the EOO of 1,709 km² calculated in the previous status report (COSEWIC 2012) is due to previous mapping errors whereby aquatic habitat in an occupied watershed outside the polygon formed by occurrence records was included. The reduction was partially offset by a range extension resulting from the discovery of the Sqemélwelh Creek subpopulation in 2018. All localities have been confirmed as extant since 2014 except Hope Slough, and its exclusion did not affect the calculation of the EOO. Salish Sucker is believed to have been extirpated from Agassiz Slough sometime after 2013, but this did not affect the EOO either.

Figure 9. The global extent of occurrence of Salish Sucker based on a minimum convex polygon drawn around confirmed locations encompasses 23,912 km², of which 1,401 km² (5.9%) is in Canada.

Current IAO:

The index of area of occupancy (IAO) within Canada is 252 km², calculated using a 2 x 2 km grid drawn over known records based on continuous stretches of river between the observation records (Continuous IAO). For Salish Sucker, however, the IAO provides a very poor estimate of actual area of occupancy and of threats to persistence, as the stream habitats the fish occupy are typically only a few metres wide. The total area of deep pool habitat (> 70 cm depth) in critical habitat was estimated at 0.48 km² by Pearson (2007); however, this number included large areas in which there is no evidence of Salish Sucker occupation. Since then, the Little Campbell River subpopulation was rediscovered, and the Sqemélwelh Creek subpopulation was discovered, both of which are very small and restricted to a small fraction of their watersheds. However, Salish Sucker is now believed to be extirpated from Agassiz Slough, a headwater wetland in Bertrand Creek, and from most of the area they previously occupied in the Salmon River mainstem. Salish Sucker do use additional habitat types—shallower pool habitats as young-of-the-year and riffles for spawning—but the actual area of occupancy is highly unlikely to exceed 1 km² of aquatic habitat in Canada.

Fluctuations and trends in distribution

Estimates of EOO and IAO have generally increased over time as additional subpopulations have been discovered. However, temporary reductions in estimates also occurred as subpopulations in the Little Campbell River and Chilliwack Delta (Atchelitz Creek) were falsely considered extirpated for several decades (see Canadian range for full discussion). IAO has declined recently due to the suspected extirpation of Salish Sucker from Agassiz Slough and portions of Bertrand Creek and Salmon River.

Biology and habitat use

Life cycle and reproduction

Salish Sucker is a small-bodied, short-lived (to 5 years), and early-maturing (2 years) fish relative to most other Longnose Sucker populations (McPhail 1987; Pearson and Healey 2003). Generation time is estimated to be 3 years. In more typical, large-bodied populations, lifespan may be 30 years, with maturation occurring at 5 to 7 years (McPhail 2007). Adults typically spawn between early April and early July (Pearson and Healey 2003). Reproduction is oviparous, with fertilization occurring in the water. The fish do not construct a nest but broadcast adhesive eggs, which stick to gravel and rocks. Those on the substrate surface are usually consumed, but many are swept under the gravel and cobble where they are more protected (McPhail pers. comm. 1998). Time required for egg hatching and fry emergence is unknown and likely varies widely with water temperature given the breadth of the spawning season. Time to hatch in other Longnose Sucker populations varies from 11 days at 10^oC to 7 days at 16^oC, and fry remain in the gravel for an additional 1 to 2 weeks (McPhail 2007). Fecundity is unknown, but in other small-bodied C. sp. cf. catostomus populations, females of 150 mm fork length contain about 3,000 eggs (McPhail 2007; LePage 2014). Adults are believed to spawn in multiple years (McPhail 1987). Pearson and Healey (2003) speculated that females may sometimes spawn twice in a season, with eggs maturing early in one ovary and later in the other. This strategy, which increases fecundity in small-bodied fishes (Burt et al. 1988), would explain the protracted (3.5-month) spawning period observed in Salish Sucker.

Habitat requirements

Although several lacustrine subpopulations occur in Washington State, all known British Columbia subpopulations occupy small lowland streams and sloughs. Within these systems, Salish Sucker is most abundant in headwater reaches, particularly marshes and beaver ponds (McPhail 1987; Pearson 2004).

Pearson (2004) studied habitat use at the watershed, reach, and channel unit scales in 10 of the 13 watersheds where Salish Sucker occur in Canada. Among the 6 watersheds in which he was able to estimate abundance, mean density was highest (> 450 fish/km) in Pepin Creek, which also had the highest percentage of deep pool habitat, the lowest proportion of shallow pool habitat, and highest proportion of forest cover within 200 m of the channel. Watersheds with high densities (> 100 fish/km) contained less shallow pool habitat and seasonally dry channel.

Salish Sucker is found in reaches with higher proportions of deep pool habitat, lower proportions of riffle habitat, and more abundant in-stream vegetation than in reaches where they were not captured. The proportion of deep pool habitat in a reach was a strong predictor of presence and often associated with beaver dams. Salish Sucker presence was also positively associated with the occurrence of riffle habitat in a reach, but these fish were not found in reaches with high proportions of riffle habitat (Pearson 2004).

Spawning occurs in gravel riffles at water velocities of up to 50 cm/s (McPhail 1987). Young-of-the-year fish are usually found in shallow pools or glides (depth < 40 cm), although they are occasionally found in deeper habitats. Large (yearling) juveniles occupy similar habitats to adults (Pearson 2004a). Riffle locations and area are very limited in the very low-gradient streams supporting many of the subpopulations (Pearson 2004). Although riffles are required for spawning and egg incubation, a relatively small amount of riffle habitat is needed to support large areas of juvenile and adult habitat. It is also likely that groundwater upwelling areas can be used for spawning because no riffle habitat is available to the Agassiz Slough subpopulation.

In winter, fish seek low velocity habitats with abundant cover. Beaver ponds and marshes are most commonly used, but agricultural or roadside ditches (often < 2 m wide) that are completely dry for months during summer may be occupied in winter (Pearson unpubl. data).

Movements, migration, and dispersal

Within watersheds, Salish Sucker subpopulations are highly clumped, with a small proportion of stream habitat harbouring the great majority of individuals. The fish occur at much lower densities or may be absent from reaches around and between these “hotspots” (Pearson 2004). Hotspots may appear, disappear, or move through the watershed in response to habitat changes due to disturbance and succession. The pattern is consistent with a metapopulation structure (see Brown et al. 1995), in which groups of local subpopulations are loosely linked by occasional migrants (Pearson and Healey 2003). Whether these aggregations function as metapopulations depends on the frequency of migration between them. Migration rates are dependent on the spatial arrangement of hotspots and the difficulty in traversing the habitat between them due to physical obstructions or unsuitable habitat (for example, large open channels, poor water quality).

Beaver dams, and probably other shallow-water areas, are significant barriers to movement in both upstream and downstream directions—and may form sink habitats (see Interspecific interactions and Pearson 2004). Pearson and Healey (2003) radio-tagged 18 adults in a Pepin Creek beaver pond and followed them for up to 153 days, locating fish a total of 730 times. Fish crossed the beaver dam on only three occasions, although all used the pond, and many ventured hundreds of metres upstream of it. This is consistent with findings of other studies on impacts of beaver dams on stream fish dispersal and colonization (Schlosser 1995; Schlosser and Kallemyn 2000). Some fish did cross the dam during the spawning period. Eight of 265 Salish Sucker marked in the beaver pond in October 1999 and 2 of 103 marked in March 2000 were captured in a fish fence 1,020 m downstream in a newly constructed tributary in spring 2000. Most were in reproductive condition when recaptured. Seven were subsequently recaptured within the tributary one or more times, always in the largest deepest available pool, a further 600 m upstream (Patton 2003).

Salish Sucker may also move off the main channel to overwinter and have been found up to 1.7 km from the mainstem in habitats that are dry in summer (Pearson unpubl. data).

Radio-tracked adults (Pepin Creek, n = 18) occupied summer home ranges (95% of locations) varying from 42 to 307 linear metres of stream (mean = 177; standard error of the mean, SEM = 24) and from 212 to 1,736 m² in area (mean = 1,273; SEM = 107). Daytime resting positions were generally in heavy cover, often among thick emergent vegetation adjacent to the open channel. Fish tended to return to the same resting location on successive days. Movements were greatest around dawn and dusk, although activity continues throughout the night (Pearson and Healey 2003).

Salish Sucker often occurs, and presumably moves, in aggregations. Typically, the great majority of individuals captured at a site are found in a small proportion of traps, sometimes a single trap, even if multiple traps are set in similar habitats (Pearson 2004). At a very few sites (one known at present), individual overnight trap sets may reliably capture more than 100 adults from spring through fall. Sex ratios within large catches are often heavily skewed towards either males or females (Pearson pers. obs.).

Adult Salish Sucker readily colonize newly available suitable habitats (Patton 2003), but details of juvenile dispersal remain unknown. Many historical dispersal routes potentially linking subpopulations have been blocked by flood control infrastructure (see Threats). Currently, occasional dispersal between Canadian subpopulations may occur in three areas, although none are likely to be used regularly. A headwater marsh of Bertrand Creek that supports a high density of Salish Sucker may connect to the upper Salmon River (Figure 5), which also contains another subpopulation, under extreme high-water conditions. Salwein Creek and Hopedale Slough outlets are on opposite banks of the fast-flowing Vedder River just a few hundred metres apart. A headwater pond near the town of Agassiz has permanent connections to both Mountain Slough and Miami Creek that are accessible to fish at least seasonally (Figure 7; Pearson pers. obs.). Dispersal is also possible between Fishtrap Creek and its tributary Pepin Creek via Washington State, just as dispersal is possible from Fishtrap Creek to its neighbouring tributary to the Nooksack River, Bertrand Creek. In these cases, though, the Canadian subpopulations are separated by long stretches of unsuitable habitat in Washington, reducing the likelihood of migration (McPhail 1987; Wydoski and Whitney 2003; Pearson 2004).

Interspecific interactions

Diet:

Adults feed on benthic insects, particularly chironomid larvae (McPhail 1987), although they likely eat a broad range of invertebrate taxa as do other C. catostomus populations (McPhail 2007; Furey et al. 2020). Detritus often forms a high proportion or majority of stomach contents in other C. catostomus populations (LePage 2014; Furey 2020). The diet of young-of-the-year Salish Sucker is undocumented but presumably consists of zooplankton, which is similar to the diet of other juvenile catostomids (McPhail 2007).

Predators and competitors:

Predation risk for adult Salish Sucker is probably quite low. Most avian predators would have little success in the deep, heavily vegetated habitats they favour, although piscivorous waterfowl may take some of these fish (see Beckman et al. 2006). No coexisting predatory fishes are large enough to consume them. Mink (Mustela vison) and River Otters (Lontra canadensis) are known to prey on Salish Sucker (Pearson pers. obs.). Young-of-the-year Salish Sucker are probably eaten by a variety of native fishes, including Coastal Cutthroat Trout (Oncorhynchus clarkii), Rainbow Trout (Oncorhynchus mykiss), and Northern Pikeminnow (Ptychocheilus oregonensis), and by the introduced Brown Bullhead (Ameiurus nebulosus). Great Blue Heron (Ardea herodias) and Belted Kingfisher (Megaceryle alcyon) likely consume some. Introduced Largemouth Bass (Micropterus salmoides) could take larger juveniles and adults. Juvenile Largescale Suckers are potential competitors. They are caught occasionally with Salish Sucker, generally in low numbers, and they seem unlikely to impact Salish Sucker subpopulations.

Host/parasite/disease interactions:

Salish Sucker are commonly infected by a trematode, Uvulifer sp. (“blackspot’’; Pearson pers. obs.). Low level infections occur across the range, but occasionally individuals show intense, potentially debilitating infections in warmer, sun-exposed reaches of Upper Salmon River and Bertrand Creek mainstem, which contain abundant aquatic snails (Pearson pers. obs.), an intermediate host (Hoffman 1967).

Other interactions:

Salish Sucker have a complex relationship with North American Beaver (Castor canadensis). Local abundances are highest in reaches with beaver ponds, presumably due to the stable presence of deep water and abundant cover. During late summer low-flow periods, beaver ponds provide the only wetted habitat available in some occupied reaches (Pearson 2004). Beaver ponds, however, also tend to be chronically hypoxic (Schlosser 1998; Snodgrass and Meffe 1998), especially in areas subject to nutrient loading and eutrophication from agricultural sources (Rosenfeld et al. 2021). The combination of a physical barrier and critically low oxygen produces occasional catastrophic mortality events (Pearson 2004; Rosenfeld et al. 2021).

Salish Sucker has been found with 16 species of fishes and amphibians. Of the 12 species caught frequently enough to permit statistical analysis, only Coho Salmon (Oncorhynchus kisutch) occurred with Salish Sucker more frequently than would be expected by chance (Pearson 2004), likely due to similar habitat preferences.

Although there is no evidence of hybridization in Salish Sucker, C. catostomus in some populations naturally hybridize with other catostomid species (McPhail 2007; Mandeville et al. 2017). Hybridization with C. macrocheilus, the only other catostomid found in Salish Sucker habitat, has not been documented (McPhail 2007).

Physiological, behavioural, and other adaptations

Salish Sucker possesses a suite of life-history characteristics associated with an “‘opportunistic life history strategy” (Pearson and Healey 2003; Cooke et al. 2005), in which small body size, early maturation, and high fecundity relative to body size facilitate rapid population growth and recovery from short-term, limited-area disturbances (Winemiller and Rose 1992). These characteristics should allow subpopulations to recover quickly in response to habitat creation/enhancement efforts (Pearson and Healey 2003).

Salish Sucker are active at temperatures as low as 7^oC (Pearson and Healey 2003). Rosenfeld and coworkers (2021) looked at water temperature and dissolved oxygen (DO) in relation to 8,583 Salish Sucker captures in 7,473 trap sets across the Canadian range. Catch per unit effort (CPUE, average number per trap) was highest between 12^oC and 20^oC, dropping sharply outside this range, at higher temperatures in particular. Salish Sucker were most likely to be caught in reaches where temperature was between 12 and 16^oC (Figure 10).

Salish Sucker are tolerant of mild (3.5 to 5 mg/L) or moderate (2.5 to 3.5 mg/L) hypoxia. Adults are regularly captured alive in waters containing less than 3 mg/L DO (Pearson 2004; Rosenfeld et al. 2021). Although the presence of Salish Sucker was significantly more likely in traps in water with 4 to 8 mg/L DO, fish were also commonly found in areas of severe hypoxia (< 2.5 mg/L; Figure 10). This is likely due to lack of options, with fish unable to escape areas of hypoxia which are large and widespread in summer across most of their range (Pearson 2015a; Rosenfeld et al. 2021). They have been found dead in traps set in water containing < 1 mg/L dissolved oxygen, which suggests that they venture into these environments temporarily to forage (Pearson 2004). Sublethal impacts occur at moderate hypoxia levels. Growth was reduced by 23% in Salish Sucker at 3.1 mg/L DO relative to 9.1 mg/L, although lower temperature at the lower dissolved oxygen level confounded results (Zinn et al. 2021). Salish Sucker use of an oxygenated refuge also increased under hypoxic conditions (Zinn et al. 2021). Evolution of small-bodied forms of otherwise larger freshwater fish species has been linked to selective pressure for hypoxia tolerance to allow exploitation of otherwise productive habitats (Landry et al. 2007). This has been reported for another Catostomus sp. cf. catostomus population (Lepage 2014).

The United States Environmental Protection Agency categorized C. catostomus as having “intermediate” pollution tolerance (COSEWIC 2012), although these data no longer appear to be publicly available. Tolerance to specific pollutants remains largely unknown. Pearson (2004) found that Salish Sucker was less likely to occur in reaches bordered by urban land use, and speculated that this may be due, in part, to toxic materials originating from stormwater outfalls.

Figure 10. Salish Sucker catches from 7,473 trap sets, across 226 stream reaches, over 16 years (2003 to 2018) in relation to water temperature (left) and dissolved oxygen (right). Top panels show frequency of presence in reaches set in different temperature ranges. Middle panels show evidence of selection (> 1) and avoidance (< 1) of these ranges. The lower graph left shows catch per unit effort (CPUE, mean number of fish/trap) in relation to temperature. The lower right graph shows that probability of capture does not differ significantly across dissolved oxygen classes. Adapted from Rosenfeld et al. (2021).

Limiting factors

Limiting factors are generally not human-induced and include intrinsic characteristics that make the species less likely to respond to conservation efforts. Limiting factors may become threats if they result in population decline.

Apart from an extremely limited post-glacial distribution which may represent a natural limiting factor, there do not appear to be any intrinsic factors that make Salish Sucker less likely to respond to conservation efforts. In fact, Salish Sucker are relatively tolerant of hypoxia, the main threat they face, and they have a high intrinsic rate of population growth (Pearson and Healey 2003), enabling subpopulations to recover quickly from short-term disturbances of limited spatial scale when habitat conditions improve. The decline of Salish Sucker is occurring because of worsening, large-scale, unmitigated threats, not intrinsic limiting factors.

Population sizes and trends

Data sources, methodologies, and uncertainties

Between 2000 and 2008, most subpopulation estimates were made using an equation relating CPUE to population density estimated from mark-recapture studies at four sites in three streams (see Appendix 2 for detailed methodology). An additional five mark-recapture studies were completed in 2012 to refine the method. Linear regression of log‑transformed density and CPUE showed that only 40% of the variation in density was explainable by variation in CPUE, which severely limits the precision of watershed-scale Abundance estimates. All subsequent estimates have been made using watershed-scale mark-recapture data (Table 2). Mark-recapture methods are also detailed in Appendix 2.

Abundance

Available subpopulation estimates for Salish Sucker range from well under 100 adults to the low thousands (Table 5). There are no “snapshot” estimates of the total Canadian Salish Sucker population from a single year. Mark-recapture-based estimates are time consuming (> 75 field days for Chilliwack Delta alone), so only a few watersheds are completed in any one year, and up to a decade elapsed between estimates for some subpopulations. Abundance has never been estimated in some subpopulations (Hope Slough, Fishtrap Creek) due to extremely low catch rates.

The most recent Abundance estimates and CPUE data suggest that drastic declines have occurred in multiple subpopulations over the past decade. Available information is summarized for each subpopulation/location in the Fluctuations and trends section. An estimate of the abundance that each subpopulation is unlikely to exceed appears in bold type at the end of each watershed summary. These upper estimates total 6,700 adults across the range (Table 5), with over 75% of the total estimate coming from just four watersheds.

Fluctuations and trends

Continuing decline^{Footnote 1} in number of mature individuals:

The number of mature Salish Sucker individuals has undergone, and continues to undergo, a clear decline across most of its range. One subpopulation (Agassiz Slough) is believed extirpated, and steep declines in abundance have been observed over the past decade in six other subpopulations/locations. The overall trend is clearly a decline and, given expected trends in threats, particularly climate change, the trend is likely to continue.

Evidence for decline over the past 10 years:

There is evidence of extreme declines in abundance in six subpopulations/locations: Agassiz Slough (100%), Bertrand Creek Mainstem/Howe’s Creek (approx. 95%), Mountain Slough (85%), Pepin Creek mainstem (85%), Salmon River mainstem (86%), and Sqemélwelh Creek (95%) over time periods ranging from 2014 to 2016 (Mountain Slough) to 2002 to 2022 (Pepin Creek mainstem) (Table 6), although a few subpopulations appear to have been fairly stable over the past decade. Details are provided for each later in this section.

Total overall decline in number of Salish Sucker adults within Canada over the past 10 years was estimated using data from 18 sites from 9 subpopulations for which abundance was estimated at two time points. Because survey intervals varied among sites (averaging 9 years but ranging from 2 to 20 years), two methods were used to standardize percentage change for each subpopulation to a 10-year period (Table 6). The first method calculated the annual change in subpopulation abundance between the two time periods, used it to project the subpopulation abundance forward 10 years, and then calculated the 10-year percentage change weighted by the abundance of each subpopulation. Using this method, the 10-year decline was estimated to be 45.8%. The second method used the IUCN (2024) Criterion A Workbook to back-calculate the abundance of each subpopulation to 2014, project subpopulation abundance to 2024, and sum projected abundances for each subpopulation. Using data from all sites for which abundance was available at the two time points, the 10-year change was -74.2% (Table 6). However, because the IUCN method is biased by very high rates of decline, Sqemélwelh Creek (which showed a 95% decline between 2019 and 2022 due to almost complete dewatering of the habitat in 2022) was removed as an outlier. Without Sqemélwelh Creek, the 10-year decline calculated with the IUCN method was 34.3%. Given the exclusion of Sqemélwelh Creek—as well as several sites where abundance at one or both time periods was unknown but where there are concerns for the species (for example, Cave Creek, Perry Homestead Creek, Semmihault Creek; see below)—34.3% appears to be a conservative estimate of decline.

Evidence for projected or suspected future decline (next 3 generations or 10 years, whichever is longer, up to a maximum of 100 years):

Declines are clearly being driven by landscape-scale hypoxia (Rosenfeld et al. 2021) and extreme weather (drought and potentially temperature). These threats are episodic in nature and non-linear in impact, making specific projections very difficult. Nutrient loading will continue to increase with livestock density in the Fraser Valley. The rate of increase in nutrient loading is determined largely by supply management of dairy and poultry linked to human population growth. When human population increases, demand for these products increases, marketing boards increase production quotas, and farmers increase herd/flock size (Heminthavong 2018). However, they continue to use the same area of land for manure disposal. The frequency and severity of severe heat waves and drought are increasing (see Threats). With the overall threat impact to Salish Sucker considered Very high, overall declines of 50%–100% seem likely under these conditions.

Long-term trends:

No abundance data extending more than 20 years into the past, and little data extending more than 10 years into the past, are available, but large-scale destruction of suitable habitat is well documented and is discussed in the Historical, Long-term, and Continuing Habitat trends section below.

The following paragraphs summarize available information on abundance and trends in each occupied watershed. For each watershed, a table is provided summarizing available CPUE data and (if available) Abundance estimates from mark-recapture studies (Tables 7 to 19). Bracketed numbers indicate the lower and upper 95% confidence limits of Abundance estimates. Specific stream reaches are identified by codes (for example, PEP9). Detailed maps showing locations of reaches are available in the recovery strategy (Fisheries and Oceans Canada 2020).

Table 14. Summary of catch per unit effort (CPUE) and mark-recapture Abundance estimates of Salish Sucker in Miami Creek, 2000 to 2023.

Year	Method	Effort (# Traps)	Salish Sucker	CPUE	Abundance estimate
2000*	G/F	12	25	2.08	Not applicable
2002*	G/F	86	44	0.51	Not applicable
2011**	F	189	209	1.11	Not applicable
2012**	F	200	137	0.69	102 (67 to 193)
2023**	F	395	198	0.50	204 (166 to 325)

*Pearson (2004)

**Pearson (unpubl. data)

***Miners and Pearson (unpubl. data)

Agassiz Slough:

Salish Sucker was first found here in 2000. Early surveys (2000 to 2005) produced very few fish (Table 7). In 2011, the catch rate soared and abundance was estimated at over 800 adults (Miners unpubl. data). The following year, the estimate fell significantly to 253 (95% CI = 203 to 254). In 2014, Salish Sucker was still present, but only eight were captured. Extensive sampling in 2021 (four sessions March to November), 2022 (April), and 2023 (April, July, October) failed to yield a single Salish Sucker. All of the habitat suffers from severe hypoxia in summer, and most of the habitat dewatered completely during the droughts of 2022 and 2023. Total effort consisted of 469 trap sets. The subpopulation is likely extirpated.

Bertrand Creek:

The Bertrand watershed consists of three subpopulations: a) Mainstem + Howe’s Creek; b) Perry Homestead Creek; and c) Cave Creek. Comparable CPUE data span the period 1999 to 2021 with one to two estimates of abundance for each subpopulation.

Upper mainstem + Howe’s Creek subpopulation:

The longest time series of data is from a large wetland complex at Naval Radio Station (NRS) Aldergrove which is confined by beaver dams (Table 8). Catch per unit effort was relatively high in 2008 and peaked in 2011, when abundance was estimated at 244 adults. CPUE declined 25-fold in the 2017 sampling, when abundance was estimated at 42 adults. In the 2021 sampling, no Salish Sucker were found. CPUE in the mainstem subpopulation (excluding NRS Aldergrove) declined more than 30-fold between 2013 and 2020, while in Howe’s Creek, it declined 24-fold. All habitat occupied by this subpopulation is subject to severe hypoxia (Rosenfeld et al. 2021). There have been a series of severe droughts in the intervening years that have dewatered most of Howe’s Creek for months each summer. Large-scale fish kills are, unfortunately, the most likely explanation for the declines. The declines in CPUE coupled with the pre-crash subpopulation estimates suggest that fewer than 50 adults remain.

Perry Homestead Creek subpopulation:

Salish Sucker were abundant in a pond on the east side of Highway 13 in 2001 and 2004. By 2017, this pond had become largely infilled with Reed Canary Grass (Phalaris arundinacea). An estimated 570 adults occupied the location when it was last surveyed in 2017 (Table 8). Severe hypoxia impacts this population (Rosenfeld et al. 2021), raising the risk of a fish kill.

Cave Creek subpopulation:

Prior to being drained in the 1960s, a large wetland in the headwaters of Cave Creek supported an abundant subpopulation of Salish Sucker. By the late 1990s, they had been extirpated, likely due to poor water quality and dewatering of most of the habitat in summer. The fish were unable to recolonize the site due to an impassable agricultural dam, although they were found in low densities downstream of the dam (Pearson 1998). A local stewardship group installed a fishway in 1999; it was functional for several years before being blocked by beavers. In 2019, sampling upstream of the dam showed that a subpopulation (estimate 315 adults) was now established in a series of beaver ponds (Table 8). Dissolved oxygen levels were dangerously low (< 2.5 mg/L in most ponds), flow had ceased (as it does every summer in Cave Creek), and water levels were below the dam crests, isolating fish in the ponds. Cave Creek has not been surveyed since then but given the severity of drought and heat in the intervening summers, there are concerns about this subpopulation.

Assuming that no declines occurred since the last surveys in Cave Creek (2019) and Perry Homestead Creek (2017), the total current abundance in all of Bertrand Creek is estimated at less than 935 adults (50+570+315), an estimated 41% decline since 2013 (3 generations).

Chilliwack Delta:

Four interconnected creeks (Atchelitz, Luckakuck, Little Chilliwack, and Semmihault) form the Chilliwack Delta subpopulation. Total numbers were estimated at 1,980 adults in 2012 and 2,254 adults in 2015 (Table 9). Very few have ever been found in the larger, downstream slough channels that connect the tributaries. Within Luckakuck Creek, most Salish Sucker inhabit a pond (approx. 2,500 m²) in a small municipal park (Manuel Park). Two Chilliwack Delta tributaries were resurveyed in 2022. Abundance appears to have increased significantly in Atchelitz Creek, but it had the lowest abundance among the tributaries in previous sampling. Low recapture rates (three fish) in Little Chilliwack resulted in large confidence intervals, perhaps due to poor water quality. Sampling was done in October 2022 under level 5 drought conditions and associated hypoxia. In summer 2023, Interception Ditch, which supported an estimated 739 adults in 2015, was found to be mostly dewatered and severely hypoxic. Only 15 Salish Sucker were caught in 84 trap sets. Semmihault Creek was too hypoxic to sample in 2023, so no current estimate is available. However, it seems unlikely that it supported over 500 individuals as it did in 2015. Based on the available evidence, abundance in the Chilliwack Delta is stable or has declined slightly over the past 3 generations. Current abundance is unlikely to exceed 2,500 adults (Table 6).

Fishtrap Creek:

Salish Sucker have been caught in the same reaches every time Fishtrap Creek has been surveyed (1999, 2000, 2013, 2019), but never in sufficient numbers to allow a subpopulation estimate (Table 10). One reach, adjacent to Abbotsford Airport, is distinguished by being located within the last remaining patch of riparian forest in the lower watershed. The other reach is in East Fishtrap Creek, which was converted to a large stormwater detention pond in 1990. Prior to this, it contained significant numbers of Salish Sucker (Inglis et al. 1992). The total number of adults in the watershed currently seems unlikely to exceed 50.

Hope Slough/Elk Creek:

A Salish Sucker was first found in Hope Slough in 2006. Targeted surveys since then have only yielded two more individuals (Table 11). City of Chilliwack fish salvages (electrofishing) have yielded a few more individuals over the years from Elk Creek (1 to 4 fish per year). Twelve were observed on a riffle during spawning season at the confluence of Elk Creek and Hope Slough in 2007 (Pearson unpubl. data). It seems unlikely that the subpopulation exceeds 100 individuals.

Hopedale Slough:

In Hopedale Slough, Salish Sucker have only ever been found in two ponds at the end of Browne Road, although other areas of apparently suitable habitat are found in the watershed. Abundance was estimated at 469 (346 to 712) adults in 2012 using mark-recapture (Table 12). An attempt to update the estimate in August 2019 failed due to a low catch rate (15 in 94 traps). Daytime dissolved oxygen was adequate for Salish Sucker, but water temperature was close to exceeding 20^oC. In spring 2021, with optimal water quality conditions, catch rates rebounded to 73 fish in 22 traps. This catch rate exceeded that of 2012 when the Abundance estimate was made. Current abundance in Hopedale Slough is unlikely to exceed 500 adults.

Little Campbell River:

This subpopulation was believed extirpated in the 1970s (McPhail 1987; Pearson 2004) but was rediscovered in 2011 (COSEWIC 2012). Since then, annual sampling by biologists with A Rocha Canada has consistently found Salish Sucker in the reach between 224thStreet and 232ndStreet. Abundance estimates ranged from 128 to 231 adults between 2017 and 2020 (Table 3), but their 95% confidence limits overlap significantly. A second area with significant numbers was found in a tributary near 192nd Street in 2018, but mark-recapture work in 2020 suggests that it contains fewer than 100 individuals. Total abundance in the watershed is unlikely to exceed 300 adults.

Miami Creek:

The Miami Creek subpopulation was first found in 2000 (Pearson 2004). Catch rates have been low to moderate in the years sampling has been completed, and abundance was estimated at 102 adults in 2012 (Table 4). In 2023, abundance was estimated at 204 adults, although confidence intervals were broad, overlapping with those from 2012. Current abundance is unlikely to exceed 325 adults.

Mountain Slough:

The Mountain Slough mainstem suffers from extreme eutrophication. When the subpopulation was first found in 2002, most of the headwater habitat was completely infilled with Reed Canary Grass, which eliminated open water habitat (Pearson unpubl. data). Following completion of a major habitat enhancement project in 2005 (reconstructing 1.8 km of mainstem channel; reaches MTN5 MTN6), catch rates increased; they peaked in 2008 (Table 15) and then returned to very low levels in subsequent years. The largest tributary, McCallum Slough, contains the primary spawning site in the watershed (200 m of pool-riffle habitat). Following habitat enhancement work (Reed Canary Grass removal and large wood complexing) in 2007 from the reach above the spawning area (MTN28), catch rates increased and then declined over the next years. Mark-recapture Abundance estimates in 2011 and 2014 gave a total of less than 100 fish. Extensive damage to the spawning and rearing areas of lower McCallum Slough occurred between 2015 and 2018 as a result of poorly executed channel reconstruction for drainage purposes (Pearson unpubl. data). Water quality in remaining tributaries in the watershed has been too poor to support fish since before 2002. However, the habitat is otherwise suitable and was likely occupied historically, when the area of suitable habitat was more than double the current area. In 2016, an attempt to estimate abundance using mark-recapture failed due to the low number caught (54 fish in 815 trap sets). Current abundance seems unlikely to exceed 100 fish.

Pepin Creek:

A watershed-scale Abundance estimate (1,754 adults) was completed in 2012, and abundance has been monitored repeatedly in several habitat enhancement projects in the watershed, some for over 20 years (Table 16). Between 1999 and 2002, abundance and CPUE was very high in the mainstem, particularly within Pepin Marsh, a complex of beaver ponds extending from Huntington Road (8th Ave) to Bradner Road (288th Street). However, abundance crashed to near-zero by 2003, likely due to extreme hypoxia (Pearson 2004). Periodic monitoring suggested that it remained near zero for close to 20 years. Some recovery was indicated by 2022, but CPUE remains less than one sixth of what it was prior to 2003. Salish Creek and Gordon’s Brook are wholly created habitats completed in 1999 (Patton 2003) and 2001 to 2010, respectively. Salish Creek has consistently supported significant numbers of Salish Sucker, with a current estimate of approximately 800 adults (combined upper and lower sections). In Gordon’s Brook, abundance has fluctuated widely in relation to documented changes in water quality (Rosenfeld et al. 2021), and it is currently too low to estimate. Total abundance in the Pepin watershed is unlikely to exceed 1,100 adults.

Salmon River:

The lower and upper sections of Salmon River are divided by a steep reach flowing in a deep ravine. Only a handful of Salish Sucker have ever been caught in the Lower Salmon River, suggesting that these fish may be strays that have descended through the ravine from the reaches upstream (east) of 248th Street. CPUE in the upper mainstem has varied widely across the years (Table 17). In 2013, abundance was estimated at 751. In 2019, despite high effort (315 traps), too few fish were caught to permit an Abundance estimate. Additional trapping in 2021 and 2022 at sites where they have been historically abundant again yielded few or none, suggesting that a population crash occurred between 2013 and 2016. In Tyre Creek, a tributary in which Salish Sucker were first documented in 2016, abundance remains relatively high at 383 adults, but severe hypoxia and lack of flow over large beaver dams in late summer is a significant threat. Total current abundance in Salmon River seems unlikely to exceed 500 adults.

Salwein Creek:

Prior to the drainage of Sumas Lake in 1920, what is now Salwein Creek was part of the extensive wetlands fringing the lake’s east side (see Woods 2001). Its current channels are entirely constructed. Although Salish Sucker has been occasionally caught in linear ditches and ponds north of the dike, the majority of the subpopulation inhabits a wetland complex between the dike and the Vedder River. Hypoxia exacerbated by flow diversion around these habitats was seriously degrading the habitats in the early 2000s, and catch rates were extremely low (Table 18). Habitat creation and enhancement for salmonids in the early 2010s greatly expanded available habitat for Salish Sucker in 2007 to 2010. Salish Sucker catch rates peaked in 2012, when abundance was estimated at 288 adults. Catch rate and estimated abundance declined in a 2020 survey (Table 18), although the results were not statistically significant. Current abundance seems unlikely to exceed 300 adults.

Sqemélwelh Creek (Chawathil):

This subpopulation was discovered in 2018, and adult abundance was estimated to be 64 individuals in 2019 (Table 19). In summer 2019 and 2021, the subpopulation was confined to a 1-ha beaver pond and perhaps 150 m of inlet stream, with the remaining watershed dewatered. In 2022, following unprecedented drought in the Fraser Valley, the beaver pond also became dewatered, presumably decimating the subpopulation. At least a few Salish Sucker likely survived in small pools in the inlet stream, because three were caught there in September immediately before the pond became dewatered (Pearson unpubl. data). Total pool area available to Salish Sucker in October 2022 was likely less than 50 m² for the entire subpopulation. Although habitat enhancement work to increase habitat area available under drought conditions is planned for 2023, recovery of the subpopulation may not be possible, depending on the numbers and demographics of survivors. Current abundance is unlikely to exceed 25 adults.

Population fluctuations, including extreme fluctuations:

Headwater habitats are naturally prone to short-term disturbances, such as drought, heat, freezing, hypoxia, and dewatering through diversion, which cause localized catastrophic mortality. The Salish Sucker is a headwater stream specialist with small body size, early maturation, short life span and a protracted spawning period (Pearson and Healey 2003). This suite of traits imparts a high intrinsic rate of population growth, allowing rapid recovery or recolonization following high mortality over small spatial scales (Winemiller and Rose 1992). In recent years, numbers of adults have shown significant fluctuations at habitat restoration sites, particularly at Gordon’s Brook in the Pepin watershed. These fluctuations are clearly associated with changes in water quality over time. Recently constructed habitats tend to be less prone to episodes of extreme hypoxia because biochemical oxygen demand (BOD) is low due to a lack of accumulated organic material. As the habitats mature, BOD increases, elevating the risk of hypoxia. At Gordon’s Brook, this process was temporarily reset by physical removal of accumulated aquatic vegetation and increasing flow in 2008 to 2009. A large increase in Salish Sucker CPUE followed, but catch rate quickly declined again in subsequent years.

Severe fragmentation

A taxon can be considered to be severely fragmented if most (> 50%) individuals or most (> 50%) of the total area occupied (as a proxy for number of individuals) is in habitat patches that are both (a) smaller than would be required to support a viable population and (b) separated from other habitat patches by a distance larger than the species can be expected to disperse.

Most Salish Sucker subpopulations are separated by unsuitable habitat (for example, Fraser River mainstem) and/or impassable barriers (for example, dikes) that the fish are unlikely or unable to cross. In the Nooksack tributaries (Bertrand, Fishtrap and Pepin watersheds), subpopulations are separated by long sections of unsuitable habitat, such as the Nooksack River mainstem and/or long riffle-rich reaches several times longer than maximum documented dispersal distances.

However, although minimum viable population size (MVP) analysis has not been conducted for Salish Sucker, there is no evidence that more than 50% of individuals occur in habitat patches that are smaller than would be required to support a viable population. Meta-analyses across hundreds of vertebrate species suggest that MVPs are typically in the thousands (Reed et al. 2003; Traill et al. 2007, 2010), but they may be in the hundreds depending on the time scale of interest and species-specific traits (Jamieson and Allendorf 2012; Rosenfeld 2014; Wang et al. 2019). Small-bodied, short-lived freshwater fishes can be highly vulnerable to catastrophic events, which increases the MVP (Velez-Espino and Koops 2012). However, Salish Sucker appears to be well adapted to recover from severe episodic declines in abundance if habitat conditions improve, suggesting that the MVP is not particularly low. If the MVP is not lower than 700 individuals, 58% of the individuals are found in two subpopulations (Chilliwack Delta and Pepin Creek, with an estimated 1,732 and 723 adults, respectively), which would be viable.

Rescue effect

Three of the Canadian subpopulations occur in streams that flow into Washington State’s Nooksack River (Bertrand, Fishtrap, and Pepin creeks). Rescue of the Canadian population is unlikely from south of the border, because there is limited suitable habitat in the American portion of these streams (McPhail 1987; Wydoski and Whitney 2003; Pearson 2004). Intensive sampling of the entire fish community at six sites in Bertrand Creek and one site in Fishtrap Creek in the U.S. from 2006 to 2010 yielded only one Salish Sucker (Vadas pers. comm. 2011).

Threats

Historical, long-term, and continuing habitat trends

Over the past 150 years, large-scale landscape changes have fragmented habitat across the Canadian range, likely reducing or eliminating migration between Salish Sucker subpopulations. Habitat fragmentation dates to at least 1875 with the diversion of the Chilliwack River through Vedder Creek, which isolated it from the delta channels through which it flowed to the Fraser River (Rafter 2001). This changed the hydrology and reduced connections between the former delta streams (presently Atchelitz, Luckakuck, Little Chilliwack, and Semmihault creeks; Schaepe 2001), all of which currently support Salish Sucker (Figure 6). In the early 1800s, old conifer forest (mean age > 400 years) covered an estimated 71% of the Fraser Valley (Boyle et al. 1997), including many areas occupied by Salish Sucker. The remaining occupied watersheds are within the Fraser River floodplain, and they would have been forested with flood-tolerant deciduous trees and shrubs or herbaceous vegetation prior to European contact (see Duffield 2001). Land clearing, road building, and settlement began (outside of the Vancouver area) in the 1860s, and these activities accelerated dramatically with the completion of the Canadian Pacific Railway in 1885. By 1918, most valley bottomland had been altered by logging or fire, and by the 1930s, it had become British Columbia’s largest clearcut (Duffield 2001). More than 60% of bank length of Salish Sucker critical habitat lacked woody vegetation or was bordered by strips less than 5 m wide in 2004 (Pearson 2008). Additional losses have occurred annually since then (Pearson pers. obs.). Such massive losses of forest cover, particularly in riparian areas, have profoundly affected Salish Sucker habitat. Removal of woody riparian vegetation elevates peak water temperatures in streams (Bowler et al. 2012; Ryan et al. 2013), which exacerbates eutrophication and hypoxia. It also reduces bank stability, leading to increased erosion and sedimentation, and reduces habitat complexity by decreasing the supply of large woody debris to the channel.

The highest densities of Salish Sucker are found in headwater wetlands, habitats that were frequently drained for agricultural development. More than 77% of the lower Fraser River Valley’s pre-settlement wetlands have been drained or infilled (Boyle et al. 1997), and 15% of its streams have been eliminated by urban or agricultural development (Fisheries and Oceans Canada 1998). The largest loss of aquatic habitat occurred with the drainage of Sumas Lake in the 1920s (Woods 2001; Watt 2006) and the isolation of sloughs from the Fraser River by dikes. Dike building began in the 1860s and was largely completed in the aftermath of the 1948 Fraser River flood (Boyle et al. 1997; Watt 2006).

Several historical dispersal routes were cut off completely or seasonally by this flood control infrastructure. The Hope Slough system connected to the Fraser River in several places across from the outlets of Agassiz and Mountain Slough. These were closed off completely by dike construction (Figure 6). The floodgates and/or pump houses at the outlets of Hope Slough, Mountain Slough, Miami Creek, Chilliwack Creek, and the Salmon River impose seasonal barriers to movement (Figures 5, 6, and 7), primarily in late spring, during the Fraser River freshet. The flood gate on Agassiz Slough (upgraded in late 2021) may have played a role in the presumed extirpation of Salish Sucker there by preventing them from exiting as habitat inside the dike became severely hypoxic and largely dewatered. The swift-flowing, turbid Fraser River also poses a formidable barrier to dispersal between its tributaries, particularly in the upstream direction and especially during the spring and summer when its discharge is highest. The recent installation of a fish-friendly pump at Mountain Slough (2016) has improved access, but a proposed dike and floodgate across lower Hope Slough will decrease it to some extent. Drainage and the infilling of headwater wetlands have eliminated what was likely a historical dispersal route between the Little Campbell River and Bertrand Creek (Pearson 1998).

Gravel mining has affected 25% of the Pepin Creek watershed, causing an estimated 10% loss in water storage capacity, which is implicated as the primary cause of a significant reduction in base flow (1984 to 2011; Wang et al. 2017). At least two large-scale sediment releases from gravel pits and a debris flow caused by a berm failure and the resulting headwater capture of Howe’s Creek in 2008 have infilled habitat in Pepin Creek (Pearson 2015a).

In the past 25 years, habitat creation projects have added substantial areas of suitable habitat for Salish Sucker in the Pepin Creek (approx. 10,000 m²) and Salwein Creek (approx. 5,000 m²) watersheds. Enhancement projects have occurred in all occupied watersheds and included Reed Canary Grass removal, expanding deep pool area, and increasing cover through the addition of large woody debris. Moderate to high Salish Sucker catch rates (CPUE > 1 fish/trap) have been documented in many of these areas (Pearson unpubl. data), but all are now seasonally degraded by severe hypoxia, primarily due to agricultural nutrient pollution (Rosenfeld et al. 2021) and/or dewatering during drought (Pearson unpubl. data). Numerous riparian planting projects have been completed in the past 25 years (Fisheries and Oceans Canada 2022), but ongoing destruction of riparian vegetation elsewhere in the watersheds has likely resulted in net losses.

At present, subpopulations in Canada are limited by poor water quality, drought, and physical habitat degradation. The human population of the Metro Vancouver and Fraser Valley Regional Districts are projected to increase by 32% from 2023 to 2045 (BC Stats 2023). The associated land development and intensification of livestock farming (through supply managed dairy and poultry) will further degrade stream habitats. Climate change is already having major impacts on habitat through drought and temperature extremes. The cumulative impacts are likely to lead to extirpation of multiple subpopulations without watershed-scale habitat restoration (particularly of riparian areas) and major reductions in nutrient loading.

Current and projected future threats

Salish Sucker is vulnerable to the cumulative effects of various threats, especially agricultural nutrient pollution, which drives eutrophication and severe hypoxia (Rosenfeld et al. 2021; Boyd et al. 2022), and climate-change induced drought and extreme temperatures. The nature, scope, and severity of these threats has been described in Appendix 3, following the IUCN-CMP (International Union for the Conservation of Nature – Conservation Measures Partnership) unified threats classification system (see Salafsky et al. 2008 for definitions and Master et al. 2012 for guidelines). The threat assessment process consists of assessing impacts for each of 11 main categories of threats and their subcategories, based on the scope (proportion of population exposed to the threat over the next 10-year period), severity (predicted population decline within the scope during the next 10 years or 3 generations, whichever is longer, up to ~100 years), and timing of each threat. The overall threat impact is calculated by taking into account the separate impacts of all threat categories and can be adjusted by the species experts participating in the threats evaluation.

The overall threat impact for Salish Sucker is considered Very high, corresponding to an anticipated further decline of between 50% and 100% over the next 10 years. These values are to be interpreted with caution, as they may be based on subjective information, such as expert opinion, although efforts have been made to corroborate the scores with available studies and quantitative data.

Pollution (IUCN 9; overall threat impact high):

Severe hypoxia is documented in critical habitat of all occupied watersheds except Sqemélwelh Creek at Chawathil (Rosenfeld et al. 2021). It may be lethal or cause sublethal impacts on growth, health, and/or reproduction. The root cause of hypoxia in these habitats is eutrophication driven by nutrient pollution. Hypoxia is most severe and extensive in late summer and fall (Figure 11). Supersaturation is relatively common in spring and early summer, indicating that late summer decomposition of algal biomass contributes to the fall peak in hypoxia. The timing of hypoxia coincides with elevated water temperatures and especially with declining stream flow (Figure 11). Although the pattern is similar across years, it is important to note that the data shown are an average of 16 years of sampling. During the unprecedented episodes of severe drought and heat the habitat has experienced in recent years (see Climate Change, IUCN 11), hypoxia has been much more extensive and severe than the figure suggests. Shade from riparian forests has been shown to reduce eutrophication and hypoxia in Salish Sucker habitat even when nutrient levels are high (Ramirez 2022), but very little riparian vegetation is present on agricultural lands within these watersheds (Pearson 2007).

Figure 11. Seasonal changes in dissolved oxygen in 180 km of Salish Sucker critical habitat (Panel C). Daytime dissolved oxygen measurements (n= 7,473, 2003 to 2018) are binned into severely hypoxic (< 2.5 mg/L, red bars), moderately hypoxic (2.5 to 4 mg/L, yellow bars) and greater than 4 mg/L (blue bars). Supersaturated measurements indicating algae blooms are included in blue bars to avoid skewing the percentage of hypoxic measurements. Panel A shows a moderate correspondence between the severity of hypoxia and water temperature (red line), but a larger correspondence with average monthly stream flow in the Georgia Depression ecoprovince (blue line). Panel B shows the incidence of supersaturation by month (green bars; from Rosenfeld et al. 2021).

Numerous studies have highlighted the predominant role of agricultural sources in nutrient loading to Fraser Valley streams through runoff, groundwater contamination, and aerial deposition. More than 20 years ago, Schreier et al. (2003) calculated that on average across the Fraser Valley, nitrogen was being applied at a rate more than 50 kg/ha over the maximum uptake ability of crops. In some watersheds occupied by Salish Sucker, the surplus exceeded 100 kg/ha. Smith (2004) showed positive relationships between animal stocking density and surplus nitrogen applications adjacent to Fraser Valley riparian areas, and she found that the rapid increase in animal density between 1973 and 2003 increased nitrate levels in stream water in winter, when plants were not growing. Leachable nitrogen in fields across the Fraser Valley increased from negative values prior to 1971, to balanced inputs from 1971 to 1976, to a surplus by 1990 (Vizcarra et al. 1997). Schindler et al. (2006) reviewed the impacts of nitrogen loading on aquatic ecosystems across Canada and concluded that the Fraser River estuary was the most threatened ecosystem in the country due to intensifying Fraser Valley agriculture and expanding human population. Animal density has continued to increase since these studies were completed. More recently, Putt et al. (2019) quantified the relative contributions of all sources of nitrogen and phosphorous to Cultus Lake in the Fraser Valley, concluding that agriculture was the largest source of nutrient inputs from both runoff and aerial deposition. The proportion of land devoted to agriculture within Fraser Valley watersheds is significantly and positively correlated with nitrate, nitrite, and orthophosphate levels (Addah 1998; Schupe 2013, 2017) and negatively correlated with dissolved oxygen (Ramirez 2022; Schupe 2013).

Other significant nutrient sources include urban stormwater, leaking septic systems (Lavkulich et al. 1999), and aerial deposition from urban sources, particularly nitrous oxide from vehicle exhaust (Putt et al. 2019).

Chronic sedimentation originating from urban stormwater systems, agricultural ditches, or upslope logging continues to affect parts of all occupied watersheds. The risk of episodic sediment release from gravel mines and construction sites is ever-present, particularly in association with extreme weather events. Sediment may infill and smother spawning gravels, reducing egg survival or, in extreme cases, infill habitats completely. Localized areas of chronic toxicity are documented within critical habitat in Agassiz Slough (stormwater sediment) and Salwein Creek (polycyclic aromatic hydrocarbons from a 2-km‑long creosote retaining wall). The severity of the impact of these pollutants on Salish Sucker is unknown. Toxic spills originating on roads and railways or from pipelines present a constant risk to Salish Sucker habitat.

Climate change and severe weather (IUCN 11; overall threat impact high):

Summer drought severity has exceeded thresholds for impacts to ecosystems in four of the past eight years in the Fraser Valley (Figure 12). Those impacts have been very evident in Salish Sucker habitats. Over 90% of habitat available to the Sqemélwelh Creek subpopulation dewatered completely in September 2022 and August 2023, when drought severity reached an unprecedented Level 5 (Figure 12). Over 50% of critical habitat in Agassiz Slough and large areas in Miami Creek were also dry. The dewatering was likely exacerbated by a change in flow pattern caused by the unprecedented flooding event of November 2021, which was also linked to climate change (Gillett et al. 2022). Air temperatures exceeded 43^oC in the eastern Fraser Valley in the June 2021 “heat dome,” a level described as |impossible” prior to the industrial revolution, a 1-in-200-year event under current climate conditions, and a projected 1-in-10-year event should the global average temperature rise by more than 2^oC, which may occur by 2050 (Bartusk et al. 2022). Fish kills were widespread in this heat wave and the multiple other heat waves that occurred in 2021 and 2022 during which air temperatures exceeded 35^oC (Pearson pers. obs.). Salish Sucker deaths have not been documented directly, but mortality likely occurred at multiple locations.

Figure 12. Maximum drought level experienced in the Fraser Valley in the past eight summers (left panel) and the potential for “adverse impacts on ecosystems and socio-economic values” (right panel; adapted from BC Ministry of Forests 2022).

Natural system modifications (IUCN 7; overall threat impact high):

Other in-stream works (both authorized and illegal) continue to damage habitat across the range. Infilling, bank hardening, and channelization also reduce habitat complexity. Licensed and illegal water withdrawals are commonplace across the range, primarily for agricultural irrigation. There are no data or estimates available on the extent or impacts of agricultural withdrawals. Potential impacts of a proposed municipal well on Little Chilliwack Creek and Luckakuck Creek are currently being studied by the City of Chilliwack (Jefford pers. comm. 2023). Both creeks already partially dewater in drought conditions (Pearson pers. obs.).

Invasive and other problematic species and genes (IUCN 8; overall threat impact high):

All Salish Sucker subpopulations in Canada have coexisted with invasive predatory fish species for decades. American Bullfrog (Lithobates catesbeianus) is present in all occupied watersheds south of the Fraser River, but none to the north (Pearson unpubl. data). The impacts of these predators on Salish Sucker subpopulations remain unknown but may be significant (see Interspecific interactions above for more discussion). Invasive plants also impact aquatic and riparian habitats. Reed Canary Grass infills channels and may form floating mats over ponds, physically infilling Salish Sucker habitat in waterways. Because the grass leaves are above water, this plant does not contribute oxygen to the water column; however, dead grass accumulates in the water and decomposes, contributing to hypoxia. Himalayan Blackberry (Rubus armeniacus) is also widespread. It suppresses the growth of native plant species through competition but does not provide the shade or bank stabilization benefits that larger, deep-rooted woody vegetation does (Murphy 2006). Invasive trees in the walnut family (Juglandaceae) dominate riparian areas in portions of Agassiz Slough and Miami Creek critical habitat (Pearson pers. obs.). They contain juglone, a toxin that leaches into the soil from fallen leaves and eliminates almost all understory plants other than their own progeny (Willis 2000), with likely impacts on soil stability and supply of terrestrial insects to the channel. Himalayan Balsam (Impatiens glandulifera) is also widespread and leaches chemicals that have adverse effects on invertebrates and algae (Diller et al. 2022). Other invasive plant species that have localized impacts on habitat include Cutleaf Blackberry (Rubus laciniatus) and nightshades (Solanum spp.). Introductions of new invasive species (animal and plant) can be expected, although the consequences for Salish Sucker cannot be predicted.

Energy production and mining (IUCN 3; overall threat impact low):

Mining activity is continuing in the Pepin Creek watershed and is steadily expanding into the neighbouring Fishtrap Creek watershed. A quarry borders critical habitat in Mountain Slough. Additional impacts on hydrology are likely to occur in these watersheds (see Wang et al. 2017).

Transportation and service corridors (IUCN 4; overall threat impact low):

Hundreds of road and farm crossings occur within or upstream of occupied habitats. While the risk of a spill at any one location is low, some significant spills will inevitably impact Salish Sucker habitats over the long term. The nature and severity of the impacts will depend on the substance and volume spilled. The existing Trans Mountain Pipeline and the Trans Mountain Expansion project (mechanical completion is anticipated in the second quarter of 2024) cross through or directly upstream of occupied habitat at 12 sites in 6 watersheds (Trans Mountain 2015).

Cumulative threats:

The cumulative impact of threats (categorized somewhat differently) on Salish Sucker has been examined by Boyd et al. (2022; Figure 13) using a land use, area-based approach. The area of land uses that contribute to various threats upstream of “habitat patches” in all occupied watersheds except Sqemélwelh Creek and Salwein Creek was mapped. “Total contributing area” was used as an index of threat severity. Non-nutrient pollution was identified as the largest threat based on this approach, with nutrient loading and riparian zone disturbance also making large contributions (Figure 13). These results broadly agree with those of the IUCN-CMP method. The lesser emphasis on nutrient pollution is likely an effect of the area-based approach used, which does not consider threat intensity, and of several mapping errors. All threats were treated as equally damaging, with only the upstream area of contributing land use considered (Boyd et al. 2022). Mapping errors in the study consist of the following: inclusion of unsuitable areas (steep, riffle/cascade-dominated reaches in Salmon River and Mountain Slough), areas that are dry most of the year, areas upstream of access barriers, inclusion of a watershed with no confirmed records of occurrence (habitat patch 10), and omission of occupied tributaries (all of Salwein Creek and two Pepin Creek tributaries, Salish Creek and Gordon’s Brook).

Figure 13. Stacked mean scores of seven threats to Salish Sucker by watershed. Top of the bar represents the mean cumulative effects score. “Habitat patches” examined were Little Campbell River (01), Cave Creek (02), Perry Homestead Creek (03), Unnamed tributary of Bertrand Creek (04), Pepin Creek (05), Fishtrap Creek (06), Bertrand Creek mainstem + Howes Creek (07), Salmon River (08), Hopedale Slough (09), Lewis Slough (not actually occupied;10) Chilliwack Delta (11), Hope Slough/Elk Creek (12), Agassiz Slough (13), Mountain Slough (14), and Miami Creek (15). Significant mapping errors in the study have affected results to an unknown degree (see text). Adapted from Boyd et al. (2022).

Number of threat locations

Each of the 13 watersheds in the Canadian range is considered a location (Table 2), although with the inferred extirpation of Salish Sucker in Agassiz Slough, 12 locations appear to be extant. With the intensification of drought, heat, and nutrient pollution in recent years, all individuals within a watershed could rapidly be affected by hypoxia and/or heat stress (for example, in a single threatening event in the summer). Although major climate change-induced events could potentially act simultaneously on multiple neighbouring watersheds—suggesting fewer threat locations—even neighbouring watersheds differ in ways that affect their vulnerability to threats. For example, Pepin Creek drains a glacial moraine and has large groundwater inputs, while the neighbouring Bertrand Creek watershed has little groundwater inflow. Consequently, Pepin Creek has much higher base flows and cooler maximum temperatures. The Agassiz Slough Salish Sucker subpopulation appears to be extirpated, but the neighbouring Miami subpopulation still seems relatively stable.

Protection, status, and recovery activities

Legal protection and status

Salish Sucker are listed as Threatened under Schedule 1 of the federal Species at Risk Act (SARA), which states that “no person shall kill, harm, harass, capture, or take…” or “possess, collect, buy, sell or trade an individual.” SARA also prohibits the destruction of a species’ residence or habitat identified as critical habitat in an approved recovery strategy or action plan. Critical habitat was protected by a ministerial Order in Council in July 2019 (SOR/2019-274). Updated maps of critical habitat are provided in the amended recovery strategy (Fisheries and Oceans Canada 2020). Aquatic habitat and some riparian habitat are also protected under the federal Fisheries Act, which prohibits harmful alteration, disruption, or destruction of fish habitat. However, meaningful enforcement actions are rare.

The British Columbia Wildlife Act prohibits the capture, transport, and possession of wildlife (or their parts) without a licence, and the Water Sustainability Act requires authorizations for most works in or around streams that might impact habitat of fish and species at risk. Municipal bylaws protecting streams and/or trees exist in some municipalities, but enforcement is often lacking. Salish Sucker are not listed under the American Endangered Species Act.

Non-legal status and ranks

Salish Sucker are considered Critically Imperilled by NatureServe at the global (G1; last reviewed in 2011), national (N2 Canada and N1 United States), and subnational (S1 Washington; S2 British Columbia) levels (NatureServe 2022). The species is on British Columbia’s Red List (BC Ministry of Environment 2009), and the American Fisheries Society ranks it as Endangered (Jelks et al. 2008). The IUCN Red List does not include Salish Sucker, although it has been listed in the past (COSEWIC 2002).

Land tenure and ownership

Approximately 154.4 of the 196.5 km identified as critical habitat for Salish Sucker occurs in waterways flowing through private land. The remainder is on a mix of federal, provincial, and municipal lands (Table 20), with the majority being federal and consisting mostly of First Nations Reserve Land. Notable exceptions include the large habitat areas on NRS Aldergrove (Department of National Defence) and several contiguous parcels (former military lands) on lower Salwein Creek.

Table 20. Length of identified critical habitat for Salish Sucker held by the federal, provincial, or municipal governments. All remaining habitat flows through private lands, although the water and (usually) the stream bed are held by the province. Critical habitat maps are available in the recovery strategy (Fisheries and Oceans Canada 2020).

Watershed	Property	Owner	Habitat length (m)
Bertrand	NRS Aldergrove	GoC1	1,500
Bertrand	Vanetta Park	ToL2	165
Bertrand	Creekside Park	ToL2	195
Chilliwack	Skway IR5	GoC1	1,142
Chilliwack	Squiaala IR8	GoC1	100
Chilliwack	Squiaala IR7	GoC1	5,900
Chilliwack	Aitchelitch IR9	GoC1	900
Chilliwack	Skowkale IR10	GoC1	550
Chilliwack	Skowkale IR11	GoC1	260
Chilliwack	Yakweakwioose IR12	GoC1	450
Hope/Elk	Hope River Park	CoC3	900
Hope/Elk	Kinsmen Park	CoC3	500
Hope/Elk	Skwali IR3	GoC1	2,300
Hope/Elk	Skwah IR4	GoC1	1,700
Hope/Elk	Skwahla IR2	GoC1	560
Fishtrap	Abbotsford Airport	CoA4	450
Fishtrap	Field north of 0 Avenue	CoA4	500
Fishtrap	East Fishtrap Creek Parks	CoA4	1,400
Hopedale	Provincial Crown Land	BC5	3,540
Little Campbell	Campbell Valley Regional Park	MVRD6	4,500
Little Campbell	Municipal Park	ToL2	500
Miami	Spring Park	VHH7	180
Miami	East Sector Lands	VHH7	3,070
Pepin	Aldergrove Regional Park	MVRD6	3,300
Salmon	NRS Aldergrove	GoC1	3,280
Salmon	MacMillan Park	ToL2	750
Salwein	Great Blue Heron Nature Reserve	CoC3	2,200
Salwein	Great Blue Heron Nature Reserve	GoC1	1,100
Sqemélwelh	Chawathil IR4	GoC8	250

¹ Government of Canada

² Township of Langley

³ City of Chilliwack

⁴ City of Abbotsford

⁵ Government of British Columbia

⁶ Metro Vancouver Regional District

⁷ Village of Harrison Hotsprings

⁸ Government of Canada, occupied habitat but not yet identified as critical habitat

Recovery activities

The majority of the following activities are described in more detail in a recent Species at Risk Act report on recovery progress (Fisheries and Oceans Canada 2022).

• Monitoring of subpopulation abundance at all known locations
• Surveying for undocumented subpopulations in suitable habitats (see Appendix 1 for details; one new subpopulation found in Sqemélwelh Creek)
• Mapping of potential winter habitat, known spawning sites, and reach-scale catch per unit effort (2015)
• Graduate research on hypoxia impacts on Salish Sucker growth and behaviour and on relative importance of flow, nutrient load, and water temperature on dissolved oxygen (Zinn et al. 2021; Ramirez 2022).
• Analysis of 16 years of field data from all known locations mapping the extent, seasonality, and severity of hypoxia, and linking water quality (dissolved oxygen, water temperature) with Salish Sucker catch rates (Rosenfeld et al. 2021)
• Aquatic and/or riparian enhancement projects targeting Salish Sucker were completed at Fishtrap Creek (2018), Chilliwack Delta (2018 to 2020), Gordon’s Brook (Pepin Creek watershed, 2018 to 2020), Miami River (2018 to 2019), Little Campbell River (2018 to 2021), Salmon River (2018), Sqemélwelh Creek (2020), Bertrand Creek 2019 to 2020), Agassiz Slough (2013, 2017, 2021), Mountain Slough (2017 to 2021), and Hope Slough (2019, 2022)
• Inventory of habitat completed and potential habitat restoration projects in occupied watersheds (Fisheries and Oceans Canada, unpubl. data 2021)
• Watershed-level, GIS riparian habitat survey of Little Campbell River (2019)
• Monitoring and maintenance at past habitat enhancement projects
• Repair of “fishway” on Cave Creek allowing access around an old agricultural dam on private land (2021)
• Mapping of habitat areas that may dewater seasonally in Bertrand Creek, Little Campbell River, and Sqemélwelh Creek
• Installation of hydrometric stations in Bertrand Creek in 2019 and 2020 (mainstem + Howes Creek)
• Launch of pilot financial incentive program for riparian protection/restoration in Salish Sucker habitat in Mountain Slough (Farmland Advantage 2022)

A review of the report on recovery progress (Fisheries and Oceans 2022) reveals a lack of action to address water quality, the most serious threat impacting Salish Sucker. Nutrient pollution, particularly from agricultural sources, was identified as the primary threat nearly two decades ago (Pearson 2004) and is clearly driving the decline in most subpopulations (Rosenfeld et al. 2021). Recovery efforts have largely focussed on opportunistic habitat creation and restoration projects. Although necessary, these efforts will not result in recovery without simultaneous action to address pervasive water quality issues.

Information sources

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Collections examined

• Beaty Biodiversity Museum, University of British Columbia, Vancouver, BC http://www.beatymuseum.ubc.ca/collections/fish
• Royal British Columbia Museum, Victoria, BC
• University of Washington/Burke Museum Fish Collection, Seattle, Washington. https://www.burkemuseum.org/collections-and-research/biology/ichthyology

Authorities contacted

• British Columbia Conservation Data Centre, Ecosystems Branch, BC Ministry of Environment. Victoria, British Columbia
• COSEWIC Secretariat, Canadian Wildlife Service, Environment and Climate Change Canada. Gatineau, Quebec
• Ilves, K.L. Research Scientist. Canadian Museum of Nature. Ottawa, Ontario
• May-McNally, S. Acting Senior Science Advisor. Species at Risk and Atlantic Salmon. Department of Fisheries and Oceans. Ottawa. Ontario
• McDonald, R. Senior Environmental Advisor. National Defence, Ottawa, Ontario
• Rosenfeld, J.S.R. Research Scientist. British Columbia Ministry of Environment/ University of British Columbia. Vancouver, British Columbia
• Species at Risk Group, Fisheries and Oceans Canada. Vancouver, British Columbia
• Sadler, K. Head. Species at Risk Recovery, Environment and Climate Change Canada, Canadian Wildlife Service Pacific Region. Nanaimo, British Columbia
• Shepherd, P. Species Conservation and Management Ecosystem Scientist III. Parks Canada. Vancouver, British Columbia
• Wilson, G.A. Aquatic Species at Risk Specialist. Ecosystem Protection and Sustainability Branch, British Columbia Ministry of the Environment. Victoria, British Columbia

Acknowledgements

Funding for the preparation of this report was provided by Environment and Climate Change Canada. Drafts of the report were prepared for COSEWIC by Dr. Mike Pearson (Pearson Ecological, 2840 Lougheed Highway, Agassiz BC, British Columbia V0M 1A1). COSEWIC is indebted to Dr. J.D. McPhail (Emeritus, UBC), who provided observations, insights, and data on many occasions. Dr. Jordan Rosenfeld (BC Ministry of Environment) has led most of the recent research on the species with the help of UBC graduate students Jill Miners, Kaitlyn Zinn, and Samantha Ramirez. Dr. Eric Taylor (UBC) provided genetic confirmation of Salish Sucker identification at Chawathil. Most of the new information presented in this report was collected in research funded by Fisheries and Oceans Canada under contribution agreements with British Columbia Ministry of Environment. Previous COSEWIC Reports on Salish Sucker were prepared by Dr. Alex Peden (2002) and Dr. Mike Pearson (2012).

Biographical summary of report writer

Mike Pearson holds a Ph.D. in Resource Management and Environmental Science from the University of British Columbia (2004). His doctoral research focused on the ecology, status, and recovery prospects of the SARA-listed Salish Sucker (Catostomus sp. cf. catostomus) and Nooksack Dace (Rhinichthys cataractae). He has led fieldwork on these species annually since 1997 and contributed to several peer-reviewed papers on them. He was a member of the National Recovery Team for Non-Game Freshwater Fishes (BC). He authored the Recovery Potential Assessment for the Salish Sucker in Canada (2015a), the guidelines for the capture, handling, scientific study and salvage (2015b), COSEWIC Assessment and Update Status Reports for Salish Sucker (2012), Nooksack Dace (2007, 2018), and Morrison Creek Lamprey (Lampetra sp.; 2010). Since 2001, Dr. Pearson has run Pearson Ecological, a small consulting firm based in Agassiz, BC and specializing in species at risk, and aquatic habitat assessment, enhancement, and monitoring.

Appendix 1.