Northern Brook Lamprey (Ichthyomyzon fossor), Silver Lamprey (Ichthyomyzon unicuspis): COSEWIC assessment and status report 2020

Official title: COSEWIC assessment and status report on the Northern Brook Lamprey Ichthyomyzon fossor (Great Lakes - Upper St. Lawrence populations and Saskatchewan - Nelson River populations) and the Silver Lamprey Ichthyomyzon unicuspis (Great Lakes - Upper St. Lawrence populations, Saskatchewan - Nelson River populations and Southern Hudson Bay - James Bay populations) in Canada

Committee on the Status of Endangered Wildlife in Canada (COSEWIC)
Northern Brook Lamprey - Great Lakes - Upper St. Lawrence populations - Special concern 2020
Northern Brook Lamprey - Saskatchewan - Nelson River populations - Endangered 2020
Silver Lamprey - Great Lakes - Upper St. Lawrence populations - Special concern 2020
Silver Lamprey - Saskatchewan - Nelson River populations - Special concern 2020
Silver Lamprey - Southern Hudson Bay - James Bay populations - Data deficient 2020

COSEWIC assessment summary

Assessment summary - November 2020 - Northern Brook Lamprey - Great Lakes - Upper St. Lawrence River populations

Common name

Northern Brook Lamprey - Great Lakes - Upper St. Lawrence River populations

Scientific name

Ichthyomyzon fossor

Status

Special Concern

Reason for designation

This small, nonparasitic lamprey is found in streams throughout the Laurentian Great Lakes basin and in southwestern Quebec. In the Great Lakes basin, most of its Canadian range, about half of the streams it is known to inhabit are subjected to ongoing chemical treatment for Sea Lamprey control, which causes significant mortality to larval lampreys. Barriers that exclude Sea Lamprey protect this species from exposure to lampricides in upper reaches of many tributaries, and it is still relatively abundant in untreated streams. The overall population is not known to be declining currently. However, it may be exposed to additional threats such as pollution from agricultural effluents and increased temperatures and decreased water flows related to climate change and water control structures. If these threats are not managed effectively, this species may become at greater risk of extinction.

Occurrence

Ontario, Quebec

Status history

The species was considered a single unit and designated Special Concern in April 1991. When the species was split into separate units in April 2007, the “Great Lakes - Upper St. Lawrence populations” unit was designated Special Concern. Status re-examined and confirmed in November 2020.

Assessment summary - November 2020 - Northern Brook Lamprey - Saskatchewan - Nelson River populations

Common name

Northern Brook Lamprey - Saskatchewan - Nelson River populations

Scientific name

Ichthyomyzon fossor

Status

Endangered

Reason for designation

This small, nonparasitic lamprey has a very limited distribution in the Winnipeg River watershed in southeastern Manitoba. The number of mature individuals is declining based on observed reductions in extent of occurrence, area of occupancy, and number of locations, and an inferred decline in quantity and quality of aquatic habitat. These populations are exposed to threats, such as decreases in stream flows under current and future climates, and are very susceptible to anticipated increases in water temperature. Substantial recent targeted sampling, using both conventional methods and environmental DNA (sampling water to confirm presence of DNA from the species), now provides sufficient data to conclude that this species is at risk of extinction.

Occurrence

Manitoba

Status history

The species was considered a single unit and designated Special Concern in April 1991. When the species was split into separate units in April 2007, the “Saskatchewan - Nelson River populations” unit was designated Data Deficient. Status re-examined and designated Endangered in November 2020.

Assessment summary - November 2020 - Silver Lamprey - Great Lakes - Upper St. Lawrence River populations

Common name

Silver Lamprey - Great Lakes - Upper St. Lawrence River populations

Scientific name

Ichthyomyzon unicuspis

Status

Special Concern

Reason for designation

This small parasitic lamprey is distributed in streams and lakes throughout the Laurentian Great Lakes basin and in southern Quebec. In the Great Lakes basin, a major part of its range, about half of the streams that it inhabits have barriers, or are subjected to ongoing chemical treatment for Sea Lamprey control. These control methods prevent migration to spawning areas or cause significant mortality to larval individuals, respectively. Throughout its range, it may be exposed to additional threats such as pollution from agricultural effluents, effects of water control structures, and increased temperatures and decreased water flows related to climate change. If these threats are not managed effectively, this species may become at greater risk of extinction.

Occurrence

Ontario, Quebec

Status history

This species was designated Special Concern in May 2011. Status re-examined and confirmed in November 2020.

Assessment summary - November 2020 - Silver Lamprey - Saskatchewan - Nelson River populations

Common name

Silver Lamprey - Saskatchewan - Nelson River populations

Scientific name

Ichthyomyzon unicuspis

Status

Special Concern

Reason for designation

This small parasitic lamprey is found in widely disjunct, but limited, areas in streams and lakes in the Nelson and Winnipeg River basins of Manitoba and northwestern Ontario. The species is susceptible to fluctuating water levels as a result of water management and climate change. Recent sampling using conventional methods and environmental DNA (sampling water to confirm presence of DNA from the species) now provide sufficient data to conclude that populations of this species may be declining and may become at greater risk of extinction if these threats are not managed effectively.

Occurrence

Ontario, Manitoba

Status history

This species was considered in May 2011 and placed in the Data Deficient category. Status re-examined and designated Special Concern in November 2020.

Assessment summary - November 2020 - Silver Lamprey - Southern Hudson Bay - James Bay populations

Common name

Silver Lamprey - Southern Hudson Bay - James Bay populations

Scientific name

Ichthyomyzon unicuspis

Status

Data Deficient

Reason for designation

This small parasitic lamprey has only recently been confirmed as present in the Southern Hudson Bay-James Bay basin based on the two specimens found on angled Northern Pike in the upper Hayes River system of northern Manitoba. There is insufficient information with which to assess the eligibility and status of this species in this system.

Occurrence

Manitoba

Status history

Species considered in November 2020 and placed in the Data Deficient category.

COSEWIC executive summary

Northern Brook Lamprey

Ichthyomyzon fossor

Great Lakes - Upper St. Lawrence populations

Saskatchewan - Nelson River populations

and the

Silver Lamprey

Ichthyomyzon unicuspis

Great Lakes - Upper St. Lawrence populations

Saskatchewan - Nelson River populations

Southern Hudson Bay - James Bay populations

Wildlife species description and significance

The Northern Brook Lamprey (Ichthyomyzon fossor) and Silver Lamprey (Ichthyomyzon unicuspis) are closely related “paired” species that are generally indistinguishable during their long larval phase, but they adopt very different lifestyles at metamorphosis and they are formally recognized as valid species. The Northern Brook Lamprey begins sexual maturation during metamorphosis and spawns and dies without feeding again. In contrast, the Silver Lamprey feeds parasitically on other fishes for approximately one year before initiating sexual maturation. Consequently, the Northern Brook Lamprey is only 120-150 mm in length at maturity, while the Silver Lamprey reaches at least 250-300 mm in length. Lampreys have special scientific significance as one of only two groups of jawless fishes that evolved more than 500 million years ago, and understanding the genetic mechanisms by which the parasitic feeding phase has been eliminated in the Northern Brook Lamprey could lead to new ways of controlling invasive Sea Lamprey (Petromyzon marinus) in the Great Lakes. Lampreys are also fed on by a variety of aquatic, aerial, and terrestrial predators.

Distribution

Northern Brook and Silver Lampreys are found in fresh water in eastern North America. In Canada, they occur in the Great Lakes - Upper St. Lawrence and Saskatchewan - Nelson River National Freshwater Biogeographic Zones (NFBZs) in Quebec, Ontario, and Manitoba. The Silver Lamprey has a slightly wider distribution than the Northern Brook Lamprey, and its occurrence has recently been confirmed in a third NFBZ, the Southern Hudson Bay - James Bay NFBZ.

Habitat

Larval Northern Brook and Silver lampreys burrow in silty substrate in rivers and streams. Northern Brook Lamprey adults remain within their home stream, moving only short distances upstream to spawn in relatively shallow areas with coarse gravel and a moderate current. In contrast, Silver Lamprey migrate downstream to large river or lake systems to feed as parasites; at maturity, they migrate upstream and spawn in similar habitats as Northern Brook Lamprey or, sometimes, in deeper rivers.

Biology

The larval stage in these species lasts for approximately 3-7 years, although it can be quite variable, and the Northern Brook Lamprey likely metamorphoses at older ages and larger sizes than Silver Lamprey. The larval stage likely averages just over 5 years in Northern Brook Lamprey (i.e., from spawning in late spring/early summer to metamorphosis in late summer/early fall) and just over 4 years in Silver Lamprey. The post-metamorphic lifespan of Northern Brook Lamprey is 6-8 months, while Silver Lamprey live for another year while feeding parasitically (and often non-lethally) on large-bodied fishes such as Lake Sturgeon (Acipenser fulvescens) and Northern Pike (Esox lucius). Like all lampreys, Northern Brook and Silver lampreys die after a single spawning season. Therefore, the average age at maturity and generation time is the same as the total lifespan, which is approximately 6 years for both species. Northern Brook Lamprey females produce an average of 1,200 eggs, while the larger-bodied Silver Lamprey produces approximately 19,000 eggs per female.

Population sizes and trends

Population estimates are not available, but changes in relative abundance can be inferred in the Great Lakes basin from incidental capture during Sea Lamprey control efforts (although this means that sampling is biased towards stream reaches with Sea Lamprey). Catch rates of larval Northern Brook and Silver lampreys (combined) have been relatively consistent over the last three generations, but they were lower in 2001-2018 than in 1989-2000. Catch rates of adult Silver Lamprey appear to have stabilized or increased over the last three generations, although they are low overall.

Threats and limiting factors

The key threat to Northern Brook and Silver lampreys in Great Lakes tributaries is the application of lampricides used to control the invasive Sea Lamprey. Dams and barriers that exclude Sea Lamprey from the upper reaches of tributaries occupied by the stream-resident Northern Brook Lamprey protect many populations of the latter species from exposure to lampricides, but these barriers block the upstream migration of Silver Lamprey so that their distribution often overlaps with that of Sea Lamprey. In the Saskatchewan - Nelson River populations, Northern Brook Lamprey may be susceptible to impacts from invasive species and climate change (e.g., increased temperatures, decreased water quantity). Silver Lamprey, being lower in the watershed, is likely less susceptible to the effects of climate change, but may be more impacted by lampricide treatments, large hydroelectric dams, and a broad array of other threats.

Protection, status and ranks

The Great Lakes - Upper St. Lawrence populations of both Northern Brook Lamprey and Silver Lamprey are listed under Schedule 1 of the Species at Risk Act (SARA) as Special Concern. The Saskatchewan - Nelson River populations of both species were assessed by COSEWIC as Data Deficient in 2007. The federal Fisheries Act and provincial legislation may provide indirect protection to both species. NatureServe ranked the global populations of Northern Brook and Silver lampreys as G4 (Apparently Secure) and G5 (Secure), respectively.

Technical summary - Great Lakes - Upper St. Lawrence River populations

Ichthyomyzon fossor

Northern Brook Lamprey

Lamproie du Nord

Range of occurrence in Canada (province/territory/ocean): Ontario, Quebec

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes

Overall threat is Very High.

1. Lampricide treatments of populations co-existing with Sea Lamprey larvae (High)
2. Dams and water management/use (Medium-Low)
3. Climate change and severe weather (Medium-Low)
4. Invasive non-native species (Medium-Low)
5. Other pollution (especially agricultural effluent) (Low)

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status history: The species was considered a single unit and designated Special Concern in April 1991. When the species was split into separate units in April 2007, the “Great Lakes - Upper St. Lawrence populations” unit was designated Special Concern. Status re-examined and confirmed in November 2020.

Status and reasons for designation:

Status:

Special Concern

Alpha-numeric codes:

Not applicable

Reason for designation:

This small, nonparasitic lamprey is found in streams throughout the Laurentian Great Lakes basin and in southwestern Quebec. In the Great Lakes basin, most of its Canadian range, about half of the streams it is known to inhabit are subjected to ongoing chemical treatment for Sea Lamprey control, which causes significant mortality to larval lampreys. Barriers that exclude Sea Lamprey protect this species from exposure to lampricides in upper reaches of many tributaries, and it is still relatively abundant in untreated streams. The overall population is not known to be declining currently. However, it may be exposed to additional threats such as pollution from agricultural effluents and increased temperatures and decreased water flows related to climate change and water control structures. If these threats are not managed effectively, this species may become at greater risk of extinction.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. No information available on population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. IAO meets threshold for Threatened, B2, but not severely fragmented and >10 locations. No continuing decline (declines occurred > 3 generations ago), and fluctuations that are more recent are more likely related to variation in search effort.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. No information available on population size.

Criterion D (Very Small or Restricted Population): Not applicable. No information available on population size.

Criterion E (Quantitative analysis): Not applicable. Data not available.

Technical summary - Saskatchewan - Nelson River populations

Ichthyomyzon fossor

Northern Brook Lamprey

Lamproie du Nord

Range of occurrence in Canada (province/territory/ocean): Manitoba

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes

Overall threat is High-Medium.

1. Climate change and severe weather (High-Low)
2. Dams and other water use management (Low)
3. Invasive non-native species (Low)

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status history: The species was considered a single unit and designated Special Concern in April 1991. When the species was split into separate units in April 2007, the “Saskatchewan - Nelson River populations” unit was designated Data Deficient. Status re-examined and designated Endangered in November 2020.

Status and reasons for designation:

Status:

Endangered

Alpha-numeric codes:

B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)

Reasons for designation:

This small, nonparasitic lamprey has a very limited distribution in the Winnipeg River watershed in southeastern Manitoba. The number of mature individuals is declining based on observed reductions in extent of occurrence, area of occupancy, and number of locations, and an inferred decline in quantity and quality of aquatic habitat. These populations are exposed to threats, such as decreases in stream flows under current and future climates, and are very susceptible to anticipated increases in water temperature. Substantial recent targeted sampling, using both conventional methods and environmental DNA (sampling water to confirm presence of DNA from the species), now provides sufficient data to conclude that this species is at risk of extinction.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. No information available on population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Meets Endangered, B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v), with small EOO (162 km²) and IAO (108 km²), < 5 locations, and observed, projected or inferred continuing decline in (i) extent of occurrence; (ii) index of area of occupancy; (iii) extent and quality of habitat; (iv) number of locations; and (v) number of mature individuals.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. EOO and IAO exceed thresholds.

Criterion D (Very Small or Restricted Population): Not applicable. No information available on population size.

Criterion E (Quantitative analysis): Not applicable. Data not available.

Technical summary - Great Lakes - Upper St. Lawrence River populations

Ichthyomyzon unicuspis

Silver Lamprey

Lamproie argentée

Range of occurrence in Canada (province/territory/ocean): Ontario, Quebec

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes

Overall threat is Very High.

1. Lampricide treatments of populations co-occurring with Sea Lamprey larvae (High)
2. Dams and water management/use (Medium-Low)
3. Invasive non-native species (Medium-Low)
4. Climate change and severe weather (Medium-Low)

What additional limiting factors are relevant? The migratory behaviour of Silver Lamprey means that its in-stream distribution overlaps considerably with Sea Lamprey in the Great Lakes, but its lower fecundity makes it a poor competitor to the invasive Sea Lamprey.

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status history: This species was designated Special Concern in May 2011. Status re-examined and confirmed in November 2020.

Status and reasons for designation:

Status:

Special Concern

Alpha-numeric codes:

Not applicable

Reasons for designation:

This small parasitic lamprey is distributed in streams and lakes throughout the Laurentian Great Lakes basin and in southern Quebec. In the Great Lakes basin, a major part of its range, about half of the streams that it inhabits have barriers, or are subjected to ongoing chemical treatment for Sea Lamprey control. These control methods prevent migration to spawning areas or cause significant mortality to larval individuals, respectively. Throughout its range, it may be exposed to additional threats such as pollution from agricultural effluents, effects of water control structures, and increased temperatures and decreased water flows related to climate change. If these threats are not managed effectively, this species may become at greater risk of extinction.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. No information available on population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. EOO and IAO exceed thresholds.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. No information available on population size.

Criterion D (Very Small or Restricted Population): Not applicable. No information available on population size.

Criterion E (Quantitative analysis): Not applicable. No data available.

Technical summary - Saskatchewan - Nelson River populations

Ichthyomyzon unicuspis

Silver Lamprey

Lamproie argentée

Range of occurrence in Canada (province/territory/ocean): Ontario, Manitoba

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes

Overall threat is High-Medium.

1. Dams and water management (Medium/Low)
2. Climate change and severe weather (Low)
3. Invasive non-native species (Low)
4. Forestry effluents (Low)

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status history: This species was considered in May 2011 and placed in the Data Deficient category. Status re-examined and designated Special Concern in November 2020.

Status and reasons for designation:

Status:

Special Concern

Alpha-numeric codes:

Not applicable

Reasons for designation:

This small parasitic lamprey is found in widely disjunct, but limited, areas in streams and lakes in the Nelson and Winnipeg River basins of Manitoba and northwestern Ontario. The species is susceptible to fluctuating water levels as a result of water management and climate change. Recent sampling using conventional methods and environmental DNA (sampling water to confirm presence of DNA from the species) now provide sufficient data to conclude that populations of this species may be declining and may become at greater risk of extinction if these threats are not managed effectively.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. No information available on population trends.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. May meet Threatened, B2ab(i,ii,iv), with IAO (954 km²) and number of locations (2 to >10) lower than thresholds, but not severely fragmented, and declines in EOO, IAO and locations likely related to search effort. No decline in habitat quality or quality.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. No information available on population size.

Criterion D (Very Small or Restricted Population): Not applicable. No information available on population size.

Criterion E (Quantitative analysis): Not applicable. Data not available.

Technical summary - Southern Hudson Bay - James Bay populations

Ichthyomyzon unicuspis

Silver Lamprey

Lamproie argentée

Range of occurrence in Canada (province/territory/ocean): Manitoba

Threats (direct, from highest impact to least, as per IUCN Threats Calculator)

Was a threats calculator completed for this species? Yes

Overall threat is unknown

Data sensitive species

Is this a data sensitive species? No

Status history

COSEWIC Status history: Species considered in November 2020 and placed in the Data Deficient category.

Recommended status and reasons for designation:

Status:

Data Deficient

Alpha-numeric codes:

Not applicable

Reason for designation:

This small parasitic lamprey has only recently been confirmed as present in the Southern Hudson Bay-James Bay basin based on the two specimens found on angled Northern Pike in the upper Hayes River system of northern Manitoba. There is insufficient information with which to assess the eligibility and status of this species in this system.

Applicability of criteria

Criterion A (Decline in Total Number of Mature Individuals): Not applicable. Data not available.

Criterion B (Small Distribution Range and Decline or Fluctuation): Not applicable. Data not available.

Criterion C (Small and Declining Number of Mature Individuals): Not applicable. Data not available.

Criterion D (Very Small or Restricted Population): Not applicable. Data not available.

Criterion E (Quantitative analysis): Not applicable. Data not available.

Preface

In 2007 and 2011, COSEWIC assessed the status of Northern Brook Lamprey and Silver Lamprey, respectively, in Canada, dividing each species into two designatable units (DUs). The Saskatchewan - Nelson River DU of each species was designated Data Deficient. Directed surveys for distribution and abundance had not been conducted on either species in these DUs, and data on trends were unavailable. However, since 2010, more targeted sampling has been conducted in these DUs (including using environmental DNA assays), and there has been increased reporting of parasitic feeding phase Silver Lamprey caught incidentally by anglers or during surveys for other fish species.

Status assessment of each species was also hampered by the inability to distinguish Northern Brook and Silver lampreys from one another as larvae, which has confounded attempts to accurately assess the distribution of each species. Even in the Great Lakes - Upper St. Lawrence DU, where both species were designated Special Concern, larval assessment data are pooled for the two species and many occurrence records have been based only on larvae that could not be identified to species.

Therefore, because it is difficult or impossible to evaluate the Northern Brook Lamprey and Silver Lamprey entirely independently, the two species are being evaluated together in a single updated report. Furthermore, the species have largely overlapping distributions and similar threats in Canada. Genetic studies show that Northern Brook and Silver lampreys are very closely related and may experience some gene flow where they co-occur. Nevertheless, although the relationship between these paired species has yet to be fully resolved, Northern Brook and Silver lampreys are recognized as distinct species using conventional lamprey taxonomy, and they maintain distinct phenotypes even where they spawn sympatrically. Each should continue to be considered as a distinct species in the accepted sense of the taxonomic hierarchy.

Since 2011, Silver Lamprey presence has been confirmed in a third National Freshwater Biogeographic Zone, the Southern Hudson Bay-James Bay NFBZ. Silver Lamprey had been reported previously in this NFBZ, but no vouchered specimens with clear locational information were kept prior to 2011.

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 (2020)

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

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Petromyzontida

Order: Petromyzontiformes

Family: Petromyzontidae

Scientific name: Ichthyomyzon fossor Reighard and Cummins 1917

Common names:

English: Northern Brook Lamprey

French: lamproie du nord

Scientific name: Ichthyomyzon unicuspis Hubbs and Trautman 1937

Common names: English: Silver Lamprey

French: lamproie argentée

Ichthyomyzon, derived from Greek, translates to “fish” (ichthys) and “suckle” (myzo). The species epithet fossor, meaning “digger,” is in reference to the Northern Brook Lamprey’s main life stage where it burrows in substrate to filter feed, and unicuspis refers to the Silver Lamprey’s distinguishing feature of having single cusps on the circumoral teeth (Scott and Crossman 1998). Previous nomenclature of the Northern Brook Lamprey includes: Ammocoetes unicolor DeKay 1842, Ammocoetes borealis Agassiz 1850, and Reighardina unicolor (DeKay 1842). Previous nomenclature of the Silver Lamprey includes: Petromyzon argenteus Kirkland 1941, Ammocoetes concolor Kirkland 1941, Ammocoetes borealis Agassiz 1850, Petromyzon hirudo Jordan and Copeland 1876, Ichthyomyzon castaneus Provancher 1876, and other variations in use up until 1933, but which Hubbs and Trautman (1937) considered were referring to Silver Lamprey (Scott and Crossman 1998).

The Northern Brook Lamprey (Ichthyomyzon fossor) and Silver Lamprey (Ichthyomyzon unicuspis) are one of three closely related species pairs in the genus Ichthyomyzon. Such “paired” species exist in seven of the 10 extant lamprey genera. In each pair, the larvae (which are microphagous filter feeders) are morphologically similar or indistinguishable but, at metamorphosis, their life-history types diverge (see Potter 1980a; Docker 2009; Docker and Potter 2019). One member of the pair (in this case, the Northern Brook Lamprey) begins sexual maturation during metamorphosis and spawns and dies the following spring without ever feeding again; these non-parasitic and non-migratory lampreys are collectively called “brook lampreys.” The other member of the pair (in this case, the Silver Lamprey) remains sexually immature following metamorphosis, feeds parasitically on ray-finned fishes for several months to more than a year (either in its natal stream or after migrating to larger waterbodies) before initiating sexual maturation and embarking on its upstream migration to spawn and die.

Conspicuous morphological (e.g., smaller adult body size, relative eye and oral disc size) and histological (e.g., lack of a functional digestive tract following metamorphosis) differences distinguish non-parasitic adults from parasitic forms, and most lamprey taxonomists recognize feeding type as a species-specific characteristic (e.g., Potter et al. 2015) because size-assortative mating was thought to result in reproductive isolation between such differently sized parasitic and non-parasitic forms (Hardisty and Potter 1971). However, plasticity of feeding type (e.g., facultative parasitism) has been observed in some lamprey populations (Manion and Purvis 1971; Beamish 1987), and molecular data on a number of paired species show no genetic differentiation between species pairs where they co-occur and evidence of contemporary gene flow (e.g., Docker et al. 2012; Rougemont et al. 2015). Such findings have led to suggestions that lamprey paired species are different ecotypes of a single species and even that feeding type might not be genetically determined (see Docker 2009; Artamonova et al. 2011; Docker and Potter 2019).

Recent genomic studies on the European Brook Lamprey (Lampetra planeri) and European River Lamprey (Lampetra fluviatilis) demonstrated that feeding type in this pair did have a genetic basis (i.e., was not due to phenotypic plasticity). Rougemont et al. (2017) identified 40 single nucleotide polymorphisms (SNPs) that were highly differentiated between European River and Brook lampreys, even where they co-occurred and showed evidence of gene flow at neutral loci (i.e., not under selection). A total of 166 species-specific loci were found in a European River-European Brook lamprey pair from southern Portugal (Mateus et al. 2013), although a subsequent study by these authors showed that the two feeding types from this population could also be differentiated at neutral microsatellite loci (F_ST 0.317; Mateus et al. 2016), suggesting that not all of the 166 fixed loci were necessarily correlated with life-history type. Rougemont et al. (2015, 2017) have suggested that these European “species” are partially reproductively isolated ecotypes that maintain distinct phenotypes because regions of the genome involved in reproductive isolation and local adaptation resist the homogenizing effect of introgression, resulting in highly differentiated “genomic islands” amid a background or “sea” of less differentiated loci. The virtual absence of later-generation hybrids in the wild suggested some form of hybrid breakdown (Rougemont et al. 2017).

Similar genomic studies have not yet been performed in the Northern Brook and Silver lamprey pair. Hybridization experiments between Northern Brook Lamprey and Silver Lamprey showed that the survival of hybrids was equivalent to that of pure individuals for the first few weeks following fertilization (Piavis et al. 1970), but there is nothing known regarding possible selection against hybrids later in development (e.g., survival at metamorphosis when the two feeding types diverge or reproductive capacity at maturity). A long-term study investigating the heritability of feeding type of Northern Brook and Silver lamprey larvae transplanted into streams experiencing different environmental conditions was inconclusive given the high rates of mortality experienced during artificial propagation, but no larvae were shown to switch feeding type (Neave et al. 2019). Nevertheless, although it is clear that Silver and Northern Brook lampreys are closely related and may experience some gene flow, it is unlikely that they represent a single panmictic (i.e., freely interbreeding, with no apparent barriers to gene flow) species. The lack of differences observed to date in mitochondrial DNA (mtDNA) and microsatellite markers does not preclude differentiation at regions of the genome related to feeding type. Furthermore, although evidence of gene flow between paired species in sympatry suggests that they are only partially reproductively isolated, it is important to distinguish between true sympatry, where the paired species come into contact (e.g., overlapping in their spawning sites), and situations where they are found in the same basin or river systems but with no opportunity for contemporary gene flow (i.e., where they are parapatric). Although Docker et al. (2012) demonstrated a lack of significant genetic differentiation between Northern Brook and Silver lampreys where they were collected from the same rivers in the Lake Huron basin, the two species were significantly differentiated in the Lake Michigan basin where Northern Brook Lamprey were collected almost exclusively from the basin’s eastern shore and Silver Lamprey were collected from the western shore. Similar patterns have been seen in other lamprey paired species (Bracken et al. 2015; Rougemont et al. 2015), where higher levels of differentiation are observed in parapatry than in sympatry. Northern Brook and Silver lampreys are not often collected from the same tributaries in Canadian waters (see Distribution), reducing the opportunity for gene flow between the species.

Thus, based on recent genomics results in other paired lamprey species and in keeping with conventional lamprey taxonomy (e.g., Renaud et al. 2009; Renaud 2011; Potter et al. 2015; Docker and Potter 2019), Northern Brook and Silver lampreys are considered distinct species here. However, given the potential for gene flow (suggesting that they may not always be entirely evolutionarily independent) and the inability to distinguish them during the long-lived larval stage (thus making it difficult or impossible to evaluate them entirely independently), the two species are being evaluated together in a combined status report. In each section, shared information on the two species will be combined and then, when warranted or possible, each species will be discussed separately in the order Northern Brook Lamprey and then Silver Lamprey.

Morphological description

Lampreys are easily distinguished from most other fishes by their elongate body shape, jawless mouth (characterized by a toothed, oral disc in adults), lack of paired fins and scales, a single large, central nostril, and seven pairs of gill pores leading to internal gills (Figure 1). All lamprey species pass through a protracted larval phase that is spent burrowed in the soft substrata in the slower-flowing regions of streams and rivers (see Biology). The larva, termed an ammocoete, has a worm-like body shape and is blind and toothless, possessing an oral hood for filter feeding rather than the sucking oral disc.

Figure 1. Adult (a) Northern Brook Lamprey (Ichthyomyzon fossor) and (b) Silver Lamprey (Ichthyomyzon unicuspis). Photos by Fraser Neave (used with permission).

The genus Ichthyomyzon can be distinguished from all other lamprey genera by possessing a single indented dorsal fin compared to the two distinct dorsal fins possessed by other genera. This trait allows identification of Ichthyomyzon spp. even during the larval stage. Thus, using this trait, Northern Brook and Silver lampreys can be distinguished from Sea Lamprey (Petromyzon marinus) and American Brook Lamprey (Lethenteron appendix), species with which they may occur in the Great Lakes basin (Renaud et al. 2009; Potter et al. 2015).

Distinguishing among congeneric lamprey species is more difficult. Of the six species in Ichthyomyzon genus, the parasitic Chestnut Lamprey (Ichthyomyzon castaneus) also occurs in Canada-in Saskatchewan and Manitoba, and possibly Ontario and Quebec (Renaud et al. 2009; COSEWIC 2010). In the juvenile (i.e., parasitic feeding phase following metamorphosis but prior to sexual maturation) and adult stages, Northern Brook and Silver lampreys are distinguished from the Chestnut Lamprey by the usual absence in their oral disc of bicuspid inner lateral (or circumoral) teeth (range 0-2; strong mode of 0) compared to typically 6-8 bicuspid inner lateral teeth (range 1-8; mode of 6) in the Chestnut Lamprey (Renaud 2011; Figure 2). Adult non-parasitic Northern Brook Lamprey are easily distinguished from Chestnut Lamprey by their smaller eye, oral disc, and body size, but variation in dentition patterns in the two parasitic species may result in some uncertainty regarding identification (see Distribution). Hubbs and Trautman (1937) showed that 98% of all Silver Lamprey had 0 bicuspid inner lateral teeth and 77% of all Chestnut Lamprey had 6-8 bicuspid inner lateral teeth. In Renaud et al. (1996), 81% of Silver Lamprey from Ontario had 0 bicuspid inner lateral teeth (the rest had 1 or 2 bicuspid inner lateral teeth). In contrast, four of the five Ontario Chestnut Lamprey specimens possessed 4 or 5 bicuspid inner lateral teeth, and the fifth possessed 3 or 4. However, Hall and Moore (1954) reported two Chestnut Lamprey specimens without any bicuspid inner lateral teeth; one specimen was from Oklahoma and the other was from Texas, where neither Northern Brook Lamprey nor Silver Lamprey have ever been reported. Furthermore, genetic analysis has been used to confirm the identity of one Chestnut Lamprey without any bicuspid inner lateral teeth (from the Rat River in Manitoba; Figure 3a) and one Silver Lamprey with one bicuspid inner lateral tooth (from the Winnipeg River near Kenora, Ontario; Figure 3b). In contrast to the subtle morphological differences, there are pronounced and diagnostic differences in mtDNA sequence (Lang et al. 2009; Docker et al. 2012) that have allowed for the development of easy, definitive genetic assays to distinguish Chestnut Lamprey from Silver and Northern Brook lampreys (Neave et al. 2007). This assay is applicable to all stages and sizes, and it has been used to test methods to distinguish Chestnut Lamprey from Northern Brook and Silver lampreys as larvae. According to Vladykov and Kott (1980) and Lanteigne (1981, 1988), Chestnut Lamprey larvae can be distinguished from Northern Brook and Silver lamprey larvae by their darkly pigmented lateral-line organs. Using genetic analysis, Neave et al. (2007) found that the lateral-line organs were not pigmented in any Chestnut Lamprey < 80 mm in total length (TL) but were darkly pigmented in 24% of those 81-104 mm, and all individuals ≥105 mm TL had pigmented lateral-line organs (Figure 4). Thus, although the absence of pigmented lateral-line organs does not definitively identify small Northern Brook and Silver lamprey larvae, their absence is thought to be diagnostic in larger larvae (≥105 mm TL) and their presence definitively identifies Chestnut Lamprey larvae of any size.

Figure 2. Oral disc of: a) Northern Brook Lamprey (Ichthyomyzon fossor); b) Silver Lamprey (Ichthyomyzon unicuspis); and, c) Chestnut Lamprey (Ichthyomyzon castaneus). Source: Food and Agriculture Organization of the United Nations, Original Scientific Illustrations Archive (reproduced with permission).

Figure 3. Atypical dentition in Chestnut and Silver lampreys: a) Chestnut Lamprey (left, as confirmed by genetic analysis) with unicuspid inner lateral teeth and normal bicuspid Chestnut Lamprey (right) collected from the Rat River, Manitoba, in 2011. Photo by Margaret Docker (used with permission); and, b) Silver Lamprey with one bicuspid inner lateral tooth (circled). Photo by Ontario Ministry of Natural Resources and Forestry, Kenora District (used with permission).

Figure 4. Chestnut Lamprey larva displaying pigmentation along its lateral line organs (circled); note that lateral line pigmentation was artificially darkened (in Microsoft Paint) to enhance visibility. Photo by Fraser Neave (used with permission).

The closely related Northern Brook and Silver lampreys are generally distinguishable from one another by mid- to late metamorphosis (Table 1). The non-parasitic Northern Brook Lamprey, which does not feed again after metamorphosis, can be distinguished from post-metamorphic Silver Lamprey by its relatively small eye, small oral disc (which is narrower than the width of the head or body), and poorly developed, knob-like teeth. Northern Brook Lamprey adults are significantly smaller than Silver Lamprey adults. TL at maturity averages 115-119 mm (Hubbs and Trautman 1937; Morman 1979; see Docker 2009). Northern Brook Lamprey also tend to be darker in colour (grey or brown) dorsally and switching to a silvery-white on the ventral surface (Vladykov 1949). It has been observed that during spawning, females can develop an orange tint on their ventral surface, where the eggs show through the body wall; after spawning, both sexes darken to black or a dark blue (Vladykov 1949; Becker 1983). They generally remain within their natal stream and stay burrowed until shortly before spawning (Dawson et al. 2015). Silver Lamprey, which feeds parasitically following metamorphosis, is recognizable by its relatively large eye, large oral disc (which is wider than the width of the head or body), and sharper, more prominent teeth. Silver Lamprey adults are considerably larger than Northern Brook Lamprey. Total length at maturity averages 224-248 mm (Hubbs and Trautman 1937; Vladykov 1951; Morman 1979; see Docker 2009), although individuals as large as 390-415 mm have been reported near the end of the parasitic feeding phase (Morman 1979; Cochran and Marks 1995; Cochran and Lyons 2004) prior to the shrinkage experienced during their non-trophic sexual maturation (see Biology). Silver Lamprey tend to reach smaller sizes in Canada compared to the United States (Scott and Crossman 1998). Vladykov and Roy (1948) reported maximum total length to be 318 mm, although a 331 mm Silver Lamprey was captured in the St. Lawrence River in October 2001 during a standardized survey conducted by the Ministère des Forêts, de la Faune et des Parcs (MFFP). Colouration of adult Silver Lamprey tends to be a tannish-yellow with a darker dorsal surface, and a lighter ventral surface (Hubbs and Trautman 1937). Despite its common name, Vladykov (1949) noted that no silvery colouration was observed in hundreds of adult Silver Lamprey specimens collected in Quebec. In both Northern Brook and Silver lamprey adults, females are generally larger than males (Scott and Crossman 1998; Docker 2009). Given the dramatic differences in size at maturity, Silver Lamprey females are considerably more fecund than Northern Brook Lamprey females (Table 1).

Despite the pronounced morphological differences that emerge at metamorphosis, Northern Brook and Silver lampreys are not distinguishable as larvae. Although there appears to be a general trend in lampreys for fewer trunk myomeres in non-parasitic species relative to parasitic species (Vladykov and Kott 1979), the difference among paired species is rarely, if ever, diagnostic (Docker 2009). Not even subtle differences in myomere number have been observed between Northern Brook and Silver lampreys, where the myomere counts average 50.9 and 50.5, respectively, and the ranges overlap almost completely (Hubbs and Trautman 1937; Table 1). Some authors have described differences between the species in pigmentation patterns in the branchial region (Lanteigne 1981, 1988; Stewart and Watkinson 2004) and tail (Vladykov and Kott 1980; Fuiman 1982). However, some of these keys are contradictory (e.g., Vladykov and Kott 1980; Lanteigne 1988), and other authors have found that such differences in pigmentation or other external features are not reliable for diagnostic species identification, particularly when comparisons are made across a broader geographic area (Purvis 1970; Morman 1979; Becker 1983; Neave et al. 2007).

There are also no diagnostic genetic differences known to exist between Northern Brook and Silver lampreys. Studies using mtDNA sequence data show that Silver and Northern Brook lampreys are not reciprocally monophyletic and lack fixed species-specific differences (Lang et al. 2009; Docker et al. 2012; Ren et al. 2016). Allele frequency differences were observed between the species by Filcek et al. (2005), who were able to distinguish Northern Brook Lamprey from the Lake Superior basin and Silver Lamprey from tributaries to Lake Michigan using microsatellite markers developed for Sea Lamprey. However, as the two species were collected from different basins, observed species differences were likely confounded by geographic differences. Using microsatellite markers, Docker et al. (2012) found no evidence of genetic differentiation between Northern Brook and Silver lampreys where they occur sympatrically in the Lake Huron basin and, although the two species were significantly differentiated when collected from allopatric localities in the Lake Michigan basin, statistical differences in allele frequencies still do not allow for diagnostic identification of individuals. Future genomic analyses (e.g., using SNPs) may identify loci capable of species identification (see Name and Classification), but none exist at present.

Ecological or life-history characteristics are sometimes used to infer species identification, although these are also not conclusive. Location of capture can be an indication of species identity, because Northern Brook Lamprey is more likely to be found in smaller streams than Silver Lamprey (Scott and Crossman 1998). Likewise, Northern Brook Lamprey are more likely to be found above barrier dams, and migratory Silver Lamprey, not surprisingly, tend to be limited to the lower stretches of rivers (see Habitat). The presence of adults of one species or the other is also used sometimes to infer species identification of larvae collected from particular localities, but this is not always reliable, because both species occur together in some tributaries and the limited search effort expended at some localities or at times of the year when adults are present makes it impossible to rule out the presence of the other species. It has also been suggested that differences in the size at which metamorphosis occurs can help distinguish between parasitic and non-para-sitic lampreys (see Docker 2009). In general, metamorphosing Northern Brook Lamprey are larger than metamorphosing Silver Lamprey (Table 1), but this only suggests that very large individuals might be Northern Brook Lamprey. Likewise, larvae of non-parasitic species tend to have a lower potential fecundity (e.g., number of oocytes per histological cross section), and individuals with very high oocyte counts (80-93 per cross section) are likely Silver Lamprey (Neave et al. 2007). However, in most individuals, the differences are likely not diagnostic and this approach requires lethal sampling and time-consuming histological preparation (Neave et al. 2007; Docker 2009; Spice and Docker 2014). Thus, in this report, most data and information on larval Northern Brook and Silver lampreys are pooled.

Population spatial structure and variability

Across larger spatial scales (e.g., across their range within the Great Lakes or between National Freshwater Biogeographic Zones, NFBZs), genetic differences in Northern Brook and Silver lampreys are greater among regions (e.g., basins) than between species. For example, within the Great Lakes and Upper St. Lawrence River NFBZ, an east-to-west gradient was observed in both Northern Brook and Silver lampreys with respect to the distribution of the mtDNA haplotypes; variation among basins was significant, but there was no significant range-wide difference in haplotype frequency between Northern Brook and Silver lampreys (Docker et al. 2012). Of the five most common composite mitochondrial haplotypes, three (A1, A2, and A4) were widespread, occurring in 93% of the > 500 individuals surveyed across this region. However, the fourth haplotype (type A3) was found only in lampreys from Lake Erie and Lake Huron tributaries, and the frequency of the fifth haplotype (B1), which was found in 6% of all individuals, decreased from east to west. Type B1 was found in 75 and 21% of Northern Brook Lamprey from Lake Champlain and Lake Erie, respectively, and in 2-10% of Northern Brook and Silver lampreys from Lake Huron and Michigan, but it was not found among any of the 117 lampreys sampled in the Lake Superior basin. A Mississippian refugium during the most recent Wisconsinan glaciation has been suggested for these species (Mandrak and Crossman 1992), and it is possible that the two observed mitochondrial lineages represent different recolonization routes. Mandrak and Crossman (1992) suggested that Ontario populations of Northern Brook Lamprey re-colonized postglacially from either or both of the Warren or Brule-Portage routes, and they suggested that Silver Lamprey recolonized via the Brule-Portage or Chicago postglacial dispersal routes. Genetic variation among Great Lakes basins was likewise significant using microsatellite loci, although to a lesser extent than using mtDNA markers (e.g., AMOVA showed that 3.1% of the variation in microsatellite allele frequencies was among basins, while 27.9% of the mtDNA variation was among basins). In general, mtDNA retains historical patterns that are more quickly lost in microsatellites, especially with ongoing gene flow among populations (Avise 2000; Heckel et al. 2005; Spice et al. 2019).

Mitochondrial DNA variation has not been systematically examined between the Great Lakes-Upper St. Lawrence and Saskatchewan-Nelson River NFBZs. However, McFarlane (2009) found significant variation between Northern Brook and Silver lampreys from the Great Lakes basin and Silver Lamprey from the Winnipeg River using Ichthyomyzon-specific microsatellite loci. Genetic differentiation (F_ST) among the Great Lakes basins averaged 0.070, but comparison between Silver Lamprey from the Winnipeg River and Northern Brook and Silver lampreys from the Great Lakes yielded F_ST values averaging 0.213. Based on its distribution, Stewart and Watkinson (2004) hypothesized that Silver Lamprey entered the Red River mainstem via Big Stone Lake and Lake Traverse, or Red River tributaries from Mississippi River tributaries in Minnesota. Silver Lamprey also presumably entered Manitoba via the Winnipeg-Rainy River system from the Great Lakes, given its distribution in western Ontario and Minnesota. Stewart and Watkinson (2004) suggested that Northern Brook Lamprey entered Manitoba during postglacial times from the Great Lakes via the Winnipeg River, but Northern Brook Lamprey from the Saskatchewan-Nelson River NFBZ were not included in the genetic analyses by McFarlane (2009).

On smaller spatial scales (e.g., within each basin), species-specific differences in spatial structure are expected given the different adult life-history types between Northern Brook and Silver lampreys. In general, non-parasitic, non-migratory (brook) lampreys show more genetic differentiation among populations than do migratory parasitic lampreys, especially because it appears that migratory lampreys do not home to their natal streams (e.g., Goodman et al. 2008; Waldman et al. 2008; Bracken et al. 2015). For example, F_ST values in Western Brook Lamprey (Lampetra richardsoni) populations separated by < 570 km in the Columbia River basin were more than an order of magnitude greater than those for anadromous Pacific Lamprey (Entosphenus tridentatus) separated by up to 2,600 km (Spice et al. 2012, 2019). Although not studied as extensively in Northern Brook and Silver lampreys, this same pattern appears to be observed, as outlined below.

Northern Brook Lamprey disperse far less widely than Silver Lamprey (see Dispersal and Migration). Therefore, as expected, McFarlane (2009) found that genetic differentiation among Northern Brook Lamprey populations was greater than that of Silver Lamprey on the same spatial scale. For example, F_ST averaged 0.078 and 0.089 among Northern Brook Lamprey populations in Lake Huron and Michigan, respectively, and 0.056 and 0.038 among Silver Lamprey populations in these basins. However, given the evidence for contemporary gene flow between sympatric Northern Brook and Silver lampreys (Docker et al. 2012), Silver Lamprey may mediate gene flow among otherwise disjunct brook lamprey populations. Preliminary observations that genetic differentiation between Northern Brook Lamprey populations is higher in areas where Silver Lamprey do not occur is consistent with this suggestion (Docker unpubl. data), but further study is required.

In contrast, there is almost certainly gene flow among different Silver Lamprey streams within a region. Like in other parasitic lampreys, feeding juveniles can be transported large distances on host fishes, and they do not appear to home to their natal streams to spawn (see Spice et al. 2012). As a result, it is not likely that Silver Lamprey populations over moderate spatial scales (e.g., within basins) are geographically isolated. However, movement between basins, especially those separated by salt water, may be restricted (but see Designatable Units re: proximity of the Nelson and Hayes river mouths). Unlike anadromous lampreys or freshwater forms that are recently derived from anadromous lampreys (e.g., landlocked Sea Lamprey), Silver Lamprey appears to have either evolved in fresh water or been freshwater resident for long periods of evolutionary time (Bartels et al. 2012). Furthermore, gene flow within some streams may be limited by physical impediments such as natural and artificial barriers (Schreiber and Engelhorn 1998; Spice et al. 2012).

Designatable units

Although the relationship between these paired lamprey species has yet to be fully resolved, Northern Brook and Silver lampreys are recognized as distinct species using conventional lamprey taxonomy, and they maintain distinct phenotypes even with the potential for contemporary gene flow when they spawn sympatrically (see Name and Classification). Therefore, using “species” in the accepted sense of the taxonomic hierarchy, each should continue to be considered as a distinct species.

In both the Northern Brook Lamprey and Silver Lamprey, the previous COSEWIC reports identified two designatable units (DUs): the Great Lakes-Upper St. Lawrence populations (DU1) and the Saskatchewan-Nelson River populations (DU2) (COSEWIC 2007, 2011). These two DUs correspond with two NFBZs used, in part, by COSEWIC for recognition of discrete and evolutionarily significant units (COSEWIC 2015).

Results from mtDNA analysis are consistent with the lampreys within the Great Lakes-Upper St. Lawrence and Saskatchewan-Nelson River NFBZs representing discrete and evolutionarily significant units. Although Northern Brook Lamprey has not yet been analysed, Silver Lamprey from the two NFBZs differ significantly in the frequency of four mtDNA haplotypes; those from the Great Lakes-Upper St. Lawrence NFBZ (n = 155) exhibited four mtDNA haplotypes (A1, A2, A4, and B1), while Silver Lamprey (n = 15) from the Saskatchewan-Nelson River NFBZ was fixed for a single haplotype (A1; Docker unpubl. data).

Furthermore, the occupancy within two NFBZs reflects isolation within distinct geographic regions with different environmental conditions and distinct fish community assemblages. In Northern Brook Lamprey, the distribution gap between the most northwesterly occurrence record in DU1 and the easternmost locality in DU2 is substantial (Figure 5, 6), especially for a small-bodied species with limited dispersal capabilities. The distribution gap (in terms of overland distances) is smaller for the Silver Lamprey (Figure 7, 8), but natural dispersal between the different drainages in these two NFBZs is unlikely. Moreover, the ecological and environmental conditions experienced by Silver Lamprey in these two NFBZs that stretch from the lower Nelson River near Hudson Bay to the upper St. Lawrence River estuary are undoubtedly quite distinct. Thus, the Great Lakes-Upper St. Lawrence populations (DU1) and the Saskatchewan-Nelson River populations (DU2) are both important to the evolutionary legacy of the species as a whole and, if lost, would likely not be replaced through natural dispersal.

Figure 5. Collections of post-metamorphic Northern Brook Lamprey (I. fossor) in the Great Lakes-Upper St. Lawrence (DU1). Larval specimens (larval Ichthyomyzon) are included only where historical records strongly support the occurrence of only Northern Brook Lamprey (see Distribution); collections of Ichthyomyzon larvae that could not be confidently identified as Northern Brook or Silver Lamprey are shown in Figure 10.

Figure 6. Collections of Northern Brook Lamprey in the Saskatchewan-Nelson River (DU2). Records include post-metamorphic specimens (I. fossor), as well as larval specimens (larval I. fossor) where recent and historical records suggest that no Silver Lamprey are present (see Distribution).

Figure 7. Collections of post-metamorphic Silver Lamprey (I. unicuspis) in the Great Lakes-Upper St. Lawrence (DU1); collections of Ichthyomyzon larvae that could not be confidently identified as Northern Brook or Silver Lamprey are shown in Figure 10.

Figure 8. Collections of post-metamorphic Silver Lamprey (I. unicuspis) in the Saskatchewan-Nelson River (DU2) and Southern Hudson Bay-James Bay (DU3).

In addition to these two DUs described in the previous reports, Silver Lamprey presence has recently been confirmed in the upper Hayes River system in a third NFBZ, the Southern Hudson Bay-James Bay NFBZ (Tyson and Watkinson 2013; Figure 8). The proximity of the mouths of the Hayes River and the Nelson River (< 50 km), combined with our current understanding of postglacial dispersal routes, suggest a Nelson River origin for the Silver Lamprey in the Hayes River (Stewart and Lindsey 1983; Mandrak and Crossman 1992). Furthermore, potential host species such as Lake Sturgeon (Acipenser fulvescens), Lake Whitefish (Coregonus clupeaformis), and Brook Trout (Salvelinus fontinalis) are known to move back and forth between the Hayes and Nelson river systems (see Tyson and Watkinson 2013). However, unlike anadromous lampreys or freshwater forms that are recently derived from anadromous lampreys (e.g., landlocked Sea Lamprey), Silver Lamprey appears to have either evolved in fresh water or been freshwater resident for long periods of evolutionary time (Bartels et al. 2012). Although increased contribution of river water along the shore might provide a lower-salinity coastal conduit between the mouths of the Hayes and Nelson rivers (Granskog et al. 2009), movement between basins separated by salt water is likely restricted. In keeping with the recommendation of Tyson and Watkinson (2013), until more information is available, the Silver Lamprey in the Hayes River should be placed in a separate DU in order to maintain consistency with the delineation of the national freshwater biogeographical zones (COSEWIC 2015).

Thus, there are now three DUs for Silver Lamprey. No additional records of Northern Brook Lamprey have been reported in any other NFBZ.

Special Significance

Along with hagfishes, lampreys are the only extant jawless vertebrates, which diverged from the rest of the vertebrate lineage more than 500 million years ago (Kuraku and Kuratani 2006). As such, they provide important insights into the origins and early evolution of vertebrates (Docker et al. 2015; McCauley et al. 2015; York et al. 2019), and they also serve as important model organisms in biomedical research (Docker et al. 2015). Lampreys are also known to play important ecological roles. For example, larval lampreys are important in nutrient cycling, facilitating the conversion of nutrients derived from detritus and algae into stored biomass that serves as a food source for other animals. For example, Lake Sturgeon and American Eel (Anguilla rostrata), two fish species of commercial, recreational, and cultural importance in the Great Lakes-Upper St. Lawrence and Saskatchewan-Nelson River biogeographic zones, are able to detect and access buried prey and likely feed on larval lampreys. Siberian and White sturgeons (Acipenser baeri and A. transmontanus, respectively) have been observed feeding on other lamprey species (Cochran 2009), and American Eel were observed to capture and consume American Brook Lamprey larvae in laboratory experiments (Perlmutter 1951). Furthermore, during migration and spawning events, lampreys are fed on by a variety of aquatic, aerial, and terrestrial predators (see Scott and Crossman 1998; Docker et al. 2015). Lampreys are also ecosystem engineers, where the burrowing and feeding activities of larval lampreys significantly increase substrate oxygen levels (Shirakawa et al. 2013) and the nest-building activity of spawning lampreys increases streambed complexity in ways that appear to benefit other fishes and stream invertebrates (Sousa et al. 2012; Hogg et al. 2014). In addition, due to their sedentary nature, larval lampreys have been used as biomonitors of organochlorine contaminants in fresh water (Renaud et al. 1995, 1999).

Further study of paired Northern Brook and Silver lampreys will be of particular scientific value to provide insight into the evolution of alternative feeding strategies and speciation in lampreys. Recent population genomic studies in European River and Brook lampreys are already shedding light on the genetic architecture of life-history type (e.g., Rougemont et al. 2017; see Name and Classification), but, in this and many other lamprey species pairs, the parasitic member of the pair is also anadromous so that feeding and migratory transitions are confounded (i.e., genetic differences observed may be related to osmoregulation and not feeding type). In contrast, the Silver Lamprey has been resident in fresh water for long periods of evolutionary time (Bartels et al. 2012), so that differences observed in the genome between sympatric Northern Brook and Silver lampreys are more likely to represent genes specifically related to feeding type. Understanding the genetic mechanisms by which the parasitic feeding phase has been eliminated in the Northern Brook Lamprey could lead to new ways of controlling the invasive Sea Lamprey (McCauley et al. 2015).

Distribution

Global range

The distribution of Northern Brook and Silver lampreys is restricted to eastern North America (Figure 9). Both species are found in the Hudson Bay, Great Lakes, St. Lawrence River, and Mississippi River drainages (Potter et al. 2015). In Canada, these species are found in Manitoba, Ontario, and Quebec. In the United States, the Northern Brook Lamprey occurs in Illinois, Indiana, Kentucky, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, Vermont, West Virginia, and Wisconsin; the Silver Lamprey has been reported from these 12 states as well as from Iowa, Mississippi, Nebraska, North Dakota, and Tennessee (NatureServe Explorer 2018).

Figure 9. Global distribution of: a) Northern Brook Lamprey; and, b) Silver Lamprey (adapted from Renaud et al. 2009).

Search effort

Northern Brook and Silver lampreys may be more widely distributed (globally and in Canada; see below) than indicated by existing records because the inability to distinguish Northern Brook and Silver lampreys from one another as larvae confounds our ability to accurately assess the distribution of each species, and Silver and Chestnut lampreys may sometimes be confused even as adults (see Morphological Description). Furthermore, the targeted sampling required to collect both species during their burrowed larval stage and Northern Brook Lamprey during their relatively brief (and also largely burrowed) post-metamorphic stages requires specialized equipment and techniques, which have generally not been used outside the Great Lakes basin. The widely used electrofishing surveys that target multiple species of fishes rarely collect larval lampreys, as they tend to become immobilized within their burrows. Pulsed DC electrical current is used in lamprey-specific electrofishing surveys because it is much more successful at influencing emergence of burrowed larvae (Weisser and Klar 1990; Bowen et al. 2003). However, even in the Great Lakes, survey activities are generally focused on streams that support Sea Lamprey and each stream is not necessarily sampled at regular intervals, and Sea Lamprey traps are ineffective in catching smaller adult brook lampreys (COSEWIC 2007). Nevertheless, the targeted larval lamprey sampling that was conducted in the Great Lakes basin (including Lake St. Clair) during Sea Lamprey Control Centre (SLCC) Sea Lamprey assessment surveys in 2008-2018 surveyed an average of 163 streams and 19,810 m² per year (SLCC unpubl. data). Targeted sampling for larval lampreys has been used more widely in recent years in Quebec and Manitoba, but search effort is variable. Parasitic feeding phase (juvenile) Silver Lamprey are taken as incidental catch by commercial and occasionally recreational fishing gear, but the potential for both capturing and reporting them is markedly lower than that of targeted species. Adult Silver Lamprey are occasionally collected in Sea Lamprey traps on their upstream (spawning) migration, although survey activities are normally restricted to assessment within streams that support Sea Lamprey (see Sampling Effort and Methods).

Search effort in DU2 has recently been augmented with the use of environmental DNA (eDNA) assays. Gingera et al. (2016) developed and tested end-point (conventional) eDNA assays to detect and diagnostically identify Sea Lamprey, American Brook Lamprey, Chestnut Lamprey, and Northern Brook and Silver lampreys; Northern Brook and Silver lampreys were treated as one species because they cannot be distinguished in sympatry by any known genetic methods (see Name and Classification). More sensitive quantitative or real-time PCR (qPCR) assays have since been developed for Chestnut Lamprey and Northern Brook Lamprey/Silver Lamprey. They amplify 167- and 159-base pair fragments, respectively, of the cytochrome c subunit I (COI) gene (Docker unpubl. data). In 2015-2017, these assays were used to test for the presence of Northern Brook Lamprey/Silver Lamprey in water samples collected from 29 tributaries of the Assiniboine, Red, and Winnipeg rivers and nine tributaries to lakes Winnipeg and Manitoba (see below). Water was collected at up to six sites within each tributary, over multiple time periods between May and November, resulting in a total of 115 sampling events. Three water samples were collected at each sampling event, and three PCRs were performed on each water sample. Further testing of the assays are required (e.g., to guard against false positives and to ensure sufficient sensitivity to reduce the chance of false negatives; see Docker and Hume 2019), but results to date have helped refine our understanding of these species in DU2 and have identified specific streams in need of follow-up sampling using traditional methods.

Canadian range

In Canada, Northern Brook and Silver lampreys are found in Ontario, southern Quebec, and Manitoba. In total (i.e., dating from the first record of Silver Lamprey in 1882 to new records included in this report), post-metamorphic Northern Brook and Silver lampreys have been recorded in 104 and 152 waterbodies, respectively (Table 2-4). Other specimens (generally larvae) identified only as Ichthyomyzon sp. have been recorded in another 205 rivers and streams in which no adults of either species have been recorded.

In the Great Lakes-Upper St. Lawrence NFBZ, Northern Brook (DU1) and Silver (DU1) lamprey adults or post-metamorphic juveniles have been recorded in 101 and 116 waterbodies, respectively. Both species are found in the four Canadian Great Lakes watersheds (Erie, Huron, Ontario, and Superior), in Lake St. Clair (which connects lakes Erie and Huron) and Lake Nipissing (which drains into Lake Huron via Georgian Bay), and in the St. Lawrence River and its major tributary, the Ottawa River (Figure 5, 7; Appendix 1, 2). In the Saskatchewan-Nelson River NFBZ (DU2), the known distribution of Northern Brook Lamprey is more restricted than that of Silver Lamprey, with adults of the two species having been recorded in 3 and 34 waterbodies, respectively. Both species have been reported in the Winnipeg River system in the Hudson Bay watershed (although only Silver Lamprey extends into northwestern Ontario), and Silver Lamprey has been reported in other river systems within the Hudson Bay watershed (i.e., Nelson, Red, and Assiniboine rivers; Figure 6, 8; Appendix 1, 2). However, some confusion about Silver Lamprey distribution within the Red and Assiniboine rivers suggests that this species may be less widely distributed in southern Manitoba than previously thought, and Northern Brook Lamprey may occur in the Rat River, a tributary of the Red River (see below). Recent confirmed reports of Silver Lamprey in the Hayes River, which flows from Knee Lake in northern Manitoba to Hudson Bay, extend the confirmed range of this species (Tyson and Watkinson 2013) into the Southern Hudson Bay-James Bay NFBZ (DU3), where it has been recorded in two waterbodies to date (see below).

Details and trends related to the distribution of Northern Brook Lamprey and Silver Lamprey in each Canadian DU since the last status reports (since 2007) and over the past three generations (i.e., 18 years) are discussed below.

Great Lakes-Upper St. Lawrence (DU1)

Northern Brook Lamprey

In the time period since the last report (i.e., 2008-2018), Northern Brook Lamprey adults were recorded in 32 waterbodies in DU1: two, 12, and five in the Erie, Huron, and Ontario basins, respectively; one tributary to Lake Nipissing; and two and 10 rivers in the Ottawa and St. Lawrence river watersheds, respectively (Figure 5; Appendix 1). This includes 14 localities at which Northern Brook Lamprey adults had not been previously observed (eight in the Great Lakes basin and six in the St. Lawrence/Ottawa River basin). In the previous status report, Northern Brook Lamprey were reported from 36 stream systems since 1990, including a number of localities with previously unrecorded populations (COSEWIC 2007). These new records likely do not represent the presence of novel populations; rather they are likely the result of increased search effort. For example, in the Great Lakes, survey efforts have historically been focused on streams that support Sea Lamprey. However, in recent years, assessment staff at the Sea Lamprey Control Centre (SLCC) have conducted broader electrofishing surveys, leading to reports of previously unknown Northern Brook Lamprey localities (e.g., Bear Creek and Wolseley River in the Lake Nipissing drainage; COSEWIC 2007). Likewise, over the past four three-generation (18-year) time periods, there has been a steady increase in the number of streams with adult Northern Brook Lamprey (Table 5), but these new records are likely the result of a lack of earlier directed survey efforts and increased recent search effort.

Conversely, streams without recent Northern Brook Lamprey records may represent reduced effort at these localities or difficulty obtaining adult specimens rather than extirpation of previously existing populations. Unidentified Ichthyomyzon larvae were recorded in 55 streams in 2008-2018 (Figure 10; Appendix 3). Based on the historical presence of Northern Brook Lamprey adults in some of these streams and their location within the stream system (i.e., above barriers), many of these additional streams likely contain Northern Brook Lamprey (Schuldt and Goold 1980). In the previous COSEWIC status report, unidentified Ichthyomyzon larvae were observed in 66 streams since 1990, and unidentified Ichthyomyzon specimens (presumably larvae) were recorded from approximately 170 waterbodies in the St. Lawrence/Ottawa River basin in the 1930s, 1940s, and 1950s (Appendix 3). It is not known what proportion of these specimens would have been Northern Brook Lamprey, nor is it known which of these populations are still extant.

Figure 10. Collections of Ichthyomyzon sp. larvae that could not be identified as Northern Brook or Silver lamprey in the Great Lakes-Upper St. Lawrence (DU1).

Some of these populations may have been extirpated since these early sampling efforts, although not necessarily within the past three-generation time period. For example, Northern Brook Lamprey adults have not been observed in the Yamaska River in the St. Lawrence River watershed since 1959 (Renaud et al. 1995; see Threats). Likewise, some Northern Brook Lamprey populations in the Great Lakes basin may have been extirpated following initiation of Sea Lamprey control. Schuldt and Goold (1980) reported Ichthyomyzon larvae in 46 Canadian tributaries of Lake Superior in 1953-1972, a period which encompassed the initiation (in 1958) of lampricide treatments in this basin (Heinrich et al. 1980). Of these tributaries, 42 were resampled between 1973 and 1977, and only 17 were found with Ichthyomyzon larvae (see Threats). Ichthyomyzon larvae have subsequently been observed in six of the 24 named streams from which they appeared to have been extirpated (and Silver Lamprey adults have been observed in two other streams), suggesting either that native lampreys recolonized these eight tributaries or that they were not observed during resampling in 1973-1977. Northern Brook Lamprey adults have not been recorded in any Canadian tributaries of Lake Superior since 2007, although the Ichthyomyzon larvae collected at some localities (e.g., Black Sturgeon, Nipigon, and Pearl rivers) are thought to be Northern Brook Lamprey based on historical records (see Table 2; Neave et al. 2019). The total number of Canadian Great Lakes tributaries in which Ichthyomyzon larvae have been observed appears to have stabilized, likely as the result of many of these populations not being exposed to lampricide treatments (Table 2).

Silver Lamprey

Since the time period covered in the last report (i.e., 2008-2018), Silver Lamprey adults were recorded in 29 waterbodies in DU1: seven, six, one, and one in the Erie, Huron, Ontario, and Superior basins, respectively; five and one waterbodies in the Lake St. Clair and Lake Nipissing watersheds; and two and six waterbodies in the Ottawa and St. Lawrence watersheds, respectively (Figure 7; Appendix 2). This includes 10 localities at which Silver Lamprey adults had not been previously observed. In the previous report, Silver Lamprey were documented in 41 streams and seven lakes in the Great Lakes-Upper St. Lawrence DU from 1989-2007 (COSEWIC 2011). The number of waterbodies where Silver Lamprey adults have been reported has increased modestly over successive three-generation time periods (Table 6), likely because increased efforts have resulted in additional populations being documented recently. Unidentified Ichthyomyzon larvae were recorded in 52 rivers in 2008-2018 (Figure 10). Although many of these populations are thought to be Northern Brook Lamprey due to their upstream location within the stream systems, 34 of the larval records were from streams in which Silver Lamprey adults have been reported historically (Appendix 3).

In the Great Lakes basin, some of these Silver Lamprey populations may have been extirpated following initiation of Sea Lamprey control. However, in other cases, the lack of more recent reports may be the result of decreased sampling effort or sampling that focuses on tributaries with Sea Lamprey. Schuldt and Goold (1980) reported that Silver Lamprey were captured at electric barriers, used to prevent upstream migration by Sea Lamprey, in 19 Canadian tributaries of Lake Superior in 1953-1972, but that none were captured in these tributaries in 1973-1977. However, Silver Lamprey were subsequently reported in seven of these 19 tributaries, indicating that this species either escaped detection in some of these rivers or recolonized since 1977. Nevertheless, since 1989, only five Silver Lamprey have been trapped in Lake Superior, all in the Big Carp River at the easternmost point of Lake Superior, and this is not entirely the result of poor search effort (see Search Effort and Methods). Although traps have been operated on only two tributaries to Lake Superior since 2015, trapping occurred on 5-6 tributaries in 2007-2014, and the Neebing-McIntyre Floodway in the western Canadian basin of Lake Superior has been monitored every year since 1994. Similarly, traps on the Wolf River, also in the western basin, were operated every year in 1981-1987 and 1991-2012. Admittedly, all the other trap sites that have been monitored in Lake Superior since 1989 are in the eastern basin (Big Carp and Carp rivers, and Stokely Creek), while earlier trapping efforts (e.g., 1953-1977, as reported by Schuldt and Goold 1980) included more sites from the western basin. Sampling efforts specifically targeting metamorphosed and adult Silver Lamprey are required to unequivocally determine which of these tributaries still have extant Silver Lamprey populations.

Saskatchewan-Nelson River (DU2)

Northern Brook Lamprey

In the time period since the last report (i.e., 2008-2018), Northern Brook Lamprey adults have been reported in two of the three waterbodies in DU2 from which they have been historically observed (the Birch and Whitemouth rivers in the Winnipeg River watershed), but not in the Winnipeg River itself (Table 3; Appendix 1). Unidentified Ichthyomyzon larvae were reported in the Winnipeg River in 2015 and 2017, and in the English River in 2015, but these larvae are suspected to be Silver Lamprey (see below). Spice and Docker (2014) suggested that three metamorphosing specimens collected from the Rat River were Northern Brook Lamprey based on histological analysis of the gonads. All three showed signs of sexual maturation (i.e., a non-parasitic life history type) and genetic analysis confirmed them to be either Northern Brook Lamprey or Silver Lamprey. Intact specimens were not retained as vouchers, and subsequent electrofishing and eDNA analysis has not confirmed presence of Northern Brook Lamprey in the Rat River (see below). More extensive sampling in the fall or spring (i.e., following metamorphosis but prior to or during spawning) is required.

Targeted electrofishing surveys in 2013-2015 failed to find Northern Brook Lamprey adults or Ichthyomyzon larvae identifiable as either Northern Brook or Silver lamprey in other waterbodies in Manitoba: Devils, Hazel, and Netley creeks and the La Salle, Morris, Pembina, Rat, and Roseau rivers in the Red River drainage or the Icelandic River in the Lake Winnipeg drainage (Collerone 2014; Docker unpubl. data). Environmental DNA (eDNA) surveys from 29 tributaries of the Assiniboine, Red, and Winnipeg rivers and nine tributaries to Lakes Winnipeg and Manitoba also indicate limited distribution of Northern Brook Lamprey in the Saskatchewan-Nelson River NFBZ (see Search Effort). However, eDNA from either Northern Brook or Silver lamprey has been detected at five sites outside the known range of Northern Brook Lamprey (Table 7). Five of 15 water samples detected Northern Brook or Silver lamprey eDNA in the Bird River, which could extend the known range of Northern Brook Lamprey within the Winnipeg River system. However, in the Seine and Whitemud rivers, only one of 12 and six water samples, respectively, tested positive for Northern Brook or Silver lamprey DNA (and in only one of three replicate PCRs), suggesting that these might represent false positives, either as a result of contamination with Northern Brook or Silver lamprey DNA from another source or cross-reactivity with Chestnut Lamprey DNA. Chestnut Lamprey is known to occur throughout many of these sites in southwestern Manitoba (Stewart and Watkinson 2004; COSEWIC 2010). There is also a 1974 record of Silver Lamprey in the Seine River, but some uncertainty exists regarding species identification (see Morphological Description). Two water samples tested positive for Northern Brook or Silver lamprey in the Little Saskatchewan and Souris rivers. Silver Lamprey has been reported from the Assiniboine River system (although not since 2002; see below), and follow-up sampling using traditional methods will be required for verification of lamprey presence and species identification.