Skillet Clubtail (Gomphurus ventricosus) : COSEWIC assessment and status report 2022

Official title: COSEWIC Assessment and Status Report on the Skillet Clubtail (Gomphurus ventricosus) in Canada

Committee on the Status of Endangered Wildlife in Canada (COSEWIC)
Special concern 2022

COSEWIC assessment summary

Assessment summary – May 2022

Common name

Skillet Clubtail

Scientific name

Gomphurus ventricosus

Status

Special Concern

Reason for designation

This dragonfly of eastern North America is rarely observed and only in small numbers at known sites. Larvae live in small to large rivers. It is thought that adults spend much of their time away from the river, foraging, and only return to breed — thus are seldom seen. Increased survey effort and reporting have resulted in the documentation of 10 new subpopulations since the first assessment in 2010, distributed across a much broader area, and there are now 13 known subpopulations. The species is exposed to urban and rural development, the cumulative effects of aquatic pollution to larvae, roadkill, boat wakes, and invasive aquatic species. Failure to mitigate these threats could result in the species becoming Threatened.

Occurrence

Ontario, Quebec, New Brunswick, Nova Scotia

Status history

Designated Endangered in November 2010. Status re-examined and designated Special Concern in May 2022.

COSEWIC executive summary

Skillet Clubtail

Gomphurus ventricosus

Wildlife species description and significance

Skillet Clubtail is one of the most striking dragonfly species in Canada. Adults are characterized by a flat, pan-like expansion at the end of their otherwise slim abdomen. The body length is 45-48 mm long, dark brown and black, with conspicuous yellow markings on the dorsal abdomen, greenish-yellow markings on the thorax, dark green eyes, and clear wings.

Distribution

The global range of Skillet Clubtail is confined to North America east of the Mississippi and Red rivers, north to Minnesota and New Brunswick, and south to Tennessee. In Canada it occurs in 13 widely separated subpopulations in southern Ontario (Saugeen River), southern Quebec (Batiscan, Bécancour, Nicolet, Nicolet-Sud-Ouest. Sainte-Anne, Godefroy, Saint-François, Chaudière, and Chicot rivers), New Brunswick (Saint John, Salmon, and Canaan rivers), with additional historical subpopulations in Quebec, Nova Scotia, and in Ontario.

Habitat

Skillet Clubtail larvae live in small to large rivers with a silt, cobble, and bedrock substrate and pools and patches of soft sediments. They inhabit a wide range of waters; ranging in clarity from clear to stained and relatively turbid. Adult habitat is poorly understood, and adults are rarely observed. Adults apparently spend most of their lives in forests and open habitats within up to approximately three kilometres of the river.

Biology

Skillet Clubtail has three life stages and develops through complete metamorphosis. Females deposit their eggs in the water, and the larvae hatch and create shallow burrows in the soft substrates, where they can take at least two years to develop before adult emergence. In the centre of the continent, the species emerges in late May and flies to mid-August, but over most of its Canadian range, the species has a synchronous adult emergence in the latter two weeks of June. Following emergence, the dragonflies fly from the river for an extended period of maturation. Adults appear to spend little time near the larval waters, and likely spend most of their life in the surrounding forest.

Population sizes and trends

The Canadian population size and trends of Skillet Clubtail are unknown. Since the first COSEWIC status report, eight previously unknown subpopulations have been documented in southern Ontario and Quebec, as well as museum specimens from two additional Quebec subpopulations. Substantial search effort in New Brunswick has produced few records of the species, suggesting that it is rare in that province. The record in Ontario from along the Ottawa River remains historical.

Threats and limiting factors

There are four low-level threats to Skillet Clubtail individuals and habitats. These threats include habitat loss to both the terrestrial adult foraging life stage, and aquatic larval stages, caused by housing and urban development; adult roadkill is ongoing at most subpopulations; wave-wash from passing boats may kill emerging dragonflies on the larger rivers; and water pollution from agricultural run-off. Threats of unknown impact include aquatic invasive species that change the habitat and/or consume dragonfly larvae, water quality changes caused by residential development, and dams and water management. Rising sea levels are a potential future threat to the Saint John River subpopulation.

Protection, status and ranks

Skillet Clubtail was designated as Endangered in 2010 and is listed under Schedule 1 of the federal Species at Risk Act. Skillet Clubtail is classified as Endangered under New Brunswick’s Species at Risk Act and Data Deficient under Ontario’s Endangered Species Act. In Quebec, this species is on the Liste des espèces floristiques et fauniques susceptibles d’être désignées menacées ou vulnérables (List of plant and wildlife species which are likely to be designated as threatened or vulnerable).

The federal Recovery Strategy identifies critical habitat for Skillet Clubtail on four sections of the Saint John River and two sections of the Batiscan River. River and stream habitats in Canada receive some protection under the federal Fisheries Act where fish habitat is present, although this protection does not specifically apply to Skillet Clubtail. Provincial water protection acts offer protection to water quality and flow in lakes and rivers. None of the larval habitats of Canadian subpopulations are within parks or other protected areas and most of the terrestrial habitat surrounding the rivers is privately owned.

Skillet Clubtail is ranked as G3 (Vulnerable) globally, N2 (Imperiled) in Canada and N3 nationally in the United States. It is ranked as S1 (Critically Imperiled) in Quebec, Nova Scotia, and Ontario, and S1S2 (Critically Imperiled to Imperiled) in New Brunswick. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species ranks Skillet Clubtail as Least Concern.

Technical summary

Gomphurus ventricosus
Skillet Clubtail
Gomphe ventru
Range of occurrence in Canada: Ontario, Quebec, New Brunswick, Nova Scotia

Demographic information

Generation time

> 2 years (larvae live in aquatic habitats for approximately two years; and after emerging, adults live approximately two months)

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

Unknown

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

[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 up to a maximum of 100 years].

Unknown

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

Unknown

[Observed, estimated, inferred, 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.

Unknown

Are the causes of the decline a.) clearly reversible and b.) understood, and c.) ceased?

1. No
2. Partially
3. Unknown

Are there extreme fluctuations in number of mature individuals?

No

Extent and Occupancy Information

Estimated extent of occurrence (EOO)

105,000 km²

Index of area of occupancy (IAO)(2x2 grid value).

240 km² (this IAO represents the terrestrial minimum; the IAO is likely larger because of the continuous aquatic waterways that larvae occupy)

Is the population “severely fragmented” i.e., is >50% of its total area of occupancy in habitat patches that are (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?

1. Unknown
2. Possibly (9 of the 13 subpopulations are separated by a distance greater than dragonflies are known to disperse)

Number of “locations”* (use plausible range to reflect uncertainty if appropriate)

Minimum of 13, based on different threats at the 13 different waterways where extant subpopulations occur

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

No

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

No

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

No

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

No; additional subpopulations identified since the previous status report likely reflects an increase in search effort, rather than an increase in number of subpopulations.

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

Yes

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

* See Definitions and Abbreviations on COSEWIC website and IUCN for more information on this term.

Number of mature individuals (in each subpopulation)

Subpopulations (give plausible ranges), N Mature Individuals

Unknown

Total

Unknown

Quantitative analysis

Is the probability of extinction in the wild at least [20% within 20 years or 5 generations whichever is longer up to a maximum of 100 years, or 10% within 100 years]?

Unknown

Threats (direct, from highest impact to least, IUCN Threats Calculator

Was a threats calculator completed for this species?

Yes. Calculated threat impact: Medium.

• 1.1 Housing and Urban Areas (Low impact)
• 4.1 Roads and railroads (Low Impact)
• 6.1 Recreational activities (Low Impact)
• 9.3 Agricultural and Forestry Effluents (Low Impact)
• 7.2 Dams and water management/use (Unknown Impact)
• 8.1 Invasive non-native/alien species/diseases (Unknown Impact)
• 9.1 Domestic and urban wastewater (Unknown Impact)
• 9.2 Industrial and Military Effluents (Unknown Impact)

What additional limiting factors are relevant?

• Species at northern edge of range in Canada
• Canadian subpopulations are isolated by over 100 km from the nearest known subpopulations in the United States

Rescue effect (immigration from outside Canada)

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

S1 to SH in states adjacent to the Canadian range

Is immigration known or possible?

Unknown; unlikely

Would immigrants be adapted to survive in Canada?

Yes

Is there sufficient habitat for immigrants in Canada?

Likely

Are conditions deteriorating in Canada?+

Yes

Are conditions for the source (i.e., outside) population deteriorating?+

Unknown in last 10 years

Is the Canadian population considered to be a sink?+

No

Is rescue from outside populations likely?

Unknown

+ See Table 3 (Guidelines for modifying status assessment based on rescue effect).

Data sensitive species

Is this a data sensitive species?

No

Status history

Designated Endangered in November 2010. Status re-examined and designated Special Concern in May 2022.

Current status and reasons for designation:

Current status:

Special concern

Alpha-numeric codes:

Not applicable

Reasons for designation:

This dragonfly of eastern North America is rarely observed and only in small numbers at known sites. Larvae live in small to large rivers. It is thought that adults spend much of their time away from the river, foraging, and only return to breed — thus are seldom seen. Increased survey effort and reporting have resulted in the documentation of 10 new subpopulations since the first assessment in 2010, distributed across a much broader area, and there are now 13 known subpopulations. The species is exposed to urban and rural development, the cumulative effects of aquatic pollution to larvae, roadkill, boat wakes, and invasive aquatic species. Failure to mitigate these threats could result in the species becoming Threatened.

Applicability of criteria

Criterion A (Decline in total number of mature individuals): Not applicable. Population trends unknown.

Criterion B (Small distribution range and decline or fluctuation). Comes close to meeting EN B2ab(iii); the IAO (at least 240 km²) is below threshold and there is an observed continuing decline in (iii) quality of habitat at some subpopulations. The number of locations (>13) exceeds thresholds, although some subpopulations do not have apparent threats. Subpopulations are not considered severely fragmented.

Criterion C (Small and declining number of mature individuals). Not applicable. Number of mature individuals unknown, but probably exceeds thresholds and there is insufficient data to show a continuing decline.

Criterion D (Very small or restricted population): Not applicable. Number of mature individuals, IAO, and number of locations exceeds thresholds.

Criterion E (Quantitative analysis): Not applicable. Insufficient data available.

Preface

Skillet Clubtail was designated as Endangered in 2010 by COSEWIC and subsequently listed under Schedule 1 of the federal Species at Risk Act. At the time of this assessment, the species was known to be extant at three subpopulations in New Brunswick. The designation was based on the apparent extirpation of subpopulations prior to 2010 from the Ottawa River (Ontario/Quebec), Yamaska River (Quebec), and Shubenacadie River (Nova Scotia).

Since 2010, increased survey effort and improved reporting have resulted in the documentation of 10 new subpopulations (one in Ontario and nine in Quebec). These new subpopulations have greatly expanded the extent of occurrence (EOO) in Canada from 2473 km² (as reported in COSEWIC 2010) to 105,000 km² (as of 2021) and the index of area of occupancy (IAO) from 44 km² to a minimum of 240 km². Records on the United States side of the Rainy River and adjacent to northwestern Ontario were reported in the 2010 status report but were not confirmed in subsequent surveys and are not treated as a Canadian subpopulation in this updated status report. The four subpopulations apparently extirpated prior to 2010 (i.e., from the Ottawa River [Ontario/Quebec], Yamaska River [Quebec], Shubenacadie River [Nova Scotia], and Mount Uniacke [Nova Scotia]) have not been confirmed. Where data are available for extant subpopulations, low-level threats to Skillet Clubtail continue.

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 (2022)

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

• Phylum: Arthropoda - arthropods
• Subphylum: Hexapoda - hexapods
• Class: Insecta - insects
• Subclass: Pterygota - winged insects
• Order: Odonata – damselflies and dragonflies
• Suborder: Anisoptera - dragonflies
• Family: Gomphidae - clubtails
• Genus: Gomphurus Needham 1901
• Species: ventricosus (Walsh 1863)

Skillet Clubtail (Gomphurus ventricosus) is a dragonfly in the clubtail family (Gomphidae). The species was first described in Walsh (1863) as Gomphus ventricosus. The genus Gomphurus was described by Needham in 1901. Molecular phylogenetic analysis supports splitting Gomphus into multiple genera including Gomphurus (Ware et al. 2017). Most Gomphus, including Skillet Clubtail, is now generally accepted in the genus Gomphurus (Paulson and Dunkle 2021)^{Footnote 1} and Gomphus as presently known is restricted to Eurasia. Skillet Clubtail is distinct and there are no proposed subspecies.

Synonyms: Gomphus ventricosus Walsh

English Name: Skillet Clubtail. The English name Skillet Clubtail was assigned in Paulson and Dunkle (1996) and is in the most recent Canadian list (Catling et al. 2005). The name “Skillet Clubtail” refers to the slender abdomen of the adult dragonfly having a broad, circular flare at the end and resembling a skillet.

French Name: Gomphe ventru (Pilon and Lagacé 1998).

Type locality: Rock Island County, Illinois.

Morphological description

Skillet Clubtail has three distinct life stages; egg, larva (nymph) and adult.

Adults

Skillet Clubtail adults are 45-48 mm long and have a strikingly widened club at the end of the abdomen (Walker 1958). Males have green to turquoise eyes, an unmarked face, and a body that is dark brown to black with a yellow stripe along the top of the abdomen and yellowish green thorax (Jones et al. 2008; Paulson 2011). The sides of the club have large yellow spots. Females resemble the males but have a thicker abdomen and reduced club.

Larvae (nymphs)

Skillet Clubtail larvae (also called nymphs) are elongate, compressed, and difficult to identify from other Gomphurus and species of the subgenus Hylogomphus. Species can only be distinguished by close examination of the mouth parts and abdominal spines (Savard and Charest 2014; Tennessen 2019). Identification of exuviae (cast larval skins) also requires close examination of the mouthparts and hooks on the sides of the thorax.

Eggs

Skillet Clubtail eggs are undescribed.

Dragonfly species that appear similar to and are within the Canadian range of Skillet Clubtail include Cobra Clubtail (G. vastus) and Midland Clubtail (G. fraternus). Both species have a similar adult body structure but have an abdomen with a narrower club and smaller spots. The larvae of Skillet Clubtail are different from Cobra Clubtail by the absence of a substantial end hook on the labial palp, and from Midland Clubtail by the straight median lobe of the prementum.

Population spatial structure and variability

The spatial structure and variability of Skillet Clubtail subpopulations have not been studied in Canada or the United States. The Barcode of Life Data System (BOLD) is an online genetics data storage and analysis platform developed at the Centre for Biodiversity Genomics in Canada (see Ratnasingham and Hebert 2007). DNA barcodes are available for 39 Skillet Clubtail specimens in BOLD, all of which are from New Brunswick. The samples constitute one Barcode Index Number (BIN). The specimens collected in New Brunswick do not reveal subpopulation differences, and it is not possible to use these data to establish spatial structure or variability between other subpopulations.

Designatable units

Skillet Clubtail has one designatable unit within Canada. No subspecies are recognized. The species occurs in both the Atlantic and Great Lakes Plains National Ecological areas (COSEWIC 2011); however, there is no information on genetic structure or data on discreteness or evolutionary significance between subpopulations from these two areas.

Special significance

Skillet Clubtail is a rare species and therefore of interest to conservation biologists and amateur naturalists. No publicly available Aboriginal Traditional Knowledge (ATK) is identified for Skillet Clubtail (COSEWIC ATK Subcommittee pers. comm. 2021). However, this species is part of Canadian ecosystems that are important to Indigenous people, who recognize the interconnectedness of all species within the ecosystem.

Distribution

Global range

The global range of Skillet Clubtail extends from New Brunswick, through southern Quebec and southern Ontario, west to Minnesota and south to Tennessee and North Carolina (Figure 1). The global range covers about 2,561,000 km², of which 105,000 km² or 4% is in Canada.

Figure 1. Male Skillet Clubtail (Gomphurus ventricosus) at Fredericton New Brunswick, July 16, 2015. Photo by Danny O’Shea.

Canadian range

The Canadian range of Skillet Clubtail extends from the Saugeen River in southwestern Ontario east to southern Quebec and New Brunswick, with historical records in Nova Scotia (Figure 2). The species occurs in 13 extant^{Footnote 2} and four historical^{Footnote 3} subpopulations^{Footnote 4} (see Table 1^{Footnote 5}).

Figure 2. Global range of Skillet Clubtail (Gomphurus ventricosus). The black dots indicate all known records of the species in Canada and county records in the United States (data from COSEWIC 2010; Odonata Central 2020). Map prepared by A. Harris.

Ontario range

In Ontario, Skillet Clubtail is known from one extant (#1) and one historical (#14) subpopulation (Table 1 and 2; Figure 3). Skillet Clubtail exuviae were reported on the Minnesota side of the Rainy River adjacent to northwestern Ontario in 1998 (Steffens and Smith 1999) but the species has not been recorded on the Canadian side of the river despite targeted surveys in 2021 (see Search effort). Some of the exuviae collected in Minnesota were morphologically ambiguous and may be the closely related Midland Clubtail (Steffens and Smith 1999). Rainy River is not treated as a Canadian subpopulation in this status report.

Figure 3. Canadian subpopulations of Skillet Clubtail (Gomphurus ventricosus) with records from 1924–2021 (Table 1). Map prepared by A. Harris.

Figure 4. Distribution of Skillet Clubtail (Gomphurus ventricosus) in Quebec. The numbers represent subpopulations and the letters (a, b, c) represent places where the species was observed within a subpopulation. Map prepared by A. Harris.

Figure 5. Distribution of Skillet Clubtail (Gomphurus ventricosus) in New Brunswick and Nova Scotia. The numbers represent subpopulations and the letters (a, b, c, d) represent places where the species was observed within a subpopulation. Map prepared by A. Harris.

A single adult Skillet Clubtail was documented as an incidental observation at the Saugeen River (#1) in southwestern Ontario in 2012 (Evans pers. comm. 2020). A historical record from “Ottawa” in July 1924 is probably from the Ottawa River (#14), but the species has not been recorded at this locality despite extensive search effort. Historical records from Forest, Ontario and Ignace, Ontario were misidentified and are not included in this report (Jones 2007).

Quebec range

Skillet Clubtail was first recorded from Quebec in 1940, when three males were collected approximately 1 km from the Yamaska River at Farnham (#15) (Robert 1963). Skillet Clubtails were first documented on the Batiscan River (#2) in 2011, on the Chaudière River (#5) in 2015, and the Godefroy River (#3) in 2016 (ECCC 2021). Older Quebec records not documented in COSEWIC (2010) include two 2005 adult specimens from the Sherbrooke area, presumably from the Saint-François River (#4) and an adult specimen from the Chicot River (#6) at Saint-Cuthbert collected in 1984 (Table 1 and 2). Surveys in 2021 found four previously undocumented subpopulations between Montréal and Quebec City (Savard pers. comm. 2022). Skillet Clubtail has not been reported at the Chicot River since 1984 but no subsequent survey effort has been documented and it is treated as an extant subpopulation.

New Brunswick range

Skillet Clubtail occurs along approximately 50 km of the Saint John River (#11) between the Mactaquac Dam and the confluence of the Jemseg River (COSEWIC 2010). Exuviae collected on the Jemseg River in 2007 and 2015 were within 10 km of the Saint John and are considered part of the Saint John River subpopulation (COSEWIC 2010). Adults were collected on the Canaan River (#13) in 2007 and one exuvia in 2021 (Klymko pers. comm. 2022). Adults were collected at the Salmon River (#12) in 2001 (COSEWIC 2010) and one or two were observed in 2021 (Klymko pers. comm. 2022).

Nova Scotia range

There are two historical records from this province: an adult at Mount Uniacke (#16) Hants County (1948) and an exuvia from the Shubenacadie River (#13) (1992). Both specimens have been lost (COSEWIC 2010). The Mount Uniacke (#16) record is not near any known potential larval habitat (COSEWIC 2010). Surveys at the Shubenacadie River (#17) in 2013 did not record the species (Klymko and Robinson 2013).

Extent of occurrence and area of occupancy

The extent of occurrence (EOO) of Skillet Clubtail in Canada is approximately 105,000 km² as measured by convex polygon encompassing all known extant Canadian subpopulations^{Footnote 6}. This calculation excludes historical subpopulations (#14, 15, 16 and 17) (Table 1).

The index of area of occupancy (IAO) is 240 km² based on a 2 km X 2 km grid, encompassing extant subpopulations. This includes an estimated 40 grid squares (160 km²) on the Saint John River (Klymko pers. comm. 2021). Dragonflies are aquatic for most of their life cycle and select specific biotopes in those aquatic environments; if they are present in a stream, they could be present throughout the same waterway within areas with similar environmental variables. The IAO should encompass both the aquatic and terrestrial life stages and be based on known and projected occurrences to provide an upper plausible bound. The calculated IAO (i.e., 240 km²) is a minimum value and based on adult observations and exuviae collection sites only. The upper limit of the IAO is unknown.

Since the previous COSEWIC (2010) status report, the increase in both the EOO (2473 km² to 105,000 km²) and IAO (44 km² to 240 km²) is a result of additional search effort and confirmation of historical subpopulations in Ontario and Quebec; not a range expansion of Skillet Clubtail.

Search effort

Skillet Clubtail was first reported in Canada at the Ottawa River (#14) in 1924 with the most recent records in 2020 from the Saint John River (#11) Bécancour River (#7), Nicolet River (#8a and 8b), Nicolet-Sud-Ouest River (#9) and Sainte-Anne River (#10) (Table 1). Targeted surveys and reporting of incidental observations have increased substantially since 2010, particularly in Quebec, New Brunswick, and Nova Scotia. Since 1924, there have been a minimum of 28 sites searched and three to four hundred specimens recorded from across 17 subpopulations.

Dragonfly search methods include searching for and collecting exuviae and net-identify-release of teneral (recently emerged) adults along river shorelines. Adults disperse from the river and are difficult to find except during the brief period when they return to the river to mate and lay eggs. Larvae are rarely found (COSEWIC 2010). Skillet Clubtail has been reported from incidental observations by naturalists (including the most recent subpopulation on the Saugeen River (#1) and as bycatch from surveys targeting other dragonfly species (e.g., Turgeon 2016).

Non-targeted survey data are included in dragonfly atlases in Ontario (Ontario Odonata Atlas Database 2020) and Quebec (Pilon and Lagacé 1998; Savard 2011), and the Atlantic Dragonfly Inventory Program (Brunelle 2010). There are 23 Canadian records of Skillet Clubtail from the Saint John River (#11) area in New Brunswick between 2007 and 2021 on iNaturalist (2021). In Quebec, there are four iNaturalist records from 2016- 2021. There are no Canadian records of Skillet Clubtail in Odonata Central (2020).

The recent documentation of the species at the Saugeen (#1), Batiscan (#2), Chaudière (#5), and Godefroy (#3) rivers suggest that the species may be more widespread than is currently known.

The following is a summary of search effort for Skillet Clubtail in Canada since 2010, including effort prior to 2010 but not documented in the previous COSEWIC (2010) status report (Table 1).

Ontario

Targeted surveys for Skillet Clubtail were completed on the Ontario side of the Rainy River in 2021 (18.5 hours) in support of this status report. Surveys targeting Riverine Clubtail (Stylurus amnicola) on the Rainy River collected all dragonfly exuviae encountered in 2010 and 2011; these surveys totalled 19 survey hours (COSEWIC 2012). On the Namakan River (another large river in the region), surveys targeting Pygmy Snaketail (Ophiogomphus howei) exuviae and larvae were conducted on eight dates in 2009 (Van den Broeck and Jones 2009). All exuviae collected were identified to species (where possible). Informal dragonfly surveys for adults and exuviae on the Rainy River and other nearby rivers have been conducted since the late 1990s (Elder pers. comm. 2020; Milne pers. comm. 2020; Oldham pers. comm. 2020; Oldham and Elder 2000).

A survey for Skillet Clubtail exuviae on the Saugeen River was completed on June 19, 2019 (7.5 survey hours) (Jones pers. comm. 2021).

As a surrogate measure of null survey effort, the Ontario Odonata Atlas maintains records of dragonflies and damselflies throughout the province. The atlas has a total of 99,208 records of which 26,922 records are since 2010 (Ontario Odonata Atlas Database 2020). The atlas includes 2 records of Skillet Clubtail (Ottawa and Saugeen rivers).

Quebec

Targeted surveys for exuviae near the historical Farnham (#15) site from about 2010 and 2018 did not record Skillet Clubtail (ECCC 2021).

A Skillet Clubtail was recorded on the Batiscan River (#2) in 2011 during inventories for the Quebec odonate atlas (Savard pers. comm. 2021). Subsequent exuviae surveys in 2012-2013 found one teneral in the process of emerging on the bank of the river. Additional surveys for exuviae and adults were conducted on the Batiscan River in 2012-2020 (Savard pers. comm. 2021; ECCC 2021). An adult Skillet Clubtail was documented on the Godefroy River (#3) in 2016 but subsequent exuviae surveys in 2017 were unsuccessful (ECCC 2021). An adult male was found in June 2019 (Savard pers. comm. 2021). Surveys in 2021 found new subpopulations at the Bécancour, Nicolet, Nicolet-Sud-Ouest, and Sainte-Anne rivers as well as new sites at the Chaudière and Saint-François subpopulations (Desrochiers pers. comm. 2022; Savard pers. comm. 2022).

Null survey effort in Quebec is not documented.

New Brunswick

Emergence surveys on the Saint John River (#11) in 2014 and 2015 found 169 exuviae (O’Malley and Monk 2016).

Surveys at the Canaan River (#13) in 2016 did not record Skillet Clubtail (Klymko and Robinson 2017) but in 2021 a Skillet Clubtail exuvia was found (Klymko pers. comm. 2022). Surveys on the Salmon River (#12) in 2021 produced one or two adult records (Klymko 2022). There have also been unsuccessful surveys on the Restigouche River and its tributaries in 2008 (ECCC 2021), the Restigouche River in 2011 (Klymko and Robinson 2011), the New, Lepreau, Magaguadavic, Didgeguash, Petitcodiac, and Oromocto rivers in 2016 (Klymko and Robinson 2017), the Saint John River between St. Francis and Edmundston in 2018, the Tobique River in 2019, and sites on the Saint John River between Grand Falls and Mactaquac headpond in 2021 (Klymko pers. comm. 2021).

Nova Scotia

An exuviae survey targeting Skillet Clubtail was conducted on the Shubenacadie River (#17) in 2012 including the historical site from 1992. No Skillet Clubtails were recorded among 1,275 exuviae collected at 32 sites (Klymko and Robinson 2017). Non-targeted surveys for dragonfly exuviae were conducted on portions of Tusket, Medway, Lahave, and Saint Mary’s rivers in 2010-2011 (Klymko 2010; Klymko and Robinson 2011). No new occurrences were found. An adult and exuviae survey on the Annapolis River in 2021 did not find the species (Klymko pers. comm. 2022).

There is no Aboriginal traditional knowledge on search effort or observations for Skillet Clubtail in Canada.

Habitat

Habitat requirements

The habitat requirements of Skillet Clubtail are poorly understood. Larval habitat typically consists of slow-running rivers with a mix of silt, cobble, and bedrock substrate (Louton 1983). Most of the rivers that Skillet Clubtail inhabit flow through a combination of forested and agricultural land. In Canada, rivers range in size from the Canaan River (#13) with a mean annual flow of 13 m³/sec (Cassie 2005) to the Ottawa River (#14) with a mean annual flow of 1,948 m³/sec (Thorp et al. 2005). Waters range from clear to stained to relatively turbid (White et al. 2010). The larvae apparently burrow into fine silt or clay substrate. Upon emergence, they drift downstream to emerge on the banks of pools or climb onto tree trunks (Paulson 2011; O’Malley and Monk 2016). Larvae sometimes inhabit lakes with sand substrate (Dunkle 2000) but have not been found in this habitat in Canada.

Skillet Clubtails apparently spend most of their adult life in forests and open habitats. Adults are rarely observed but most records are within 3 km of the river. Most adults are observed when they return to the river to mate (COSEWIC 2010). The relative importance of forest and other vegetation types is unknown. Oviposition has not been documented for Skillet Clubtail, but based on information from similar species, it probably occurs onto the surface of the water at rapids (Corbett 1999).

Habitat trends

Historical habitat trends that have degraded Skillet Clubtail habitat in most of its Canadian range include the loss of forest cover, installation of dams, and long-term chronic water pollution. Water pollution trends have been slowed or reversed in some rivers over the past 10 years; however, data are incomplete and reported differently in the different provinces (see Threats).

In southern Ontario, approximately 19% of the Saugeen River (#1) watershed is forested with 30% forest cover in riparian areas (Saugeen Conservation 2019). Forest cover remained stable or increased slightly between 2002 and 2016. Total phosphorus concentrations decreased between 2002 and 2016 (Saugeen Conservation 2019), but overall water quality (Canadian Council of Ministers of the Environment 2017) deteriorated between 2003 and 2018 (ECCC 2020).

In southern Quebec, water quality is generally fair to poor, but stable in the Saint Lawrence River tributaries between Montréal and Quebec City (ECCC 2020). Water quality in tributaries of the Batiscan River (#2) improved between 2003 and 2015 (SAMBBA 2015). Most of the Quebec subpopulation watersheds have predominantly agricultural lands near the Saint Lawrence River and variable amounts of forest cover inland.

Water quality tends to be good to excellent (determined by comparing specific water quality data to water quality guidelines [ECCC 2020]) in Atlantic Canada except in more human populated areas (ECCC 2020). Most of the Saint John River watershed (87%) is forest and wetland but removal of riparian vegetation may have contributed to poor water quality at some sites (New Brunswick Department of Environment 2007a). Water quality has deteriorated at three monitoring stations on the Saint John River between 2004 and 2018 (ECCC 2020). Lands surrounding the Saint John River (#11) subpopulation consists of a large, growing urban and agricultural area where natural vegetation required by adults has declined (COSEWIC 2010).

The Canaan River (#13) watershed remains mostly forest and wetland (93%) but land clearing, removal of riparian vegetation, and erosion of streambanks by livestock has caused locally impaired water quality (New Brunswick Department of Environment 2007b).

Biology

The biology of Skillet Clubtail is poorly known. Previously unpublished data from New Brunswick surveys were provided by Paul Brunelle in COSEWIC (2010). Where data are lacking, details are based on other Gomphurus and related species.

Life cycle and reproduction

Skillet Clubtail have three morphological life stages: egg, larva [nymph] and adult. The egg and larval life stages are aquatic, and the adult life stage is terrestrial.

Skillet Clubtail adult flight period extends from late May until August, but on the Saint John River (#11), emergence is synchronous with all individuals emerging over about a week in late June (COSEWIC 2010). After emerging, adults disperse to surrounding forests and fields and spend little time at the river (COSEWIC 2010; Paulson 2011). Adults feed on flying insects. Mating may occur away from the larval habitat (COSEWIC 2010), but males sometimes make short patrols over the river from a perch on the bank, suggesting territorial defence (Dunkle 2000). Females apparently dip the end of the abdomen into the water to release eggs (COSEWIC 2010) but oviposition behaviour is poorly documented. When eggs hatch, Gomphurus larvae burrow into fine sediments in slow to moderately flowing sections of streams (Paulson 2011; Tennessen 2019) where they feed on aquatic invertebrates.

Larvae of other Gomphurus species take at least two years to develop to adulthood (Tennessen 2019). When mature and ready to emerge from aquatic (e.g., gill breathing) to terrestrial (e.g., air breathing), larvae drift downstream to pools where the current slows. There they climb onto the riverbank or tree trunks where they emerge within 11 m of the edge of the water (COSEWIC 2010; O’Malley and Monk 2016). The adult life span is unknown but probably about two months based on the flight dates. The life span is unknown but estimated at under 2.5 years.

Physiology and adaptability

Little is known on the physiology and adaptability of Skillet Clubtail. Unlike some clubtails, larvae are apparently tolerant of turbid waters (White et al. 2010).

Dispersal and migration

There is little information on the dispersal ability or long-range movements of Skillet Clubtail. Adults have been observed at Fredericton, 3 km from the Saint John River (#11) (COSEWIC 2010), suggesting they disperse at least this far from larval habitat. Other dragonflies are known to disperse up to tens of kilometres from larval habitat (Corbett 1999). The separation distance^{Footnote 7} between subpopulations is set at 10 km, based on information from other similar species (NatureServe 2022). Skillet Clubtail is non-migratory.

It is unknown if the Skillet Clubtail population in Canada is severely fragmented^{Footnote 8}. At least nine of the thirteen extant subpopulations (Table 4) are separated by a distance greater than dragonflies are known to disperse (i.e., their separation distance); however, the viability of these subpopulations is unknown and/or stable (based on its presence at surveys over multiple years) and severity of threats at these subpopulations is unknown.

Interspecific interactions

Skillet Clubtail larvae are likely eaten by turtles, fish, amphibians, crayfish, birds, and other dragonfly larvae. At the Saint John River (#11), tenerals are eaten by birds and caught in spider webs in trees during emergence when unable to fly and larvae are swarmed by ants as they crawl from the water (O’Malley and Monk 2016). Predation by birds on tenerals may be proportionally lower than more abundant dragonflies (Sabine pers. comm. 2021). Adults are also likely prey of amphibians (Corbett 1999) and probably the Dragonhunter (Hagenius brevistylus), a large dragonfly which feeds predominantly on other Odonata and is common throughout the Canadian range of Skillet Clubtail (COSEWIC 2010).

Twenty-two other Odonate species are recorded with Skillet Clubtail on the Saint John River (#11) at Fredericton (COSEWIC 2010). Of these, Black-shouldered Spinyleg (Dromogomphus spinosus), Cobra Clubtail (Gomphurus vastus), Boreal Snaketail (Ophiogomphus colubrinus), Rusty Snaketail (O. rupinsulensis), Zebra Clubtail (Stylurus scudderi), and Prince Baskettail (Epitheca princeps) mostly closely share habitat requirements and probably compete for food with Skillet Clubtail at least in the larval stage.

Population sizes and trends

Sampling effort and methods

To date, Skillet Clubtail surveys have focused on recording the species’ presence at a site and data collection methods have not gathered information to estimate population size or detect population changes in Canada. Given the difficulty in finding larvae and adults, counting exuviae is probably the most efficient method of estimating population size and trends but is limited to a very restricted period in early summer.

Abundance

Data are insufficient to estimate the abundance of Skillet Clubtail in Canada. Hundreds of adults and exuviae have been collected on the Saint John River (#11). A total of 169 Skillet Clubtail exuviae were among 3638 exuviae collected on the lower Saint John River and Grand Lake between 2014 and 2016 (O’Malley 2018). At Batiscan River (#2), 192 Skillet Clubtail exuviae were collected between 2011-2020 with 52 in 2016, 73 in 2017, and 118 in 2020 (Desrosiers pers. comm. 2018; Savard pers. comm. 2021; Charest in prep.). There are no studies that enable dragonfly populations to be derived from exuviae observations.

Fluctuations and trends

Data are insufficient to estimate population fluctuations and trends of Skillet Clubtail in Canada. Over the past ten years, subpopulations recorded in Ontario and Quebec reflect increased search effort and reporting rather than range expansion.

Rescue effect

Rescue from the United States is unlikely. Skillet Clubtail is absent from Maine (Maine Damselfly and Dragonfly Survey 2021) making rescue of New Brunswick subpopulations (#11, 12, 13) improbable. Subpopulations in southern Ontario and Quebec are more than 100 km from the nearest known occurrences in New York, New Hampshire, and Vermont where the species is ranked as Critically Imperiled (S1) (NatureServe 2022) and unlikely to serve as a source population.

Threats and limiting factors

The Skillet Clubtail threat assessment (Table 3) is based on the IUCN-CMP (International Union for Conservation of Nature–Conservation Measures Partnership) unified threats classification system. The IUCN-CMP Threats Classification system is consistent with methods used by COSEWIC, federal agencies, provinces and territories, and it adopts an international standard. For a detailed description, see the Open Standards website (Conservation Measures Partnership 2016a). For information on how the values are assigned, see Salafsky et al. (2008), Master et al. (2012), and Table 3 footnotes for details.

Table 3. Results for the Skillet Clubtail (Gomphurus ventricosus) threats assessment in Canada. The classification is based on the IUCN-CMP (International Union for the Conservation of Nature–Conservation Measures Partnership) unified threats classification system. For a detailed description of the threat classification system, see the CMP web site (CMP 2019). Threats may be observed, inferred, or projected to occur in the near term and are characterized here in terms of scope, severity, and timing. Threat “impact” is calculated from scope and severity. For information on how the values are assigned, see Master et al. (2009) and footnotes to this table. The assigned overall threat impact for Skillet Clubtail is Low.

Species name
Skillet Clubtail (Gomphurus ventricosus)

Date:
March 4 2021; revised May, 2022

Assessors:
Kristiina Ovaska (Facilitator), Jennifer Heron (Arthropods Specialist Subcommittee [SSC] Co-chair), David McCorquodale (Arthropods SSC Co-chair), Rosana Soares (COSEWIC Secretariat), Allan Harris (report writer, SSC member), John Klymko (SSC), Jeff Ogden (SSC member), John S. Richardson (SSC member), Brian Starzomski (SSC member), Leah Ramsay (SSC member), Robert Buckowski (SSC member), Dawn Marks (SSC member), Jayme Lewthwaite (SSC member), Colin Jones (Ontario COSEWIC member, SSC member), Mary Sabine (New Brunswick COSEWIC member), Ken Tuninga (CWS), Kathy St-Laurent (ECCC), Nathalie Desrosiers (Ministère des Forêts de la Faune et des Parcs du Québec), Michel Savard (Initiative pour un atlas des libellules du Québec, Entomofaune du Québec (EQ) Inc.), Julie Mcknight (ECCC), Marianne Gagnon (CWS-QC). Threats calculator updated following discussion at the May 2022 COSEWIC Wildlife Species Assessment Meeting.

Assigned overall threat impact:
Medium Impact.

Impact adjustment reasons:
No adjustment.

Overall, threat comments:
The threats appear to be Low across each subpopulation.

Threats are defined as the proximate activities or processes that have caused, are causing, or may cause in the future the destruction, degradation, and/or impairment of the Skillet Clubtail in Canada. Limiting factors are not considered during this assessment process. For purposes of threat assessment, only present and future threats are considered. Historical threats, indirect or cumulative effects of the threats, or any other relevant information that would help understand the nature of the threats are described in the text below. Threats with a scored impact (e.g., the four Low impact threats) are discussed first, followed by those of Unknown impact.

Threats for Skillet Clubtail were assessed for the entire Canadian range. The calculated overall threat impact is Low based on input from various regional experts and specialists (see Table 4).

Threat 1. Residential and commercial development (low impact)

1.1 Housing and urban areas (low impact)

Residential development along riparian areas has the potential to damage both terrestrial adult habitat and aquatic larval habitat. These impacts include clearing of vegetation (e.g., loss of adult foraging habitat, water quality degradation, and increased human access to the watercourse). Housing and urban area development refers to the clearing and conversion of land, and impacts the adult (terrestrial) foraging, resting, and mating (territory) habitat. The Saint John River (#11) is subject to development pressure, but most occurred historically with much of the undeveloped land zoned for flood protection and wetland conservation (Sabine pers. comm. 2021). Development pressure is probably relatively low along the Batiscan (#2), Salmon (#12), and Canaan (#13) rivers, but could be more significant along the Saugeen (#1), Chicot (#6), Saint-François (#4), Godefroy (#3) and Chaudière (#5) rivers, depending on the exact location of the egg-laying and larval emergence sites.

The scope of housing and urban areas was scored as Small because housing and urban area development are only a threat for parts of some subpopulations. The severity was Moderate because adult Skillet Clubtails can probably use low density housing and urban areas for foraging. The timing is High (Continuing) because the threat is ongoing.

Threat 4. Transportation and service corridors (low impact)

4.1 Roads and railroads (low impact)

Vehicle traffic on riverside roads can cause mortality (roadkill) of adults (Rao and Girish 2007). The risk is greatest at roads where vehicles travel at more than 50 km/hr, which is the speed at which dragonflies are unable to avoid approaching vehicles (COSEWIC 2010). The amount of traffic and the nature of the road are significant. Well constructed roads through woodlands and secondary highways, which allow high speed but have narrow rights of way, seem particularly dangerous for dragonflies (COSEWIC 2010). Larger highways with wide rights of way are much less so (COSEWIC 2010).

Roads near Skillet Clubtail habitat (i.e., parallel to the river at less than 100 m from the shore and/or bridge crossings) are present at all subpopulations (GoogleEarth imagery). Road density is highest along sections of the Saint-François (#4), Batiscan (#2), Godefroy (#3), Chicot (#6), Chaudière (#5), and Saint John (#11) rivers and lowest at Salmon (#12) and Canaan (#13) rivers. The urban area of Fredericton presents a road-kill danger to dispersing adult Skillet Clubtails, although urban areas have a low speed limit (50 km/hour), and the TransCanada Highway (2001) moved most traffic away from the Saint John River. The Princess Margaret Bridge is elevated and may be high enough to minimize mortality (Sabine pers. comm. 2021). Trends in vehicle traffic are unknown.

The impact of road mortality at the population level is unknown but probably slight to negligible. Skillet Clubtail and other gomphids are probably less susceptible to roadkill than other odonates (e.g., darners, emeralds, and baskettails), which are more inclined to feed over roads (Sabine pers. comm. 2021). Roadkill of Skillet Clubtails has not been documented in New Brunswick (Sabine pers. comm. 2021).

Toxic chemical spills are a potential threat, particularly where road and rail corridors are adjacent to the river.

The scope of roads and railroads was scored as Pervasive because roads are present near all subpopulations. The severity was Slight because Skillet Clubtail foraging habits put them at relatively low risk of mortality and the timing is High (Continuing) because the threat is ongoing.

Threat 6. Human intrusions and disturbance (low impact)

6.1 Recreational activities (low impact)

Wakes from boats can result in mortality during emergence by washing tenerals and larvae into the river (COSEWIC 2010; O’Malley and Monk 2016). The impact of this threat probably varies between subpopulations. Most larval emergence on the Saint John River (#11) was on tree trunks between 0 and 11 m from shore (O’Malley and Monk 2016; O’Malley et al. 2020; Sabine pers. comm. 2021) where the impact of boat wakes would presumably be low. In Quebec emergence was observed on the riverbank less than 1 m from the shore where wakes may have a greater effect (Desrosiers pers. comm. 2020). The severity may be greatest when there is heavy boat traffic during a mass emergence.

Boat traffic is greatest at the Saint John River (#11), Batiscan River (#2), and Saint-François River subpopulations and likely a low or negligible threat at other subpopulations. Motorboat wake is a demonstrated threat on the Saint John River at least when larvae are moving from the water to the emergence site (O’Malley and Monk 2016). Because this dragonfly emerges within a short time period, wakes caused by boat traffic could have a substantial impact to a subpopulation. The scope was scored Restricted, severity scored Slight, and the threat is ongoing (High timing).

Threat 9. Pollution (low impact)

9.1 Domestic and urban wastewater (unknown impact)

Skillet Clubtail may be intolerant of eutrophication caused by increased nutrient input from domestic and urban wastewater and other sources. Eutrophication can degrade habitat by decreasing dissolved oxygen. Increased salinity from de-icing salts in urban runoff is also a threat (Castillo et al. 2018). Elevated salinity can impair osmoregulation in freshwater dragonfly larvae and cause death at high salt concentrations (Corbet 1999).

The headwaters of the Batiscan River (#2) watershed are largely forested with few or no sources of wastewater or effluent (SAMBBA 2015). Tributaries downstream of Saint-Adelphe, however, have poor water quality due to drainage from the eutrophic waters from Lake Pierre-Paul and runoff from residential and agricultural lands (SAMBBA 2015). Water quality in these tributaries improved between 2003 and 2015 (SAMBBA 2015).

The Godefroy (#3), Saint-François (#4), Chicot (#6), and Chaudière (#5) rivers flow through largely agricultural landscapes and are probably subject to similar water quality changes as the Batiscan River (#2). The Chicot River (#6) has higher levels of suspended solids, total phosphorus, and nitrites and nitrates than the other rivers (Gouvernement du Québec 2020).

Although water quality has generally improved on the Saint John River (#11) since the 1960s (CRI 2011), discharge from food processing plants, pulp and paper mills, non-municipal and municipal sources, and urban runoff continue to cause locally elevated turbidity and total phosphorus concentrations, and depleted dissolved oxygen (New Brunswick Department of Environment and Local Government 2019). Flooded septic systems caused sewage and other runoff to spill into the Saint John River during a record flood in 2018 (Sabine pers. comm. 2021).

9.2 Industrial and military effluents (unknown impact)

As described under 9.1, industrial runoff has probably contributed to eutrophication and decreased dissolved oxygen at the Saint John River (#11) subpopulation. There are also two paper mills on the Saint François River (#4) near Sherbrooke and a former asbestos mine less than 1 km from the Nicolet-Sud-Ouest River subpopulation (#9). No large sources of industrial effluent are found near the other subpopulations.

9.3 Agricultural and forestry effluents (low impact)

All rivers supporting Skillet Clubtail subpopulations have agricultural lands within their watersheds. As is the case with urban runoff (see 9.1), nitrates/nitrites and phosphorus in fertilizers in agricultural runoff have probably contributed to stream eutrophication and decreased dissolved oxygen.

Pesticide use on agricultural lands in these watersheds is not documented but probably includes glyphosate and neonicotinoids. Exposure to glyphosate (and the surfactant used with the herbicide) reduced survival and altered behaviour and physiological processes in odonate larvae (Janssens and Stoks 2017) and reduced invertebrate species richness in aquatic communities (Relyea 2006).

The neonicotinoid insecticide imidacloprid was registered for use in the United States and Canada in 1994 and 1995, respectively (Cox 2001). Approvals for other neonicotinoid insecticides followed. Neonicotinoid pesticides usually are applied in a systemic manner and travel throughout plant tissues, can persist and accumulate in soils and are water soluble and prone to leaching into waterways (Goulson 2013). They are used routinely on golf courses and agricultural lands (Sur and Stork 2003; Jepsen et al. 2013), in forestry, and aquaculture as well as in veterinary products (Simon-Delso et al. 2015). Currently most application is via a seed coating, but application on foliage also occurs. Neonicotinoid insecticides are widely used on Corn (Zea mays) and Soybean (Glycine max) crops in Ontario and Quebec (Labrie et al. 2020; Ontario Ministry of Agriculture, Food and Rural Affairs 2014). Declines in dragonfly populations have been attributed to agricultural use of neonicotinoids through direct toxic effects or declining prey availability (Nakanishi et al. 2018; Van Dijk et al. 2013). Sub-lethal impacts of neonicotinoids on invertebrates include altered foraging behaviour, reduced reproduction, and greater susceptibility to pathogens (Goulson 2013, van der Sluijs et al. 2013). Health Canada (2021a; 2021b) published new guidelines/restrictions for thiamethoxam and clothianidin (both neonicotinoids) risk to aquatic invertebrates. A study by Schmidt et al. (2022) compared experimental (mesocosm) and observational (field) studies and concluded the synergistic effects were consistent, indicating that neonicotinoid mixtures pose greater than expected risks to stream health.

Chemical herbicides are used for forestry in Ontario and New Brunswick. However, these herbicides were banned on provincial forestlands in Quebec in 2001 (Thiffault and Roy 2010). Both provinces restrict application of pesticides near water bodies (Thiffault and Roy 2010; Ogden pers. comm. 2021). Glyphosate is the most frequently used herbicide for forestry in Canada (Rolando et al. 2017), the impacts of which are described above. Forest insect pests are typically controlled with Bacillus thuringiensis var. kurstaki (Btk) (Canadian Forest Service 2020), which has relatively low toxicity to dragonfly larvae (Corbett 1999). Tebufenozide, which acts by inducing premature moulting, is used in New Brunswick to control Spruce Budworm (Choristoneura fumiferana) (Ogden pers. comm. 2021). Impacts on dragonflies are unknown.

Threat 7. Natural system modifications (unknown impact)

7.2 Dams and water management/use (unknown impact)

Dams affect freshwater ecosystems by altering the natural hydrology of river systems, including changes to flow regimes, water temperatures, sediment transport, and nutrient loads (Nilsson and Berggren 2000; Bednarek et al. 2001; Saunders et al. 2002). Upstream of dams, the creation of reservoirs can lead to permanent terrestrial and riparian habitat loss (Nilsson and Berggren 2000), and lasting changes to species diversity (Nilsson et al. 1997). Reservoirs created from damming activities can also cause changes to water temperatures, resulting in habitat that enables warm water fishes and encouraging further colonization by introduced species (Canadian Rivers Institute 2011). A detailed assessment of the effects of dams and water level regulation on Skillet Clubtail has not been conducted but the species has persisted in the Saint John River below the Mactaquac Dam for many decades (Sabine pers. comm. 2021).

The Saint John River (#11) is actively regulated for power generation and flood control by an upstream dam at Mactaquac (Canadian Rivers Institute 2011) and this has the greatest potential impacts on Skillet Clubtail habitat. Most of the other rivers supporting Skillet Clubtail subpopulations have smaller dams in the watershed intended for wildlife and recreational purposes. These include 21 dams in the Saugeen River (#1) watershed (Saugeen Conservation 2019), 103 dams in the Batiscan River (#2) watershed (SAMBBA 2015), and over 200 dams in the Saint John River Basin (#11) (Canadian Rivers Institute 2011).

Threat 8. Invasive and other problematic species and genes (unknown impact)

8.1 Invasive non-native/alien species/diseases (unknown impact)

Invasive non-native species have the potential to have direct and indirect effects on Skillet Clubtail, but no effects have been demonstrated in Canada. Introduced fish and crayfish are potential predators on Skillet Clubtail (Corbett 1999).

Introduced species in New Brunswick River systems containing Skillet Clubtail that may be a threat for the species include Muskellunge (Esox masquinongy), Chain Pickerel (Esox niger), Smallmouth Bass (Micropterus dolomieu), Spinycheek Crayfish (Orconectes limosus), and Virile Crayfish (Orconectes virilis) (McAlpine et al. 2007). Smallmouth Bass and Chain Pickerel have been in the lower Saint John River for over 100 years and Muskellunge for over 40 years (Sabine pers. comm. 2021). Largemouth Bass (Micropterus salmoides) were recently detected in the Saint John River above Mactaquac Dam (Sabine pers. comm. 2021). The aquatic introduced species in the rivers supporting other Skillet Clubtail subpopulations are unknown. The impacts of these non-native species are unknown but the southern portions of the United States range of Skillet Clubtail largely overlaps with the natural range of many of these fish and crayfish species, suggesting that they can coexist. The long period of coexistence between Skillet Clubtail and introduced fish in the Saint John River suggests that the severity is slight to negligible but the impacts of newer invasives are unknown.

The diatom Didymo (Didymosphenia geminata) was found in 2006 in the Restigouche and upper Saint John (#11) river systems and several rivers in eastern Quebec (New Brunswick Natural Resources and Energy Development 2009). Didymo may be native to eastern Canada, but blooms have occurred recently because of warming climate (Lavery et al. 2014). Didymo can form dense mats resulting in decreases in mayflies, caddisflies, and stoneflies and increases in chironomids (Gillis and Chalifour 2010). At high densities, Didymo mats can restrict invertebrate movement (Gillis and Chalifour 2010).

Invasive aquatic plants such Eurasian Watermilfoil (Myriophyllum spicatum) are present in the Saint John River (#11) and possibly other rivers supporting Skillet Clubtails. After invading a waterbody, this plant can grow to a high density, followed by a die-off that can deplete dissolved oxygen (Ontario Ministry of Environment Conservation and Parks 2021), potentially causing mortality or inhibiting growth of larvae.

Limiting factors

Skillet Clubtail is at the northern limit of its range in Canada and may be vulnerable to increased mortality, lower recruitment, or slower development caused by colder climate than in the United States range. Most Canadian subpopulations are isolated by over 100 km from the nearest United States subpopulations and are inherently vulnerable to extirpation.

Number of locations

Skillet Clubtail is known from 13 subpopulations in Canada. Each subpopulation represents at least one location^{Footnote 9} and the threat category, scope, and severity of the threats are different at each of the 13 extant subpopulations. The main threats present at most locations include urban and agricultural wastewater, roadkill of adult dragonflies, and invasive species (Table 4).

Protection, status and ranks

Legal protection and status

Skillet Clubtail was listed as Endangered on Schedule 1 of the Species at Risk Act (SARA) in June 2017. SARA includes prohibitions against the killing, harming, harassing, capturing, taking, possessing, collecting, buying, selling, or trading of individuals. In the case of invertebrates, these protections apply only on federal Crown lands. The Recovery Strategy (ECCC 2021) partially identifies critical habitat (see Habitat protection and ownership) and includes a schedule of studies required to complete the identification of critical habitat.

In New Brunswick, Skillet Clubtail was classified as Endangered under the Species at Risk Act in May 2013 (New Brunswick Natural Resources 2020a). In Ontario, it is listed as “Data Deficient” under the Endangered Species Act (Ontario Ministry of Environment Conservation and Parks 2020). In Quebec, this species is listed on the Liste des espèces floristiques et fauniques susceptibles d’être désignées menacées ou vulnérables (List of plant and wildlife species which are likely to be designated as threatened or vulnerable) under the “Loi sur les espèces menacées ou vulnérables” (RLRQ, c. E-12.01) (LEMV) (Act respecting threatened or vulnerable species) (CQLR, c. E-12.01) (Québec 2021).

Non-legal status and ranks

Skillet Clubtail is ranked as G3 (Vulnerable) globally by NatureServe (2022) and N3 (Vulnerable) nationally in the United States (NatureServe 2022). In Canada it is ranked as N2 (Imperiled) by Wild Species 2015 (Canadian Endangered Species Conservation Council 2016). The IUCN Red List of Threatened Species ranks Skillet Clubtail as Least Concern (IUCN 2020).

Skillet Clubtail is ranked as S1 (Critically Imperiled) in Quebec, Nova Scotia, and Ontario, and as S1S2 (Critically Imperiled to Imperiled) in New Brunswick (NatureServe 2022). It has the following ranks in the United States: Connecticut (S2), Indiana (S1S2), Iowa (SNR; not ranked), Kentucky (S1S2), Maryland (SH; historical), Massachusetts (S2), Michigan (SNR), Minnesota (SNR), Missouri (SU; unknown), New Hampshire (S1), New Jersey (SU; unknown), New York (S1), North Carolina (S1S2), Ohio (S2), Pennsylvania (SH), Tennessee (S3), Vermont (S1), Virginia (S1), and Wisconsin (S4; apparently secure).

Skillet Clubtail is not listed on the United States Endangered Species List.

Habitat protection and ownership

The federal Recovery Strategy identifies critical habitat for Skillet Clubtail, spatially defined as four sections of the Saint John River (#11) and two sections of the Batiscan River (ECCC 2020). However, there are no federal lands in these areas and no habitat protection is afforded under SARA.

River and stream habitats in Canada receive some protection under the federal Fisheries Act where fish habitat is present. Ontario’s Lakes and Rivers Improvement Act, Quebec’s Watercourses Act, and New Brunswick’s Clean Water Act and Clean Environment Act offer protection to water quality and volume.

None of the larval habitats of Canadian subpopulations are within parks or other protected areas. Terrestrial habitat surrounding the rivers is mainly privately owned at the Saugeen (#1), Ottawa (#14), Yamaska (#15), Godefroy (#3), Saint-François (#4), Chaudière (#5), Chicot (#6), Saint John (#11) and Shubenacadie (#17) rivers (Energie et Resources Naturelles Québec 2020; New Brunswick Department of Natural Resources 2020; Nova Scotia Department of Natural Resources 2020; Ontario Ministry of Natural Resources 2020). Parts of the lands surrounding the lower Saint John River are in the Grand Lake Protected Natural Area. The upper reaches of the Batiscan (#2), Salmon (#12), and Canaan (#13) river watersheds are mainly provincial land along with parts of the lower Saint John River (Energie et Resources Naturelles Québec 2020, New Brunswick Department of Natural Resources 2020b).

Acknowledgements

We thank Nathalie Desrosiers, Isabelle Gauthier, Colin Jones, John Klymko, Don McAlpine, Ilka Milne, Mike Oldham, Dwayne Sabine, Mary Sabine, Michel St-Germain, and Michel Savard for providing information on Skillet Clubtail populations and habitat. Emmanuelle Fay, Julie McKnight, and Karine Picard of the Canadian Wildlife Service shared information from the recovery strategy. Pierrette Charest, Dwayne Sabine, Michel Savard, and Ken Tennessen examined exuviae collected at Rainy River. Rainy River First Nations allow access to their lands to conduct surveys. Jeremy DeWaard at the Centre for Biodiversity Genomics, University of Guelph conducted barcoding of exuviae.

Jennifer Heron (Arthropods SSC Co-chair) provided editorial and review comments. Thanks also to the COSEWIC Arthropod Species Subcommittee members Robert Buchkowski, Syd Cannings, Jeremy deWaard, Colin Jones, John Klymko, Jamie Lewthwaite, Jessica Linton, Jeffrey Ogden, John Richardson, Sarah Semmler, Leah Ramsay, Michel St-Germain, Dawn Marks, and Brian Starzomski; COSEWIC member Paul Grant and COSEWIC Secretariat Rosanna Soares and Joanna James.

Paul M. Brunelle wrote the first COSEWIC status report.

Front cover photograph of a male Skillet Clubtail (Gomphurus ventricosus) at Fredericton, New Brunswick, July 16, 2015. Photograph by Danny O’Shea (with permission).

Authorities contacted

Anderson, R., Research Scientist, Canadian Museum of Nature, Ottawa, Ontario

Boyne, A., Head of Protected Areas, Canadian Wildlife Service, Environment and Climate Change Canada, Dartmouth, Nova Scotia

Davy, C. M., Wildlife Research Scientist, Species at Risk, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario

Desrosiers, N., Biologiste, Service de la conservation de la biodiversité et des milieux humides, Direction de l’expertise sur la faune terrestre, l’herpétofaune et l’avifaune, ministère des Forêts, de la Faune et des Parcs, Québec.

Fay, E., Biologist, Conservation Planning Unit, Canadian Wildlife Service, Québec Region, Environment and Climate Change Canada / Government of Canada, Québec, Québec

Gardiner, L., Acting Ecosystem Scientist, Species Conservation, Conservation Programs Branch, Parks Canada Agency, Government of Canada, Grasslands National Park, Val Marie, Saskatchewan

Gauthier, I. Biologiste, Coordonnatrice provinciale des espèces fauniques menacées ou vulnérables, Direction générale de la gestion de la faune et des habitats, ministère des Forêts, de la Faune et des Parcs, Québec, Québec

Girard, J., Species at Risk Biologist, Conservation Planning, Ontario, Canadian Wildlife Service, Toronto, Ontario

Hurlburt, D., Wildlife Division, Nova Scotia Department of Lands and Forestry, Kentville, Nova Scotia

Faulkner J., Head of Conservation Partnerships, Canadian Wildlife Service, Environment and Climate Change Canada, Sackville, New Brunswick

Jones, C.D., Provincial Arthropod Zoologist, Ontario Natural Heritage Information Centre, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario

Klymko, J., Zoologist, Atlantic Canada Conservation Data Centre, Sackville, New Brunswick

Kling, A., Senior Science Advisor, Marine Mammal Science, Fisheries and Oceans Canada, Ottawa, Ontario

Lonsdale, O., Collections Manager, Canadian National Collection of Insects, Arachnids and Nematodes, and Manager, National Identification Service (Invertebrates), Agriculture and Agri-Food Canada, K.W. Neatby Building, Central Experimental Farm, Ottawa, Ontario

McAlpine, D., Head, Department of Natural History, Zoology Section, New Brunswick Museum, Saint John, New Brunswick

McDonald, R., Senior Environmental Advisor, National Defence, Ottawa, Ontario

McKnight, J., Species at Risk Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Dartmouth, Nova Scotia

Picard, K., Species at Risk Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Québec, Québec

Pickett, K., Species at Risk Biologist, Canadian Wildlife Service, Environment and Climate Change Canada, Toronto, Ontario

Pruss, S., Species conservation specialist, Natural Resources Conservation Branch, Parks Canada, Government of Canada, Fort Saskatchewan, Alberta

Sabine, D., Wildlife Biologist, Fish and Wildlife Branch, Natural Resources and Energy Development, Fredericton, New Brunswick

Sabine, M., Biologist, Species at Risk Program, Forest Planning and Stewardship Branch, Department of Natural Resources and Energy Development, Fredericton, New Brunswick

Savard, M., Initiative pour un atlas des libellules du Québec, EQ inc.

Saint-Germain, M., Chef de division, collections entomologiques et recherche, Insectarium de Montréal, Montréal, Québec

Sam, D. Biologist, Species at Risk, Nova Scotia Department of Lands and Forestry, Kentville, Nova Scotia

Savard, M. Saguenay, Québec

Schnobb, S., Program Support Specialist, COSEWIC Secretariat, Canadian Wildlife Service, Environment and Climate Change Canada, Gatineau, Québec

Shaw, J., Fish Population Science, Fisheries and Oceans Canada, Ottawa, Ontario

Shepherd, P., Species Conservation and Management Ecosystem Scientist, Parks Canada, Vancouver, British Columbia

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Biographical summary of report writer

Allan Harris is a biologist with over 30 years’ experience in northern Ontario. He has a B.Sc. in Wildlife Biology from the University of Guelph and an M.Sc. in Biology from Lakehead University. After spending seven years as a biologist with Ontario Ministry of Natural Resources, he co-founded Northern Bioscience, an ecological consulting company based in Thunder Bay, Ontario. Together with Rob Foster, Al has written or cowritten over twenty COSEWIC status reports including 15 insects, 5 vascular plants, a spider, a land snail, and a bird. He was a member of the Committee on the Status of Species at Risk in Ontario (2009 - 2014) and presently serves on the Arthropod Species Subcommittee of the Committee on the Status of Endangered Wildlife in Canada.

Collections examined

The following collections were examined in preparation for the first (COSEWIC 2010) and updated status report:

• Atlantic Dragonfly Inventory Program (ADIP) Dartmouth, Nova Scotia. Paul Brunelle personal database.
• Canadian National Collection of Insects, Arachnids and Nematodes (CNC), Agriculture and Agri-Food Canada, K.W. Neatby Building, Ottawa, Ontario
• Carleton University, Ottawa, Ontario
• David G. Furth, MRC 165, P.O. Box 37012, Washington, DC, 20013-7012.
• Lyman Entomological Museum, Macdonald Campus, McGill University, Ste-Anne-de Bellevue, Québec (Stéphanie Boucher, Curator)
• Insectarium de Montréal, Montréal, Québec
• New Brunswick Museum (NBM), Saint John, New Brunswick
• Royal Ontario Museum (ROM), Department of Natural History, Toronto, Ontario
• Smithsonian Institution, National Museum of Natural History (NMNH), Washington, DC