COSEWIC Assessment and Status Report on the Lake Erie Watersnake Nerodia sipedon insularum in Canada - 2015
Committee on the Status
of Endangered Wildlife
Comité sur la situation
des espèces en péril
COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:
COSEWIC. 2015. COSEWIC assessment and status report on the Lake Erie Watersnake Nerodia sipedon insularum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xi + 37 pp. Species at Risk Public Registry website.
COSEWIC 2006. COSEWIC assessment and update status report on the Lake Erie watersnake Nerodia sipedon insularum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 23 pp.
COSEWIC would like to acknowledge Rob Willson and Glenn Cunnington for writing the draft of the status report on Lake Erie Watersnake (Nerodia sipedon insularum) in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Jim Bogart, Co-chair of the COSEWIC Amphibians and Reptiles Specialist Subcommittee with contributions from the Amphibians and Reptiles Specialist Subcommittee members.
For additional copies contact:
c/o Canadian Wildlife Service
Environment and Climate Change Canada
Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur la Couleuvre d’eau du lac Érié (Nerodia sipedon insularum) au Canada.
Lake Erie Watersnake -- Photo courtesy of Joe Crowley.
COSEWIC Assessment Summary
Assessment Summary – November 2015
- Common name
- Lake Erie Watersnake
- Scientific name
- Nerodia sipedon insularum
- Special Concern
- Reason for designation
- The Canadian distribution of this unique population of watersnakes is confined to four small islands in Lake Erie. In the United States, subpopulations have recovered because of an increased fish prey base, provided by introduced Round Goby. It is uncertain whether a similar recovery has occurred in Canadian subpopulations. There is concern that the largest subpopulation on Pelee Island continues to be threatened by road mortality, shoreline development, and persecution by humans.
- Status history
- Designated Endangered in April 1991 and in April 2006. Status re-examined and designated Special Concern in November 2015.
COSEWIC Executive Summary
Lake Erie Watersnake
Nerodia sipedon insularum
Wildlife Species Description and Significance
Lake Erie Watersnake, Nerodia sipedon insularum, is one of two subspecies of the Common Watersnake, Nerodia sipedon (family Colubridae), found in Canada. Lake Erie Watersnakes range in appearance from being regularly patterned with dark dorsal and lateral blotches to a uniform grey (often a drab greenish or brownish) without pattern. The colour of the ventral scales is generally white or yellowish white, often with dark speckling. Lake Erie Watersnakes are heavy-bodied. The head is large and covered with broad, smooth scales and the body scales are “keeled”. Long-term studies on Lake Erie Watersnakes have served as models for understanding evolutionary processes such as gene flow and selection, as well as provided researchers with an example of a rare species benefiting from the introduction of an invasive species.
Lake Erie Watersnake has one of the smallest distributions of any snake in North America. In its Canadian range, Lake Erie Watersnake is known to occur only on four small islands in the western basin of Lake Erie (Pelee, Middle, East Sister, and Hen Islands). In the United States, Lake Erie Watersnake occurs in a small shoreline area of the Ohio mainland and on 11 Ohio islands in the western end of Lake Erie.
During the active season, Lake Erie Watersnake occupies rocky or sandy shorelines, and limestone or dolomite shelves and ledges with cracks and varying levels of vegetation. Natural and human-made rock berms are also used. The snakes feed in the water but rarely go more than 200 m from shore while foraging. Watersnakes are rarely found more than 100 m inland during the active season, instead most of the time they are within 13 m of the water’s edge. Distance travelled inland during the active season is dependent on the availability of shelter habitat and possibly conspecifics during the mating season. Hibernation habitat is farther inland and the sites used are usually cavities and crevices, and are typically composed of soil and rock substrates.
Lake Erie Watersnake can live up to 12 years in the wild. This species reaches sexual maturity at 3–4 years of age. Courtship involves scramble competition in which several males court one female simultaneously. Annual reproduction by females is common. Females give birth to live young and litter size averages 23 and is positively related to the female’s size. Lake Erie Watersnake’s historical diet has been largely replaced with Round Goby (Apollonia melanostomus), an invasive species that arrived in Lake Erie in the early 1990s.
Population Size and Trends
Lake Erie Watersnakes were reported in great numbers on several islands of western Lake Erie from the early 1800s and up to the early 1960s. Populations decreased in the latter half of the 20th century but are now increasing on U.S. islands, apparently associated with increased prey base from the introduction of Round Goby, which is an invasive fish. There is no information on trends on the Canadian islands, but the persistence of several threats suggests that populations may still be in decline.
Threats and Limiting Factors
Intentional and accidental human-induced mortality, particularly mortality on roads is likely the most significant threat to the species. Another important threat is the reduction of habitat quantity and quality. Additional threats include environmental contamination and elevated levels of predation. The small geographic range and small population size of Lake Erie Watersnake are limiting factors and increase the vulnerability of the snakes to perturbations.
Protection, Status, and Ranks
Globally, NatureServe lists the Lake Erie Watersnake taxon as imperilled (global rank is G5T2). NatureServe lists Lake Erie Watersnake as imperilled (S2) in Ontario. In Canada, Lake Erie Watersnake was assessed as Endangered by COSEWIC in 1991 and 2006 and was added to Schedule 1 of the federal Species at Risk Act as Endangered in 2009. Ontario’s Endangered Species Act, 2007 (ESA; Government of Ontario 2007) came into force in 2008 and protection is provided for Lake Erie Watersnake (designated Endangered on the Species at Risk in Ontario List). Under Ontario’s Fish and Wildlife Conservation Act, the taxon is considered a specially protected reptile. On Middle Island, the species is protected under the Canada National Parks Act. Lake Erie Watersnake was removed from the U.S. list of federally endangered and threatened species on August 16, 2011. Lake Erie Watersnake has a status of Endangered assigned by the state of Ohio.
- Scientific Name:
- Nerodia sipedon insularum
- English Name:
- Lake Erie Watersnake
- French Name:
- Couleuvre d’eau du lac Érié
- Range of occurrence in Canada:
|Generation time (usually average age of parents in the population; indicate if another method of estimating generation time indicated in the IUCN guidelines(2011) is being used)||ca. 6 yrs|
|Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?||Yes, inferred continuing decline based on the persistence of several threats, including accidental and intentional mortality and habitat loss.|
|Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations]||Unknown|
|[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations].||Unknown|
|[Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations].||Unknown|
|[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 years, or 3 generations] period, over a time period including both the past and the future.||Unknown|
|Are the causes of the decline a. clearly reversible and b. understood and c. ceased?||a. yes, for some of the causes b. yes, for some of the causes c. yes, for some of the causes in some locations; no for several causes such as intentional and accidental mortality|
|Are there extreme fluctuations in number of mature individuals?||No|
Extent and Occupancy Information
|Estimated extent of occurrence||188 km2|
|Index of area of occupancy (IAO) (Always report 2x2 grid value).||2x2 grid value = 72 km2|
|Is the population “severely fragmented” ie. 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?||a. no|
|Number of locations|
(Note: See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.)
|3–4 (see Number of Locations under section Threats and Limiting Factors)|
|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?||Possible decline in index of area of occupancy if subpopulation on smallest, privately owned island (Hen) was extirpated|
|Is there an [observed, inferred, or projected] decline in number of subpopulations?||Possible decline in number of subpopulations if subpopulation on smallest, privately owned island (Hen) was extirpated|
|Is there an [observed, inferred, or projected] decline in number of “locations”?|
(Note: See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term.)
|Possible decline in number of locations if subpopulation on smallest, privately owned island (Hen) was extirpated|
|Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat?||Yes, observed|
|Are there extreme fluctuations in number of subpopulations?||No|
|Are there extreme fluctuations in extent of occurrence?||No|
|Are there extreme fluctuations in index of area of occupancy?||No|
Number of Mature Individuals (in each subpopulation)
|Population||N Clones (index of Mature Individuals)|
|Middle Island||119 (67–246 95% CI)|
|East Sister Island||50|
|Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years].||Analysis not completed|
Threats (actual or imminent, to populations or habitats, from highest impact to least)
- Intentional and Accidental Human-induced Mortality
- Habitat Loss and Degradation
- Environmental Contamination
- Geographic Range (small populations that are more susceptible to demographic and environmental stochasticity)
Was a threats calculator completed for this species and if so, by whom?
Yes, in May 2015
Attended by Jim Bogart (COSEWIC Amphibians and Reptiles Specialist Subcommittee co-chair), Ruben Boles (Canadian Wildlife Service), Richard King (Northern Illinois University), Patrick Nantel (Parks Canada), Scott Reid (Ontario Ministry of Natural Resources and Forestry), Kristin Stanford (Ohio State University Stone Laboratory), Rob Willson (status report author) Facilitator: David Fraser; COSEWIC Secretariat (notes): Bev McBride
Rescue Effect (immigration from outside Canada)
|Status of outside population(s) most likely to provide immigrants to Canada.|
Status of outside population(s)?
USA: Lake Erie Watersnake was removed from the U.S. list of federally endangered and threatened species on August 16, 2011; the taxon will remain as a species of concern throughout a mandatory five-year post-delisting monitoring period (USFWS 2010)
Lake Erie Watersnake has a status of Endangered assigned by the state of Ohio.
|Is immigration known or possible?||Yes|
|Would immigrants be adapted to survive in Canada?||Yes|
|Is there sufficient habitat for immigrants in Canada?||Yes|
|Are conditions deteriorating in Canada? See Table 3 (Guidelines for modifying status assessment based on rescue effect)||Possibly|
|Are conditions for the source population deteriorating?|
See Table 3 (Guidelines for modifying status assessment based on rescue effect)
|Is the Canadian population considered to be a sink?|
See Table 3 (Guidelines for modifying status assessment based on rescue effect)
|Is rescue from outside populations likely?||Yes|
|Is this a data sensitive species?||Only the locations of hibernation areas are sensitive.|
COSEWIC: Designated Endangered in April 1991 and in April 2006. Status re-examined and designated Special Concern in November 2015.
Status and Reasons for Designation:
- Special Concern
- Alpha-numeric code:
- Not applicable
- Reasons for designation:
- The Canadian distribution of this unique population of watersnakes is confined to four small islands in Lake Erie. In the United States, subpopulations have recovered because of an increased fish prey base, provided by introduced Round Goby. It is uncertain whether a similar recovery has occurred in Canadian subpopulations. There is concern that the largest subpopulation on Pelee Island continues to be threatened by road mortality, shoreline development, and persecution by humans.
Applicability of Criteria
- Criterion A (Decline in Total Number of Mature Individuals):
- Does not meet criteria. While a continuing decline is inferred and projected, its magnitude is unknown.
- Criterion B (Small Distribution Range and Decline or Fluctuation):
- Meets Endangered B1 and B2 because both the EOO (188 km2) and IAO (72 km2) are well below the thresholds for Endangered; meets sub-criterion “a” because the species is found in fewer than 5 locations but there is no evidence for a decline in number of mature individuals.
- Criterion C (Small and Declining Number of Mature Individuals):
- Does not meet criteria. While the number of adults is below the threshold for Endangered, there is more than one subpopulation and more than 1000 mature individuals in one subpopulation but there is no evidence for a decline in number of adults.
- Criterion D (Very Small or Restricted Population):
- Does not meet criteria.
- Criterion E(Quantitative Analysis):
- Not applicable. Not done due to lack of data.
The most important occurrence since the previous COSEWIC status report on Lake Erie Watersnake is the removal of the species from the U.S. list of federally endangered and threatened species on August 16, 2011 (USFWS 2010). The delisting of Lake Erie Watersnake in the U.S. is primarily the result of increasing numbers of individuals on the U.S. islands. There are no recent comparable data for the Canadian population.
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.
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 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.
- 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)
(Note: Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.)
- 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)
(Note: Formerly described as “Not In Any Category”, or “No Designation Required.”)
- A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.
- Data Deficient (DD)
(Note: 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.)
- 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.
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
Nerodia sipedon insularum (Lake Erie Watersnake / couleuvre d’eau du lac Érié) is one of two subspecies of Common Watersnake (Nerodia sipedon) in Canada, the other being Northern Watersnake (Nerodia sipedon sipedon) (Crother 2012). Lake Erie Watersnake occurs solely on the islands and the Catawba-Marblehead Peninsula of western Lake Erie (Conant and Clay 1963; USFWS 2003), whereas Northern Watersnake is found on the mainland in Ohio and many other central and eastern states in the U.S. and in Ontario and Quebec in Canada. Nerodia s. insularum was designated as a distinct taxon by Conant and Clay (1937) and continues to be recognized as such in the official names list of North American herpetological organizations (Crother 2012). Nevertheless, thresholds for the recognition of subspecies are continually changing and this taxon may warrant further assessment. It should be recognized, however, that subspecific recognition is not a requirement of COSEWIC status.
Lake Erie Watersnakes have grey, drab greenish, or brown dorsal colouration. Patterning is highly variable among individuals, ranging from unpatterned to regularly patterned with darker (sometimes reddish) dorsal banding and lateral blotches (Conant and Clay 1937; 1963; King 1986; King and Lawson 1997; Rowell 2012). The relative size and position of the blotches remain fixed over the life of the snake (King and Lawson 1997). The ventral surface tends to be white or yellowish white, often with dark speckling, and the bases of the ventral scales are the same colour as the dorsum (Conant and Clay 1937). The body scales are keeled, that is, each scale has a ridge down the middle, and there is a single anal plate (Conant and Collins 1998).
Lake Erie Watersnake differs from other watersnakes by being more greyish in colouration and by having a partial or complete lack of blotches or banding (Conant and Clay 1937), whereas Northern Watersnake has a regular pattern of blotches and banding (although the patterning can be very faint and hard to see on darker individuals).
Lake Erie Watersnake is a medium-sized snake with snout-to-vent lengths (SVL) ranging from 15.5 cm (both sexes) to 86 cm SVL for males and 110 cm SVL for females (King 1986; Stanford 2012).
Population Spatial Structure and Variability
Watersnake populations on the islands of western Lake Erie are separated from watersnake populations on the Ohio and Ontario mainland by 5 to 14 km of water, which acts as a natural barrier to movement (USFWS 2003). Reduced and intermediate patterns appear to be favoured on islands because reduced patterning is more cryptic against the bare, rocky shorelines (Ehrlich and Camin 1960; King and Lawson 1997). In addition to unpatterned individuals, both intermediate and regularly patterned individuals are found on the islands. This variation suggests that mainland Northern Watersnakes and the island-dwelling Lake Erie Watersnakes still intergrade. Gene flow is created by movement among and between islands and the mainland (King and Lawson 1997). Inter-island movements appear to be rare and have only been documented twice (King 2002; D. Jacobs pers. comm. September 2005). Genetic analysis of allozyme variation suggests that 0.08% to 1% of island subpopulations (N. s. insularum) are replaced by mainland Northern Watersnake individuals per generation (King and Lawson 1995; 1997). Frequency of the various colour patterns seems to have been stable from 1980 to the present, suggesting that selection and gene flow have also remained stable over this time period (Ray and King 2006).
The entire portion of the Lake Erie Watersnake’s geographic range in Canada occurs on the islands in the western basin of Lake Erie. As such, Lake Erie Watersnakes occur in a single Faunal Province (Carolinian) and single ecoregion (7E-Carolinian Zone). A single designatable unit is warranted.
Relative to many other snake taxa, Lake Erie Watersnake has been studied extensively (e.g., Camin et al. 1954; Camin and Ehrlich 1958; Ehrlich and Camin 1960; King 1986; King and Lawson 1997; Hendry et al. 2001; King et al. 2006b; Stanford 2012 and references therein). Richard King and his associates have conducted fieldwork on the species during four intensive time periods: 1980–1985, 1988–1992, 1996–1998, and 2000–2004 and work is continuing (King et al. 2006b; Stanford 2012). The duration of these studies make Lake Erie Watersnake one of the longest studied snakes in North America.
The colour pattern polymorphism found in Lake Erie Watersnakes is a classic example of microevolutionary change in which effects of selection, gene flow, inheritance, and population history are well-understood (King 1987; 1992; 1993a; King and Lawson 1995; 1997; Hendry et al. 2001; Ray and King 2006).
In addition to serving as a model for understanding evolutionary processes, the Lake Erie Watersnake’s interaction with Round Goby (Apollonia melanostomus) has provided researchers with a rare example of a threatened species actually benefiting from the introduction of an invasive species (King et al. 2006b; King et al. 2008; Jones et al. 2009; USFWS 2010).
Lake Erie Watersnake is restricted to the islands of the Lake Erie Archipelago and a small shoreline area of the Catawba-Marblehead Peninsula in Ohio (Figure 1; but see USFWS 2003 for discussion of intergrades with Northern Watersnake on the peninsula). The Lake Erie Archipelago consists of 22 islands: nine Canadian (Pelee, Middle, East Sister, Middle Sister, Hen, North Harbour, Big Chicken, Chick, and Little Chicken) and 13 American (Kelleys, South Bass, Middle Bass, North Bass, West Sister, Rattlesnake, Sugar, Green, Ballast, Gibraltar, Gull, Starve, and Lost Ballast). Reports dating back to 1893 suggest that Lake Erie Watersnakes may have been observed on all of the islands in the western basin of Lake Erie (King 1998); however, as indicated in Rowell (2012; pp 274), there are no historical records from Chick, Big Chicken, or Little Chicken. These three small islands are little more than reefs, that in high water levels or storm events are underwater or nearly so. Although it is possible that a Lake Erie Watersnake would move onto these islands to forage or while moving between the other islands, there is no evidence at this time to indicate that these islands function as habitat for this species. Lake Erie Watersnake has one of the smallest geographic distributions of any snake in North America, having a global range of less than 40 km in diameter (King et al. 2006b).
In Canada, Lake Erie Watersnake is known to be extant on Pelee, Middle, and East Sister islands (Figure 1). Lake Erie Watersnakes were observed on Hen Island in 1990, but it is unknown whether they still occur on that island (Figure 1). The Canadian islands account for 41 km (or approximately 38%) of the global 109 km of shoreline habitat (King 1998). Pelee Island is the largest island (4148 ha) in the Lake Erie Watersnake’s range. The Canadian population of Lake Erie Watersnake is defined as the individuals living on the Canadian islands in the western basin of Lake Erie (Figure 1). Because movements between islands are rare (see Dispersal and Migration) it seems prudent to assess this population as distinct from the U.S. population.
As discussed in the section on Threats and Limiting Factors and indicated in the threats calculator results (Appendix 1), the number of threat-based locations was determined to be 3–4 (depending on whether or not the subpopulation on Hen Island is extant). Pelee Island is considered a single location where the most plausible threat is road traffic. Middle, East Sister, and possibly Hen islands would each be considered separate locations. The most plausible threat for these smaller islands is demographic stochasticity that could adversely affect the small subpopulations.
Extent of Occurrence and Area of Occupancy
The extent of occurrence (EOO) of Lake Erie Watersnake in Canada is estimated to be 188 km2. The index of area of occupancy (IAO) of Lake Erie Watersnake in Canada is estimated to be 72 km2. The IAO accounts for all shoreline habitat and possible hibernacula on the four islands in Canada (Pelee, Middle, East Sister, and Hen) where Lake Erie Watersnakes are known to occur (see Figure 2).
Efforts to document Lake Erie Watersnakes on the Canadian islands have varied. The species has been consistently observed on East Sister, Middle, and Pelee islands. In contrast, although Lake Erie Watersnakes may have historically occurred on Middle, Sister and North Harbour, these islands were searched during the 1980s and 1990s and no watersnakes were observed (King et al. 1997). Lake Erie Watersnakes were observed on Hen Island in 1990; however, similar to Middle Sister and North Harbour, Hen is privately owned and efforts to gain access to these islands since the early 1990s have been unsuccessful. Middle Island is managed by Parks Canada and targeted surveys for Lake Erie Watersnakes were conducted up until 2011 (Parks Canada Agency 2012); since 2011 search effort has been limited to incidental observations during the course of other monitoring efforts (T. Dobbie pers. comm. October 2014). East Sister Island Provincial Nature Reserve and two areas on Pelee Island (Lighthouse Point and Fish Point Provincial Nature Reserves) are managed by the Ontario Ministry of Natural Resources and Forestry (OMNRF) and as such are visited regularly by ministry staff.
Based on the radio telemetry studies conducted by Stanford et al. (2010), the USFWS (2003) categorized all of the habitats used by Lake Erie Watersnake into two groups: “Essential Summer Habitat” and “Essential Hibernation Habitat”. Given that the radio telemetry studies on Lake Erie Watersnake conducted by Stanford et al. (2010) on the U.S. islands were more extensive than those conducted on Pelee and Middle islands by the OMNRF (D. Jacobs unpubl. data), this classification into two habitat categories is followed here, with the exception that summer habitat is referred to as active season habitat and the “essential” has been removed as a modifier. The habitat types and descriptions follow Ontario’s recovery strategy for Lake Erie Watersnake (Willson and Cunnington 2015).
Cracks and fissures in bedrock, rock and soil piles, and berms, rodent burrows in soil substrates, root masses, building foundations, drainage tiles, and old wells have been used as hibernation habitat (USFWS 2003, D. Jacobs unpubl. data). Adult snakes may hibernate singly or communally (USFWS 2003; D. Jacobs unpubl. data), and occasionally hibernation areas are shared with Eastern Foxsnakes (Pantherophis gloydi), Blue Racers (Coluber constrictor foxii) and Eastern Gartersnakes (Thamnophis sirtalis sirtalis) (B. Porchuk and R. Willson unpubl. data).
In Ontario, radio tracked Lake Erie Watersnakes hibernated at sites at least 13 m from the water’s edge (range = 13–105 m; mean = 53 m); 50 percent of the hibernation sites were within 56 m of the shore, 75 percent were within 69 m, and 90 percent were within 95 m of shore (D. Jacobs unpubl. data). On Pelee Island, probable sites for hibernacula have been identified up to 500 m from the shore based on observations of snakes early in the spring that were located at sites with the potential to function as hibernation habitat based on physical characteristics (R. Willson unpubl. data). It may be noteworthy that many of the Lake Erie Watersnakes found greater than 95 m from the shoreline are juveniles. For example, young individuals have been found up to 610 m inland in the spring (R. Willson unpubl. data).
On the U.S. islands, 75 percent of the radio tracked Lake Erie Watersnakes hibernated within 71 m of the shoreline (Stanford et al. 2010). Emergence from hibernacula usually occurs in mid- to late April and into May (Stanford et al. 2010). Within one to one and a half months after emergence, most Lake Erie Watersnakes will have dispersed from hibernacula towards the Lake Erie shoreline where they can be found under rocks, in rock berms, in woody debris or brush piles, under wooden boards or pieces of refuse washed upon the beach, and underground (D. Jacobs unpubl. data).
Active Season Habitat
Active season habitat includes areas used for basking, gestation, shelter, foraging, mating, birthing, and movement. With the exception of inland movements to hibernation habitats, Stanford et al. (2010) found that 75% of the relocations of radio tracked Lake Erie Watersnakes were within 13 m of the water’s edge. Within the terrestrial portion of this shoreline band, Lake Erie Watersnakes use fractures in the limestone/dolomite bedrock, rock fragments, armour stone, cobblestone, vegetation (living or dead), rock and/or soil piles (berms), and discarded sheet metal or wooden boards (Campbell et al. 1991; USFWS 2003; M.J. Oldham pers. comm. 2005). These features are used by Lake Erie Watersnakes for basking, gestation, shelter, mating, and birthing. Sandy shorelines, which are more common on Pelee than other islands, that do not have rock or vegetation within a few metres of the water seem to be used less frequently (D. Jacobs, R. Willson, B. Porchuk unpubl. data). However, Lake Erie Watersnakes have been observed moving onto sandy beaches to finish swallowing prey items (R. Willson unpubl. data), and they have been observed resting or basking in these areas in relatively high numbers (J. Crowley pers. comm. 2013). Lake Erie Watersnakes forage in water along the shoreline, in canals, and in wetlands (B. Porchuk unpubl. data). Stanford (2012) found that the linear extent of shoreline used by 95 percent of the snakes they were radio tracking was 952 m or less. Systematic boat surveys found that 95 percent of Lake Erie Watersnakes (n = 130) foraged ≤178 m from shore (Jones et al. 2009; Stanford 2012). As in the case of hibernation habitat, Lake Erie Watersnakes exhibit fidelity to specific areas or features along the shoreline (USFWS 2003, D. Jacobs unpubl. data). On Pelee Island, Lake Erie Watersnakes have been documented in the canals that drain parts of the island and have also been found using inland ponds/wetlands created by quarrying activities (M.J. Oldham pers. comm. 2005; B. Porchuk and R. Willson unpubl. data).
Pelee is the largest of the islands in western Lake Erie, both in terms of area (approximately 4148 ha) and linear shoreline (approximately 37.5 km). The shorelines of Pelee Island and the other Canadian islands were digitized from orthorectified aerial photographs (2010, leaf-off, 20 cm resolution, horizontal and vertical accuracy of 50 cm; Southwestern Ontario Orthoimagery Project, OMNRF). The digitization and calculation of geospatial values were done in a GIS environment.
On Pelee Island, the linear extent of shoreline, and hence habitat for Lake Erie Watersnake, is variable largely owing to lake currents that deposit sediment and fluctuating water levels. For example, the shape of Lighthouse Point in the northeast corner of the island is influenced by two lake currents flowing along the north shore of the island (Kamstra et al. 1995). Lake Henry has changed from farmland prior to 1972, to a shallow bay of Lake Erie as described by Kamstra et al. (1995; as visible in 2000 orthoimagery), to a wetland enclosed by sand bars (2010 orthoimagery). Similar but smaller scale changes have also occurred at Fish Point in the southwest corner of the island, where lake currents, storms, and water levels periodically alter Fox Pond’s hydrological connection to Lake Erie (B. Porchuk and R. Willson unpubl. data).
Changes to Lake Henry since the previous status report have likely increased the linear extent of shoreline habitat available to the species. It is difficult to know if the amount of aquatic foraging habitat in Lake Henry is changing as the sand deposits become more extensive. Substantial portions of the sand deposits have been colonized by European Common Reed (Phragmites australis australis), and it seems likely that the interior of large patches of European Common Reed would reduce solar radiation to levels too low for Lake Erie Watersnakes to maintain preferred body temperatures. However, the edges of the monocultural, dense patches of European Common Reed may provide suitable terrestrial habitat in portions of Lake Henry that were formerly open water. European Common Reed is also present at other sites along the shoreline of Pelee Island, and the spread of this species may constitute an ongoing loss of thermoregulation habitat along the shoreline. European Common Reed is invasive and spreads rapidly, and it will likely continue to spread to new areas now that it is established on the island.
Visible loss of active season habitat due to construction of homes, docks, and structures for erosion protection has occurred since the previous status report, but the level of development has been moderate. Whether any of the construction along the shoreline has resulted in loss of hibernation habitat is unknown and loss of these types of microhabitats is very difficult to document. In at least one instance a known communal hibernaculum on Pelee Island was destroyed on private land during a property “cleanup” in the late 1990s (A. Woodliffe and B. Porchuk unpubl. data).
Middle and East Sister islands are protected parks and no sanctioned habitat loss or degradation should occur. Forest cover has been reduced substantially on Middle and East Sister islands because of increased nesting populations of Double-crested Cormorant (Phalacrocorax auritus; Hebert et al. 2005); however, it is unknown whether these changes would have adverse effects on Lake Erie Watersnakes. Although North Harbour Island has been highly modified by its owner, the north and west sides of the island have the potential to function as habitat from a structural perspective (2010 orthoimagery). Hen Island, as well as Middle Sister Island, is privately owned and is difficult to monitor. Both islands appear to have areas with the potential to function as habitat based on review of 2010 orthoimagery. The Chick islands (collective name for Big Chicken, Little Chicken, and Chick islands) are little more than reefs and likely do not face development threats, although they probably offer only minimal, low-quality transitory habitat for Lake Erie Watersnakes. Although Lake Erie Watersnake habitat on all Canadian islands is protected by provincial and federal legislation and policy, monitoring and enforcement are difficult because many of the areas are relatively inaccessible.
Although there are sections of shoreline on the Canadian islands that are unusable as habitat (e.g., hardened surfaces such as cement docks or retaining walls), none of these sections are longer than regular movement distances of Lake Erie Watersnakes. Thus, the level of fragmentation of active season habitat is minor. Although the traffic flow on Pelee Island’s roads is not high enough to act as a barrier to movement, the quality of the habitat transected by the roads is decreased because of vehicle-induced mortality.
Life Cycle, Demographic Parameters and Reproduction
The longevity of Lake Erie Watersnake is up to 12 years in the wild (King et al. 2006b). Sexual maturity is reached at three to four years of age, which for males occurs at approximately 56 cm SVL and for females at approximately 66.5 cm SVL (King 1986; Stanford 2012).
Courtship and mating occurs from early May to early June and, as in other natricine snakes, involves scramble competition (several males court one female simultaneously), that can result in aggregations of numerous watersnakes (USFWS 2003). Lake Erie Watersnake is viviparous, meaning they give birth to live young (Ernst and Ernst 2003). King (1986) reported litter sizes of 9–50 and studies on Pelee Island documented an average embryo count of 26.9 (range 13–46) for 29 Lake Erie Watersnakes (Bishop and Rouse 2006). A litter size of 57 was reported from Middle Island in 1945 (Thomas 1949). Litter size is positively correlated with female size (King et al. 2008). Parturition occurs from mid-August to late September (King 1986). Although not all female Lake Erie Watersnakes are gravid each year, annual reproduction in females is common in the U.S. populations studied (Stanford 2012). Average neonate size is 18.1 cm SVL and 4.8 g (King 1986).
Physiology and Adaptability
The diet of Lake Erie Watersnake has undergone a rapid and nearly complete shift since the invasion of Lake Erie by Round Goby in the early 1990s (King et al. 2006b). Round Gobies now make up greater than 90% of Lake Erie Watersnake diet (King et al. 2008), whereas previously the species preyed upon native fishes and amphibians (King 1993b; King et al. 2006b). Evidence indicates that this change in diet, which occurred in just one or two watersnake generations (King et al. 2006b), has benefited Lake Erie Watersnake via increased growth rate, body size, and fecundity (King et al. 2006b; King et al. 2008; Jones et al. 2009). The beneficial effects on Lake Erie Watersnake populations of the dietary switch to the Round Goby may have had a substantial impact on the recovery and subsequent delisting of the taxon in the U.S. (see USFWS 2010).
Lake Erie Watersnakes can adapt to some modification of the shoreline by humans. The species has been documented using anthropogenic structures such as riprap, rock-filled timber, and steel crib docks for basking and shelter habitat (USFWS 2003). However, Lake Erie Watersnakes do not use sheet steel docks and poured concrete structures constructed for erosion control (USFWS 2003). In addition to observations of the species using these anthropogenic features, some of the most highly developed study sites on the U.S. islands had the highest watersnake population densities in recent surveys (Stanford 2012). As suggested by Stanford (2012), it is plausible that areas with higher human populations have fewer avian predators of Lake Erie Watersnake (e.g., Great Blue Heron (Ardea herodias), Snowy Egret (Egretta thula)).
In the U.S. and Canada, radio telemetry studies have demonstrated that individual Lake Erie Watersnakes show fidelity to hibernation sites and specific stretches of shoreline for active season habitat (D. Jacobs pers. comm. 2005; Stanford et al. 2010). It is unknown how adaptable individuals are to being displaced by habitat development/destruction from their preferred sites.
The phenology and activity level of Lake Erie Watersnakes is heavily dependent on seasonal and local weather conditions. Lake Erie Watersnakes have been observed entering water in the first week of May when water temperatures were approximately 5°C (King 1986). Egress from hibernation typically starts when the mean maximum daily air temperature rises to 12.8°C (April/May) and ingress into hibernation commences when the mean minimum daily air temperature drops to 15.5°C (September/October) (King 2003).
Dispersal and Migration
Lake Erie Watersnakes have been documented to move several kilometres between islands or between islands and mainland sites. For example, one Lake Erie Watersnake travelled a straight-line distance of 11 km to Middle Island from Kelleys Island in 2002 (D. Jacobs unpubl. data). Additionally, a watersnake that was marked with a PIT tag on Middle Bass Island was captured at Point Pelee (mainland) in 2007 (minimum straight-line distance is 32.9 km; Parks Canada Agency 2012). Radio telemetry and capture-recapture data indicate that these long distance movements from island to island, or island to mainland are rare (Stanford 2012; D. Jacobs unpubl. data ). For example, the fact that none of the 54 Lake Erie Watersnakes radio tracked on the U.S. islands (Stanford et al. 2010) were documented on islands other than the ones from which they originated contrasts with the regularly documented inter-island movements of Eastern Foxsnakes radio tracked in Georgian Bay (Lawson 2005; MacKinnon 2005; COSEWIC 2008).
As described in the section on Habitat Requirements, in-water activity and movements by Lake Erie Watersnakes occur largely within 178 m of the shore (Stanford et al. 2010). The limited distance Lake Erie Watersnakes have been observed offshore, as well as the relatively small linear extents of shoreline used by individual watersnakes during the active season, provides further support that inter-island/mainland movements are likely rare. Furthermore, the differences in contamination levels found in Lake Erie Watersnakes from different study areas on Pelee Island (Bishop and Rouse 2006) suggest that most individuals are not highly vagile.
Lake Erie Watersnakes now feed almost exclusively on Round Goby, an invasive species that arrived in Lake Erie in the early 1990s (King et al. 2006b; Jones et al. 2009; Stanford 2012). Lake Erie Watersnake populations have benefited from this dietary change (Stanford 2012). Because foraging by Lake Erie Watersnakes is largely confined to a narrow shoreline band, it is possible that there will be local effects on Round Goby populations (Jones et al. 2009).
Known predators of Lake Erie Watersnake include the Herring Gull (Larus argentatus), Great Blue Heron, American Robin (Turdus migratorius), Raccoon (Procyon lotor), Red Fox (Vulpes vulpes), Blue Racer, and domestic animals such as cats and dogs (King 1986; USFWS 2003). Dead Lake Erie Watersnakes with wounds from birds have been found on islands inhabited by Double-Crested Cormorants (D. Jacobs pers. comm. November 2004); however, no direct evidence of predation has been documented during surveys on Middle Island where Lake Erie Watersnake subpopulations appear to be increasing (Parks Canada Agency 2012).
Population Sizes and Trends
Sampling Effort and Methods
The majority of the sampling efforts to document subpopulation sizes and trends for the Lake Erie Watersnake have been focused on the U.S. islands, particularly since 1999 when the species was listed as threatened under the U.S. Endangered Species Act (USFWS 2003). Richard King conducted surveys for the species on several Canadian islands from 1980–1985 (King 1985, 1986), 1989–1990 (Campbell et al. 1991), and in 2003 (King et al. 2006a). However, the latest survey in 2003 was restricted to a single visit (King et al. 2006a). In contrast, the intensity and scope of population surveys on the U.S. islands has increased as per the recommendations in the U.S. recovery plan (USFWS 2003, 2010).
The OMNRF and Parks Canada have conducted subpopulation surveys for Lake Erie Watersnake on East Sister Island and Middle Island (Parks Canada Agency 2012; D. Jacobs unpubl. data). Limited surveys were also conducted on Pelee Island in 1999 (Brooks et al. 2000) and from 2004–2005 (D. Jacobs pers. comm. 2015). No targeted surveys for Lake Erie Watersnake have been conducted by the OMNRF on Pelee Island since 2005 (M. Cairns pers. comm. 2014) and efforts on Middle Island since 2011 have been limited to incidental observations during the course of other monitoring programs (T. Dobbie pers. comm. 2014). Surveys on both the U.S. and Canadian islands involved a combination of capture-recapture and time- and area-constrained methods.
As indicated in the section on Sampling Efforts and Methods, Lake Erie Watersnake surveys on Pelee Island in the last 18 years have been limited in scope. In contrast, the surveys on the U.S. islands have been intensive and extensive (King et al. 2006a; USFWS 2010). As such, the following approach has been used to generate population estimates for Pelee Island using the U.S. data.
First, the entire shoreline of Pelee Island was classified into land-cover types that were relevant to active season habitat for Lake Erie Watersnakes. In addition to the 37.5 km of shoreline that includes permanent docks, the 5.5 km of shoreline bordering Lake Henry was also classified, as it is similar structurally and functionally to the Lake Erie shoreline. This classification was done manually in a GIS environment by examining the 2010 orthoimagery overlaid with relevant distance-to-shoreline buffers. Table 1 provides the shoreline classifications and rationale.
Second, habitat quality ranks were assigned to each shoreline section type. For example, hardened shoreline was given a rank of zero, whereas armour stone at the water’s edge was given the highest rank of five. A limited number of ranks were assigned (i.e., fewer than the number of land-cover types), but the values can be varied accordingly in the future. Figure 3 illustrates the shoreline rankings assigned.
Third, density estimates (adult watersnakes per km of shoreline) derived by King et al. (2006a) for the U.S. islands were multiplied by the varying lengths of shoreline (based on quality ranks) computed for Pelee Island. The density estimates selected as multipliers were varied according to the habitat quality ranks assigned. This approach was used by King et al. (2006a) to generate abundance estimates for sections of shoreline on U.S. islands that were never surveyed. Table 2 provides the quality ranks, rationale, and population estimates for Pelee Island. The overall population estimate generated for Pelee Island was 3286 adults. Density estimates from King et al. (2006a) for the U.S. islands were used to generate abundance estimates on Pelee Island because they are more recent and robust than density values derived from Pelee Island survey data. The density assigned to the highest quality habitat on Pelee Island was 141 adults/km, and this corresponded to the sites of intermediate watersnake density of King et al. (2006a). For comparison, King’s median density at the 10 sites having the highest watersnake density was 370 adults/km (range = 217–1107). For each of the different quality ranks assigned, the selection of the density estimate (0–141 adults/km) was intended to generate conservative abundance estimates for Pelee Island. Therefore, it seems probable that the subpopulation estimate of 3286 adults on Pelee Island (Table 2) is a minimum. For context, the population sizes estimated for the four largest U.S. islands in 2008 as reported by USFWS (2010) are as follows: Kelleys, 3270; South Bass, 2270; Middle Bass, 2610; North Bass, 970 (see Figure 1 for relative size of islands).
|Land-cover type||Summed length (km)||Description|
|Armour stone at edge of water||10.08||Most extensive type|
|Armour stone with fill on top at edge of water||0.10||Single section|
|Bedrock with armour stone or rock fragments visible on orthoimagery less than 5 m from water||4.20||Distance of 5 m used to classify sections of shoreline that likely function as the highest quality habitat because of the lowest distance-to-cover values|
|Sand with armour stone or rock fragments visible on orthoimagery less than 5 m from water||1.78||Distance of 5 m used to classify sections of shoreline that likely function as the highest quality habitat because of the lowest distance-to-cover values|
|Bedrock with vegetative cover less than 5 m from water||0.72||Distance of 5 m used to classify sections of shoreline that likely function as the highest quality habitat because of the lowest distance-to-cover values|
|Sand with vegetative cover less than 5 m from water||1.66|
|Bedrock with armour stone or rock fragments visible on orthoimagery less than 13 m from water||1.41||Distance of 13 m used to classify sections of shoreline wherein Stanford et al. (2010) documented 75 percent of radiolocations for 54 radiotagged Lake Erie Watersnakes; 13 m was used as key habitat value in U.S. recovery plan (USFWS 2003)|
|Sand with armour stone or rock fragments visible on orthoimagery less than 13 m from water||1.20||Distance of 13 m used to classify sections of shoreline wherein Stanford et al. (2010) documented 75 percent of radiolocations for 54 radiotagged Lake Erie Watersnakes; 13 m was used as key habitat value in U.S. recovery plan (USFWS 2003)|
|Bedrock with vegetative cover less than 13 m from water||1.44||Distance of 13 m used to classify sections of shoreline wherein Stanford et al. (2010) documented 75 percent of radiolocations for 54 radiotagged Lake Erie Watersnakes; 13 m was used as key habitat value in U.S. recovery plan (USFWS 2003)|
|Sand with vegetative cover less than 13 m from water||3.57|
|Sand with barrier wall less than 13 m from water||0.06|
|Bedrock with no cover less than 13 m from water||1.25|
|Sand with no cover less than 13 m from water||9.46|
|European Common Reed (Phragmites australis australis) edge||3.95||Found exclusively in Lake Henry|
|Short vegetation within 5 m of water: grass||0.24||Single section|
|Vertical wall along north shore set back approximately 13 m from water||0.08||Single section|
|Dock: long, narrow docks at north end||0.58||-|
|Dock: old, short dock at north end||0.03||-|
|Hardened surface: boat launch||0.01||-|
|Hardened surface: vertical wall||1.15||Includes most of primary ferry dock on west side|
|Quality rank||Land-cover type||Rationale for quality rank||Density (adults/km) assigned||Rationale for selection of density||Population Estimate|
|5||Easy access to cover/shelter, watersnakes regularly observed in these areas on Pelee and similar U.S. islands||141||From King et al. (2006a): “median density at the 10 sites having intermediate watersnake density = 141 adults/ km (range = 83–203)” Value chosen to keep Pelee Island estimates conservative||2599|
|4||Bedrock with armour stone or rock fragments visible on orthoimagery less than 13 m from water||Still relatively easy access to cover/shelter, rock-based cover assigned higher rank than vegetative cover because latter degrades more quickly||48|
From King et al. (2006a): “This value represents the median of the 10 sites with the lowest Lake Erie watersnake density based on mark-recapture and capture-rate estimates (range = 11–68 adults/km).”
This low density value used for multiple quality ranks to keep Pelee Island estimates conservative
|3||Bedrock with vegetative cover less than 13 m from water||Still relatively easy access to cover/shelter||48||-||69|
|2||Vegetative cover assigned lower rank than rock-based cover because it degrades more quickly||48||-||430|
|1||Lesser quality because of greater distances to cover but still likely to provide habitat for watersnakes||11||Value is the minimum density for U.S. island estimates from sites with the lowest density, i.e., “(range = 11–68 adults/km).” (King et al. (2006a)||120|
|0||Watersnakes unlikely to use hardened surfaces; unknown if these docks are usable as habitat||0||Watersnakes unlikely to use hardened surfaces; unknown if these docks are usable as habitat||0|
Middle Island was surveyed between 1980 and 1984 by R. King and 0.27 snakes per person-hour were documented over 1.10 km of shoreline; based on these data, estimates of 35 (15–112) individuals for the island (less than 30 adults) or 32 individuals per km of shoreline were derived (Campbell et al. 1991). On 31 May 1990, 13 Lake Erie Watersnakes, 12 of which were adults, were captured and five others seen in 4.5 hours, for a capture rate of 2.89 per person-hour (Campbell et al. 1991). Between 2001 and 2005, OMNRF personnel visited Middle Island 25 times and documented 54 adult Lake Erie Watersnakes (D. Jacobs unpubl. data; D. Jacobs pers. comm. 2005). In 2002, the minimum number of known adults on Middle Island was 43 (assuming no immigration) (D. Jacobs pers. comm. 2005). The number of mature Lake Erie Watersnakes estimated for Middle Island in the 2006 COSEWIC report was 50.
Additional surveys have been conducted on Middle Island since 2005 as part of Parks Canada’s management program (Parks Canada Agency 2012). Based on data collected since 2001, Zorn (2007; as cited in Parks Canada Agency 2012) provided the following subpopulation estimates: 2002 = 77 (32–265 95% CI), 2003 = 69 (30–235 95% CI), 2004 = 141 (60–386 95% CI), 2005 = 54 (35–111 95% CI), 2006 = 96 (51–234 95% CI), and 2007 = 119 (67–246 95% CI). These estimates are likely an underestimate due to the relatively low numbers of samples that are recaptures (Zorn 2007). Recent survey results summarized in Parks Canada Agency (2012) not included in the estimates above are as follows: “In 2008; 19 individuals (three dead) were captured during four visits, of which all were new captures; in 2010, 43 individuals were captured during three visits, of which 34 were new captures; and in 2011, 56 individuals were captured during four visits, of which 39 were new captures (PPNP, 2011).”
East Sister Island
In 1980 and 1983, East Sister Island was surveyed four times and King (1986) found 0.21 adult snakes per hour over 1 km of shoreline and derived a mean subpopulation estimate of 25 adults for the entire island. From fieldwork completed in 1988–1992, King (2002) estimated the subpopulation density at 52 adults per km, and estimated the island subpopulation to be 109 adults. Between 2001 and 2005, OMNRF personnel visited East Sister Island 17 times and documented 30 adult Lake Erie Watersnakes (D. Jacobs pers. comm. 2004). In 2002, the minimum number of known adults on East Sister Island was 19 (assuming no immigration) (D. Jacobs pers. comm. 2005).
There have been no new reports on numbers of Lake Erie Watersnakes on Hen Island since Campbell et al. (1991). The 1991 report notes that in 35 minutes in May 1990, 10 to 15 watersnakes were seen along the shoreline by R. King. OMNRF researchers have attempted to gain access to this island, but permission has been refused by the landowner. Given the increase in Lake Erie Watersnake numbers on the U.S. islands since 1990 (King et al. 2006a), it seems likely that the species is present on Hen Island, unless there has been a localized extinction event.
Fluctuations and Trends
As indicated in the previous sections, sufficient data has not been collected on the Canadian islands to document recent population trends. The USFWS (2010) reported that the realized population growth of adult Lake Erie Watersnake populations at eight intensively studied sites between 2001 and 2008 was approximately 6 percent per year (95% CI: 2–10 percent). This growth coincides with efforts of the Ohio Division of Wildlife and the USFWS to halt persecution of snakes, as well as the positive effects Lake Erie Watersnakes have experienced as a result of changing their diet to a super abundant food source, i.e., Round Goby (USFWS 2010).
It is possible that the Canadian population has grown as well; however, it is difficult to extrapolate trends from the U.S. to the Canadian population due to potential differences in the magnitude of the threats currently acting on them (see Threats and Limiting Factors). Road mortality remains relatively high on Pelee Island, persecution is likely still occurring to some degree, and habitat loss from development and invasive species (European Common Reed (Phragmites australis australis)) continues, albeit at a low rate. Therefore, it is possible that the Canadian population of Lake Erie Watersnake is still declining to some extent, despite the positive influence of an increased food source.
There is evidence that watersnakes occasionally move between islands and between islands and the mainland. Thus, immigration of individuals from U.S. islands does occur, albeit rarely (see Dispersal and Migration). Whether this level of immigration would be sufficient to maintain the Canadian population is unknown.
Threats and Limiting Factors
Results from the IUCN threats calculator assessment completed in May 2015 indicated that the overall threat impact was “low” to “low” (Appendix 1). Several low impact threats were calculated and they are discussed below.
Intentional and Accidental Human-induced Mortality
Intentional and accidental human persecution was identified as the primary threat or limiting factor for U.S. populations of the Lake Erie Watersnake (USFWS 2003). Similarly, this threat was recognized as significant in Ontario’s recovery strategy for the species (Willson and Cunnington 2015).
A significant proportion of the human population harbours a dislike or fear of snakes and this dislike seems to increase with snakes that inhabit areas where people swim. Lake Erie Watersnakes can grow to be fairly large and they are easily visible along the shoreline of the Erie islands where they occur. They will also use areas in close proximity to humans and can readily be found in boats and even in and around human dwellings. When approached, Lake Erie Watersnakes usually retreat quickly into the water or under cover objects. Snakes that do not retreat will often flatten their heads and bodies and occasionally strike out. Although not venomous, Lake Erie Watersnakes may bite when handled. Other defensive behaviours when being handled include writhing and exuding a foul-smelling fluid from the anal glands. These characteristics have resulted in intentional killing. In addition to haphazard persecution, Campbell et al. (1991) compiled a number of accounts of snake extermination campaigns that targeted this species, including those on Rattlesnake Island and Middle Island. As documented in Campbell et al. (1991) and USFWS (2003), Lake Erie Watersnake has been heavily collected and persecuted over the last 150 years.
Collection of Lake Erie Watersnakes no longer occurs on the scale that it did historically, and widespread killing is not known to occur on either the U.S. or Canadian islands. However, several dead Lake Erie Watersnakes were found on both Middle and East Sister Islands in 2006, and although the cause of death could not be confirmed, it is most consistent with human persecution (D. Jacobs, unpubl. data). Additionally, Ashley et al. (2007) demonstrated that a subset of the snakes killed by motor vehicles on roads are intentionally run over. On both the Canadian and American islands, some landowners see the snake’s protected status as a threat to their private property rights or an impediment to development (Olive 2012), and this further increases the likelihood of persecution.
As described in Seymour (2009), analysis of the opinions of U.S. island residents indicates that an acceptable percentage of the human population no longer kills snakes intentionally. Consequently, the USFWS determined that the requirement to reduce intentional persecution to an acceptable level for the purposes of delisting had been achieved (Seymour 2009). However, it is unlikely that these trends have been mirrored in Ontario. In the late 1990s, a perceived conflict between snake conservation efforts and private property rights led to hostility toward several snake species at risk on Pelee Island, including Lake Erie Watersnake. Some residents still harbour negative attitudes toward snake species at risk, and persecution likely remains a threat to this species in Canada.
Pelee Island is the only Canadian island in the Lake Erie Archipelago with roads. Almost the entirety of Pelee is encircled by a road in close proximity to the water’s edge (Figure 3), resulting in a relatively high risk of road mortality. Observations of road-killed Lake Erie Watersnakes have been made regularly over the years by naturalists and OMNRF staff. The colouration of Lake Erie Watersnakes may make them difficult to see against unpaved or dust covered roads, and this species will often cease moving when approached by a vehicle or a human (R. Willson unpubl. data).
Roadkill surveys were conducted for all snake species on Pelee Island from 1993 to 1995 (Brooks and Porchuk 1997), 1998 to 1999 (Brooks et al. 2000), and during the springs of 2000 to 2002 (Willson 2002). Although the primary intent of these surveys was to document the distribution of the Lake Erie Watersnake on Pelee Island, the following values provide an estimate of how many individuals can be killed on the island’s roads in peak years. In 1995, there were 64 Lake Erie Watersnakes found dead on Pelee Island’s roads (Brooks et al. 2000). Researchers did not record the age class of road-killed Lake Erie Watersnakes during this survey period; however, only four of the 64 records were recorded in August when newborn snakes would be present and the road survey was not conducted in September. Therefore, at least 60 of the road-killed Lake Erie Watersnakes were adults, juveniles, or yearlings (snakes born the previous year). During the spring surveys of 2000–2002 (13 April to 15 May), there were 12 adults, two juveniles, and seven yearlings (age classes based on King ) documented as roadkills (Willson 2002). Eight of the adult roadkills were female (R. Willson unpubl. data). Based on these data, it is evident that numerous Lake Erie Watersnakes are killed by automobiles on the island’s roads each spring when they are presumably moving from inland hibernation habitat to active season habitat along the shoreline. It is reasonable to infer that Lake Erie Watersnakes are also killed regularly on the roads in September and October as they move from active season habitat along the shoreline to inland hibernation habitat, although roadkill surveys have not been conducted during this time of year (R. Willson and B. Porchuk unpubl. data). Some of the roads on Pelee Island are close enough to the shoreline that they bisect summer active season habitat and, at these sites, road mortality likely occurs throughout the summer as well.
In the 5-year review completed by the USFWS in 2009 (Seymour 2009), it was concluded that “accidental human-induced mortality due to roadkill events is not a significant threat to the Lake Erie Watersnake population.” The Proposed Rule to remove the Lake Erie Watersnake (Nerodia sipedon insularum) from the Federal list of Endangered and Threatened Wildlife (USFWS 2010) makes the same conclusion. based on the same rationale as follows.
A road mortality survey was conducted on the four large U.S. islands between 26 June and 15 July 2005 (Reider 2005; as cited by Seymour ). As per Seymour (2009; pp 13):
Dr. King’s 2007 Annual Report (King 2007) states: “Of 71 dead snakes found, 45 were [Lake Erie] watersnakes. Among the [Lake Erie] watersnakes, 38 were neonates, 5 were juveniles, and 2 were adults. These results suggest that adult [Lake Erie] watersnake roadkill mortality is relatively low (Brown and Weatherhead 1999). Available data on watersnake mortality suggest that survivorship of neonates is low. Thus, roadkill mortality of this age-class likely has little impact on watersnake population trends.”
While this study was limited by only one season of mortality surveys, and further mortality surveys would likely provide a more thorough understanding of levels of roadkill mortality, it does provide evidence that adult Lake Erie Watersnakes are not subject to high levels of roadkill mortality. Further, the adult Lake Erie Watersnake population continues to grow, despite presumably continuous rates of roadkill mortality since before the time of listing.
As far as providing insight into the importance of road mortality as a threat on Pelee Island, the U.S. road survey data are limited, particularly because they are from a single 19-day period at a time of the year when Lake Erie Watersnakes would not be moving between active season and hibernation habitat; thus, these data do not provide a useful estimate of adult mortality. Furthermore, potential differences in traffic patterns, as well as spatial distribution of roads make a direct comparison difficult. For example, the roads on Pelee Island tend to be in very close proximity to the shoreline, which likely results in an elevated risk of road mortality compared to other sites where roads may be situated further inland. Given the close proximity of the roads on Pelee Island to the shoreline and the relatively high rate of road mortality that has been observed, it is possible that road mortality is contributing to population declines. Row et al. (2007) demonstrated that an annual road mortality rate of three adult female Gray Ratsnakes (Pantherophis spiloides) was sufficient to increase the likelihood of subpopulational extirpation from 7% to greater than 90% over 500 years. Although there are differences in generation time and reproductive rate between these species, annual road mortality rates of Lake Erie Watersnakes may still be high enough to result in similar population-level consequences.
Given that the other Canadian islands only support small subpopulations of Lake Erie Watersnake, vehicle-induced mortality on Pelee Island’s roads is likely the most important threat to survival and recovery of this species in Canada. It is possible that the adverse effects of road mortality on Lake Erie Watersnake subpopulations on Pelee Island are being offset by the same factors that are causing the U.S. subpopulations to increase.
Lake Erie Watersnakes are also susceptible to injuries or death inflicted by other motorized vehicles. Lawnmowers have caused mortality in this species (B. Porchuk unpubl. data) and it seems plausible that boat propellers inflict occasional wounds and/or mortality as well. Stanford (2004; cited in Seymour ) sent a questionnaire to registered boaters to assess the level of intentional or inadvertent mortality of Lake Erie Watersnakes as a result of fishing or boating activities. Based on Stanford’s results, Seymour (2009) concluded that accidental human-induced mortality from boating or fishing encounters is not high enough to cause subpopulation-level impacts.
U.S. researchers have documented numerous Lake Erie Watersnakes entangled and killed in gardening and erosion-control nets (USFWS 2010). There is similar documentation of snake mortality in Ontario resulting from these types of nets.
Habitat Loss and Degradation
Vegetation clearing, mowing, and spraying; infilling; rock berm disruption; shoreline hardening and general shoreline property cleanup can all damage or destroy Lake Erie Watersnake habitat (USFWS 2003). Shoreline development that results in the aforementioned activities reduces the quantity and quality of habitat for Lake Erie Watersnakes.
It is possible that large stands of European Common Reed could reduce habitat quality and availability for Lake Erie Watersnake. Currently there are areas in Lighthouse Point Provincial Nature Reserve where European Common Reed occurs at high densities and provides seemingly poor habitat conditions for Lake Erie Watersnakes.
As described in the Habitat Trends section, it is unknown whether the alteration of the ground cover and tree communities on Middle and East Sister islands by nesting Double-crested Cormorants will have an adverse effect on Lake Erie Watersnake habitat.
Severe weather events and changes in water level in Lake Erie also have the potential to adversely affect Lake Erie Watersnake subpopulations. Severe weather events would likely affect a significant portion of each subpopulation on the small islands. Furthermore, changes in water level have the potential to reduce available habitat on the three small islands.
Fernie et al. (2008) found that Lake Erie Watersnakes at the three sites sampled on Pelee Island had some of the lowest mean concentrations of polychlorinated biphenyl (PCB) and dichlorodiphenyldichloroethylene (DDE) levels reported in their study. However, it remains to be determined whether the concentrations observed would have negative effects on the reproductive parameters of female Lake Erie Watersnakes, particularly embryonic survival (Fernie et al. 2008). Bishop and Rouse (2006) found that contaminant levels in Lake Erie Watersnakes on Pelee Island did not have adverse effects on embryonic survival.
Predation of young Lake Erie Watersnakes by Double-crested Cormorants may be a threat on Middle and East Sister islands. The Canadian Wildlife Service has been monitoring these birds since their arrival in the area in the early 1980s, and populations reached an all-time high in the past couple of years, with close to 6,000 nests per island (C. Weseloh, unpubl. data), representing an approximate population of 24,000 birds per island (assuming two adults and two young per nest). In 2001, snake researchers found a juvenile Lake Erie Watersnake that appeared to have been killed (but not eaten) by an unknown species of bird (D. Jacobs, unpubl. data). Evidence that Double-crested Cormorants prey upon Lake Erie Watersnakes is, however, lacking and the USFWS (2003, 2010) did not consider this risk of predation to be a potential threat to American subpopulations of Lake Erie Watersnakes. Additionally, there is no evidence to suggest that this threat would be elevated for Canadian subpopulations.
Turkeys (Meleagris gallopavo) pose a potential threat to juvenile Lake Erie Watersnakes on Pelee Island. Approximately 25 breeding Wild Turkeys were released at various points on Pelee Island in 2002 with the co-operation of the Ministry of Natural Resources, the Wild Turkey Release Program, the Township of Pelee and the Pelee Island Sportsman’s Club. Following this initial release, a large population of Wild Turkeys now exists on the Island. Starting in 2004 there has been a Wild Turkey Hunt on the Island (OMNR 2007).
The small geographic range of the Lake Erie Watersnake and the small subpopulation sizes on some of the islands make it vulnerable to extinction from demographic and environmental stochasticity, catastrophic events, and loss of genetic variability (Caughley 1994; Burkey 1995; Madsen et al. 1996; Frankham 1998). This phenomenon may have already occurred on some of the Lake Erie islands where Lake Erie Watersnakes have been extirpated (e.g., West Sister Island; USFWS 2003). The fact that subpopulations inhabiting smaller islands are vulnerable to extinction has been understood since MacArthur and Wilson (1963) (i.e., the theory of island biogeography). For taxa such as Lake Erie Watersnake that are restricted to small geographic areas composed of islands, this phenomenon is a limiting factor.
Number of Locations
The most plausible threat on Pelee Island is road mortality. As shown in Figure 3, a large proportion of the island’s shoreline is bordered by roads. Many of these roads occur within the area regularly traversed by Lake Erie Watersnakes (e.g., when moving between active-season and hibernation habitat). Consequently, a large increase in traffic volume (e.g., resulting from a large development), would adversely affect a large portion of the Lake Erie Watersnake subpopulation on Pelee Island. The Pelee Island subpopulation is by far the largest subpopulation, comprising more than 50% of the Canadian population; therefore, subpopulations on the remaining different small islands can be each considered a separate location, bringing the total number of locations to four, assuming that the Hen Island subpopulation is still extant. On Middle Island, a cormorant roosting site has extensively modified the habitat, but it is unclear what (if any) impacts they may have on the watersnakes. Severe weather events and changes in water level in Lake Erie are the most plausible events that could negatively affect a large proportion of each of the subpopulations on Middle, East Sister, and Hen islands. These events, if they are severe enough, also have the potential to affect a large proportion of the Lake Erie Watersnakes on Pelee Island as well, although they were not identified as a threat in the threats calculator assessment, and there is much uncertainty about the magnitude of the impact. Each of these islands should be considered separate locations because each is vulnerable to threats that could rapidly affect all individuals present or at least a large percentage of each subpopulation.
Protection, Status and Ranks
Legal Protection and Status
In Canada, Lake Erie Watersnake was designated Endangered by COSEWIC in 1991 and 2006 and was added to Schedule 1 of the federal Species at Risk Act as Endangered in 2009. Ontario’s Endangered Species Act, 2007 (ESA; Government of Ontario 2007) came into force in 2008 and protection is provided for Lake Erie Watersnake (designated Endangered on the Species at Risk in Ontario List) under Sections 9 and 10 of the ESA. Under Ontario’s Fish and Wildlife Conservation Act, the taxon is listed as a specially protected reptile. On Middle Island, the species is protected under the Canada National Parks Act.
Lake Erie Watersnake was removed from the U.S. list of federally endangered and threatened species on August 16, 2011; the taxon will remain as a species of concern throughout a mandatory five-year post-delisting monitoring period (USFWS 2010).
Lake Erie Watersnake has a status of Endangered assigned by the state of Ohio. The Ohio Division of Parks and Recreation and Division of Natural Areas and Preserves owns and manages portions of U.S. islands including one for watersnake conservation and protection (USFWS 2003).
Non-Legal Status and Ranks
NatureServe (2014) lists the Lake Erie Watersnake’s global status as G5T2 (demonstrably widespread, abundant and secure, but taxon is imperiled). The National status in both the U.S. and Canada is N2 (imperilled). According to NatureServe (2014), the Ontario rank of the Lake Erie Watersnake is S2 (imperilled). The IUCN has not evaluated the Lake Erie Watersnake.
Habitat Protection and Ownership
- General habitat protection is provided for Lake Erie Watersnake under Section 10 of Ontario’s ESA.
- As of 2014, the following properties were known to contain Lake Erie Watersnake habitat and were owned by organizations that have natural heritage protection as one of their primary objectives:
- Lighthouse Point Provincial Nature Reserve (OMNRF);
- Fish Point Provincial Nature Reserve (OMNRF);
- East Sister Island Nature Reserve (OMNRF);
- Stone Road Alvar Conservation Area (Essex Region Conservation Authority);
- Middle Island (Parks Canada);
- Stone Road Alvar (Nature Conservancy of Canada); and
- Middle Point Woods (Nature Conservancy of Canada).
- Management at these properties has varied according to the objectives of the responsible agencies (for example, see NCC 2008; Parks Canada Agency 2012).
- The owners of some additional lands with Lake Erie Watersnake habitat have entered into conservation easements with the NCC.
- Landowners whose properties contain Lake Erie Watersnake habitat (with certain size restrictions) are eligible to apply to participate in the Conservation Land Tax Incentive Program (CLTIP). This program offers 100 percent tax relief to landowners for the portion of their property that was considered to be endangered species habitat.
Acknowledgements and Authorities Contacted
The authors would like to thank all of the contributors to the previous status report in addition to the authorities contacted and listed below. Funding, provided by the Canadian Wildlife Service, Environment Canada. The cover photograph was taken by Joe Crowley.
Tammy Dobbie, Park Ecologist, Point Pelee National Park, Parks Canada
Joe Crowley, Herpetology Species at Risk Specialist, Ontario Ministry of Natural Resources and Forestry (OMNRF)
Amelia Argue, A/Policy Analyst, Species at Risk Branch, OMNRF
Kate MacIntyre, A/Management Biologist, Aylmer District, OMNRF
Melody Cairns, Zone Ecologist, Ontario Parks, Southwest Zone, OMNRF
Martina Furrer, Biodiversity Information Biologist, Natural Heritage Information Centre
Neil Jones, ATK Coordinator, COSEWIC Secretariat
Jenny Wu, COSEWIC Secretariat
Deb Jacobs, Lake Erie Watersnake Researcher, Ontario Ministry of the Environment and Climate Change
Richard King, Professor, Northern Illinois University
Kristin Stanford, Lake Erie Watersnake Research Scientist, Ohio State University Stone Laboratory
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King, R.B. 1992. Lake Erie water snakes revisited: morph- and age-specific variation in relative crypsis. Evolutionary Ecology 6:115-124.
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King, R.B. 1993b. Microgeographic, historical, and size-correlated variation in water snake diet composition. Journal of Herpetology 27:90-94.
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Willson, R.J. and G.M. Cunnington. 2015. Recovery strategy for the Lake Erie Watersnake (Nerodia sipedon insularum) in Ontario. Ontario Recovery Strategy Series. Prepared for the Ontario Ministry of Natural Resources and Forestry. Peterborough, Ontario. vi + 24 pp.
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Biographical Summary of Report Writers
Rob Willson obtained his BSc and MSc from the University of Guelph. He conducted research on Pelee Island’s snakes from 1994 to 2004. Additional investigations of snake ecology and conservation include eight years working on Eastern Massasaugas and Eastern Hog-nosed Snakes as part of Killbear Provincial Park and Parry Sound OMNRF projects. Rob has authored COSEWIC reports on several of Ontario’s snakes and co-authored the provincial recovery strategy for the Lake Erie Watersnake. He currently works as an ecological consultant in Ontario.
Glenn Cunnington obtained his BSc and MSc from Trent University. His MSc research included a study of the ecology of the Eastern Hog-nosed Snake. Glenn obtained his PhD from Carleton University wherein he investigated the effects of traffic noise on the characteristics of amphibian vocalization. He co-authored the provincial recovery strategy for the Lake Erie Watersnake and works as an ecological consultant in Ontario.
No collections were examined for this report.
Threats Assessment Worksheet
- Species or Ecosystem Scientific Name:
- Lake Erie Watersnake Nerodia sipedon insularum
- Element ID
- May 11, 2015
- Jim Bogart (COSEWIC Amphibians and Reptiles Specialist Subcommittee co-chair), Ruben Boles (Canadian Wildlife Service), Richard King (Northern Illinois University), Patrick Nantel (Parks Canada),Scott Reid (Ontario Ministry of Natural Resources and Forestry), Kristin Standford (Ohio State University Stone Laboratory), Rob Willson (status report author) Facilitator: David Fraser; COSEWIC Secretariat (notes): Bev McBride
|Threat Impact||Threat Impact (descriptions)||Level 1 Threat Impact Counts:|
|Level 1 Threat Impact Counts:|
|-||Calculated Overall Threat Impact:||Low||Low|
- Assigned Overall Threat Impact:
- Impact Adjustment Reasons:
- Overall Threat Comments
- Generation time 6 years.
|1||Residential and commercial development||Negligible||Small (1-10%)||Negligible (<1%)||High (Continuing)||-|
|1.1||Housing and urban areas||Negligible||Small (1-10%)||Negligible (<1%)||High (Continuing)||-|
|1.2||Commercial and industrial areas||Unknown||Unknown||Unknown||High (Continuing)||Need to check for plans for commercial dock expansion or marina development in coming years.|
|1.3||Tourism and recreation areas||-||-||-||-||No new developments anticipated in next 10 years.|
|2||Agriculture and aquaculture||Unknown||Unknown||Unknown||High (Continuing)||-|
|2.1||Annual and perennial non-timber crops||Unknown||Unknown||Unknown||High (Continuing)||Need to check for any plans to expand vineyards in relevant areas.|
|3||Energy production and mining||D - Low||Small (1-10%)||Small (1-10%)||High (Continuing)||-|
|3.2||Mining and quarrying||D - Low||Small (1-10%)||Small (1-10%)||High (Continuing)||Quarrying may result in loss of individuals, but it also creates new habitat.|
|4||Transportation and service corridors||D - Low||Pervasive (71-100%)||Slight (1-10%)||High (Continuing)||-|
|4.1||Roads and railroads||D - Low||Pervasive (71-100%)||Slight (1-10%)||High (Continuing)||Need more information on traffic and traffic increases to substantiate this (particularly if the severity is later determined to be higher than presently shown). How do changes to ferry services affect traffic levels and what is expected over the next 10 years?|
|4.2||Utility and service lines||Unknown||Unknown||Unknown||High (Continuing)||Changes would be related to new developments, which are not known.|
|5||Biological resource use||Negligible||Pervasive (71-100%)||Negligible (<1%)||High (Continuing)||-|
|5.1||Hunting and collecting terrestrial animals||Negligible||Pervasive (71-100%)||Negligible (<1%)||High (Continuing)||Collection for pets/pet trade, if any, would be insignificant. Persecution does take place. The rate could be influenced by education and outreach.|
|5.4||Fishing and harvesting aquatic resources||-||-||-||-||Species can be bycatch in gill netting near shore, but this is not known to occur around Pelee Island at this time.|
|6||Human intrusions and disturbance||-||-||-||-||-|
|7||Natural system modifications||Unknown||Small (1-10%)||Unknown||High (Continuing)||-|
|7.2||Dams and water management/use||Not a Threat||Restricted - Small (1-30%)||Neutral or Potential Benefit||Moderate (Possibly in the short term, < 10 yrs)||Canals, which the species uses, are occasionally dredged. Timing imposed by dredging permits should prevent adverse effects to individuals. Habitat is probably improved by dredging.|
|7.3||Other ecosystem modifications||Unknown||Small (1-10%)||Unknown||High (Continuing)||-|
|8||Invasive and other problematic species and genes||Unknown||Small (1-10%)||Negligible (<1%)||-||-|
|8.1||Invasive non-native/alien species||Unknown||Pervasive (71-100%)||Unknown||High (Continuing)||For this assessment Wild Turkey was considered an introduced species that was never native to Pelee Island. It is suspected that Wild Turkey might consume the species. Studies are anticipated in the summer of 2015. Meanwhile, unpublished studies through the Ontario government, from Pelee Island, the Carden Alvar and the Bruce Peninsula, found that Wild Turkeys had not consumed any vertebrates at all. Invasive Phragmites grass is not thought to be a threat. Species appears to benefit from invasive fish Round Goby.|
|8.2||Problematic native species||Negligible||Small (1-10%)||Negligible (<1%)||High (Continuing)||Double-crested Cormorants, primarily on Middle Island and East Sister Island, may consume the species and have increased in number. Raccoons have been found on Pelee Island since the 1990s. Impacts are not known.|
|8.3||Introduced genetic material||-||-||-||-||While variation in individuals suggests that the mainland Northern Watersnake and the Lake Erie Watersnake intergrade, movement between islands and the mainland is rare. Introduced genetic material is not expected to be an issue for the Lake Erie Watersnake over the next 10 years.|
|9||Pollution||Unknown||Pervasive (71-100%)||Unknown||High (Continuing)||-|
|9.2||Industrial and military effluents||Unknown||Pervasive (71-100%)||Unknown||High (Continuing)||Residual PCB and DDE amounts found in some samples. Effect unknown.|
|9.3||Agricultural and forestry effluents||Unknown||Pervasive (71-100%)||Unknown||High (Continuing)||Agricultural effluent suspected to contribute to harmful algal blooms. Effect unknown.|
|11||Climate change and severe weather||-||-||-||-||-|
Classification of Threats adopted from IUCN-CMP, Salafsky et al. (2008).
- The degree to which a species is observed, inferred, or suspected to be directly or indirectly threatened in the area of interest. The impact of each threat is based on Severity and Scope rating and considers only present and future threats. Threat impact reflects a reduction of a species population or decline/degradation of the area of an ecosystem. The median rate of population reduction or area decline for each combination of scope and severity corresponds to the following classes of threat impact: Very High (75% declines), High (40%), Medium (15%), and Low (3%). Unknown: used when impact cannot be determined (e.g., if values for either scope or severity are unknown); Not Calculated: impact not calculated as threat is outside the assessment timeframe (e.g., timing is insignificant/negligible or low as threat is only considered to be in the past); Negligible: when scope or severity is negligible; Not a Threat: when severity is scored as neutral or potential benefit.
- Proportion of the species that can reasonably be expected to be affected by the threat within 10 years. Usually measured as a proportion of the species’ population in the area of interest. (Pervasive = 71–100%; Large = 31–70%; Restricted = 11–30%; Small = 1–10%; Negligible < 1%).
- Within the scope, the level of damage to the species from the threat that can reasonably be expected to be affected by the threat within a 10-year or three-generation timeframe. Usually measured as the degree of reduction of the species’ population. (Extreme = 71–100%; Serious = 31–70%; Moderate = 11–30%; Slight = 1–10%; Negligible < 1%; Neutral or Potential Benefit > 0%).
- High = continuing; Moderate = only in the future (could happen in the short term [< 10 years or 3 generations]) or now suspended (could come back in the short term); Low = only in the future (could happen in the long term) or now suspended (could come back in the long term); Insignificant/Negligible = only in the past and unlikely to return, or no direct effect but limiting.
- Date Modified: