Lake Erie Watersnake Nerodia sipedon insularum

Transcription

1 COSEWIC Assessment and Status Report on the Lake Erie Watersnake Nerodia sipedon insularum in Canada SPECIAL CONCERN 2015

2 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 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. ( Previous report(s): COSEWIC 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. ( Campbell, C.A COSEWIC status report on the Lake Erie watersnake Nerodia sipedon insularum in Canada. Committee on the Status of Endangered Wildlife in Canada pp. Production note: 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: COSEWIC Secretariat c/o Canadian Wildlife Service Environment Canada Ottawa, ON K1A 0H3 Tel.: Fax: ec.cosepac-cosewic.ec@canada.ca 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. Cover illustration/photo: Lake Erie Watersnake Photo courtesy of Joe Crowley. Her Majesty the Queen in Right of Canada, Catalogue No. CW69-14/ E-PDF ISBN

3 COSEWIC Assessment Summary Assessment Summary November 2015 Common name Lake Erie Watersnake Scientific name Nerodia sipedon insularum Status 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. Occurrence Ontario Status history Designated Endangered in April 1991 and in April Status re-examined and designated Special Concern in November iii

4 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. Distribution 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. Habitat 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. iv

5 Biology 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 Sizes 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 20 th 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 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, Lake Erie Watersnake has a status of Endangered assigned by the state of Ohio. v

6 TECHNICAL SUMMARY Nerodia sipedon insularum Lake Erie Watersnake Range of occurrence in Canada: Ontario Couleuvre d eau du lac Érié Demographic Information 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) Is there an [observed, inferred, or projected] continuing decline in number of mature individuals? Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations] [Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generations]. [Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations]. [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. Are the causes of the decline a. clearly reversible and b. understood and c. ceased? Are there extreme fluctuations in number of mature individuals? ca. 6 yrs Yes, inferred continuing decline based on the persistence of several threats, including accidental and intentional mortality and habitat loss. Unknown Unknown Unknown Unknown 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 No Extent and Occupancy Information Estimated extent of occurrence Index of area of occupancy (IAO) (Always report 2x2 grid value). 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? 188 km² 2x2 grid value = 72 km² a. no b. no vi

7 Number of locations (use plausible range to reflect uncertainty if appropriate) Is there an [observed, inferred, or projected] decline in extent of occurrence? Is there an [observed, inferred, or projected] decline in index of area of occupancy? Is there an [observed, inferred, or projected] decline in number of subpopulations? Is there an [observed, inferred, or projected] decline in number of locations *? Is there an [observed, inferred, or projected] decline in [area, extent and/or quality] of habitat? Are there extreme fluctuations in number of subpopulations? Are there extreme fluctuations in number of locations? Are there extreme fluctuations in extent of occurrence? Are there extreme fluctuations in index of area of occupancy? 3 4 (see Number of Locations under section Threats and Limiting Factors) No Possible decline in index of area of occupancy if subpopulation on smallest, privately owned island (Hen) was extirpated Possible decline in number of subpopulations if subpopulation on smallest, privately owned island (Hen) was extirpated Possible decline in number of locations if subpopulation on smallest, privately owned island (Hen) was extirpated Yes, observed Yes, projected No No No No Number of Mature Individuals (in each subpopulation) Subpopulations (give plausible ranges) N Mature Individuals (values are approximate, see Abundance section) Pelee Island 3286 Middle Island 119 ( % CI) East Sister Island 50 Hen Island <15 Total 3470 Quantitative Analysis Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years]. Analysis not completed See Definitions and Abbreviations on COSEWIC website and IUCN (Feb 2014) for more information on this term vii

8 Threats (actual or imminent, to populations or habitats, from highest impact to least) i. Intentional and Accidental Human-induced Mortality ii. Habitat Loss and Degradation iii. Environmental Contamination iv. Predation v. 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. Is immigration known or possible? Would immigrants be adapted to survive in Canada? Is there sufficient habitat for immigrants in Canada? Are conditions deteriorating in Canada? + Are conditions for the source population deteriorating? + Is the Canadian population considered to be a sink? + Is rescue from outside populations likely? 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. Yes Yes Yes Possibly No No Yes Data Sensitive Species Is this a data sensitive species? Only the locations of hibernation areas are sensitive. + See Table 3 (Guidelines for modifying status assessment based on rescue effect) viii

9 Status History COSEWIC: Designated Endangered in April 1991 and in April Status re-examined and designated Special Concern in November Status and Reasons for Designation: Status: Special Concern Alpha-numeric codes: 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. ix

10 PREFACE 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. x

11 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 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. Wildlife Species Extinct (X) Extirpated (XT) Endangered (E) Threatened (T) Special Concern (SC)* Not at Risk (NAR)** Data Deficient (DD)*** DEFINITIONS (2015) 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. A wildlife species that no longer exists. A wildlife species no longer existing in the wild in Canada, but occurring elsewhere. A wildlife species facing imminent extirpation or extinction. A wildlife species likely to become endangered if limiting factors are not reversed. A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats. A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances. 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 ** 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 Definition of the (DD) category revised in The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat. xi

12 COSEWIC Status Report on the Lake Erie Watersnake Nerodia sipedon insularum in Canada 2015

13 TABLE OF CONTENTS WILDLIFE SPECIES DESCRIPTION AND SIGNIFICANCE... 4 Name and Classification... 4 Morphological Description... 4 Population Spatial Structure and Variability... 4 Designatable Units... 5 Special Significance... 5 DISTRIBUTION... 6 Global Range... 6 Canadian Range... 6 Locations... 8 Extent of Occurrence and Area of Occupancy... 9 Search Effort... 9 HABITAT... 9 Habitat Requirements... 9 Hibernation Habitat Active Season Habitat Habitat Trends...11 BIOLOGY Life Cycle and Reproduction Physiology and Adaptability Dispersal and Migration Interspecific Interactions POPULATION SIZES AND TRENDS Sampling Effort and Methods Abundance Fluctuations and Trends Rescue Effect THREATS AND LIMITING FACTORS Intentional and Accidental Human-induced Mortality Habitat Loss and Degradation Environmental Contamination Predation Geographic Range Number of Locations PROTECTION, STATUS, AND RANKS... 27

14 Legal Protection and Status Non-Legal Status and Ranks Habitat Protection and Ownership ACKNOWLEDGEMENTS AND AUTHORITIES CONTACTED Authorities Contacted INFORMATION SOURCES BIOGRAPHICAL SUMMARY OF REPORT WRITERS COLLECTIONS EXAMINED List of Figures Figure 1. Global range of Lake Erie Watersnake (Nerodia sipedon insularum) in North America (inset) and in the western Lake Erie island region Figure 2. Figure 3. Calculated extent of occurrence (EOO) and index of area ccupancy (IAO) for Lake Erie Watersnake (Nerodia sipedon insularum) in Canada Habitat quality ranks for Lake Erie Watersnake assigned to the shoreline of Pelee Island (see Tables 1 2 for methodology and rationale). Orthoimagery (2010) from SWOOP (OMNRF) List of Tables Table 1. Land-cover types composing Pelee Island s shoreline as determined from 2010 orthoimagery Table 2. Population estimates based on shoreline habitat assessment for Pelee Island using density estimates from King et al. 2006a List of Appendices Appendix

15 Name and Classification WILDLIFE SPECIES DESCRIPTION AND SIGNIFICANCE 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. Morphological Description 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 4

16 the islands. This variation suggests that mainland Northern Watersnakes and the islanddwelling 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). Designatable Units 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. Special Significance 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: , , , and 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). 5

17 DISTRIBUTION Global Range 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). Canadian Range 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. 6

18 Figure 1. Global range of Lake Erie Watersnake (Nerodia sipedon insularum) in North America (inset) and in the western Lake Erie island region. 7

19 Figure 2. Calculated extent of occurrence (EOO) and index of area ccupancy (IAO) for Lake Erie Watersnake (Nerodia sipedon insularum) in Canada. Locations 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. 8

20 Extent of Occurrence and Area of Occupancy The extent of occurrence (EOO) of Lake Erie Watersnake in Canada is estimated to be 188 km 2. The index of area of occupancy (IAO) of Lake Erie Watersnake in Canada is estimated to be 72 km 2. 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). Search Effort 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. Habitat Requirements HABITAT 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). 9

21 Hibernation Habitat 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 = 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 10

22 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). Habitat Trends Canadian Islands 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. 11

23 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 and Reproduction BIOLOGY 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). 12

24 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, rockfilled 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. 13

25 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. Interspecific Interactions 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). 14

26 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). Sampling Effort and Methods POPULATION SIZES AND TRENDS 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 (King 1985, 1986), (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 (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. Abundance Pelee Island 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. 15

27 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 = ). 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). 16

28 Figure 3. Habitat quality ranks for Lake Erie Watersnake assigned to the shoreline of Pelee Island (see Tables 1 2 for methodology and rationale). Orthoimagery (2010) from SWOOP (OMNRF). 17