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Recovery Strategy for the Tiger Salamander (Ambystoma tigrinum) (Great Lakes Population) in Canada (Proposed)
- 1.1 Species Assessment Information from COSEWIC
- 1.2 Description
- 1.3 Populations and Distribution of the Eastern Tiger Salamander
- 1.4 Needs of the Tiger Salamander (Great Lakes Population)
- 1.5 Threats
1.1 Species Assessment Information from COSEWIC
Date of Assessment: November 2001
Common Name (population): Tiger Salamander (Great Lakes population)
Scientific Name: Ambystoma tigrinum
COSEWIC Status: Extirpated
Reason for Designation: This salamander was last seen in southern Ontario in 1915 at Point Pelee. Despite repeated inventories over the last 80 years, it has not been seen since that time.
Canadian Occurrence: Ontario
COSEWIC Status History: Last seen in Ontario in 1915. Designated Extirpated in November 2001. Assessment based on a new status report.
The Great Lakes population of the Tiger Salamander, a mole salamander in the family Ambystomatidae, was, until 2008, considered to belong to one of six subspecies of Tiger Salamanders (Ambystoma tigrinum), the Eastern Tiger Salamander (A. t. tigrinum) (Green 1825, Crother 2000). Recent mitochondrial DNA, allozyme1, and fine-scale morphological investigations strongly suggest that the Eastern Tiger Salamander is a species separate from the other forms (Shaffer and McKnight 1996, Irschick and Shaffer 1997, Powell et al. 1998). Based on these findings, the Eastern Tiger Salamander, including the Great Lakes population, is now considered to be a species (A. tigrinum) distinct from the five remaining former subspecies, now collectively recognized as A. mavortium. This taxonomic arrangement has only recently received acceptance in the Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico (Crother 2008). This checklist is the standard followed by the three major herpetological societies in North America, as well as NatureServe, and the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) (Oldham pers. comm. 2008). This recovery strategy, however, will follow the former taxonomic arrangement recognized at the time of COSEWIC's designation, which also makes it easier to follow discussions related to the species (Tiger Salamander), subspecies (Eastern Tiger Salamander), and population (Great Lakes) levels.
The Tiger Salamander is one of the largest terrestrial salamanders in the world. It reaches a total length of 30 to 35 cm, although it more often measures between 18 and 21 cm (Behler and King 1998, Petranka 1998). Smith (1949) recorded an Eastern Tiger Salamander measuring 33 cm in total length. Colouration, form, and life history vary across the range of the Tiger Salamander in North America, and it is on this basis that the six previously recognized subspecies were identified. Terrestrial, adult, Eastern Tiger Salamanders typically have a dull black to deep brown or dark green ground colour on their back, with lighter olive to yellow spots, blotches, or vertical streaks, and an olive-yellow belly marked with irregular, pale, yellow blotches (Dunn 1940, Pope 1964, Vogt 1981, Conant and Collins 1991, Petranka 1998). These spots increase in number with age in most areas, and are as prevalent on the top of the salamander's body as on its sides (Dunn 1940).
Male and female Tiger Salamanders differ only slightly, with females showing less lateral compression than males. Females also have shorter tails in proportion to their body length, and shorter vents. The male's vent swells during the breeding season (Pope 1964).
Clusters of pigmented eggs, 10 to 12 mm in diameter, are attached to twigs or stems of emergent plants, 30 cm or more below the surface of the water. Each egg mass contains 18 to 110 eggs, the average number of which varies geographically. An average cluster of eggs measures approximately 5.5 cm by 7 cm (Pope 1964, Vogt 1981, Petranka 1998), and requires a month or more to incubate, depending on water temperature.
Upon hatching, Tiger Salamander larvae are silvery gray, and have broad snouts, three pairs of conspicuous, feathery gills, broad, dorsal fin membranes, and lack the fleshy protrusions, or balancers, found in other mole salamander larvae. Gill rakers2, numbering from 19 to 20 on the anterior face of the third arch, can be used to help distinguish Eastern Tiger Salamanders from the other five subspecies (Dunn 1940). Larval Eastern Tiger Salamanders vary in total length from 9 to 17 mm (Petranka 1998). Paired blotches on their upper surface tend to darken with age, and a greenish colouration may appear along the outer surface of the gills (Petranka 1998, Schock 2001). Front limbs develop first, shortly after hatching, followed by the hind appendages (Schock 2001). Juveniles develop adult colouration and patterning during, or within one month of, metamorphosis (Engelhardt 1916, Webb and Roueche 1971). The gills, along with the dorsal and caudal fin membranes, are absorbed during metamorphosis, the latter of which may remain visible as a dark line down the centre of the back for a short period of time (Schock 2001).
The time from hatching through transformation to the terrestrial form varies from two to five months in the Eastern Tiger Salamander, depending on food availability, climate, density, and seasonal time of pond drying. Populations in New York, Michigan, and Indiana take approximately two to three, three, and three and a half months respectively to metamorphose (Ruthven et al.1928, Bishop 1941, Wilbur and Collins 1973, Sever and Dineen 1978, Petranka 1998). A minimum of three to seven months of water availability is, therefore, needed for the entire process to occur, from pairing and mating, through egg incubation and hatching, larval development and transformation, to the emergence of juveniles in their terrestrial form. Eastern Tiger Salamander larvae are even known to overwinter in permanent ponds before transforming (Brandon and Bremer 1967). The time to reach sexual maturity also varies from population to population, based on climate and genetic factors (F. R. Cook pers. comm. 2008). However, larvae typically reach sexual maturity in two years for males, and three to five years for females (Wilbur and Collins 1973, Petranka 1998).
Cannibalistic larvae, which are rare in the Eastern Tiger Salamander, are believed to develop in response to high larval densities, especially when there are large variations in larval size (Gehlbach 1969, Collins et al. 1980, Pfennig et al. 1991). These individuals have broad, flattened heads and enlarged teeth on the roof of their mouth that allow them to catch and eat salamander larvae that can be almost equal to them in size (Schock 2001). A neotenic morph, which reaches sexual maturity without undergoing metamorphosis into the terrestrial form, may also occur, although, again, they are not common in the Eastern Tiger Salamander (Petranka 1998). These forms remain in the water throughout adulthood, in areas where water is guaranteed year-round, likely representing an adaptation to terrestrial habitats that become dry and inhospitable for much of the year. Neotenic morphs can reach very large sizes (350 mm and more in total length), and occasionally may be cannibalistic.
1.3 Populations and Distribution of the Eastern Tiger Salamander
1.3.1 North American
The Eastern Tiger Salamander ranges from Long Island, New York along the Atlantic coastal plain southward to northern Florida; westward along the Gulf of Mexico to southern Mississippi and southeastern Louisiana; then northward through Alabama, Tennessee, western Kentucky, Indiana and much of Lower Michigan. They also range unevenly through Wisconsin and Illinois to Iowa, northeastern Kansas, extreme eastern Nebraska, and southeastern South Dakota, northward to Minnesota, and extreme southeastern Manitoba. It is absent from most of the Appalachian uplands, and the lower Mississippi River delta region. A large, disjunct population exists in eastern Texas, with smaller, isolated populations in Missouri, northern Arkansas, extreme southeastern Kansas, Michigan's Upper Peninsula, and Ohio, including Kelleys Island, in western Lake Erie (Conant and Collins 1991, Petranka 1998, Frost 2007, Figure 1). While Tiger Salamanders were reported from Ohio's South Bass and Middle Bass Islands between 1940 and 1966 (Langlois 1964, Downs 1989, King et al. 1997), they have not been reported since then. It has been suggested that they have been eliminated from these islands as a result of habitat destruction (Downs 1989, King et al. 1997, J. P. Bogart pers. comm. 2008).
The Great Lakes population of the Tiger Salamander, a COSEWIC-designated unit, based on geographic distribution of the species, is considered extirpated from Ontario and, therefore, from Canada. A similar designation does not exist in the United States.
COSEWIC's designation of a Great Lakes population of the Tiger Salamander in Canada is based on a single, adult specimen, housed at the Canadian Museum of Nature (CMNAR 623, Zoology Accession Number 1915-77). P. A. Taverner collected this individual on October 2, 1915 from Point Pelee, Ontario. (Logier 1925, M. Steigerwald pers. comm. 2005, F. R. Cook pers. comm. 2008). Identification is based on morphology, but cannot be confirmed via genetic testing due to the preservation of the specimen in formaldehyde for a period of time. Unfortunately, this record lacks further information regarding the exact location of the collection and the habitat in which the Tiger Salamander was found. Point Pelee National Park was 15.6 km² in size in 1931. However, a map, created by Taverner in 1908 (Taverner and Swales 1907-1908), shows that the area that was considered "Point Pelee", at that time, was likely larger than that, probably by one concession along the eastern half of its present-day northern boundary.
Questions remain regarding the origin of the specimen from Point Pelee. This is despite Taverner's knowledge of the Point Pelee area, extending back to at least 1905, his membership in the Great Lakes Ornithological Club that conducted extensive fieldwork at Point Pelee, and his position as Ornithologist at the Geological Survey of Canada, Victoria Memorial Museum Branch/National Museum of Natural Sciences, Ottawa from 1911 to 1942 (now the Canadian National Museum) (Cranmer-Byng 1996).
Since 1915, and despite extensive herpetofaunal research and surveys in what would become Point Pelee National Park (Taverner 19144; Patch 19193; Logier 1925; Cook 1967; Cook 1971; Ross 1971; Rivard 1973a, b; Damas and Smith Ltd. 1981; Wigle undated; Mason and Mason 1986; Kraus 1991; Hecnar and M'Closkey 1994, 1995; Oldham and Weller 2000), and herpetological notes recorded by staff (Bouckhout 1967, Roy 1967, Wyett 1967, Dutcher 1968, Mundy 1968, Wyett 1968, Neill 1968-1969, Burhoe 1969, Gemmell 1969, Bevan 1972), no other individuals of Eastern Tiger Salamander, or any other salamander species, have been found. Logier (1925), when describing a six week Royal Ontario Museum of Zoology expedition to Point Pelee National Park, in the summer of 1920, just five years after Taverner's discovery, noted "I was struck by the apparent absence of both newts and salamanders".
While unpublished Great Lakes Ornithological Club records (1915) and Taverner's personal communications (1915a, 1915b) document that Taverner was present at Point Pelee at a holiday reunion of the club on October 2, 1915, when the Tiger Salamander was reported to be collected, the collection is neither noted in the club records, which did document the collection of birds on that trip, nor in Taverner's Geological Survey of Canada field notes. However, the Great Lakes Ornithological Club records do document reptiles and amphibians collected on other trips. It is perplexing that Taverner could not recall the circumstances of the salamander's capture (Logier 1925), despite its significance (i.e. first record and first collection of Tiger Salamander in Ontario) and his occupation at the time. However, as his primary interest was birds, it is possible that he didn't realize the significance of the record. This is reinforced by the fact that the accession record for the specimens collected on that day simply notes "1 - salamander", with "Ambystoma tigrinum Green" noted above it in a different style of writing and ink. This suggests that identification took place at a later date. Similarly, the 1913 amphibians collected during the Victoria Memorial Museum expedition were simply identified as frogs when they were first catalogued, despite the presence of the now Threatened Fowler's Toad (Bufo fowleri) and the now Endangered Northern Cricket Frog (Acris crepitans) in the collection. Furthermore, neither Taverner (1914) nor Patch (1919) reported on the amphibians that they collected during their 1913 expedition, in their report on the reptiles found (F. R. Cook pers. comm. 2008). These facts suggest that neither of the men were familiar with amphibians (F. R. Cook pers. comm. 2008). It has also been noted that Taverner's specimen is quite emaciated, suggesting that it may have been held for some time prior to preservation and tagging (F. R. Cook pers. comm. 2008). A note to Taverner, from a colleague at the Royal Ontario Museum, less than two months after the Tiger Salamander was collected, suggesting that he should keep notes of his work beyond his field journal as "There are so many things that you do in the course of your work that you forget." (Fleming to Taverner, 22 November 1915, ROM as cited in Cranmer-Byng 1996) raises further questions regarding the adequacy of details recorded. These pieces of information have led experts to hypothesize that Taverner's specimen may have originated from the United States mainland, or have been collected on one of the western Lake Erie islands (J. P. Bogart pers. comm. 2008, F. R. Cook pers. comm. 2008). That this might have occurred is supported by the fact that this is not the only specimen for which Taverner's collection locality has been questioned. Two Dorcas Copper (Lycaena dorcas) butterfly specimens in the University of Michigan Museum of Zoology Collection labelled "Point Pelee, July 25, P. A. Taverner" are absent from Taverner's journals, despite the fact that he regularly listed butterflies he encountered at Point Pelee. No other records of the species exist for this locality. As such, it is suspected that the Dorcas Coppers may have originated from Michigan, where Taverner lived and regularly collected (Wormington 1982).
It is also possible that Taverner's specimen may represent a waif, from populations that include pure and hybrid individuals, existing on the nearby Kelleys or the Bass Islands in Ohio, rather than a representative of an Ontarian population (F. R. Cook pers. comm. 2008). King et al. (1997) stated "amphibians and reptiles represented by a single observation or specimen from a given island may represent waif or transient individuals, rather than representatives of resident breeding populations." This possibility is given further support by a single, live Timber Rattlesnake (Crotalus horridus), recorded at Point Pelee in 1918, where no apparent overwintering habitat is present (Cook 1974). The closest population of this species occurred on South Bass Island (F. R. Cook pers. comm. 2008). Similarly, two Northern Cricket frogs, known from Pelee Island and the Ohio Islands, are the sole representatives of their species from the Point Pelee area (Cook 1974, F. R. Cook pers. comm. to M. J. Oldham 2000). More recently, on September 17, 2007, a live, PIT-tagged5 Lake Erie Watersnake (Nerodia sipedon insularum), that had originally been captured and marked on May 30th of that year on East Point of Middle Bass Island, was captured within Point Pelee National Park (Point Pelee National Park unpublished data 2007). These individuals may all represent waifs that have drifted over to Point Pelee from the western Lake Erie islands (F. R. Cook pers. comm. 2008).
Two specimens, an adult and a transforming juvenile, originally reported to be Spotted Salamanders (A. maculatum), were collected on the 6th of June and the 19th of July, 1950 from Pelee Island by A. Reid (ROM 80966) and V. Kohler (ROM 8083), respectively (Froom 1972, M. J. Oldham pers. comm. 2005, R. MacCulloch pers. comm. 2008). These were re-determined, to be Tiger Salamanders by C. A. Campbell, E. J. Crossman7, and later J. P. Bogart. C. A. Campbell and R. Mitton collected two larvae in 1972 from an ephemeral, flooded (in some years), Red Ash (Fraxinus pennsylvanica) woods/Sartwell's Sedge (Carex sartwellii) lowland, along Stone Road on Pelee Island (Oldham 1983, M. J. Oldham pers. comms. 2005 and 2008, C. A. Campbell pers. comm. 2008). Gehlbach, a United States authority on Tiger Salamanders, identified these specimens as Tiger Salamanders (M. J. Oldham pers. comms. 2005 and 2008, C. A. Campbell pers. comm. 2008). However, all of the specimens from Pelee Island were identified based on visual characteristics (morphology, colouration, patterning), prior to recognition of the confusing array of hybrid Blue-spotted (A. laterale) and Small-mouthed (A. texanum) Salamanders present on the island, and the difficulties that such hybridization presents to accurate identification (Bogart et al. 1985, M. J. Oldham pers. comm. 2005, F. R. Cook pers. comm. 2008). Both ROM specimens have since been relabeled as Ambystoma species due to the uncertainty surrounding their identification (R. MacCulloch, pers. comm. 2005). Individual salamanders collected from the Campbell/Mitton Stone Road collection site on multiple occasions between the early 1980s and early 1990s were genetically determined by J. P. Bogart to be Blue-spotted/Small-mouthed Salamander hybrids (Oldham pers. comm. 2005).
Other Ontario records include a specimen of Gray Tiger Salamander (A. t. diaboli), in the United States National Museum (USNM 133948), noted as "taken at Ottawa 1883 [April 21] by Dr. Robert Bell" (Nash 1908, USNM). However, Dr. Bell, a Geologist for the Geological Survey of Canada in Ottawa, was likely involved in the Geological Surveys' western Canadian fieldwork taking place at the time. It is highly probable that he shipped the specimen from Ottawa, at the end of one of these expeditions, and that the USNM assigned a collection location based on where the specimen had been shipped from, as they occasionally did (F. R. Cook pers. comm. 2008). This theory is supported by the fact that the specimen is identified as a Gray Tiger Salamander, a more western subspecies than the Eastern Tiger Salamander. Similarly, a specimen, labelled A. conspersum (a Latin name used in the past for Tiger Salamander), recorded, at one time, in the ROM Collection catalogue and annotated by Dr. J. H. Garnier 1889, was reportedly from Kintail, Ashfield Township, Huron County (C. A. Campbell pers. comm. 2008). However, Garnier (ca. 18--) refers to a specimen of Siredon canadense (an unpublished synonym for Gray Tiger Salamander) "Perfected in Bruce, Ontario". F. R. Cook (pers. comm. 2008) suggests that this may refer to a Tiger Salamander kept in captivity at Garnier's residence at Lucknow on Lake Huron, Bruce County until it transformed (and thus "perfected"). As Kintail and Lucknow are very close to each other geographically, it is possible that this specimen was also labelled based on where it had been held in captivity, rather than where it was collected. Unfortunately, this specimen cannot be located within the ROM collection today.
An unsubstantiated report of Eastern Tiger Salamanders was made on an anonymous note found at Rondeau Provincial Park, indicating that these salamanders were once plentiful there (Campbell 1971, Froom 1972). Based on the commonness of the species suggested in this report, the extent to which Rondeau has been studied (Campbell 1971; Ontario Ministry of Natural Resources 1978; Weller and Oldham 1988; Hecnar and M'Closkey 1996, 1998; Gillingwater 2001; Timmermans et al. 2005), and the fact that no other observations of this species exist for Rondeau, this report can likely be discounted as a case of misidentification, possibly of the Blue-spotted Salamander which does occur in the park (Timmermans et al. 2005, F. R. Cook pers. comm. 2008).
Today, visual identification to the level of a pure species and subspecies is considered inconclusive. Genetic testing is needed to confirm identification and genetic purity (J. P. Bogart pers. comm. to F. R. Cook 2008). As such, none of the above specimens, or any other reports of Tiger Salamander from southwestern Ontario, including Point Pelee and Pelee Island, can be considered confirmed. While Campbell and Mitton's specimens from Pelee Island cannot be considered confirmed at this time (M. J. Oldham pers. comm. 2005), at least one specimen, preserved in alcohol in C. A. Campbell's private collection, still exists which may lend itself to genetic testing in the future (C. A. Campbell pers. comm. 2008).
At the present time, Taverner's specimen is the only record of the Great Lakes population of the Tiger Salamander accepted by COSEWIC (Schock 2001), although it too has not been, and cannot be, genetically tested. This single specimen, and sole, confirmed Canadian observation, does not provide convincing evidence of the presence of a population in the Great Lakes region of Canada.
More significantly, given the intensive studies and electrophoretic work that has been completed, the absence of a Tiger Salamander genetic complement in hybrid mole salamanders on either the Ontario mainland or the Canadian islands of western Lake Erie, and Pelee Island in particular, suggests that Tiger Salamanders are neither present, nor were they likely present in the past (J. P. Bogart pers. comm. 2008).
In extreme southeastern Manitoba, adults and larvae that, in colouration and patterning, appear to be Eastern Tiger Salamanders (i.e. the same subspecies as the Great Lakes population), were collected from the Roseau River, in 1970 (CMNAR 12182, 12198, and 30016, F. R. Cook pers. comm. 2008). Additionally, egg masses collected near Tolstoy, Roseau River, and Stuartburn, in 1985, were raised through metamorphosis, and subsequently identified as Eastern Tiger Salamanders (CMNAR 14: 30975, 29: 30977, and 7: 30981, F. R. Cook pers. comm. 2008, L. A. Lowcock pers. comm. 2008). Several range maps (Conant and Collins 1998, Petranka 1998), likely based on these records, include extreme southeastern Manitoba within the distribution of the Eastern Tiger Salamander. While all Manitoba Tiger Salamanders are currently geographically ascribed, by COSEWIC, to the Prairie/Boreal population (COSEWIC in press), the isozyme9 and mitochondrial DNA of these salamanders does not appear to be significantly different from the Eastern Tiger Salamanders of Kelleys Island, mainland Ohio, or Indiana (J. P. Bogart pers. comm. 2008). However, their DNA also showed little, to no, differentiation from the DNA of Gray Tiger Salamanders found elsewhere in Manitoba. The Red River, which separates the range of Manitoba's Eastern and Gray Tiger Salamander subspecies, is suspected to form only a partial barrier to gene flow, and intergrade specimens appear to have been found (ROM 18729, F. R. Cook pers. comm. 2008, L. A. Lowcock pers. comm. 2008). Based on the above, the relationship of Manitoba's Eastern Tiger Salamanders to a possible former Great Lakes population, and Gray Tiger Salamanders to the west, remains unclear.
1.4 Needs of the Tiger Salamander (Great Lakes Population)
The Canadian Great Lakes population of the Eastern Tiger Salamander is recognized from a single, ambiguous record that is now more than 90 years old. While the population is now considered extirpated, it is not clear whether a population of Eastern Tiger Salamanders ever actually existed in southwestern Ontario. The specific locality of the collection is not known, and the habitat is not described. Thus, all information on the habitat and biological requirements that follow are hypothesized based on United States populations of the Eastern Tiger Salamander.
1.4.1 Habitat and biological needs
Tiger Salamanders require broad areas of woodland or forest to support terrestrial adults, which spend the majority of their time below the ground. They burrow deeply in loose soil or leaf mould, or live in abandoned mammal runways, often over wintering in these sites. Eastern Tiger Salamanders have also been found under rocks, limestone flakes, piles of debris or manure, in sewers and drains, in cellars, and even in window wells (Pope 1964, Vogt 1981, Bogart et al. 1987).
Forested areas must include, or be located adjacent to, fish-free, vegetated ponds or marshes for breeding, with minimal barriers or threats to salamander passage in between (Duellman 1954, Conant and Collins 1991). The breeding ponds are typically deeper than those employed by other mole salamanders, though shallower ponds may be used (Downs 1989). While these ponds do not need to be permanent, they must hold water long enough (at least three to seven months) to allow for mating, egg laying, hatching, and for the larvae to develop and metamorphose.
In early spring (usually between February and April), on rainy nights, as the ground thaws, and nighttime temperatures near 0°C, adult Eastern Tiger Salamanders migrate from over wintering sites to breeding ponds (Sever and Dineen 1978, Vogt 1981, Semlitsch and Pechmann 1985). After mating, a cluster of pigmented eggs is attached to twigs or stems of emergent plants, 30 cm or more below the surface of the water.
At the end of the breeding season, which may vary from year to year, the adults return to the terrestrial portions of the forest (Hassinger et al. 1970, Sever and Dineen 1978, Vogt 1981, Semlitsch and Pechmann 1985, Petranka 1998). Once the eggs have hatched, and the larvae have metamorphosed, the juveniles also leave the ponds and migrate to their terrestrial habitat in the forest, though they may still be found at the margins of the pond for some time (Kraus 1985, Bogart et al. 1987, Petranka 1998).
Due to their secretive, and largely underground nature, the area required to support a stable population of Eastern Tiger Salamanders is not currently known. In addition, migration distances for the subspecies have not been documented. However, radio telemetry studies of other species of mole salamanders have shown considerable variation in migration distances, from an average of only 35.9 m for the California Tiger Salamander (A. californiense) (Loredo et al. 1996) to a maximum distance of 213 m for the Spotted Salamander.
Larval and neotenic adult Tiger Salamanders feed on herbivorous zooplankton, amphipods, molluscs, and insect larvae, as well as small frogs and other salamanders (Moore and Strickland 1955, Pope 1964, Dodson and Dodson 1971). Terrestrial juveniles and adults feed on a variety of earthworms, molluscs, insects, including crickets, grasshoppers, moths, flies, beetles, and cicadas, as well as spiders, small field mice, frogs, and other salamanders (Bishop 1941,
Pope 1964, Petranka 1998).
1.4.2 Ecological role
Because representatives of the Great Lakes population of the Tiger Salamander have not been seen in Ontario since 1915, and the population is only accepted based on a single, ambiguous record, it may not have been a significant part of the Canadian faunal community for a prolonged period of time, if ever. Given the time since Taverner's collection, and the likelihood, as noted by experts, that a self-sustaining population may never have existed in Canada, the niche of this population may be occupied by other organisms.
Where common, Eastern Tiger Salamanders may be important predators of aquatic and forest floor invertebrates, as well as an opportunistic predator of small vertebrates (see Section 1.4.1). Despite popular belief, they do not seem to be a serious predator of fish fry and fingerlings (Schock 2001). Aquatic forms may be important predators of herbivorous zooplankton, consuming them in such quantities that phytoplankton biomass increases, resulting in a decline in orthophosphate levels in the water (Holomuzki et al. 1994). Tiger Salamanders may, themselves, serve as prey for larger predators in the area, such as aquatic vertebrates (especially predaceous fishes) and invertebrates, gartersnakes, and crows (Webb and Roueche 1971, Sprules 1972, Collins and Wilbur 1979, Vogt 1981, Petranka 1998, Larsen 1999).
1.4.3 Limiting factors
Eastern Tiger Salamanders appear to exhibit high site fidelity with respect to the breeding ponds from which they emerge (i.e. they return to same pond year after year). Translocated specimens in Long Island, New York bred in the ponds where they were placed, but seldom returned to them in subsequent years. However, individuals that were not translocated used the same pond across breeding seasons (Madison and Farrand 1998). As such, the species may be limited by the loss of its breeding locations.
Threats to the Eastern Tiger Salamander in the Great Lakes region of Canada are not known. As the Great Lakes population is only recognized from the single, ambiguous record of 1915, and confirmed reports have not been documented since, it is impossible to determine the threats that may have faced a population, had one been established in Canada. If a population did exist, the factors that ultimately led to its extirpation can only be surmised. Data from populations of Eastern Tiger Salamander south of the Great Lakes, discussed in Sections 1.5.1 through 1.5.5 below, however, may provide insight into potential threats to this population, past and present, if a population did indeed exist.
1.5.1 Road mortality
In general, road mortality is a significant threat to Tiger Salamanders. Because Tiger Salamanders migrate to and from breeding ponds (Section 1.4.1), they are susceptible where roads separate overwintering sites from breeding ponds (Duellman 1954, Conant and Collins 1991). In Point Pelee National Park, a road stretches approximately 80% of the park's length, separating a portion of the forest from potential breeding areas. This and a few other minor roads were already in place by 1908, when Taverner penned a map of the area (Taverner and Swales 1907 – 1908, Battin and Nelson 1978). At that time, traffic would likely have been considerably less than the volumes experienced today. More recently, researchers and staff at Point Pelee National Park have noted amphibian road mortality events, when weather conditions are optimal for anuran10 migration (Hecnar and M'Closkey 1995). Elsewhere, amphibian populations have been shown to decrease in size with increasing traffic volume (Fahrig et al. 1995). Duellman (1954), while surveying a 3.54 km stretch of highway in Michigan, found 274 Eastern Tiger Salamanders in 30 hours. Of these, only 46 were alive, the remainder having been run over by automobiles.
1.5.2 Agricultural and septic run-off
Run-off of agricultural pesticides and fertilizers, and septic system seepage, also pose threats that have been demonstrated to impact Tiger Salamanders (Power et al. 1989). Nitrates, from agricultural fertilizers, cause reduced activity and feeding, as well as increased deformities in frog tadpoles (Hecnar 1995), and are likely to have similar effects on larval Eastern Tiger Salamanders. Rouse et al. (1999) evaluated environmental concentrations of nitrates in North American waters. The levels of nitrates were compared to controlled laboratory experiments on amphibian larvae and other species that play an important role in amphibian ecology. The watersheds of Lake Erie and Lake St. Clair, in Canada and the United States, had nitrate levels high enough to cause physical and behavioral abnormalities in some amphibian species, in 19.8% of 8,000 water samples. Disturbingly, 3.1% of the samples had nitrate levels high enough to kill tadpoles of some native species of frogs.
Over 20% of Point Pelee National Park's terrestrial environment was farmed at one time, with DDT, other pesticides, and fertilizers applied to agricultural crops, particularly the orchards. In addition, DDT "Toss-it Bombs" were deposited directly into the marsh, and terrestrial areas of the park were fogged for mosquito control (D. Reive pers. comm. 2008). Because Eastern Tiger Salamanders prey on vertebrates and invertebrates, they are subject to bioamplification of toxins such as DDT, and its breakdown products DDD and DDE. These toxins were found in Spring Peepers (Pseudacris crucifer) in Point Pelee National Park in 1993, at levels exceeding the limit for fish, despite discontinuation of DDT use in 1967 (Russell et al. 1995). Given the toxicity effects, the extent of agricultural development in the area, and the fact that pesticides can also indirectly impact habitat and food quantity and quality, the risks posed by runoff cannot be dismissed (Bishop 1992).
While septic systems were not of concern in 1915, when the Taverner Tiger Salamander was recorded at Point Pelee, by the late 1950s and early 1960s, the Park had over 350 buildings within its boundaries, many of those being houses and private cottages with septic tanks and weeping beds. While many septic tanks have been pumped out, and either removed or broken down and filled in with sand, and park infrastructure has been replaced, the old weeping beds remain in place, and may still be leaching small amounts of effluent (D. Reive pers. comm. 2008). In the late 1990s, a large plume of effluent in the groundwater around the Marsh Boardwalk/Blue Heron Day Use Area was identified. As a result, the Blue Heron septic system was replaced. However, this plume could continue to have an impact on marsh water quality near the Marsh Boardwalk area for an unknown period of time (D. Reive pers. comm. 2008).
1.5.3 Development and habitat loss
Human disturbances, in the form of development, traffic, wetland conversion to other uses, and land clearing, would likely have impacted any population that existed historically, while traffic would present a threat today (Section 1.5.1). The extensive development of the area north of Point Pelee National Park, with its associated wetland drainage and road construction, has already reduced, if not eliminated, available habitat north of the national park. Only 6% of Essex County, excluding Pelee Island and the city of Windsor, remains in tree cover (Ontario Ministry of Natural Resources 2006). However, Vogt (1981) indicates that urbanization and agricultural activity do not always result in the extirpation of Eastern Tiger Salamanders from an area. Extensive shoreline hardening, along with installation and expansions to the Wheatley Harbour, has resulted in increased erosion along Point Pelee National Park's eastern shore (W. F. Baird & Associates et al. 2007). This erosion has narrowed the east barrier beach, to the extent that breaches can occur during periods of high water. The potential for predatory fishes to enter the swamps' vernal pools, should marsh levels peak, render them unsuitable for Eastern Tiger Salamander breeding, at least in some years.
1.5.4 Infectious disease
Infectious disease is also a potential threat to Eastern Tiger Salamanders (Davidson et al. 2000, Seburn and Seburn 2000). The iridovirus (Ambystoma tigrinum) Virus (ATV) has been isolated from populations of the Sonoran Tiger Salamander (A. t. stebbinsi) in Arizona, and periodically causes mass mortality in populations of this subspecies (Jancovich et al. 1997). Chytrid fungus (Batrachochytrium sp.) and another iridovirus, Ranavirus, have been implicated in declines or die-offs of Canadian populations of Tiger Salamander (Schock et al. 1998, Bollinger et al. 1999, Schock 2001). Transfer of iridovirus between salamanders and other organisms may also be possible. In California, sympatric Red-legged Frogs (Rana aurora) and Three-spined Sticklebacks (Gasterosteus aculeatus) were found to be carrying the same strain of iridovirus, suggesting that fish introduction, and subsequent host switching of the disease from fishes, may also be a threat (Mao et al. 1999).
In addition to being potential disease vectors, various fishes, including native predaceous fishes, are well known predators of Tiger Salamander eggs and larvae (Blair 1951, Carpenter 1953, Collins and Wilbur 1979, Collins 1981, Orchard 1992, Degenhardt et al. 1996, Corn et al. 1997, Hammerson 1999). Therefore, the presence of predaceous fish in the Tiger Salamander's breeding ponds is considered detrimental to their populations (Blair 1951, Carpenter 1953, Collins and Wilbur 1979, Collins 1981, Orchard 1991, Sarell 1996, Corn et al.1997). The permanent ponds in the Point Pelee National Park marsh are, and probably always have been, occupied by a broad array of fish species (47 species recorded to date), including many that are predatory (Surette and McKay 2007). In addition, exotics like the Goldfish (Carassius auratus) have become established, likely through introductions by the public. Many, if not all, of the ponds are interconnected, with three prone to breaching, connecting them to Lake Erie during periods of high water. Man-made irrigation canals in the park are also occupied by fishes, as they are connected with the marsh, at least when water levels are high (T. Dobbie pers. comm. 2008). This predator presence in the marsh and man-made canals would likely restrict any Tiger Salamander breeding activity to temporary pools, or sloughs, within Point Pelee National Park's deciduous, swamp forest. However, when Lake Erie water levels were high in the mid-1970s, the barrier beach separating the marsh from Lake Erie breached, and water levels became so high in the marsh that water overtopped the former East Beach Road into the swamp forest, bringing fishes, particularly Bowfin (Amia calva), into the sloughs (D. Reive pers. comm. 2008). While this has only been noted on one occasion, in the last 30 or so years, the duration of this flooding lasted a year or two, suggesting that even the sloughs of the swamp forest may not be suitable, in all years, for the breeding activities of Eastern Tiger Salamander.
1 An allozyme is any of the forms of an enzyme that are determined by the different forms of a gene at a single genetic location. Different allozymes are responsible for the inheritance of different genetic traits.
2 Gill rakers are stiff projections, found along the inner margin of the structures supporting the gills of fishes, which help prevent food and other particles from being carried into the gills.
3 Canadian Museum of Nature Amphibian and Reptile Collection catalogue number.
4 These two reports were based on the same 1913 biological field expedition of the Victoria Memorial Museum (Geological survey of Canada) (F. R. Cook pers. comm. 2008).
5 Passive integrated transponders are used to uniquely identify individuals.
6 Royal Ontario Museum Collection catalogue number.
7 Former Curator of Ichthyology and Herpetology, Royal Ontario Museum.
8 United States National Museum Collection catalogue number.
9 Any of the chemically distinct forms of an enzyme that perform the same function.
10 Frogs and toads.
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