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Recovery Strategy for the Tiger Salamander (Ambystoma tigrinum) (Great Lakes Population) in Canada (Proposed)
2. Recovery feasibility
- 2.1 Availability of Individuals
- 2.2 Habitat Availability
- 2.3 Potential to Mitigate Threats to Individuals and Habitat
- 2.4 Existence of Effective Recovery Techniques
- 2.5 Recovery Feasibility Conclusion
The singularity of the specimen upon which the Great Lakes population is based is of note for several reasons. Dunn (1940) states that, "Unless one has a series of adults from a locality it is difficult to be certain what form is present there. Single specimens may be very misleading." The Point Pelee specimen was identified based on patterning and morphology. The fact that it was preserved in formaldehyde for a period of time precludes genetic confirmation today. Further complicating identification is the propensity of Tiger Salamander to hybridize with other mole salamander species (J. P. Bogart pers. comm. to F. R. Cook 2008). Genetic testing of one of the nearest populations to Point Pelee, located on Kelleys Island approximately 50 km away in the western Lake Erie islands of Ohio, shows hybridization with the Small-mouthed Salamander, with some of the resulting hybrids containing genetic material from the Blue-spotted Salamander (Bogart et al. 1987). Given the potential for Taverner's specimen to be a waif from Kelleys or the one of the Bass Islands, and the fact that difficulties exist in identifying not only the hybrids, but also the pure subspecies, on morphology alone, it can be questioned whether Taverner's specimen was a genetically pure individual (F. R. Cook pers. comm. 2008).
The uncertainty surrounding the existence of an historic, native Great Lakes population of the Tiger Salamander in Canada renders the appropriateness of recovery questionable. Nevertheless, an examination of the feasibility constraints is presented in Sections 2.1 to 2.5 below.
2.1 Availability of Individuals
No self-sustaining population of the Eastern Tiger Salamander, or individuals capable of reproduction, has been confirmed to exist in the presumed historic range (extreme southwestern Ontario) of the Canadian Great Lakes population. Consequently, recovery would necessitate the establishment of a new population in this area. The only genetically confirmed Canadian population of the Eastern Tiger Salamander is found in extreme southeastern Manitoba (L. A. Lowcock pers. comm. 2008). Isozyme and mitochondrial DNA analyses of Eastern Tiger Salamanders from this area did not appear to be significantly different from the Eastern Tiger Salamanders of Kelleys Island, mainland Ohio, or Indiana. However, they also did not appear to differ from another subspecies, the Gray Tiger Salamander, found on the opposite side of the Red River in Manitoba (J. P. Bogart pers. comm. 2008). Bogart speculates that the different colour patterns seem to be adaptive, having recently evolved. As such, the geographic isolation of individuals in southeastern Manitoba, from the reported Great Lakes' specimen, may have resulted in the development of their own environmental adaptations that cannot be easily observed, or tested (J. P. Bogart pers. comm. 2008). COSEWIC currently considers Manitoba's Eastern Tiger Salamanders to be part of a separate designatable unit, the Prairie/Boreal population, based on ecozones rather than subspecies (M. J. Oldham pers. comm. 2008).
As such, the southeastern Manitoba Eastern Tiger Salamanders are not currently considered appropriate for recovery of a Great Lakes population (J. P. Bogart pers. comm. 2008, F. R. Cook pers. comm. 2008, L. A. Lowcock pers. comm. 2008).
Recovery, therefore, would require the introduction of individuals from one or more self-sufficient, source populations located outside of Canada. However, the subspecies is considered at risk in much of its range in the United States (Appendix 1). It is unclear if populations on the nearby South and Middle Bass Islands are extant (Downs 1989, King et al. 1997, J. P. Bogart pers. comm. 2008). Consequently, populations on these islands could not be considered as appropriate sources. The most appropriate source population would be from Kelleys Island, Ohio due to its proximity, within 50 km, of Point Pelee National Park. However, the Kelleys Island population of pure Eastern Tiger Salamanders may not be large enough to both serve as a source for animals and/or egg masses to be translocated and remain self-sustaining. This is further complicated by the existence of a complex hybridization system on Kelleys Island involving Eastern Tiger, Small-mouthed, and Blue-spotted Salamanders (Kraus 1985, Bogart et al. 1987). While populations of pure Eastern Tiger Salamanders are known from nearby mainland Ohio and Michigan, at least some of these are hybrids involving other species of mole salamanders (J. P. Bogart pers. comm. 2008, L. A. Lowcock pers. comm. 2008). This complicates selection of potential source animals due to the need to find pure individuals as hybrids, if introduced, may "steal" spermatophores11 from pure Eastern Tiger Salamanders. In addition, these mainland United States populations are still substantially separated from the presumed range of the Canadian Great Lakes population by the lakes themselves. It is not certain that individuals from United States populations would have the same genetic make-up as individuals from Canada might have had, particularly as isolation from United States populations may have resulted in local environmental adaptations, with a suite of unique genetic and ecological characteristics. Such characteristics may not be reflected in introduced animals from the United States. These differences would only be greater the farther away source populations are from southwestern Ontario. Consequently, selection of a source population is problematic.
2.2 Habitat Availability
As previously discussed, neither the collection location of the Point Pelee voucher specimen nor its habitat was recorded. Consequently, and because there are no clearly documented Canadian Eastern Tiger Salamander populations nearby, the habitat requirements in Canada, including the area needed to support a self-sustaining population, are not known. Habitat and ecological requirements may differ from more southerly populations of Eastern Tiger Salamander, and from Canadian populations of the other subspecies of Tiger Salamanders: the Gray Tiger Salamander and Blotched Tiger Salamander (A. t. melanostictum). However, as there was no other more fitting alternative, the potential habitat needs of the Great Lakes population of the Tiger Salamander were hypothesized in Section 1.4, based on populations of the Eastern Tiger Salamander in the United States. Based on these assumptions, a discussion of the availability of potentially suitable habitat in the presumed range of the historic population follows.
Selection of recovery sites must be done with careful consideration of both the subspecies' needs and potential threats to survival. For the Eastern Tiger Salamander, the following requirements need to be satisfied: the presence of contiguous forest and relatively unpolluted breeding ponds, that are free of predatory fishes, and that are distant from potential pesticide and fertilizer runoff and roads.
Point Pelee National Park has approximately 325 ha of thicketed, woodland, or forested friable, sandy soil appropriate for Eastern Tiger Salamander burrowing, sheltering, and overwintering. Eastern Moles (Scalopus aquaticus) that occur along the southern shoreline of Essex County (Waldron et al. 2000), and other small rodents, would provide the necessary tunnels. However, the forested habitat within Point Pelee National Park is split by the main road and several smaller driveways totaling 13.84 km (J. Keitel pers. comm. 2007). Parking lots also occur. As discussed in Section 1.5.1, the network of roadways would pose a mortality risk to salamander migration.
While permanent ponds occur in Point Pelee National Park, these are not fish-free. Permanent water in the man-made irrigation canals also has fishes. The presence of several species of predaceous fishes makes these locations unsuitable for Eastern Tiger Salamander breeding. The lingering pesticide and septic contamination in the marsh compound the problem, as discussed in Section 1.5.2. Together, these factors would be expected to restrict reproductive activity to the flooded depressions in the park's 13 ha deciduous swamp or slough forest (Dougan & Associates 2007). This forest has a ridge and trough formation, that temporarily holds water in the depressions, or sloughs, between the ridges in the spring. These sloughs remain fishless during most years. However, the barrier beach between Point Pelee National Park's marsh and Lake Erie has been known to breach when water levels are high and/or storms are severe. Such breaches may not have occurred or may have occurred less frequently in the early 1900s, when the beach was much wider along this shoreline. However, the increasing susceptibility of the barrier beach to breaching events, as it narrows due to on-going erosion, combined with cyclical high water levels in Lake Erie, may make the entry of fishes into the sloughs a more regular event. This would suggest that these sloughs may no longer provide long-term breeding habitat suitable for Eastern Tiger Salamanders. In addition, these vernal pools may be too ephemeral to allow larval Tiger Salamanders to develop and metamorphose. With time required for salamanders to pair and mate, a month or more required for egg incubation, followed by another two to five months before metamorphosed salamanders can emerge from the water, the earliest emergence could be expected would be late June. However, Cook (pers. comm. 2008) suggests that transformation in Point Pelee, near the northern edge of the Eastern Tiger Salamander's range, would not likely occur until late July or August. Logier (1925) noted that the many temporary pools should serve, at least in rainy summers, to tide Wood Frogs (Rana sylvatica) (also absent from the park), over the larval stage, which usually finished in July. It is unknown if this referred to the sloughs of the swamp forest, or to temporary pools of water elsewhere in the park. Either way, this would suggest that the temporary pools he referred to might not remain wet for a sufficient period of time for Eastern Tiger Salamanders to emerge in some or all years. In the 1990s, the swamp forest sloughs typically dried by late July or early August, although they usually refilled in the fall (T. Dobbie pers. comm. 2008). However, given the droughts of the last half decade or more, even the deepest of the sloughs have dried, or are no more than muddy, by late May or early June (V. McKay pers. obs.). Habitat, that would provide sufficient time for Tiger Salamander larvae to fully mature and transform to terrestrial form, is, therefore, currently unavailable, should recovery be proposed.
The area immediately north of the Point Pelee National Park, along with the majority of Essex County, is largely agricultural, and heavily drained. Minimal, patchy, forest cover or appropriate breeding areas exist, with most water found in roadside ditches. Road mortality risks, and associated pollution threats, also render adjacent areas unsuitable for Tiger Salamanders.
These considerations render Point Pelee National Park, and the areas north of it, which encompass the surmised original range of the Canadian Great Lakes population of the Eastern Tiger Salamander, less than suitable in terms of habitat availability.
2.3 Potential to Mitigate Threats to Individuals and Habitat
The potential for significant threats to the Eastern Tiger Salamander or its habitat to be mitigated, or avoided, must also be considered in assessing recovery feasibility. Some threat mitigation may be possible with regards to both road mortality and habitat loss, in terms of the availability of suitable breeding sites. However, these are unlikely to be sufficient to support effective Eastern Tiger Salamander recovery.
Under-road culverts are widely used to reduce road-related mortality for wildlife, including other mole salamanders (Jackson and Tyning 1989, Jackson 1996). Anecdotal evidence exists of at least some use of these structures, but no solid data yet substantiate their effectiveness (J. P. Bogart pers. comm. 2008).
Dredging could potentially improve breeding habitat by deepening the swamp forest sloughs enough to hold water throughout the season. However, this approach may not be viable for long-term management if lake water levels and precipitation continue to decline with regional warming trends. Reinforcement of the east barrier beach might prevent fishes accessing the ponds during periods of high water. While such actions might benefit other amphibian species in the park, modification of natural habitats to benefit one, or a select group of, species would have to be carefully considered, with potential negative impacts to other species and the ecosystem, and corresponding mitigation, addressed in greater detail in a project level environmental assessment under the Canadian Environmental Assessment Act (1992, c. 37).
Restoration of habitat bordering the park is also not feasible, without extensive land retirement and long-term habitat restoration estimated in the millions of dollars (W. F. Baird & Associates et al. 2007). Such work, if extensive enough, could potentially mitigate the threats presented by development, habitat loss and road mortality. However, past, intensive agricultural use of the land, involving pesticide, herbicide, and fertilizer application, might render restored wetland areas unsuitable for Eastern Tiger Salamander recovery. In addition, it would be highly unlikely that fishes could be excluded from such a restoration site over the long-term. Thus, even large scale, costly restoration activities might not prove effective.
Unfortunately, pesticide and septic contamination are also a legacy of Point Pelee National Park. To date, no feasible methods have been found to effectively remediate these threats. Ongoing shoreline erosion, that threatens the suitability of the swamp forest sloughs as Eastern Tiger Salamander breeding habitat, is also very much the result of past actions. Remediation alternatives have been investigated, and are estimated to cost millions of dollars (W. F. Baird & Associates et al. 2007). In addition, while steps can be taken to reduce the chance of introducing infectious disease through translocations, natural occurrences of disease may be unavoidable.
2.4 Existence of Effective Recovery Techniques
Repatriation of the Eastern Tiger Salamander has been executed in Long Island, New York, although with limited success (Lindberg 1988, 1991). Due to breeding site fidelity of Tiger Salamanders, translocation of egg masses, allowing the larvae to catch and develop in the target pond, is preferable to the movement of adult specimens (Enge and Stine 1987). However, egg mortality, under natural conditions, is high. In a study of the natural survival rate of Eastern Tiger Salamander eggs in New Jersey, Anderson et al. (1971) found that 96% of the eggs at their three study ponds died, with 100% dying in one pond.
Captive propagation in the lab, with translocation of egg masses, might be an option. However, there are no substantiated records of non-hormonally induced, captive reproduction of terrestrial forms of Eastern Tiger Salamander. Further, this effort would only minimally reduce the number of animals that would have to be removed from a source population, since the same number of egg masses must still be translocated from the lab to the target site.
Should translocation occur under either scenario, the high rate of egg mortality would remain a major concern. In addition to this, the potential for predation on larvae, and the two to five years required for an Eastern Tiger Salamander to reach sexual maturity would pose significant hurdles to recovery. Consequently, any translocation effort would require a carefully monitored, multi-year plan, and a large source population. Any attempt to establish a viable population would be
a costly and difficult task, even if all threats could be sufficiently mitigated.
2.5 Recovery Feasibility Conclusion
Recovery of the Great Lakes population of the Tiger Salamander, if a population ever existed, is considered neither biologically nor technically feasible at present. No self-sustaining population of the Eastern Tiger Salamander has been confirmed to exist in the presumed historic range of the Canadian Great Lakes population, and no adjacent populations are considered appropriate or secure enough to serve as a source of natural immigrants, or translocated individuals. The rarity of the Eastern Tiger Salamander throughout much of its range may render it impossible to recruit sufficient numbers of suitable animals for recovery, without negatively impacting the source population(s). Even then, the disjunct nature of the presumed former range implies genetic differentiation from United States populations. This raises concerns about how well translocated individuals would adapt to a new habitat. In addition, suitable breeding habitat does not appear available, or easily established, and existing terrestrial habitat presents threats of pesticide contamination. Repatriation attempts elsewhere have had limited success, largely due to the breeding site fidelity exhibited by Eastern Tiger Salamanders, and their high rate of egg mortality. Furthermore, given that Tiger Salamanders have been absent from the region for over 90 years, if a population ever existed, other organisms may now fill the ecological niche that they would occupy. Most importantly, however, is that recovery of the Great Lakes population is considered inappropriate at the current time, in light of the uncertainty surrounding the record(s) of the species, putting the very existence of an historic, native Great Lakes population of Tiger Salamanders in Canada in question.
11 Sperm packets transferred from males to females.
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