Allegheny Mountain dusky salamander COSEWIC assessment and status report: chapter 9

Population Sizes and Trends

Search Effort

Desmognathus ochrophaeus was only recently confirmed to occur in Canada. This is not because the Canadian localities were unknown. The species is easily mistaken for D. fuscus and it was not reported simply because its presence was not suspected. This is true of specimens from both Covey Hill and the Niagara Gorge prior to the genetic confirmation of their identity (Sharbel and Bonin, 1992; Markle and Green, 2005). There has been considerable search effort made for this species subsequent to its recognition, especially in Quebec (Boutin 2003, 2006; Jutras 2003). Studies of the population in Ontario are only just beginning. Surveys up to this point have been to verify the presence of the species, to get an indication of its habitat, and to try and determine the potential extent of its distribution (R. Tervo, pers. comm).


Abundance

The size of the Canadian population is difficult to estimate. Because the seepages and temporary streams that these salamanders inhabit are not mapped on topographic charts or even air photos, the abundance of D. ochrophaeus is difficult to quantify without surveying the whole area by foot. In Quebec, the majority of the habitat is privately owned by several owners, making field surveys more complicated. In Ontario, the population exists in a very steep and treacherous section of the Niagara Gorge, which also makes population estimates difficult.

At Covey Hill, approximately 120 individual D. ochrophaeus plus about 12 hybrids (D. ochrophaeus x D. fuscus) were found in 5 temporary streams and 2 seepages in the early 1990s. In July 2003, a stream salamander inventory was conducted in three sectors of Covey Hill in a joint project between the University of Montréal, the Quebec provincial government and non-government societies (Boutin 2003). The study was carried out to gather information on the distribution and abundance of Quebec’s four species of stream salamanders and to determine the presence and frequency of hybrids of D. ochrophaeusand D. fuscus. While abundances remain unknown, 97 D. ochrophaeus were found recently in the Covey Hill area over a five month period consisting of 36 days of sampling (Boutin 2006).

In Quebec, salamander densities were measured in three temporary streams. Densities (not including hybrids) varied from 0.67 to 1.19 individuals/m of stream with hybrids representing less than 10% of the total (Bonin 1993; Sharbel et al. 1995). Only a portion of the salamanders present are found during surveys, however, as individuals may be underground or in inaccessible crevices. Determination of the actual density would require capture-recapture studies and/or more exhaustive (and likely destructive) survey methods. These densities, though, are comparable to the 0.96 - 1.20 animals/m2 estimated by Orr (1989) in Ohio and the 0.62 - 1.07 animals/m2 estimated by Hall (1977) in Pennsylvania. However, population densities of this species in favourable rock face habitats in North Carolina are known to be as high as 25 animals/m2 (Huheey and Brandon 1973).

In the single cascading stream in the Niagara Gorge in which it occurs, the total number of Desmognathus ochrophaeus so far identified by molecular analysis is 22. Determination of the actual abundance of this population would require capture-recapture studies and potentially destructive survey methods. Eggs and juveniles have been located at the site, indicating that successful reproduction is occurring (R. Tervo pers. comm.).


Fluctuations and Trends

It is not possible to determine population trends as insufficient data have been collected to allow an estimation.


Rescue Effect

The range of D. ochrophaeusonly just crosses the border into Canada. While the distribution in the United States is large and continuous, both Canadian populations are separated from populations south of the border by physical barriers, such as the Niagara River, or by distance (>90 km). The distances and physical barriers individuals would need to overcome to reach Canada make it unlikely that gene flow is presently occurring, and the potential for natural immigration is extremely low. As a result, there is little rescue potential for Canadian populations in the event of a decline or extirpation.

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