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Conservation genetics and ecology of the threatened Coastal Giant Salamander in managed forests of British Columbia: setting priorities for an integrative species recovery plan
Richardson, John S.
The Coastal Giant Salamander (CGS) (Dicamptodon tenebrosus) is a highly vulnerable amphibian that only occurs on the west coast of North America. In Canada, CGS is on the provincial Red List in British Columbia (BC) and is designated as Threatened in Canada (COSEWIC 2002), in addition to being one of BC?s ?Identified Wildlife?. CGS is restricted to approximately 60 streams within a single watershed in Canada, occurring in less than 100 kmē in the Chilliwack River Valley of BC. This species is highly susceptible to habitat loss and degradation due to encroaching development, logging and road building. Logging reduces CGS habitat quality by disturbing stream and bank geomorphology, reducing canopy cover, and altering prey assemblages. There is a distinct possibility that CGS could go extinct in Canada as a direct result of forestry activities. The continued survival of this fragile species therefore depends primarily on ecologically sensitive forestry practices. Previous research has shown that CGS may suffer from reduced larval density, restricted movement and lower genetic variation in clear-cut sites compared with forested sites [1, 2]. This signifies the disruption of important population processes that can alter the dispersal ability, mating system and social organisation of CGS populations. The likely consequences are elevated genetic relatedness and subsequent inbreeding depression, leading to population declines and an increased risk of extinction. Although these threats are recognized in a general sense, their specific effects on population processes remain largely unknown, and hence there are inadequate data to devise strategies to avoid or mitigate the threats. Current forest management policies provide limited protection for CGS habitat. Although vegetation buffer strips are retained along fish-bearing streams these measures do not protect threatened CGS populations because they rarely occur in streams containing fish. Habitat protection through the establishment of forested buffer strips and Wildlife Habitat Areas along small headwater streams is considered most important for CGS recovery. However, the effectiveness of WHAs and buffer strips for maintaining natural population dynamics and processes in CGS remains unexamined. A small number of sites with buffer strips containing CGS exist, while 18 Wildlife Habitat Areas have been approved under the CGS recovery strategy, enabling this core management option to be assessed. There have been some studies on the limited dispersal ability of CGS larvae and terrestrial adults, with evidence for restricted movement in clear-cut sites [3, 4, 5], but little is known about age and sex specific dispersal and long distance movements over extended time periods in both aquatic and terrestrial habitats. This information is critical to identify, maintain, or restore a connected network of terrestrial and aquatic dispersal habitats for CGS. Knowledge of the long-term effects of forestry practices and the mitigating effects of buffer zones on CGS dispersal pathways is needed to prioritise habitat conservation measures. Obtaining information on salamander dispersal distance and reproductive behaviour is difficult or impossible using standard ecological tools, but with the advent of highly variable molecular markers such questions can be efficiently addressed. Although reduced genetic variation has been found in CGS within clear-cut sites compared with second and old-growth sites [2], the consequences of this for population dynamics at finer geographical scales is unstudied. By altering patterns of dispersal, habitat alteration and fragmentation through forest harvesting has the potential to disrupt the social organisation and mating system of CGS. Such habitat changes can lead to an increased chance of mating among relatives and elevated levels of inbreeding, resulting in population declines and increased risk of extinction. We aim to investigate the impact of fore ...
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