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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Northwestern Salamander
Ambystoma gracile
Family: Ambystomatidae
COSEWIC status:- Not at Risk
- No Status
- Least Concern
Description
The Northwestern Salamander is large, heavy-bodied salamander that can grow up to 26 cm in total length. The dorsal colour is usually dark brown but is occasionally grey to black, the belly is light brown, and some individuals have yellow or white specs or flecking. This species has 10–12 costal groves, a broad head with protruding eyes, a laterally compressed tail with a glandular ridge along the top and large parotid glands behind the eyes. Neotenic individuals (see biology) tend to attain larger sizes than terrestrial adults. Aquatic larvae have feathery gills behind the head, legs (both front and back) and a tail fin and are brown, black or green with light flecking or mottling and dark blotches on the back.
Similar Species
This species can most easily be differentiated from other western salamander species by the uniform dark colour, large parotid glands and laterally compressed tail.
Distribution
Click for larger image
The Northwestern Salamander occurs along the West Coast in southern B.C., including Vancouver Island. Its distribution extends south into the United States along the coast as far south as central California.
Habitat
Northwestern Salamanders inhabit mature forest, typically within close proximity to breeding sites. Leaf litter and cover objects, such as logs and rocks, are important microhabitats where the salamanders forage and seek shelter. This species breeds in permanent or semi-permanent lakes, ponds, slow-flowing streams or wetlands that are fish-free. Northwestern Salamanders overwinter underground below the frost line in mammal burrows, root cavities and other underground crevices.
Biology
Northwestern Salamanders migrate to breeding sites on rainy nights in the early spring. After breeding, each female will attach a gelatinous mass of 30 to 270 eggs to submerged sticks or vegetation about a half metre to a meter below the surface of the water. The eggs hatch into aquatic larvae after about four to six weeks, depending on water temperature. Individuals spend one or two full years as larvae before transforming into terrestrial juveniles, and they take another one to two years to reach sexual maturity. Some individuals retain larval features as adults and remain aquatic their entire life (neoteny). The lifespan of this species is not known, although individuals can live for at least five years. Terrestrial individuals are highly fossorial and spend most of their time in underground burrows and cavities, but they are active above ground throughout the breeding season and during periods of rainy weather. Adults and juveniles eat insects, spiders, worms and other terrestrial invertebrates, while larvae prey on immature aquatic insects, microcrustaceans and tadpoles. When threatened, Northwestern Salamanders secrete a sticky toxin from pores on the tail and the parotid glands.
Threats
Habitat loss and fragmentation, primarily from urban development and logging, is a threat to this species in some parts of its Canadian range. Road mortality can be a significant threat to Ambystoma salamanders when roads bisect spring migration routes. Pollution, such as herbicides, agricultural effluent and road salt can be detrimental to salamanders since toxins are easily absorbed though their skin. The introduction of predatory sport fish into breeding habitats can quickly decimate local populations. Climate change and introduced pathogens pose potentially serious threats to Canadian salamanders.