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Canadian Herpetological Society Société d'Herpétologie du Canada |
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Coastal Tailed Frog
Ascaphus truei
Family: Ascaphidae
COSEWIC status:- Special Concern
- Special Concern
- Least Concern
Description
The Coastal Tailed Frog is a small frog that is generally under 5 cm in body length, with males being smaller than females. Individuals are tan, reddish brown, brown, olive green or black, sometimes with light and dark blotching on the back. There is often a dark-edged light bar or triangle between the eyes, and some individuals have a dark stripe on the face. The belly is yellowish-white. Coastal Tailed Frogs have a vertical pupil, granular, bumpy skin, flattened hind toes with webbing, and they lack tympani (outer eardrums) and dorsolateral folds (folds of skin running down each side of the back). The “tail”, after which the species is named, is only present in males and is an extension of the cloaca that is used for copulation. Larvae (tadpoles) have a laterally compressed tail with a straight fin, a flattened body, a large, sucker-like mouth, and lack front legs (newly hatched tadpoles are legless). They are dark grey to dark brown and become lighter in colour, possibly with lighter flecks, as they age. The larvae can grow up to 6 cm in total length before metamorphosis. This species does not have a mating call.
Similar Species
The Coastal Tailed Frog may be confused with the Rocky Mountain Tailed Frog. However, the distributions of these two species do not overlap. Rocky Mountain Tailed Frogs have fine black speckling on the body and larvae have distinct light mottling, both of which are absent on the Coastal Tailed Frogs. Coastal Tailed Frog can be differentiated from all other Canadian Frogs based on the absence of the tympanum and the presence of the “tail” in the males.
Distribution
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This species has a limited Canadian distribution and occurs in the coastal mountains of B.C. south of Prince Rupert, as well as in the southernmost portion of the Cascade Mountains. In the United States, this species occurs along the West Coast south to northern California.
Habitat
Coastal Tailed Frogs inhabit and breed in clear, cool headwater streams in old growth coniferous forests. This species requires streams with clear, fast-flowing water, rocky bottoms, little aquatic vegetation, a dense forest canopy and low summer temperatures. Coastal Tailed Frogs are highly aquatic and adults are typically found in streams or in the surrounding forest understory. Coastal Tailed Frogs hibernate under rocks in unfrozen, snow-covered streams or underground in nearby terrestrial areas.
Biology
In Canada, Coastal Tailed Frogs hibernate during the winter and are active from April or early May until October. The breeding season generally occurs from late August to early October. This species has internal fertilization and the male uses it’s “tail” to transfer sperm directly into the female’s cloaca. Females lay eggs the following summer. The female lays 50–1300 eggs in clutches contain 30–80 eggs, which are attached to the underside of rocks in flowing water. The eggs are creamy white to yellowish, are surrounded by two clear jelly envelopes, and are enclosed in two gelatinous strings. The eggs develop slowly and hatch after 4–6 weeks, and the larvae do not undergo metamorphosis until they are 3–5 years of age in Canada. Coastal Tailed Frogs reach maturity about 4 years after metamorphosis (7–9 years after hatching) and can live up to 20 years. Adults and juveniles forage in aquatic and terrestrial habitats, though most terrestrial activity occurs at night. They eat a variety of small arthropods, particularly spiders. Coastal Tailed Frogs have small home ranges and typically do not move far from the streams that they inhabit.
Threats
Pollution, particularly sedimentation from forestry operations, cattle grazing or roads, is the most significant threat to this species in Canada. Logging damages terrestrial and aquatic habitats by removing forest cover and it can also alter hydrological regimes, all of which can cause local decline and extirpation. Road mortality is not a major issue, but it can occur in areas where roads bisect the species’ habitat. Pathogens, such as chytrid fungus and Ranavirus, can cause mass mortality of frog and toad populations; however, chytrid fungus does not appear to be present in Canadian Coastal Tailed Frog populations. Climate change also poses a threat to this species, particularly by increasing the frequency and severity of droughts and flood events.