Conservation and Population Recovery of Critically Endangered Oregon Spotted Frog
The main purpose of this project is to determine the hatching success of eggs of Oregon spotted frogs in locations pre- and post-BC hydro tower construction in the southwest corner of British Columbia.
To maintain a stable adult breeding population of Oregon spotted frogs, adequate reproduction is essential. This research will measure the number of egg masses oviposited and embryonic survivorship at the Oregon spotted frog habitat remaining in the wild, particularly pre and post monitoring at a site where hydro towers were newly erected in 2016. This information will be used by the Oregon Spotted frog Recovery team and other groups to ensure successful management and recovery of the species.
Photo: Christine Bishop
The Oregon Spotted Frog historic range is within California, Oregon, Washington and British Columbia within the Fraser Valley. This species prefers large wetlands with natural floodplains with clean flowing, water - now rare sights throughout the range of this species. Draining and diking of natural wetlands has destroyed the shallow natural floodplains the Oregon Spotted Frog requires for breeding across much of its range, and agricultural effluent contaminated with pesticides, manure and industrial waste is a problem in many other areas.
Breeding habitats have also been comprised by the introduction of exotic grasses that clog floodplains and overrun areas of shallow warm water this species requires for egg-laying. Oregon Spotted Frogs are also threatened by introduced Bullfrogs which can consume both adult frogs and tadpoles.
Given the small population of Oregon Spotted Frogs in Canada the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) designated R. pretiosa as an Endangered Species in 1999. This marked the first instance that COSEWIC applied a designation to a Canadian floral or faunal species in an emergency listing.
A Unique Lifecycle
The Oregon Spotted Frog is one of the very first frogs to breed in the spring. When the spring sun warms the water and water temperatures rise to 6oC in March, the male frogs gather together and make calls that sound like small hammers tapping on wood. The male and female frogs congregate in a single location where males are calling. They mate and the females tend to lay all their egg masses in a communal location which can incorporate as many as 100 egg masses in one location-50 000 eggs in a jelly covered mass of eggs 1 metre wide. Each female can lay as many as 500 or more eggs, not bad for a frog that is 8 cm long!
Laying their eggs in 'one basket' and in the early spring makes the eggs susceptible to freezing and predation, but the strategy is that even if only a few tadpoles make it, they will be the frogs with the longest period from spring to autumn growth and can bulk up their size and strength for survival over the winter and to avoid predators such as Bullfrogs, herons, fish, snakes and turtles. Tadpoles that survive to be adults still only live for 5 to 8 years. Males can start to breed at 2 years of age, females only start breeding once they are 3 years old.
