Populations

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Historic range, historic and current occurrences of Oregon Spotted Frogs in the Fraser Valley.

A skinny male Oregon Spotted Frog basking in the early spring before breeding. Photo: Andy Wright

Historically, Oregon Spotted Frogs occurred on the west coast of North America from northern California to to southern British Columbia. They are no longer found in California, and are considered Endangered by both US and Canadian federal governments, and by state and provincial governments in Oregon, Washington and British Columbia. There are only six known populations of Oregon Spotted Frog in British Columbia – in Abbotsford, Chilliwack and in the District of Kent – with under 500 breeding females in all the populations combined.

We consider a ‘population’ a breeding group within a watershed that has no suitable aquatic connection to another group of frogs. For example, we consider all of the frogs in the Mountain Slough watershed (in Agassiz) to be one population, and those in Maria Slough to be another. These two populations would historically have been connected by waterways and shared floodplains but are now extremely unlikely to interbreed following development of rail-ways, highways, and dikes that keep the Fraser River floods at bay.

Land use changes since European settlers arrived in the Fraser Valley have resulted in the elimination of seasonal marshes and shallow wetlands in the Fraser Valley, with remnant populations of frogs squeezed into agricultural ditches or deeper pools and channels. As wetlands and floodplains were eliminated, connections between watersheds and waterways were lost, trapping the aquatic Oregon Spotted Frogs into linear stream systems that may not be able to sustain a population due to lack of permanent water, unsuitable habitat features, or too few frogs to maintain genetic integrity and survive environmental pressures. Some, however, have survived in these modified ecosystems, and it seems that with some careful planning, and a better understanding of the frogs’ needs and sensitivities, these frogs can survive (and maybe even thrive) in a shared-use agricultural landscape.

We believe that more populations may be out there – but they are hard to find! The most likely people to find new populations are environmental technicians and monitors working with farmers, municipalities and developers in stream channels. Two of the six known populations were found as recently as 2014, both by technicians who were working on fish research and ecological monitoring. By educating field technicians and frog-catching kids, we hope to identify more populations in the Fraser Valley, and improve our understanding of how people and frogs can coexist on the same landscape.