Sunday, April 4, 2010

Paradise drained. A frog's perspective.

Sumas Prairie, looking south to Vedder Mountain. Mount Baker (Washington State) behind.

One of the most endangered amphibians in Canada is Rana pretiosa, the Oregon Spotted Frog. I have previously posted about recent efforts to conserve it. The chief factor in the frog's precipitous decline over the past century or more has been habitat loss. It is the most aquatic of our ranid frogs, and lays its eggs communally in shallow, weedy wetlands, the sort found in low-lying areas prone to flooding.

It is likely, based on present and known historical breeding sites for R. pretiosa that the flat pan of rich farmland between Abbottsford and Chilliwack BC, known as the Sumas Prairie, contained prime habitat for this frog.

Until the early 1920s, this area contained a wildly undisciplined body of water called Sumas Lake, which during spring run-off could fill the valley south of the Fraser River between Sumas Mountain (the Canadian one; the Americans have one too), and Vedder Mountain, which is shared by Canada and the US. It would stretch from south of what is now the urbanized part of the City of Abbottsford to below the US border, and northeast across what is now the farmland of Chilliwack. Its extent changed from year to year, depending on amounts of winter-spring rain and mountain snowmelt.


Sumas Lake at maximum size. Yellow line is Canada-US border.

You can assume that Oregon Spotted Frogs would be very happy with this situation. As the lake receded, impermanent shallow, plant-filled ponds would remain in which to lay eggs.


Sumas Lake. Approximate area of permanent water.

A smaller, shallow lake was present year-round, its outline represented by the blue polygon above. The wetlands around its perimeter would have provided prime frog habitat.

In the late 19th and early 20th centuries, Euro-Canadians were their own flood, filling the region and recognizing its farming potential. It is difficult to farm in land that is frequently, not always predictably, flooded. It is also difficult to build transportation infrastructure across such a a landscape.

In 1919 it was decided the lake would be drained. In 1924 the Vedder Canal was excavated to channel the flow of the Vedder(Chilliwack) River, which enters the lowland from the north end of Vedder Mountain, across what was to become the Sumas Prairie to the Fraser River, the banks of which were diked. Floodwater from the south was flushed on through, and floodwater from the north was blocked. End of lake.


Sumas Prairie, sans lake. Vedder Canal runs diagonally through valley slightly right of centre.

Driving east across Sumas Prairie, approaching berm of Vedder Canal.

There are presently three known extant populations of Oregon Spotted Frog in Canada. One is in Aldergrove, about nine miles west of Abbottsford (and the once western end of flooded Sumas Lake) and five miles north of the border. It's not far off the left side of the map. Two more are near Agassiz, BC, which is on the north side of the Fraser River, 11 miles upstream from Chilliwack, not far off the right side of the map.

But they're far apart from each other.

The disparateness of these Canadian localities is characteristic of the distributions of the frog in Washington and Oregon, the only two states in which populations remain. (They formerly also occurred in California, but there are now extirpated). For innumerable reasons, significantly-sized wetlands and their associated ephemeral breeding habitats have been changed, lost. The distribution of the species has become fragmented, reducing or removing the chances for successful dispersal. A single catastrophic event, man-made or natural, can eliminate a population.

Certainly in 1919, there was little thought of conserving a pain-in-the-neck lake for the sake of a frog. The Sumas Prairie is one of Canada's most productive agricultural areas. It's not likely to be turned back into a lake any time soon.

There remains one small remnant of Sumas Lake. It's a small wetland, snug against the south side of Sumas Mountain. A few years ago a concerted effort was made to determine if Oregon Spotted Frogs occurred there. None were found.


Rana pretiosa. Photo courtesy of Mountain View Conservation and Breeding Centre Society .



Ref: Haycock, R.D. 2000. COSEWIC Status Report on the Oregon Spotted Frog Rana pretiosa in Canada.

3 comments:

Amber Coakley said...

It is amazing to me that we can and do alter such core functions of our planet as the flow of rivers and the elimination or creation of entire lakes. I hope that the Oregon spotted frog is alive and well, staying well hidden from people!

PSYL said...

Sad news for the frogs.

Thanks for the paper link and YouTube video. I'm a fan of Hayao Miyazaki's movies, they usually revolve around the topic of environmentalism.

Seabrooke said...

I'm always saddened by some of the things we did to our ecosystems before we "knew better" aka cared. (Even now, many people quite frankly still don't care a whit.) At least destruction of habitat for our own subsistence and survival I can understand (even if I don't agree), but things like the wanton slaughter of Passenger Pigeons, just to see who could kill the most, always makes me sick to think about.