A fossil heritage of salmon and other sporting fish that, on the West Coast, dates back to the Early Cenozoic 50 or 60 million years ago is hanging by a thread

A 30 cm long specimen of Eosalmo driftwoodensis from the Eocene of Smithers, B.C. This is the earliest known salmon. University of Alberta Collections. (Photo by BDEC (c).)

The 1990s witnessed ruinous declines in salmon stock throughout British Columbia. The massive Coho migrations on the Fraser and Skeena rivers were reduced to pitiful trickles. The Sockeye runs on the Wanuk River in central B.C. have all but disappeared and, in 1994, the spectacular Adams River Sockeye run came within a few hours of being fished into extinction. The story is depressingly similar on almost every river on the west coast -- salmon runs previously in the millions have been reduced to a couple of thousand or fewer. This catastrophe has ecologic and economic consequences, but also an important paleontological dimension.

Our friend and colleague Mark Wilson, a professor at the University of Alberta, described and named an Eocene fossil fish Eosalmo driftwoodensis in 1977 from Driftwood Creek near Smithers in British Columbia. This is the oldest known fossil of the family Salmonidae that includes salmon, trout, char, grayling and whitefish. Smithers is famous among anglers for the waterfall and gorge where it used to be possible to see enormous numbers of salmon and steelhead as they run up the Bulkley River. Near this waterfall, fishermen of the local first nation band netted the salmon as they mounted these falls on the edge of the town. At Driftwood Creek Eosalmo comes from beds that are about 50 million years old. Other Eosalmo specimens have been collected from rocks of the same age near Princeton and in the Republic area of Washington State.

Mark Wilson believes that Eosalmo, a fish as long as 30 cm, lived in lakes and rivers draining into the Pacific Ocean. Many of the salmonid species alive today in the same region of British Columbia migrate to the sea at a young age, and then return to fresh water as adults to spawn. However, the presence of an almost complete age range of this species in the ancient lake sediments near Smithers, including juveniles as small as 15 cm, suggests that the species did not migrate to the sea. If the young fishes went to the sea and only returned as much larger adults, the lake sediments should lack small and medium sized specimens of this fish. These fossil fish suggest that the ancestors of the salmon did not migrate to the sea, and this habit evolved relatively recently. Wilson also pointed out that Eosalmo driftwoodensis is an almost perfect morphological intermediate ("missing link") between the two subfamilies of the Salmonidae -- the Salmoninae (salmon, trout, and char) and the Thymallinae (grayling). This observation indicates that salmon evolved from a more grayling-like form.

Set of nodules preserving parts of land-locked Kokanee salmon from Pleistocene clay on the shore of Kamloops Lake. University College of the Cariboo Collections. (Photo by BDEC (c).)

Much younger salmon have been collected from the south shore of Kamloops Lake where they are found in lumpy concretions that weather out of Pleistocene clays. These fossil salmon belong to Oncorhynchus, the genus that includes both Pacific salmon and trout. The heads are small, and some possess the prominent hooked jaw characteristic of spawning salmon. Carbon-13 measurements of the bone collagen, however, indicate that these salmon never consumed protein from marine sources. It therefore appears that they are Kokanee, the landlocked and stunted variety of Sockeye. Radiocarbon dates suggest that these fossils are 15,000 to 18,000 years old and, as such, are the only Late Pleistocene salmon in North America.