Fraser River

As Vancouver, B.C., watches Fraser River stocks of sockeye fail, the count of steelhead passing the Bonneville Dam in Vancouver, Wash., is soaring. And while low Alaskan Yukon runs of king and chum salmon predict a devastating winter for subsistence fishermen, salmon are even making a comeback in the Seine, as InvestigateWest reported last week. What differences could account for these drastic population changes?

Multiple environmental factors could be affecting populations. Warmer weather can heat up rivers, especially those overdrawn by humans, and discourage the cold-water-loving fish from heading upstream. Shifting ocean currents or other predator influences could be altering food sources. Pollutants from stormwater can accumulate in the fish. Overfishing can deplete numbers. Sea lice from farmed salmon could be transferring to wild salmon, weakening them and increasing the likelihood of succumbing to disease or predators. Even superb returns from previous years could be problematic, as too many fish spawning and then decomposing could produce excess bacteria, possibly resulting in disease.

Between 10.6 and 13 million sockeye salmon should be rushing up the Fraser River in British Columbia this summer, weaving in and out of Chinook runs, reports Mark Hume in the Globe and Mail. But only 1.7 million have returned so far, according to the Department of Fisheries and Oceans. What happened to the 9-million-plus missing fish?

Some believe sea lice are to blame. The tiny parasites live on fish at farms in the Strait of Georgia, an area the young sockeye pass through on their journey to the sea. Dr. Brian Riddell of the Pacific Salmon Foundation says sockeye infested with sea lice could be more vulnerable to predators or environmental conditions, but doubts the parasites are entirely responsible for the collapse of the species.

Researcher Alexandra Morton disagrees. After correctly forecasting a collapse of pink salmon due to sea lice in the Broughton Archipelago several years ago, she predicted in March of this year that a similar collapse could happen to sockeye on the Fraser.

The situation is especially dire for many tribes on the Fraser that depend on the salmon to get them through the winter. It's similar to the weak returns of king salmon on the Yukon and other Alaskan rivers – the fish just aren't there.

Other species of salmon are expected to return with healthy runs on the Fraser later this year, but with the unexpected sockeye collapse occurring only weeks after their runs appeared healthy, no one is making any predictions.

– Emily Linroth