Study reveals remarkably high Chinook salmon mortality in BC’s Strait of Georgia

By on March 3, 2015
Tumultuous natural conditions in the Strait of Georgia may be the root of remarkably low Chinook salmon survivability in recent years. (Credit: Charlie Llewellin, via Flickr/CC BY 2.0)

Chinook salmon are a major target of commercial and recreational anglers, but their popularity has contributed to the species’ decline in many places where the fish once thrived. Chinook fisheries in British Columbia’s Strait of Georgia essentially collapsed in the mid-1990s, dealing a serious blow to the province’s economy.

A study conducted in part by Fisheries and Oceans Canada tagged and tracked nearly 300 juvenile Chinook salmon to monitor their migration throughout the strait and its connected tributaries. Published online in the journal Transactions of the American Fisheries Society, the study revealed very low survival rates among fish leaving the strait, particularly between 2006 and 2008.

Researchers from Fisheries and Oceans Canada and the University of Tromsø in Norway tagged Coho salmon in 2006, before employing the same method on Chinook salmon in 2007 and 2008. Out of the 278 tagged specimens, only eight fish were detected leaving the strait. However, the researchers observed significant changes to population structure between spring and fall sampling periods, suggesting that most of the tagged fish remained and died in the strait.

Juvenile Chinook salmon rely on plankton and other invertebrates for early-life survival. (Credit: Roger Tabor / USFWS)

Juvenile Chinook salmon rely on plankton and other invertebrates for early-life survival. (Credit: Roger Tabor / USFWS)

An earlier study — also conducted by Fisheries and Oceans researcher Richard Beamish — points out that declines in Chinook survivability seem to coincide with similar trends among other salmon species in the area, as well as Pacific herring. The authors propose that poor wind and runoff conditions in 2006 and 2007 reduced nutrient mixing in the strait’s surface waters, harming plankton populations relied upon by juveniles of each species for sustenance. Diminishing availability of that common prey could explain the reduced migration rates of salmon from the Strait of Georgia during the study period.

While the precise cause of the Chinook’s decline in recent years remains unknown, the researchers contend that the overall health of any given brood-year is largely determined within the Strait of Georgia. Natural conditions in the strait are quite variable. That variability, combined with the critical needs of juvenile fish, makes an already trying life stage even more dangerous.

Top image: Tumultuous natural conditions in the Strait of Georgia may be the root of remarkably low Chinook salmon survivability in recent years. (Credit: Charlie Llewellin, via Flickr/CC BY 2.0)

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