Predators from seabirds to sharks may be helping gobble up the Fraser River’s declining sockeye salmon.
A new study tabled with the Cohen Commission concludes there’s no evidence any single predator can be blamed for the sockeye collapse.
But collectively they may be hurting stocks, especially when considered in concert with other threats.
“There is no sign of a smoking gun among the long list of potential predators of Fraser River sockeye salmon,” according to the technical report by UBC researchers.
“Instead, predation is more likely to be part of the cumulative threats that sockeye contend with.”
Salmon sharks, blue sharks and an obscure species called daggertooth are thought to have increased in number in the ocean off B.C., where they are target migrating sockeye.
Salmon sharks – which grow up to 2.6 metres and 220 kilograms – are among the likeliest suspected sockeye predators from a list of 26 species considered, Dr. Villy Christensen told the inquiry earlier this month.
An estimated 10,000 sharks may lurk in a “hot zone” in Queen Charlotte Sound near the southern tip of Haida Gwaii on the migration path of Fraser sockeye, the inquiry heard.
Death may also come from above – Caspian terns and double-crested cormorants feast on sockeye smolts in freshwater and those seabirds may be increasing in number.
Other prime suspects include the lamprey, blood-sucking eels that attack in the Fraser River and its estuary.
Various other salmon, trout and perch species can also eat juvenile sockeye in freshwater.
Sablefish, arrowtooth flounder and Humboldt squid also target sockeye, according to the study.
The researchers note once-abundant prey species like walleye pollock, Pacific cod, mackerel and hake have all declined and that may be forcing larger predators to eat more sockeye than before.
Seals, sea lions, killer whales and dolphins also eat sockeye, but the findings did not point to any of the marine mammals as a significant culprit.
Seals were once regularly culled or hunted but their populations have soared 10-fold since that practice ended in 1970.
The inquiry heard evidence that past culls of seals or sea lions have not necessarily succeeded in preserving salmon and can have unpredictable consequences.
A separate study commissioned by the inquiry looked at contaminants in the Fraser River from pulp mills, sewage discharges and other sources in the watershed.
More than 200 chemicals of concern were detected that may harm salmon in the river.
Selenium and dioxin-type compounds were found in salmon eggs at high levels likely to affect sockeye reproduction, the report found.
Elevated levels of metals and phenols were also found at several locations in the river, but were not likely to harm sockeye salmon.
The report concludes contaminant exposure did not likely trigger the collapse in sockeye numbers over the past 20 years, but may have contributed to the decline.
The Cohen commission was named after the collapse of the 2009 sockeye run, when just over a million fish returned, about a tenth the expected number. A huge return last year is thought by many experts to be an anomaly in a long-term decline.