Three keys to sockeye decline: study
Competition with pink salmon in the open ocean could be an important factor in the long-term decline of Fraser River sockeye salmon populations, according to a new study by SFU scientists and international colleagues.
Salmon farming along migration routes for juvenile Fraser River sockeye and warming sea temperatures could also play a role.
“None of these three factors can explain much of the declines in sockeye salmon by themselves,” says Brendan Connors, a post-doctoral fellow in SFU’s School of Resource and Environmental Management (REM).
But when considered in combination “they appear to play a very important role.”
Conners, lead author of the study published May 17 in the journal Conservation Letters, says increasing numbers of pink salmon across the North Pacific Ocean appear to be leading—directly or indirectly—to increasing competition for food with Fraser sockeye. The results are particularly evident in years when the juvenile sockeye salmon first migrate past large numbers of farmed salmon.
“It is possible that passing close to salmon farms early in their ocean life may weaken the ability of sockeye to compete for food with pink salmon in the open ocean,” says co-author Lawrence Dill.
“This could arise if sockeye pick up viruses, bacteria or parasites as they pass by salmon farms,” adds Dill, fellow of the Royal Society of Canada and professor emeritus of SFU Biological Sciences.
The study also found that increasing ocean temperature early in life reduces survival of juvenile sockeye, but the effect of warming oceans is weaker than increasing numbers of the competitively dominant pink salmon.
The SFU study is the first to consider simultaneously evidence related to multiple possible explanations for the declines in Fraser sockeye populations that began in the early 1990s.
Those declines triggered a $25-million federal judicial inquiry, the Cohen Commission, which held hearings in 2010 and 2011. Its final report is due by Sept. 30