New research from Oregon State University finds that the number of Chinook salmon harvested along the West Coast has increased dramatically over the past forty years, with more fish now being taken by seals and orcas than by commercial and recreational fisheries.
The news shows the complexities of species management practices, as recovering sea lion, harbor seal and killer whale populations —all protected under the US Endangered Species Act— may now pose a threat to Chinook salmon, itself under protection.
Scientists estimate that there are only 80 members left of the southern resident population of orcas which live in waters off the coast of southern British Columbia and Washington State. Shipping traffic, environmental pollutants and declines in Chinook salmon (the orca’s main food source) are all to blame. But conservation efforts have had a positive impact, as the small population has actually seen an uptick over recent decades, from a low of just 71 animals counted in the 1970s.
Yet southern resident recovery efforts could be under threat from another source: harbor seals and sea lions, both of whom have their own protected species status and are now found to be consuming more salmon in terms of individual fish than are orcas.
A collaboration between federal, state and tribal scientists in the US, the new study found that between 1975 and 2015, the yearly biomass of Chinook salmon consumed by sea lions, harbor seals and orcas together shot up from 6,100 to 15,200 metric tonnes and from five to 31.5 million individual salmon.
During the same period, fisheries harvests declined from 16,400 to 9,600 metric tonnes, due to ever-tighter governmental restrictions. These findings show that despite conservation efforts, salmon stocks could be in danger from the rebounding predator species.
“We have been successful at restoring and improving the population status of protected marine mammals,” said Brandon Chasco, a doctoral candidate at Oregon State University and lead author of the study, in a press release. “But now we have the potential for protected seals and sea lions to be competing with protected killer whales, all of which consume protected chinook salmon.”
The conundrum speaks to both the successes of marine conservation, which worldwide began in earnest during the mid-20th century, and the sometimes difficult situations now being faced due to recovering populations. Some species of baleen whales, for example, have seen their populations bounce back to the point where commercial fisheries catches are feeling the impact, leaving some now calling for prescribed whale culling.
“The better we understand the different obstacles to salmon recovery, the better we can account for them as we plan and carry out recovery programs,” says Isaac Kaplan, fishery biologist at the US National Oceanic and Atmospheric Administration’s Fisheries’ Northwest Fisheries Science Center in Seattle, Washington. “Recovery efforts must account for all of these challenges.”
In BC, a coalition of fishermen this year received approval to release 220,000 Chinook salmon into the ocean off Vancouver Island, in effort to bump up salmon stocks and provide more fish for the orca population.
The new study is published in the journal Scientific Reports.