Long-held assumptions about where salmon go during their years of swimming in the Pacific Ocean may need to be revised, according to Dick Beamish, a Canadian salmon researcher who helped organize two scientific expeditions into the Pacific Ocean.
For example, sockeye salmon have been caught in nets farther south than conventional wisdom would suggest, Beamish said, while fishing was hit-and-miss in the same area at different times, suggesting that pink and chum salmon were schooling more than expected.
The second International Gulf of Alaska Salmon Expedition ended Tuesday after nearly a month of travels, mostly off the coast of British Columbia. Findings at this point are fairly general, since key data have not yet been analyzed. In fact, conclusions from the first expedition a year ago are still being worked up by many researchers.
The two expeditions provide distinct pieces of a much larger puzzle about where the salmon go and what they eat during the majority of their lives, Beamish said.
“We need to do more science,” he said, “then it’s just a matter of time before we understand what the mechanisms are.”
The ocean is often described as a mysterious “black box” where little is known about the fate of salmon after they leave the inland streams and head out to sea. Yet the ocean is where most salmon spend the majority of their lives.
It has taken a little time for analysis, Beamish said, but it appears that the ages of the chum salmon caught in the ocean a year ago provided an early hint that last fall’s chum run would be lower than forecast by salmon managers — which is what occurred. While the expedition caught more chum this year, an age analysis is needed to determine whether more chum can be expected to come back this fall. (The majority of chum return when they reach 4 years old, with some 3-year-olds in the mix).
Last year, some of the fish were found to be unusually thin, but that was not observed this year, according to Beamish.
Indirectly, the coronavirus had a major effect on the expedition, including a revised route for the Pacific Legacy, a trawler rigged for scientific investigations. About midway through the cruise, all three American scientists on board left the ship and were not replaced out of concern that they might not be allowed to return home to Alaska amid the COVID-19 outbreak.
Six Canadian and three Russian scientists continued on, but the absence of Americans meant that the ship was not allowed to fish in U.S. waters off Alaska, Beamish said. Rather than spending time traveling farther off the coast, the ship returned to the same area that was fished during the first half of the expedition.
Surprisingly, the results were quite different, with far more pink and chum salmon caught during the first half of the expedition than in the same areas during the second half.
“Scientifically, to me that’s huge,” Beamish said. “Catching nothing is as relevant as catching something. It tells us that there had to be huge schools of pink and chum.”
That’s not what Russian researchers have seen during their years of sampling in the western Pacific Ocean, he said. There, the catches seem to be more uniform across broad areas.
By the way, the three Russians on the latest expedition were waylaid on their trip home because of a travel ban imposed by the Russian government during the COVID-19 outbreak. The three are waiting in Nanaimo, B.C., for approval to return to Russia.
“Nothing like these two expeditions (in the eastern Pacific) have ever been done before,” Beamish said. “The overwhelming conclusion, according to me, is that we need to see a bigger picture.”
While salmon returns to British Columbia and Japan are at all-time lows, Alaska and Russia are seeing unusually high numbers of sockeye. Clearly something is changing, and it could be related to global warming. To improve the overall picture, the expeditions not only sample for fish but also for temperature, ocean chemistry and other physical conditions as well as observing the entire food web — from plankton to the top predators. Few predators, however, have been seen during either expedition.
Funds for this year’s research cruise were raised privately with strong support coming from commercial fishing groups interested in understanding why salmon abundance may be high or low for any given year.
All the data from these expeditions are provided to anyone who wishes to study these problems, Beamish said, adding that he hopes that the best scientific minds will bring together other pieces of the puzzle to help explain what conditions are driving salmon populations. His working hypothesis is that salmon survival generally depends on getting enough food early in life.
An expedition being planned for next year by the North Pacific Anadromous Fish Commission could involve several ships in an effort improve the picture. The idea is to sample different parts of the ocean at the same time. The research is being conducted as part of the International Year of the Salmon.
Previous blog posts on this topic:
- March 11, 2020: Second Pacific salmon expedition gets a change to see the effects of cooler water
- March 22, 2019: Salmon expedition reports unexpected findings
- Feb. 15, 2019: Scientists from five countries seek out the secrets of salmon