A draft of the latest look into the secret lives of Pacific salmon is now in print, and it echoes the key finding of the 2019 voyage of the R/V Professor Kaganovsky in the Year of the Salmon:
Humans have a lot to learn about salmon at sea.
In summarizing the latest research, the authors concede they are taking but baby steps into a void of knowledge.
“Overall, the 2020 expedition has made an important contribution of data furthered a unique collection of the GoA (Gulf of Alaska) high seas ecosystem components, including Pacific salmonids,” they wrote. “It will advance our knowledge on a poorly understood open ocean phase of Pacific salmon in the GoA during winter-spring.”
The findings of the March 11 to April 7 sailing of the Pacific Legacy are hard to compare to those of the Kaganovsky given that the eruption of the SARS-CoV-2 pandemic pushed the study area out of U.S. waters in the Gulf and into Canadian and far offshore waters.
Where you find them
As in 2019, however, researchers found a very fluid situation with both salmon and their prey scattered and shifting in numbers across vast distances.
On the third and fourth trawls of the expedition, the Legacy hit the salmon jackpot 300 to 400 miles off the coast near the latitude of Seattle far to the south in the Gulf. The third trawl there netted 165 chum salmon and 126 pinks, the biggest catch in 52 sets of the net. The fourth, a night-time tow just to the west of trawl 3, caught 96 coho and 10 chum.
Seventeen days later, the Legacy returned to the same area and caught nothing.
“An additional trawl was set 60 nautical miles south of these locations to test whether salmon had migrated south, however, no salmon were encountered there either,” the researchers reported. “Salmon were caught again only after moving 250 nautical miles northeast, suggesting high salmon migration activity during the winter-spring period.
“It is plausible that salmon schooling behavior may have contributed to differences in catches at the same location17 days apart,” the researchers added. “DNA analyses and underwater camera recordings could provide additional evidence to support or reject this hypothesis.”
That work is still in progress. Many scientists are curious as to whether those big catches of chums and pinks were fish from the U.S. Pacific Northwest, Canada or Alaska, the latter being by far the largest producer of pinks in the Gulf. The DNA tests will eventually reveal the origins of the fish.
The Kaganovsky last year found strangely few pinks, the most plentiful salmon in the Gulf. Scientists at the time theorized they might be south of the search zone in the Gulf’s warmer waters.
The fish were found far to the south this year, but the size of the catch came as a surprise given that odd-year pink salmon and even-year pink salmon are genetically distinct with the odd-year fish being historically far more plentiful.
“Interestingly, pink salmon abundance was significantly higher in 2020, despite their odd-even cycle dynamics suggesting the opposite,” the scientists observed. They suggested the low 2019 catches might have been reflected in low pink salmon returns along the West coast of North America, although Alaska was an exception.
The Alaska statewide catch of 129 million humpies, as they are often called, accounted for 62 percent of the entire state harvest, according to the Alaska Department of Fish and Game. The catch fell just 6 percent short of a state forecast for a harvest of 138 million.
But the pink return to the Alaska Panhandle was weak, and pink returns got weaker south along the coast. Whether the catches in the Gulf will be reflected in a boost in Lower 48 pink returns this summer, only time will tell.
The larger catch could also have been due to the shift in fishing zones caused by the pandemic. The “focus on the southern stations allowed a greater effort to try to locate abundances of pink salmon which were not in the northern area of the 2019 survey,” the researchers noted.
And they did find those fish, along with a lot of chums.
“Salmon distribution in 2020 was very irregular, with the majority of specimens (70 percent) being caught during two trawls,” they wrote. “Similar to the 2019 survey, chum salmon was the most abundant salmon species (234 fish, 29 percent of total salmon catch), followed by pink salmon (136 fish, 28 percent), and coho salmon (118 fish, 18 percent).
“Sockeye salmon was predominantly caught at northern stations with sea surface temperature less than 7 degrees Centigrade (45 degrees Fahrenheit). Juvenile and immature Chinook salmon were only caught at two stations in close proximity to
Vancouver Island. One steelhead trout was caught in set 8, approximately 600 nautical miles from the shore.
“Some of the most interesting preliminary results included high salmon catches, especially for fish in their first marine year, on the (continental) shelf:
- “In trawl 25 near Dixon Entrance, 34 salmon were caught: 7 pink salmon, 14 juvenile sockeye salmon, 19 juvenile chum salmon, and three, large maturing chum salmon.
- “In trawl 52, close to Vancouver Island, 26 salmon were caught – all Chinook salmon, 24 of which were juveniles.”
One key observation was that salmon caught on the continental shelf were generally in better condition than fish caught far at sea. Better condition is usually associated with access to better food supplies.
The study continued to add information to the portrait of an incredibly complicated ecosystem hidden beneath the sea. There is there a violent jungle teeming with predator and prey where every day is a battle for survival for every species.
Salmon sharks, daggertooth and long-snouted lancetfish, in particular, are constantly on the hunt for salmon, and the scientists found wounds from attacks on 3.4 percent of the salmon they handled.
“Wound types included both healed and open injuries, lesions, and abrasions such as those associated with sea lice,” they said.
Sea lice are a common salmon parasite and were found on fish in 75 percent of the trawls. Five percent of the salmon were described as suffering from sea lice infestations with the problem more common in sockeye, chum and Chinook salmon in their second year at sea.
Black spots, likely caused by a trematode fluke, were also found on 3.2 percent of the total salmon catch. Both kinds of parasites reduce the survival odds for the fish.
Abundances of prey, on the other hand, increase the odds of survival. The researchers found large numbers of smelt in some parts of the sea and squid in others.
“Squid are a major diet item of Pacific salmon in offshore waters and therefore are an important component of the growth and survival of salmon in high seas,” they noted. They are especially important for Chinook (king) and coho (salmon).
“Despite their importance, very little is known about squid in high seas with the winter period being particularly understudied. Gulf of Alaska winter expeditions of 2019 and 2020 are the first major studies of squid in the Gulf of Alaska in the winter,” the report noted.
One species of squid favored by coho salmon was caught in five trawls near the continental shelf and all those trawls also caught salmon. The species “was commonly observed in coho salmon stomachs in the 2020 expedition,” the report noted. “During the GOA 2019 expedition,” none of those squid were caught in trawls and were only sporadically seen in coho and Chinook stomachs.
The report contains a wealth of data and charts detailing catches of salmon and other species of fish, plankton densities, water temperatures at the surface and at depth, currents, salinity, dissolved oxygen and chlorophyll biomass, an indicator of the base productivity of the plants of the ocean.
Scientists could spend years trying to fit the pieces together to sort out the key factors affecting salmon abundance. Meanwhile, Canadian scientist Richard Beamish is already at work trying to raise the funds to put another research vessel to sea next spring.
“Winter is the least studied and thus least understood period in the life history of Pacific salmon, yet it is believed to be a time when their abundance is strongly affected,” Beamish argues. “There is a general understanding that ocean and climate conditions are major factors regulating salmon abundances. However, the reasons for increasing and decreasing trends in abundance are not known. Thus, there is a critical need to study Pacific salmon in winter in the open ocean to identify the fundamental mechanisms regulating salmon production and increase accuracy of forecasts.”
The state of Alaska, once a world leader in salmon research, has largely ignored issues in significant parts because of its success in producing salmon with a focus on spawning-ground management.
Alaska salmon returns are now at record numbers and annual, average harvests have risen in every decade since the 1970s. Returns to streams and rivers in Canada and the Lower 48 have generally trended in the opposite direction over those decades.