A second research cruise to study the winter travels of salmon in the Pacific Ocean got underway today, when 12 scientists from three countries left Victoria, B.C., aboard the trawler Pacific Legacy.

Researchers say they have learned a great deal from the first salmon cruise a year ago, when 21 scientists from five countries ventured out into the Pacific to take samples of fish and other marine life. The samples are being shared with dozens of biologists trying to piece together the complex food web that supports five species of salmon struggling to find food, escape predators and survive a variety of environmental threats.

Lower water temperatures this year should allow researchers to draw some conclusions about how salmon respond to changing ocean conditions, said Ed Farley, who heads the Ecosystem Monitoring and Assessment Program for NOAA’s Alaska Fisheries Science Center.

Much of last year’s cruise is being replicated this year to figure out where each species of salmon go under different ocean conditions and whether their overall numbers have increased or declined. As with last year, key questions surround the type of food that different salmon are eating and whether the amount of prey is adequate to keep them healthy, Ed told me.

Preliminary findings from last year’s research can be found on the website of the International Gulf of Alaska Expedition, including a slideshow (PDF 4.4 mb). Also check out the story I wrote last year after talking with Laurie Weitkamp of the Northwest Fisheries Science Center, a member of last year’s research team.

Chum salmon tend to feed on different prey species than do pink salmon, Ed noted, but sockeye and pinks have a good deal of overlap in what they eat. Chinook generally eat small fish, which are higher on the food web than what is consumed by the other salmon species. Examining the stomach contents of various fish provides insight into their recent diets.

Genetic analysis of the salmon caught in the trawl net should allow researchers to tell where the fish originated, including streams in Washington, Oregon and California as well as Canada, Alaska and even parts of Asia.

“We don’t know what is killing these fish in winter,” Ed noted. “It is hard to starve a fish, but based on other winter surveys … it appears that their fat content is not so good.”

One hypothesis is that salmon in better shape with higher fat stores may be able to go without eating and find places to avoid predators, including salmon sharks. But if the salmon need food to survive, they may be forced to venture into areas with increased prey but also more predators.

Another major question raised by some researchers is whether competition among salmon is causing problems for one or more species. Hatchery production of chum and pink salmon has reached an all-time high, and the effects of competition — especially during lean years — could be a factor in salmon survival.

Because the wide ocean holds so many life-or-death questions for salmon, researchers often call it the “black box” in the life cycle of the migrating fish.

Answers regarding salmon survival may be complex, Ed said, but a lot can be learned by studying the multitude of species caught in nets during these winter cruises. The International Gulf of Alaska Expedition, conducted as part of the International Year of the Salmon, is scheduled to end when the 121-foot Pacific Legacy returns to Victoria on April 4.

The 12 scientists on board are based in Canada, Russia and the United States, including two from the Alaska Fisheries Science Center, two from the Alaska Department of Fish and Game, and one from the Southern Regional Aquaculture Association.

Dick Beamish, a longtime Canadian salmon researcher who organized last year’s winter survey, helped raise more than $1.4 million for this year’s cruise. Money was provided by provincial and federal governments in Canada, the seafood industry as well as personal and business donations.

Plans are already underway for next year’s expedition, which will involve three to five vessels surveying areas where salmon migrate in various regions of the Pacific Ocean, from North America to Asia.

Twitter: @yearofthesalmon and #GoA2020