Forget the distribution charts: ask a fisherman
Scientists have launched the 2019 Northern Bering Sea survey as part of the NOAA Alaska Fisheries Science Center’s plan to study impacts of receding sea ice on the marine ecosystem.
Dr. Lyle Britt, research scientist, has been with the Center for 23 years. He leads a group of scientist on bottom trawl surveys in the Southeast Bering Sea, SEBS for short, and Northern Bering Sea, NBS for short.
Britt came ashore off a research vessel at the end of the SEBS survey to share past survey findings and whet the appetites of local attendees at Strait Science for results of both 2019 surveys after the data has been worked through and he returns to Nome in November.
Nome people have seen Britt and heard his reports over the past three years because of dramatic conditions observed in northern waters in the Bering Sea.
Year 2010 is the base year for comparisons in subsequent surveys of the NBS. Alaska Fisheries Science Center decided to survey NBS every two years to accomplish a time series to track changes and impacts from climate warming.
However, startling findings in the 2017 Bering Sea surveys brought the team back to the area for an unscheduled rapid response survey in 2018. They found the NBS a hot spot to investigate impacts of warming ocean waters and loss of sea ice. The rapid response survey was conducted in response to data on warmer than average sea floor water temperatures and changes in patterns of fish and invertebrate distribution, coupled with reports from Northern Bering Sea communities citing bird die-offs, warmer waters, marine mammal strandings and sightings of unusual invertebrates and fish—salmon sharks, for example.
Last year the scientists found that the shrinking “cold pool,” a thermal barrier affecting distribution of fish in the North and South Bering Sea, had almost totally been erased by warmer sea bottom temperatures.
NOAA Fisheries scientists doing their annual trawl survey of the southern Bering Sea ecosystem survey found unprecedented conditions—warm ocean temperatures and significant changes in the cod and pollock numbers and conditions. As a result, they received emergency funding to unexpectedly bring their trawl survey north from St. Matthew Island to Diomede Island to investigate. They found a shocking lack of the colder ocean waters that separate the northern and southern Bering Sea marine ecosystems. The thermal curtain is another expression for cold pool that acts as a barrier to keep some species—pollock and Pacific cod, for example, from migrating across the eastern Bering Sea shelf and northward toward the Bering Strait. They are crediting some potentially big changes in fish species distribution to the disappearance of a “cold pool” within the Bering Sea south of St. Lawrence Island. The cold pool is created by super-cooled briny water made from salt leaking from winter sea ice and dropping to the seafloor. This annual thermal barrier typically keeps the fishes of the southern Bering Sea in their preferred warmer water. After many years of diminishing sea ice, the past winter of 2017 was unprecedented with near open water conditions throughout the winter months. It seemed the extended open water season in 2017 was long enough to make a big difference.
As in years 2010, 2017 and 2018, Britt and the team will save, weigh, and analyze all the fish taken aboard the boats when they drag their bottom trawl net at 20 by 20 nautical mile survey stations. Scientists use the trawl data to estimate relative abundance, population biomass, population numbers and population abundance for size class for measured species.
Commercial and subsistence fishers are awaiting the results to see if the fish distribution has changed since last summer. What has happened with the cold pool? Have the Pacific cod remained in large numbers? Did the walleye pollock maintain their 2018 biomass through the 2018-2019 winter?
Members of the Howard Farley Sr. family fishing business who have decades of experience in Northern Bering Sea and Norton Sound waters, attended the Strait Science session.
Howard and son Harvey Farley said the number of Pacific cod pulled up in their crab traps has increased dramatically.
When they were crabbing near Sledge Island, three miles from town from about 2003 to 2009, “we kept records. We'd write down cod caught in the pot, or halibut, or anything else when you look back at our records. Maybe in a season we’d catch 50 cod; that’d be a lot in one season,” Harvey Farley said. Based on crab migration and length of seasons, the Farleys moved their operation waters in front of Nome, where they would see only a couple cod per season, he added. The family still keeps records.
While crabbing in Norton Sound offshore Nome around 2009, they would see a few cod in a season, Harvey Farley said.
However, “in 2017 when we had that warming spell, we’re catching cod in every pot, about two, three, maybe five,” he said, “and they were two to three feet long.”
The Farleys wondered how the large cod got their big heads through the small opening in their crab pots.
“They would turn sideways and wiggle in there?” Harvey asked. “Yep, they love crab!
“In 2017 when we pulled our pots from the middle of Norton Sound—I had a good year—we had cod so big they outnumbered the crab. We’re pulling up empty pots and we’re seeing cod circling the pots. I said ‘Sharks!’ They were three feet long! Circling and waiting for the bait to come out of the crab pots,” Harvey continued. This season they found pollock inside of Pacific cod, he said.
Cod will pretty much eat whatever they can get into their mouths, Britt interjected.
Britt had talked to longliners off St. Lawrence Island this year. They were doing well with halibut, but even better with cod, he said.
Britt wanted to talk more with the Farleys’ he said, because his program had data only for the years they had surveyed. They had seen hints of such incursions of fish (like cod and pollock into the NBS) in the southern Bering Sea that they were trying to validate.
“So of you had historical records of when you caught cod and when you didn’t, we might be able to do something like that,” Brit said. Marine scientists consistently acknowledge they depend on community members’ experience and reports to augment data.
Cod were eating whole crab, Howard Farley Sr. said.
On their sonar, the Farleys had seen crab pyramids 15 to 20 feet high, with cod circling them, they said. They had seen two in a row, a rare sight, Howard said.
Pyramids? Those are when small crabs pile on top of one another to escape predators, Howard Farley explained.
Howard Farley Sr. was elated finding out that Britt and team would return to Strait Science in November with crab data.
“Great, great!” he said. We want to hear it first hand.”
In the 2018 NBS survey, scientists found in comparison with numbers from 2010, an increase in Pacific cod by about 2,000 percent and an astounding 6,000 percent increase in pollock.
Northern rock sole had increased over 500 percent. On the other hand, cooler water fish had decreased: arctic cod by 100 percent; saffron cod by 11 percent; and snow crab by 45 percent.
Citizen scientists can track the 2019 NBS survey online at www.fisheries.noaa.gov
With records being smashed as concerns bottom and surface water temperatures as well as a drastic loss of sea ice in the Bering Sea region, there is keen interest in information Lyle Britt will bring back to Nome in November.
Strait Science is sponsored by Alaska Sea Grant and University of Alaska Fairbanks.