Chaos in the Bering Sea ecosystem demands more surveys next year
Preliminary results of NOAA bottom trawl surveys in the Bering Sea say that similar surveys in the record warm waters of the Bering Sea need to be repeated next summer, according to fisheries research biologist Lyle Brit.
Unless hell freezes over, unlikely in the current climate conditions in the Arctic, Brit and his team will be trawling the bottom of the Bering Sea next summer and the project is already funded.
Scientists are coming to the end of the 2019 survey and the next should occur in 2021 according to the biennial schedule that would go 2021, 2023, and so forth. Not soon enough, according to Brit, who has worked for the Alaska Fisheries Science Center for the past 23 years and has served as chief scientist on vessels during survey operations.
Some species are where they have not been in the past. Some species have diminished in biomass or almost gone missing. Fish are on the move and so is their prey. Fish may be traveling to where they are in more comfortable waters to reproduce or drawn by prey availability.
“It’s disconcerting that some of our Arctic species are in such low abundance. We’re going to want to track that, but the thing I’m finding the most interesting with this is, that even though we have now three years of warm year data, is that they’re not consistent,” Brit said in a phone interview Sept. 26. “We’re actually seeing very different patterns of distribution to the fish and what they’re doing.”
The Bering Sea puts billions of dollars worth of seafood in markets for dinner tables and nourishes people in small coastal villages who depend heavily for subsistence on fish, shellfish and marine mammals from its waters.
Walleye pollock in the Northern Bering Sea is down by 11 percent from biomass estimate in 2017 of 1.32 million metric tons compared to this year’s 1.17 million metric tons.
Pacific cod shows actually a 30 percent increase in the Northern Bering Sea compared to 2017.
Biomass of Pacific cod jumped up to 368,000 metric tons. The Pacific cod may have come to stay awhile in the Northern Bering Sea where sampling found all ages of Pacific cod from very young to very old. However, in Southeast Bering Sea, the team is seeing very young and very old, but limited intermediate fish on the Southeast Bering Sea shelf.
One would think that lots of old fish in the Southern Bering Sea makes heavy fishing difficult as you take out the old fish. “It’s more that the old Pacific cod are not the desired size, commercially,” according to Brit. “Normally you would see things—animal behavior is no different in some ways than human behavior. Things like to try to get into a pattern or a rhythm. We’re not seeing that develop yet,” Brit said, “so I don’t know for sure yet what it means.”
Sea temperatures are hot. The Northern Bering Sea this summer had water at 20°C (or 68°F!)—the tipping point for salmon, according to Brit. The rivers are hot. The ocean is hot. Which is the cause, which is the effect? Record surface and bottom temperatures, as well as the disappearance of ice in the Bering Sea and Chukchi Sea are causing a big “Yikes!” among those monitoring the northern ecosystems.
Scientists are wondering why and how climate warming is impacting fish health and distribution. They are putting telemetry tags on cod to track the movement of cod all year to see if they are staying resident or moving south or west into Russia.
Marine researches are tracking prey as part of the ecosystem also. They are going through stomach contents of pollock and cod and other species collected this summer weighing and logging what they are dining upon.
This summer’s bottom trawl showed Arctic cod numbers were poor in the Bering Sea. Arctic cod is a cold water fish and a key component in the Arctic food web, feeding narwhal, belugas, ringed seals as well as seabirds and larger fish.
“Oddly enough, there were more Arctic cod in Southern Bering Sea this year than last year. We caught zero in 2018 and one fish in 2019,” Brit said. “That extrapolates to two metric tons for the Eastern Bering Sea shelf—not great.”
“In 2017 the biomass estimate in Northern Bering Sea was 4,140 metric tons of Arctic cod, down from what we saw in 2010,” he said. This year in the Northern Bering Sea, the estimate is 47 metric tons, like a 99 percent decrease in the Northern Bering Sea.
“It is not a mortality event—Arctic cod just staying where water is cooler,” Brit said.
“So, will warming of waters bring a shortage of Arctic cod to fish and other creatures who prefer them for prey? Maybe we will see Arctic cod when cooler weather comes and we start getting ice, not in summer,” Brit mused.
Researchers sampled in some fashion three warm years in the Northern Bering Sea in 2017, 2018 and 2019. The survey in 2018 was incomplete, a rapid response survey set of by changes observed in 2017.
“All three years have not been exactly the same in where fish are hanging out. The ecosystem is in flux,” Brit said. “Nothing has hit any kind of equilibrium to tell us where the fish want to be or why they are there.
Fish migrate for two reasons: to find food, other resources, or to reproduce. “We have been monitoring pollock, cod and other fish reproducing in the Northern Bering Sea area, or are they following food and going somewhere else to reproduce?” Brit asked.
The scientists are looking at what the fish are eating, but they move around. In 2017, the first time they saw pollock and Pacific cod in the Northern Bering Sea, the fish didn’t look healthy, he said. But then in 2018, researchers found the fish looked healthy and in 2019, they looked very healthy.
Besides collecting stomachs to see what is going on and how much the fish are eating, the researchers are also looking at livers as an index for pollock and cod condition. They look at the overall weight and size of the fish in relation to size of liver, Brit explained. Pollock and Pacific cod store a lot of fat (energy) in their livers. They are also using fat meters on the fish. The scientists are working with Alaska Dept. of Fish and Game and Norton Sound Economic Development Corp. is also interested in learning more. People in Savoonga on St. Lawrence Island and other communities are providing observations and local knowledge.
“There are a lot of players involved,” Brit said.