After two winters of alarmingly scarce sea ice over Alaska’s Bering Sea, a NOAA ecosystem report showed qualified improvement last winter, which could bode for well for pollock, crab, and other fish stocks in one of the world’s most productive seafood regions.
Researchers were shocked after the winter of 2017/18, when for the first time on record there was little to no sea ice over the Bering Sea shelf. Climate change models had predicted this might happen – but not for decades into the future. It happened again in 2018/19.
Last winter (2019/20) saw sea ice extent return to historical norms in the Bering Sea, according to Elizabeth Siddon, a NOAA fishery research biologist and the lead editor of the Eastern Bering Sea Ecosystem Status Report.
“This is certainly more normal than the previous two years, which was all warm top to bottom. This may be a little bit of reprieve for species like pollock,” Siddon told SeafoodSource.
Ecosystem Status Reports, like the one Siddon oversees, are an important part of what fisheries managers consider when they set acceptable biological limits (ABC) and the subsequent total allowable catch (TAC) on species like pollock, the largest fishery in the U.S. by volume.
Siddon said that while the extent of the ice was encouraging, it was thin and quickly dissipated under warm southerly winds in the spring of 2020.
“This is a new, unusual feature in the progression and retreat of sea ice in the Bering Sea. My take home to the managers was that we can get into this false sense of security. Yes, it was average extent, but now we’ve added this dimension where we need to pay attention to the quality of the sea ice,” Siddon said.
The warmer temperatures that liquified the ice in the spring of 2020 led to a return to warm sea surface temperatures, which persisted through the fall of last year. The brief on the report states that this winter should be a middling one for ice.
“Modestly warm conditions over the Bering Sea shelf are predicted to result in a light sea ice year. Sea surface temperature projections in the tropical Pacific indicate a weak to moderate La Niña. This is predicted to bring some cooling to the eastern Bering Sea shelf into spring 2021,” the status report said.
Siddon explained that the importance of sea ice to Bering Sea fish stocks is two-fold. First, the sea ice is a platform for the growth of sea algae, which creates the base of the food web. The algae fuels the spring phytoplankton bloom, which then goes to zooplankton and on to fish before continuing all the way up through the food chain to mammals.
Second, sea ice creates the cold pool: a mass of cooler, fresh water that drops to ocean floor in the spring as the ice melts. This stratification – warm water on top and cold at the bottom – guides fish and provides spacial separation. It also serves an especially important refuge for juvenile pollock.
“Juvenile and adult pollock have better separation, so there’s a reprieve from predation when there’s a cold pool present,” Siddon said.
This year’s ecosystem monitoring report was complicated by the pandemic, with traditional bottom trawl surveys cancelled. This meant biologists were forced to get creative, piecing together information gathered from unmanned sail-drones, university partners, tribal governments, coastal community members, fishermen, and satellite-derived data.
In particular, Siddon said biologists tapped local knowledge to get data on seabirds, which function as samplers for the presence of fish and zooplankton.
“All the information that was gathered on seabirds this year was from local community and tribal members, and then we all collaborated – with Fish and Wildlife as the experts – to interpret what the community members were seeing in the region,” Siddon said.
In December, the North Pacific Fisheries Management Council dropped the 2021 pollock quota to 1.375 metric tons (MT) from last year’s quota of 1.425 MT. The pollock A season starts 20 January.
Photo courtesy of SandyShusterPhotography/Shutterstock
