Scientists find dramatic increase in pollock in Northern Bering Sea
Three researchers from the NOAA Alaska Fisheries Science Center completed a trawl survey of the Northern Bering Sea in 2017 and found a dramatic increase in pollock. The valuable fish normally associated with more southern latitudes grew in biomass from 20,972 metric tons in 2010, the year of the last trawl survey, to 1,312,620 tons this year.
That’s a 6,157 percent increase.
“We couldn’t believe what we were seeing and had to run the numbers five times,” said Bob Lauth, chief scientist of the research survey. “In 2010 there wasn’t a heck of a lot of pollock in the Northern Bering Sea.
“They were right along the edge of the Russian American border in very high densities,” said Lauth.
Lauth and two other fish biologists involved in the survey were in Nome to talk with local people about their findings. He gave a lecture at the UAF Northwest campus in Nome, part of the Strait Science series of lectures sponsored by the university and Alaska Sea Grant. Jeff Napp is administrator for NOAA’s Resource Assessment and Conservation Engineering program, known by its acronym RACE and he accompanied Lauth. Lyle Britt is the survey coordinator and also a fish biologist.
Alaska pollock has been called be “the largest remaining source of palatable fish in the world.” In terms of total catch it is the world’s second most important fish. In the Alaska economy its value is second only to salmon.
The Northern Bering Sea Groundfish and Crab Trawl Survey, funding available, is planned for every two years. It is a fundamental part of the Alaska Fisheries Science Center’s LOSI program, short for Loss of Sea Ice Research Plan. LOSI was organized to study the impact of diminished sea ice on marine ecosystems.
“This all started in the mid-2000s when people were concerned about the warming taking place in the Bering Sea,” said Lauth. “They got together and put together a research plan because they were concerned about what the loss of sea ice was going to have on the whole ecosystem. So this has been focused since the very start on what’s going to happen if this plays out.”
The survey collects data on everything that comes up in the bottom trawl. The objective is to create a comparison of what the ecosystem looks like compared to what it looked like in 2010.
Where the giant increase in pollock came from the scientists don’t know.
“They could have come from the west, they could have come up as larvae and grown up here. We don’t know that they’re actually migrating and then staying. That’s one of the things we need to find out by doing these multiple years of sampling,” said Jeff Napp.
Genetic analysis of the fish can determine where the stocks come from. They could be coming from off Russia’s Kamchatka coast.
“We haven’t seen an increase in the Pollock numbers,” said local fisherman Phil Pryzmont, who attended the lecture at UAF. “It’s not like we’re seeing more pollock every year. This year there’s pollock everywhere. We’ve always had pollock. I’ll be real curious to see what your future surveys show. This didn’t feel like a trend, it felt like an anomaly.”
“Water temperature has something to do with it,” said Lauth “We don’t know what the environmental drivers are. There must be food, there must be a trail for them to move. They can come from different directions. We don’t know where they came from or where they’re going. It may be an anomalous event. But we just don’t know. The net trend in the Arctic and the near Arctic is a warming trend. It’s the new normal. This may be an anomaly but if it’s a temperature induced anomaly and if the trend is going to keep being warm we better hope we keep doing these surveys every two years.”
“In 2012 in both the Gulf of Alaska and the Bering Sea there was a huge year class of Pollock,” said Jeff Napp. “And they succeeded in both places. And those might also be some of those fish up here in the north. Why they all survived we don’t know. We need to find out what happened in that year that made such a great year class for pollock.”
Pollock eat krill and they are cannibalistic. The large numbers of them eating plankton will affect the food web. Jellyfish increased by 405 percent and they also eat krill. The presence of the two species is changing the food web dynamic because they’re hitting what’s in the water column.
“Just having those two animals in the Northern Bering Sea is going to impact the whole food web,” said Lauth.
“This survey is going to be a real wake-up call and people are going to be talking about it,” said Lauth.