Surveys and preliminary modeling for the 2018 Pacific cod stock assessment show that Pacific cod biomass is down substantially in the Gulf of Alaska, a NOAA Fisheries research biologist told the North Pacific Fishery Management Council during its fall meeting in Anchorage.
The data for the report by Steve Barbeaux of the Alaska Fisheries Science Center in Seattle only became available several days before the council meeting and the council’s Scientific and Statistical Committee expressed its appreciation of the rapid and extensive investigation that Barbeaux and others made, the SSC said.
The most salient survey result was a 71 percent reduction in the Gulf of Alaska bottom trawl survey Pacific cod biomass estimate from 2015 to 2017, a drop observed across the Gulf and particularly pronounced in the Central Gulf, Barbeaux told the SSC.
Barbeaux also presented additional data sets to the SSC that appeared to corroborate the trawl survey results, including a 53 percent drop in the National Martine Fisheries Service 2017 longline survey, and low estimates in recent years by the Alaska Department of Fish and Game large mesh trawl survey. Barbeaux said Pacific cod fishery data from 2017 indicated slower rates of catch accumulation and lower catch per unit effort over the season, at least in the central Gulf, compared to other recent years, and a change in depth distribution toward deeper waters.
Size information presented by Barbeaux from the trawl survey and Pacific cod fishery were consistent with a large drop in abundance of the 2012 year class, which has for several years been estimated to be an important component of the stock.
Additional reviews are upcoming, by the stock assessment team, the groundfish plan team, and the SSC, before the numbers are finalized, he said.
Meanwhile evidence indicates that the likely culprit is the Blob, that large mass of warm water in the Pacific Ocean that adversely impacts marine life.
Available temperature records indicate very warm temperatures across a broad range of depths from 2014 through 2016, temperatures associated with low forage fish amounts in Pacific cod diets, which likely were the result of low prey availability in 2015 and 2016, the report said.
In very warm temperatures, the cod would have needed to eat more in order to grow and survive, but there was less food in the water column available.
Barbeaux called it “the black swan effect,” a random and unexpected event.
“It has never happened before as far as we know,” he said. “We have had warm years before, but this Blob went on for three years, and throughout the entire water column across the Gulf of Alaska shelf, even in winter.”
In a situation where they would have needed to eat a lot more for three years straight, “they were in the worst condition we’ve seen, the lowest weight for a given length,” he said.
Barbeaux said that cod are a highly productive species, so if conditions are right they can bounce back fairly rapidly, but that still it would take at least three years for the cod to then become large enough to harvest.