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NOAA investigates threats to fish stocks in a warmer Bering Sea

  • Author: Hannah Colton
  • Updated: September 28, 2016
  • Published October 13, 2015

Researchers last week wrapped up a month-long cruise through the unusually warm waters of the Bering Sea, investigating how the second year of a warming pattern is affecting the ecosystem, including the nation's largest fishery, pollock.

Onboard the research vessel Oscar Dyson, a dozen scientists trading 12-hour shifts as the ship traced a grid pattern over the eastern Bering Sea Shelf, "...from Unimak Island up to about 60 degrees north," explained Janet Duffy-Anderson, a research biologist with NOAA's Alaska Fisheries Centers. Her co-lead on the Bering Sea project is Phyllis Stabeno, an oceanographer at NOAA's Pacific Marine Environmental Laboratory.

At each stop, the ship's researchers took water measurements -- temperature, salinity, nutrients – and biological samples, Stabeno explained.

"So you pull in your last net, fish and everything comes in and you begin sorting them," said Stabeno. "But the ship now is moving to the next station. It takes about two to three hours to get to the next station. … So everybody is madly running all their samples so they can be ready to do this again."

The goal of this daily hustle was to study the effects of an unusual phenomenon in the Bering Sea: Last year, the waters warmed dramatically after a seven-year cold spell.

This sudden warming bodes ill for some species, including walleye pollock. Duffy-Anderson says the last time there was an extended warm spell "... was between 2001 and 2006, and it was a very poor recruitment period for pollock."

The poor pollock return is due to a deficiency in the fish's food source. Duffy-Anderson says during warm years, the plankton or copepods that pollock eat are not as fatty and nutritious as plankton during cold years.

"And what we see is the fishes that eat that prey base are also in worse condition in warm years than in cold years," says Duffy-Anderson. "They're not getting this high-fat diet. They're getting kinda more like a potato chip diet, I guess."

This skimpy warm-water diet results in skinny pollock that have a hard time surviving the following winter. In contrast, pollock during a cold spell are eating fat-rich plankton.

"And so by the end of the summer they're short and fat and they can make it through the winter much more successfully than the long, skinny guys in warm years," explained Stabeno.

Duffy-Anderson says the warm years cause another disturbing trend: an increase in cannibalism among pollock.

"In the warm years, when the nutrient base is poor, they go after each other," she explained.

A drop in pollock survival may be the biggest economic impact of this new warm spell. But these scientists say the changes go much deeper than a single species.

Historically, Bering Sea temperatures have fluctuated randomly from year to year -- a warm year, followed by a cold, followed by a medium year and so on.

But over the last 15 years, those brief highs and lows have stretched out into five-, six-, seven-year periods.

Stabeno says this could signal a big change in the region's climate patterns.

"Has the Bering Sea shifted from this high year-to-year variability to a more (pattern) -- where you have groups of warm and groups of cold -- which would have profound impacts on the ecosystem if it happens? And we don't know if it is. Is this a random occurrence? Statistically, it's looking less and less like it."

With the warm mass of Pacific water known as the Blob and El Nino in the forecast, continued warm conditions are expected.

Duffy-Anderson and Stabeno say a "snapshot" of their data will be provided to NOAA fisheries managers and the North Pacific Fisheries Management Council within a month. A more thorough analysis of the data will be released in about a year.

Hannah Colton is a reporter and host at KDLG in Dillingham, where this story first appeared. It is republished here with permission.

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