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Arctic Report Card

Fisheries in the Bering Sea

J. Overland

NOAA, Pacific Marine Environmental Laboratory, Seattle, WA

October 5, 2009
Conditions in 2010 remain similar to those in 2009

With warm sea temperatures during 2000 to 2005, the Bering Sea was showing indications that Arctic species that require the presence of sea ice were being replaced by sub-Arctic species that don't require sea ice. This is shown schematically in the Figure F1 as a shift of the biological energy pathway that favors bottom animals (Benthic) to one favoring species that live closer to the ocean surface (Pelagic).

Bering Sea ice shifting from Benthic to Pelagic Pathway
 
Figure F1. Bering Sea Ice shifting from Benthic to Pelagic Pathway.

However since 2005, the Bering Sea has been relatively cold with more sea ice in the winter and spring than normal. In 2008 and 2009, the winter sea ice extent in the Bering Sea was at a near record maximum, not seen since the early 1970s, and ocean temperatures were at a near record minimum (Figure F2). Under these conditions, cold water species, such as Arctic cod, have returned toward the south. At present Bering Sea climate change and ecosystem response are more effectively characterized by natural variability with multiple years of warm and cold temperatures, than by an emerging global warming trend or by an influence from the major summer sea ice losses in the Arctic Ocean proper.

Southeast Bering Sea summer ocean bottom temperatures
 
Figure F2. Southeast Bering Sea summer ocean bottom temperatures. From NOAA, P. Stabeno.

Pollock are a major economic resource from the Bering Sea. Warm temperatures and lack of sea ice have tended to favor pollock in the recent past, creating one of highest biomass for any large marine ecosystem throughout the world. The biomass for pollock in the Bering Sea and the number of new fish added each year (called recruitment) are shown in Figure F3. In recent years pollock recruitment has been low, with the decrease beginning before the return of the cold temperatures (Figure F2). The Bering Sea pollock population is now in collapse. It is suggested that during the end of the warm period (2003-2005), the normal food supply for pollock shifted to less favorable species and that pollock predators, such as arrowtooth flounder, became well established. With the recent shift to a cold period, the favorable food supply for pollock returned to the Bering Sea, but it was less available due to the presence of sea ice. Further, the continued presence of arrowtooth flounder as a predator on pollock remained a negative factor.

Bering Sea Pollock
 
Figure F3. Bering Sea Pollock. Diamonds indicate biomass, and vertical bars indicate recruits to the population each year. From the NOAA/NMFS SAFE report.

Bering Sea temperatures respond both to global warming and large natural variability. While the Bering is cold at present we anticipate a swing back to average temperatures in the coming winter due to El Niño conditions. By 2020 or before, we anticipate a swing back to prolonged warm temperatures. This scenario would continue the negative impact on Arctic and bottom species, such as crab, while favoring sub-Arctic species such as salmon.

Reference

Stock Assessment and Fishery Evaluation Report (SAFE Report) from NOAA / AFSC.

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