May 5, 2015 — Long-term research surveys enabled scientists to detect changes in the subarctic marine food web during a warm period. Over this time frame, large-bodied plankton were replaced by small-bodied plankton, a lower quality, less fat-rich food source for the fish and marine mammals that eat plankton. Other research studies by NOAA Fisheries showed that saffron cod have a much higher temperature tolerance than more fat-rich Arctic cod. If climate change results in sustained warmer water temperatures and a loss of sea ice, how will this affect the marine food web? Through their continued research, NOAA Fisheries and other scientists hope to find out.
The Relationship Between Walleye Pollock and Plankton
Since 1982, NOAA Fisheries’ Alaska Fisheries Science Center has been conducting regular surveys to monitor the health of the groundfish population. From 2004 to 2008, they observed that the abundance of adult pollock (age-3 fish) was declining. Fishery managers were concerned that the decline could negatively impact the more than $500 million per year commercial pollock fishery. However, after 2008 age-3 pollock abundance began increasing and is now back to historic levels. Even though pollock abundance rebounded, NOAA scientists were still curious about what had caused the temporary decline. As it turns out, sea ice coverage may have played a role.
NOAA Fisheries discovered this through their ongoing work with a team of scientists from various state and academic institutions who conduct regular surveys to study plankton, juvenile fish and oceanographic conditions such as water temperature and ocean acidity. These integrated ecosystem studies in collaboration with the University of Alaska Fairbanks, U.S. Fish and Wildlife Service (seabird observers), Alaska Department of Fish and Game, Bureau of Ocean and Energy Management, Arctic Yukon Kuskokwim Sustainable Salmon Initiative, Pacific Marine Environmental Laboratory, and the North Pacific Research Board have been ongoing in the eastern Bering Sea during August to October for more than 14 years and for two recent years farther north in the Chukchi Sea in August to September. During 2002 to 2005, scientists noted a warming trend. Sea temperatures were also 2°C to 4°C warmer than average. Sea ice didn’t extend into the southeastern Bering Sea in the spring. Over these four consecutive years in the spring, the species of plankton available to young pollock to feed on changed. Large-bodied plankton were replaced by small-bodied plankton which were not as rich in fat. This meant that young pollock were having to eat more to survive.