Unusual conditions threaten Bering Sea ecosystem

During the summers of 1997 and 1998, scientists from the National Oceanic and Atmospheric Administration (NOAA) studying the Bering Sea observed extensive die-offs of seabirds, rare algal blooms, low salmon runs, warmer than usual ocean temperatures and altered ocean currents and atmospheric conditions.

Workshop participants at a NOAA international workshop in Seattle, Washington last year agreed on the importance of carrying out long-term, integrated research to determine any links between the unusual conditions and the Bering Sea’s substantial salmon and pollock resources.

The workshop, composed of 75 scientists, environmentalists, administrators, resource managers, native Alaskans, and representatives of the fishing industry, recommended the implementation of the recently written Draft Science Plan for the Bering Sea Ecosystem and the incorporation of traditional knowledge from native communities into the information available to research programs.

Participants also discussed how best to preserve the diverse populations of fish, marine mammals, and birds in the Sea’s highly variable environment.

The eastern Bering Sea provides almost half of the fish and shellfish caught in the US. Most of the catch comes from the continental shelf, a broad, shallow area larger than the state of California that borders Alaska’s western coast. Besides producing abundant fish and shellfish, the shelf also supports large numbers of resident and migratory birds and marine mammals.

The workshop heard that NOAA Fisheries surveys in 1997 and 1998 located fewer young-of-the-year pollock than in previous years. However, other studies conducted in 1998 suggest that young pollock were quite abundant but were found further onto the shelf than usual.

This could have been caused by the displacement of pollock larvae northeastward from their spawning area during windy conditions in spring 1998. However, the implications of these changes won’t be known for several years until the young pollock mature and are harvested.

“The warmest water temperatures ever recorded on the eastern Bering Sea shelf occurred during the summer of 1997,” said Phyllis Stabeno, an oceanographer at NOAA’s Seattle lab.

Extensive areas of milky, aquamarine water appeared over most of the shelf in 1997. The water’s unusual colour was caused by a massive bloom of coccolithophores (a type of non–toxic, microscopic marine plant). These blooms have never before been observed in the Bering Sea for extended periods.

The coccolithophores replaced the normal summer plankton community. This replacement made profound, but not well understood, effects on the rest of the food chain. Despite different atmospheric conditions in 1998, the bloom recurred.

Other recent changes in the ecosystem included unprecedented mortality of short-tailed shearwaters and unsuccessful reproduction rates for kittiwakes (both common seabirds frequenting the area during summer).

Salmon runs were far below expected levels. The fish were smaller than average, and traditional migratory patterns seemed altered. There was an unusual sighting of Pacific white-sided dolphins in Bristol Bay, and large numbers of baleen whales appeared on the shelf. Taken together, these events show how responsive the ecosystem is to climate and suggest that climate change would have a strong effect on the ecosystem.

Reports from the workshop are now available on the Internet for comment by US and world environmental scientists. A summary of the workshop is available on the Bering Sea and North Pacific Ocean web site. The Draft Science Plan for the Bering Sea Ecosystem is also available. A chat room will be incorporated into the website, as recommended by workshop participants.

For specific information, email Allen Macklin.

Picture Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center, by permission of the US Dept. of Commerce, NOAA, Pacific Marine Environmental Laboratory