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SAN DIEGO, California -- A recent study by a team of 30 leading scientists, published in Fisheries Oceanography, suggests that a single climate change event may be the missing link that helps explain why some populations of Steller sea lions are on the brink of extinction while others are thriving.
Nearly 30 years ago, an abrupt change in ocean conditions swept through the North Pacific Ocean. This shift in 1976-77 was a natural event in the ocean's climate cycle, but the effects are still felt today according to the recently released study led by Dr. Art Miller of the Scripps Institution of Oceanography, Dr. Andrew Trites of the Marine Mammal Research Unit at the University of British Columbia, and Dr. Herb Maschner at Idaho State University.
"We're finding that large natural shifts in ocean climate appear to reset the ecological time clock of the North Pacific Ocean," says Dr. Trites. "They unleash a domino series of events that ends with some species falling to low numbers and others rising to high numbers. Steller sea lions need the ocean to shift to cooler conditions if they are to recover, but global warming may prevent this from ever happening again and may permanently keep sea lions on the brink of extinction in Alaska."
Just east of Prince William Sound in the Gulf of Alaska sits an unassuming geographical feature known as Cape Suckling. Beginning in the 1980s, scientists began to observe a curious pattern among the populations of Steller sea lions living on either side of the Cape: those sea lions living to the west of Cape Suckling in the Gulf of Alaska and Aleutian Islands declined sharply while the eastern populations from Southeast Alaska to Oregon State began to grow and thrive. Many theories attempt to explain these curious events, ranging from epidemic disease to killer whale predation and shifts in prey abundance, but until now no single theory alone could adequately explain the timing, location, and the curious pattern of increase to the east and decline to the west.
Field research has uncovered that the waters to the west of the Cape are governed by a different set of currents than those to the east. New Steller sea lion research suggests that when ocean conditions shifted 30 years ago, a combination of changes in water temperatures and ocean currents altered the type of food available for western sea lions to predominately low-quality prey such as cod and pollock. Therefore, sea lions to the west were left with a mostly junk-food diet while those to the east kept their healthier menu of fattier fish such as herring and sand lance.
The authors suggest that eastern Steller sea lions won't be living the high life forever, however, as climate fluctuations will continue in the future. The study indicates that shifts in ocean temperatures and currents can have cascading impacts on ecosystems worldwide.