|
Alaska: Have scientists found the reason for the mysterious sea lion disappearance? |
| March 6, 2007 |
 | | For Alaska’s Steller sea lions, the difference between poverty and abundance is location and climate change. Photo: North Pacific Universities Marine Mammal Research Consortium |
|
There’s been a mysterious decline in some Alaskan Steller sea lion populations in the past 30 years. Have scientists finally found the answer? Perhaps…
An abrupt change in ocean conditions swept through the North Pacific Ocean in 1976-77. This shift was a natural event in the ocean's climate cycle, but its effects are still felt today, according to a recent study by a team of 30 leading scientists, published in Fisheries Oceanography.
This 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 in Alaska.
The great divide
Just east of Prince William Sound in the Gulf of Alaska sits the unassuming 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: They range 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 strange divide of increase to the east and decline to the west.
It comes down to ocean currents
Field research has now 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 mostly low-quality prey such as cod and pollock. Therefore, sea lions to the west were left with a junk-food diet while those to the east kept their healthier menu of fatty fishes such as herring and sand lance.
The authors suggest that the eastern Steller sea lions won’t be living the high life forever, however, since climate fluctuations will continue in the future.
“We’re finding that large natural shifts in ocean climate appear to reset the ecological time clock of the North Pacific Ocean,” says Dr. Andrew Trites of the University of British Columbia. “They unleash a domino series of events that ends with some species falling to low numbers and others rising to high numbers.”
According to Trites, the declining western populations of Steller sea lion 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 these sea lions on the brink of extinction in Alaska.
This study indicates that shifts in ocean temperatures and currents can have cascading impacts on ecosystems worldwide. It is 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.
Further details of this research by the North Pacific Universities Marine Mammal Research Consortium, which conducts some of its research at the Vancouver Aquarium, are available at the Consortium website.
| Source: Vancouver Aquarium, North Pacific Universities Marine Mammal Research |
|
