Dead murres, auklets washing ashore with little in their stomachs
Originally published Tuesday, April 3, 2007
West Coast seabirds are dying, apparently from a lack of food -- and some researchers think the phenomenon may be linked to global climate change.
This is the third year that scientists have found unusually large numbers of marine birds -- mainly common murres, but also rhinoceros auklets and tufted puffins -- washed up on beaches in California, Oregon and Washington. In 2005, the first year of the phenomenon, large numbers of Cassin's auklets also died.
Hannah Nevins, the coordinator for Moss Landing Marine Laboratories beach survey program, said 253 dead murres were recovered on 11 Monterey Bay beaches during the first week of March. During the past nine years, an average of nine dead birds were collected on the same beaches during the same week, she said.
About 180,000 breeding murres live along the West Coast, so it is unlikely the recent spate of deaths is enough to drastically harm the overall population.
"But if this continues for multiple years, then we could have real problems," Nevins said.
Most of the casualties were young birds that had just gone through their first winter.
"They were all in poor condition, and generally had empty stomachs," she said. "Either they were not finding food, or they were unable to capture the food they did find."
Bill Sydeman, the director of marine ecology at PRBO Conservation Science, a Bay Area group that specializes in avian research, said the deaths are worrisome because it now appears they are not isolated events. In the two past years, the winter deaths were followed by less successful breeding at the Farallon Islands, one of the West Coast's most productive seabird rookeries, he said.
"I would not be surprised to see the same thing this year," Sydeman said.
Sydeman said the trend appears to be linked to changes in the California Current -- a vast oceanic stream that delivers cold, nutrient-rich water from the Gulf of Alaska to the continental West Coast. Plankton thrives in this water, forming the basis of a food web that sustains everything from small fish to whales.
Fluctuations in the current in recent years appear to have resulted in regions of warmer water that support less plankton, Sydeman said. That can also reduce upwelling, a seasonal phenomenon that results in the replacement of warmer water along the Pacific Coast with cold, nutrient-laden offshore water.
Yet Howard Freeland, a research scientist with the Institute of Ocean Sciences in Sidney, British Columbia, said the California Current generally has remained strong during the past two years, though he said there have been some fluctuations.
But Julia Parrish, an associate professor in the school of aquatic and fisheries science at the University of Washington, said the North Pacific Ocean appears to be in major flux. During the past two years, she said, offshore upwelling did not begin off the continental Pacific Coast until summer, two months later than usual.
That was bad news for the birds because the warm water provided them little food during the height of the breeding season, Parrish said.
The once generally predictable North Pacific currents, she said, are "swinging like a pendulum." For example, in summer 2006, an unexpected "super upwelling" happened off the Oregon coast, sucking in vast quantities of abyssal water that was so low in oxygen that a temporary dead zone formed along the coast.
In typical years, said Parrish, very few horned puffins -- a bird that breeds in Alaska and winters offshore as far south as California -- are found dead on West Coast beaches.
"But during the last three years, we have found tens of them each season," she said. "That may not seem like a lot, but it is very significant, considering past statistics. More of them may be dying, or the currents may be shifting so that more are washed up on the beach instead of sinking. We don't know - but we do know things are changing, and that there are casualties."
Sydeman said the anomalies could be linked to global climate change.
"What's clear is that during the past decade, there's much more variability out there than there was during the preceding 40 years," he said.
"That probably causes some disability in the ecosystem to recover from human-caused impacts such as pollution, coastal development and fishing," he said.
Affected populations
For the third year in a row, large numbers of seabirds are dying off the California coast -- probably due to starvation. Scientists think fluctuating currents in the North Pacific are delaying or weakening the influx of cold, nutrient-rich water to the coastal areas of the western continental United States, resulting in less zooplankton and fewer small fish, the staple of marine birds.
Common murre: Duck-size, penguin-like birds that nest on rocky ledges along the California coast. They consume small fish and krill, and have suffered from population declines even before the recent die-offs.
Cassin's auklet: A small seabird that feeds heavily on krill and nests in burrows or crevices. They breed from Alaska to Baja, including the Farallones. Although these birds had a large die-off in 2005, scientists are also worried about them this year.
Rhinoceros auklet: Larger than the Cassin's auklet and smaller than the common murre, this bird is distinctive for a small "horn" on its bill. It eats krill and small fish and breeds largely in Alaska and northern British Columbia, though some are found year-round in Washington, Oregon and California.
Horned puffin: A distinctively marked bird that generally stays out to sea, the horned puffin subsists on small fish. Dead puffins seldom wash up on beaches; recent discoveries of horned puffin carcasses in Oregon have led to worries that mortality for the species may be increasing.
Source: Chronicle research
E-mail Glen Martin at glenmartin@sfchronicle.com.
No comments:
Post a Comment