Arctic Science Journeys
Radio Script
1997

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Warm water bad for birds
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STORY: The first sign that something was wrong in the North Pacific Ocean came in May when residents of Nunivak Island in far western Alaska began seeing dead murres and other seabirds wash ashore. Throughout July, fishermen reported hundreds of dead seabirds floating in the Bering Sea. Vivian Mendenhall is a biologist with the U.S. Fish and Wildlife Service in Anchorage.

MENDENHALL: "People started calling us. Some of them were villagers calling directly from their homes. Fishermen called from their homes or fishing vessels. Around that time we also started to get calls from Fish and Wildlife field stations and from wildlife refuges. It was a mixture of short-tailed shearwaters and black-legged kittiwakes. In July we started to get reports from the Bering Sea and that was entirely short-tailed shearwaters for quite a while."

By September, dead seabirds had washed ashore throughout the 1,500-mile-long Aleutian Island chain that stretches toward Russia. Mendenhall estimates the number of dead seabirds in the tens of thousands. Marine scientist George Hunt says that judging from what he's seen, the number appears reasonable. Hunt recently returned from the Bering Sea. He spoke from his office at the University of California Irvine.

HUNT: "In one area near the Pribilofs, near Saint Paul Island, I don't have the exact numbers in front of me, but I think we saw 20 or 30 dead shearwaters in the space of an hour or so. The normal thing that one would expect in a two- to three-week voyage would be to see one or two dead birds in the whole voyage."

Normally, shearwaters and other seabirds should be quite fat by now, having spent the summer gorging on prey in preparation for the long flight back to nesting grounds in Australia. But the birds George Hunt saw had lost nearly 20 percent of their body weight.

HUNT: "Their breast muscles, their flight muscles were diminished in size. It looked like their breastbone, or keel, was sticking out and the muscles were much smaller than what one would expect on a healthy bird about to start migration."

Fish and Wildlife Service laboratories in Wisconsin are studying more than 40 seabirds to determine cause of death. But from preliminary observations and past experience, Vivian Mendenhall says the cause seems clear.

MENDENHALL: "Die-offs like this occur once or twice each decade. So far all of the ones that have been investigated--a few of them very intensely--have been found to be due to starvation."

What changes occurred in the ocean to cause the birds to starve is of course the million dollar question. No one knows for sure, but some clues are emerging. For example, scientists know that it's been a very warm summer in the Bering Sea and the Gulf of Alaska. Some have pointed to El Niño, an unusually warm water current that occurs every few years off the coast of Chile. But scientists say the El Niño's warm water hasn't made its way to Alaska yet. Instead they point the finger skyward. Tom Weingartner is a marine scientist at the University of Alaska Fairbanks.

WEINGARTNER: "I think what that is related to is due to the fact that over this past summer we've had very mild wind conditions, and a lot of relatively clear conditions compared to most summers and springs. So there's been an abundance of sunshine and a reduction in the strength of the wind. So what the wind does is mix the ocean, and by mixing it takes colder water up from depth and mixes it with surface water, so the reduction of wind reduces the mixing and the increased clear weather results in warming."

Without wind, the ocean came to resemble a layer cake. Warm, stagnant water on top--nutrient-rich cold water below. George Hunt says his samples found nothing in the way of plankton and other nutrients in the upper 60 meters of water. Especially absent were euphausids, a zooplankton that is the major prey of shearwaters.

HUNT: "They look like micro-shrimp. Many people will have heard of krill or Antarctic krill which is the basis of the major Antarctic food chains. These are relatives of krill but they are much smaller than the Antarctic krill. They are clear in color to slightly pinkish because they carry some lipids, drops of oil, and when they are cooked in the stomach they turn pink. I don't know what they weigh but I think it's on the order of a tenth of a gram or so. When you see a bird that has eaten well, it may have 100 grams or more of euphausids packed into its stomach. We did not see birds that were eating that well."

Hunt speculates that euphausids and other prey species may have moved farther offshore to colder water, or were too deep in the water to be caught by surface-feeding birds. But at least one plankton species found the warm ocean to its liking. They're called Coccolithophorids. A type of algae, coccolithophorids underwent a population explosion.

HUNT: "These turn the water a pale milky green. Absolutely amazing. These coccolithophorids have a skeleton made up of calcium carbonate, and so the sunlight penetrates the water and reflects off this calcium carbonate. It's as though you took a green soup and stirred chalk into it."

Fortunately, by late September, things were beginning to get back to normal. Just as George Hunt left the Bering Sea, fall storms had started to bring nutrients back to the surface. Vivian Mendenhall of the Fish and Wildlife Service says that while the numbers of dead shearwaters were large, their overall population--estimated at 15 million--remains healthy.

OUTRO: For Arctic Science Journeys, this is Robert Hannon reporting from Fairbanks, Alaska.