Albatrosses Fly Around World After Mating, Tags Reveal
for National Geographic News
|January 13, 2005|
It is well known that albatrosses take an 18-month break between mating
seasons. Less clear has been where the globe-trotting birds go during
their year-and-a-half respite. That is until now.
A new study reveals that some albatrosses fly around the world once. Others twice. Still otherscall them relative homebodiesstick closer to their breeding grounds in the southern reaches of the Atlantic Ocean.
The research was conducted by British scientists, who developed special tags to track the seabirds. Their study, for the first time, lifts the fog on the migration routes of albatrosses between breeding seasons. It also provides conservationists with new information they hope can help divert the birds' rapid flight to extinction.
"This should lead to defining critical year-round habitat for [albatrosses for] the first time," said John Croxall, head of biological sciences at the British Antarctic Survey in Cambridge, England. Croxall led the study published in tomorrow's issue of the journal Science.
Albatrosses are the world's most threatened family of birds. The World Conservation Union, based in Geneva, Switzerland, lists 19 of 21 albatross species as globally threatened. Conservationists warn that unless urgent action is taken, the seabirds will be lost forever.
Albatrosses fall prey to longlines, baited hooks stretched for miles across the oceans by commercial fishing fleets. Intended to lure tuna, swordfish, and other creatures, fish bait on longlines is equally attractive to albatrosses.
The seabirds become unintentionally hooked and drown and become what's known as bycatch. In 2001 conservationists estimated that the world's longline fisheries kill 300,000 seabirds annually, of which at least a third are albatrosses.
Croxall, the study author, is keen to protect the seabirds. His protection plan seeks to provide fisheries managers with the information they need to prevent bycatch. "The idea is not to ban or to displace fishing, but to manage it more strictly," he said.
Euan Dunn, head of marine policy for the United Kingdom's Royal Society for the Protection of Birds, said that accurate information on the distribution of albatrosses at sea is key to implementing effective conservation steps.
"This [study] enables us to identify where the birds are most vulnerable and to safeguard their critical habitat," Dunn said.
The mating habits and habitats of breeding albatrosses have been well documented, since the seabirds tend to breed in a few well-studied areas. However, many species breed for only a few months every two years and spend the rest of their time at sea.
Until now, conservationists had scant data on where these non-breeding birds foraged.
But Croxall and his colleagues were able to track 22 out-of-breeding-season birds for about 18 months each. To do so, the researchers developed a new generation of small, lightweight recording devices, which they attached to the legs of gray-headed albatrosses (Thalassarche chrystostoma).
The tags were designed to last more than three years and to record the amount of light they receive. The devices, called light-level loggers, determine the time of local dawn and dusk each day. With this data, researchers are able to infer the bird's location to within a range of about 100 miles (160 kilometers).
The gray-headed albatross tracking results reveal that the birds reliably stick to one of three patterns: Some seabirds stayed close to their breeding grounds in the southern reaches of the Atlantic Ocean; others migrated to a specific region of the Indian Ocean; and a third group made at least one trip around the world in as little as 46 days.
Writing in Science, Croxall and his colleagues concluded that the finding "reinforces the message that protecting albatross and petrel species requires appropriate mitigation measures to be used in longline fisheries throughout all oceans south of 30 degrees [south latitude]."
Additionally the data shows that female gray-headed albatrosses are more likely to stick close to their breeding area. Males are more likely to make at least one trip around the world. Understanding the reason for this distinction will be the subject of future studies.
Croxall hopes that by identifying year-round critical habitat for the gray-headed albatrosswhich has seen its breeding population plummet from 100,000 to 50,000 over the last 20 yearsfishing fleets will know where to use methods that reduce bycatch.
A number of proven methods exist: To deter birds from areas of risk, streamer lines can be attached to fishing vessels. Pairs of streamers are suspended above the longline, creating an "alley" that albatrosses are reluctant to enter.
Weighted lines, which sink longline bait more quickly, also work.
Croxall said the right combination of bycatch-reducing measures will lower seabird mortality rates by 75 to 95 percent, depending on the type of fishery.
The biologist said employing such steps are preferable to banning commercial fishers from critical habitat: The latter "would only lead to the worse problem of pirate fishing in the same areas and more birds killed," Croxall said.
Dunn, of the Royal Society for the Protection of Birds, agreed. But he stressed that in extreme cases "it could be helpful to close certain critically important areas, perhaps only at certain times of the year."
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