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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