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Of the tens of millions of fish caught globally every year, nearly 10 percent get chucked back into the ocean. Many animals, from fish to dolphins to seabirds, feed on these castoffs—a behavior that has biologists concerned that they are becoming reliant on the food source. In places like Europe’s North Sea, where fishing vessels dump fish waste with impunity, seabird populations are soaring to artificially—and unsustainably—inflated numbers, says Daniel Oro, a biologist at the Spanish National Research Council.
One nation, however, has resolved to minimize the amount of fish wasted at sea, and new research suggests its decades-old effort is influencing the ways seabirds forage.
Iceland, in 1984, became one of the first European nations to ban discarding fish waste at sea. (The European Union didn’t follow suit until 2015.) The ban first started with the cod fishery, reducing by-catch of undersized cod to boost declining stocks, and has since expanded to most other species. Icelandic fishers have adopted special mesh nets that allow small fish to escape. Inspections and surveillance have further shrunk the amount of discards.
The discard ban in Iceland offered researchers the perfect opportunity to investigate how seabirds fare without easy access to jettisoned fish. Bethany Clark, a graduate student studying seabird foraging at England’s University of Exeter, led a team that used GPS trackers to follow 36 northern gannets, a large plunge-diving seabird known to forage around fishing boats. Analyzing their movements, she translated specific patterns of speed and direction into particular behaviors: moving fast in a straight line meant the birds were traveling; moving in a twisting path at moderate speed meant they were foraging. Clark combined each bird’s GPS data with records on the locations of Icelandic fishing vessels to understand how the gannets adjusted their behavior around the boats.
The analysis revealed that northern gannets rarely switch from traveling to foraging when near a fishing vessel. “Their scavenging rate is very, very low,” says Clark.
There are several reasons why gannets seem to be ignoring fishing boats, says Clark. The birds aren’t flying very far to feed, which indicates there’s an abundance of local fish. With plenty of fish to go around, competition between the birds is also low.
Another potential reason is the discard ban. Though the researchers can’t say for certain that Iceland’s regulations have changed the birds’ behavior—they would need data from before 1984 to say for sure—they can be confident that these gannets behave differently from gannets elsewhere. In the Celtic Sea, for instance, gannets specialize in scavenging around fishing boats.
Oro, who was not part of the study, says Clark’s finding is surprising given that a hungry bird could still take advantage of any fish that are discarded by Icelandic boats. For birds, he says, this should be “a very easy resource.”
In Iceland, northern gannets seem unlikely to switch to these paltry discards any time soon. How birds adjust to the more recently imposed discard ban in the European Union remains a lingering question.