Living on Earth’s Cynthia Graber reports that some large predatory birds may start eating more small birds when fishing bycatch is reduced.
CURWOOD: Just ahead: finding the flow and the culprits that assault underground drinking water supplies. First, this Note on Emerging Science from Cynthia Graber.
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GRABER: Bycatch – unwanted fish caught accidentally and thrown back in the ocean – has been reduced in recent years. That’s because the fish catch is down in general, and because new technology has helped limit bycatch. Now, scientists say that the reduction in bycatch may have an unexpected effect. Predatory seabirds may turn to eating more small birds instead of waiting for a free lunch off the back of a fishing boat.
For example, predatory birds called great skuas had been on the decline a hundred years ago. Humans shot them for food and to keep them away from small livestock. But when factory fishing boats started throwing back huge amounts of unwanted fish, the birds followed the vessels, and their numbers rapidly increased.
The great skuas’ diet usually consists of fish and smaller birds. After they eat, skuas regurgitate small pellets of the indigestible parts of their meal. For the past 30 years, scientists have been collecting these pellets and analyzing skua meals, checking for feathers, or specific types of fish bones. They’ve compared this information against official information about levels of bycatch in any particular year.
In years when bycatch has been lower, fish intake has decreased, and the eating of small bird has gone up. This change in skua diet over the long-term could decrease the numbers of small birds such as the black-legged kittiwake, a type of gull that’s already on the decline. That’s this week’s Note on Emerging Science. I’m Cynthia Graber.
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