Fishing bycatch is 'junk food' for sea birds

Roger Highfield, The Telegraph 13 Feb 08;

The seven million tons of fisheries waste that marine birds feed on each year is "junk food" that could be starving their chicks.

Most have assumed that the vast volumes of waste generated by fleets would benefit scavenging birds such as albatrosses, petrels, large gulls and skuas and boost their populations.

But a detailed study on gannets, Morus capensis, concludes that the converse is true, and that the waste causes harm to the birds because it is low fat.

The team from Centre National de la Recherche Scientifique, Montpellier, with colleagues in South Africa and the University of Birmingham, studied the birds in the western cape of South Africa that fed in the Benguela current, where natural fish stocks have been depleted by overfishing and the effects of climate change.

The birds substitute their natural diet feed with the waste left by trawlers fishing for hake - some 45,000 trawls per year - and the team studied the impact on gannets in Malgas Island, where one fifth of the world gannet population breeds and around 27,000 trawls occur nearby.

"We showed that non-breeding gannets benefit from fishery wastes, but that most of their chicks die when they try to reproduce while feeding on such low-quality 'junk food'," says Dr David Gremillet, one of the team that did the study on the colony of around 160,000 birds, published in the Proceedings of the Royal Society, Biological Sciences.

"Fishery waste of the trawler fishery off South Africa only has half the calorific value of pelagic fish (the 'natural' prey of the birds, such as anchovy and sardine), which is much fatter," he says. "This is why gannet chicks fed with such lean food starve."

Marine management policies should not assume that fishery waste is beneficial to seabirds, and will automatically inflate their populations, they conclude.