New research will assess the extent to which gannets rely on unwanted fish and offal thrown from fishing boats to successfully breed and raise their chicks. The European Union has proposed to ban the discarding of unwanted fish overboard from commercial boats. (Courtesy: Keith Hamer)

U. LEEDS (UK)—A proposed European Union ban on throwing unwanted fish overboard from commercial boats in the North Sea could put the survival of a sea bird at risk.

“The North Sea has undergone massive environmental changes over the last twenty years, which has put pressure on nearly all sea bird species,” explains Keith Hamer, from the University of Leeds Faculty of Biological Sciences.

“Only gannets have consistently bred successfully, partly because they can travel as far as South West Norway to feed, but also because they are able to target food thrown overboard by fishing boats.

“Although discards should be stopped to protect marine biodiversity, research is needed on the impact of a ban, so policy makers can understand the best way to implement it.”

Hamer will work with colleagues at the universities of Exeter and Plymouth to fit GPS tracker devices on breeding pairs of gannets from twelve colonies around the U.K.

The birds will also be fitted with miniaturized, fast-acting depth recorders, so the researchers can see how deep the birds dive and how they pursue prey underwater—both indicative of the kinds of food they are targeting.

Blood and feather samples from the gannets will be analyzed to determine their diet and their nests monitored to check how well they are feeding their chicks.

The data will be plotted against the location of fishing vessels in the North Sea to calculate how many of the birds are relying on discards to breed successfully.

Gannets are believed to have specialized feeding habits, with some relying heavily on discards while others focus on finding sand eels or diving for mackerel and herring. If this is so, a ban would disproportionately affect some breeding pairs, rather than impacting to a lesser degree on the whole colony.

Details of the research are published in the March issue of the Journal of Applied Ecology.

“We think gannets have different aptitudes and specialities and for some, that skill might be finding and following fishing boats,” explains Hamer.

“If our hypothesis is wrong and gannets are in fact generalists, with all of them making occasional use of discards, that has a different implication for policy.”

The European Union has been increasingly pressured to ban discards and legislation is likely in the near future, Hamer says.

“Although the long-term benefits of a ban will be positive, we need to accurately predict short-term impacts as well,” says Hamer.

“If gannets have specialized to the extent we believe, rather than cut off a crucial food source overnight, a gradual phasing in of the ban would allow them time to retrain to find food elsewhere.”

The three-year research project is funded by the Natural Environment Research Council.

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