A proposed EU ban on throwing unwanted fish overboard from commercial boats could put one of the North Sea's most successful sea birds at risk, say researchers at the University of Leeds.
New research led by Dr Keith Hamer 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 North Sea has undergone massive environmental changes over the last twenty years, which has put pressure on nearly all sea bird species," said Dr Hamer, from 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."
Dr 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 UK. The gannets will also be fitted with miniaturised, 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 analysed 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.
The researchers believe that gannets may have specialised feeding habits, with some individuals relying heavily on discards while others focus on finding sand eels or diving for mackerel and herring. If this theory is correct, a ban would disproportionately affect some breeding pairs, rather than impacting to a lesser degree on the whole colony.
The research builds on more than 10 years of research on gannets by Dr Hamer in addition to work by research team members Stephen Votier in the Marine Biology & Ecology Research Centre, University of Plymouth, and Stuart Bearhop, University of Exeter, published this month in 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," said Dr 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."
There is increasing pressure on the EU to ban discards and legislation is likely in the near future. The three-year, £700,000 research project, funded by the Natural Environment Research Council (NERC), will help inform policy makers of how to ensure new regulations minimise potential impact on the gannets. It could also help the UK government decide where to impose marine protected areas in the North Sea.
"Although the long-term benefits of a ban will be positive, we need to accurately predict short-term impacts as well," says Dr Hamer. "If gannets have specialised 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."
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