The population crash of an Atlantic seabird colony

An Atlantic seabird
© Dawn Osborn

The population crash of the Atlantic seabird, the Sooty Tern, has been linked to a poor diet. Industrial fishing and ocean warming are likely causes.

The new study by the University of Birmingham found that poor diet was the partial cause of the decline in this breed of Atlantic seabird. But does this evidence, which highlights the sensitivity of marine ecosystems, support the case for creating a protected reserve such as the Ascension Island Ocean Sanctuary (AIOS)?

The Sooty Tern

Sooty Terns are the most numerous seabird of tropical waters. They breed on Ascension Island. The Atlantic seabird population on Ascension Island has declined from several million during the middle of the last century to around a few hundred thousand today.

The causes of the Atlantic seabird population crash

Dr Jim Reynolds, the lead author, said: “We believe that a number of factors might influence the size of the breeding population of sooty terns on the island but we wanted to understand such factors in greater detail, resulting in causal explanations of the tern population decline over the past 60 years.”

Reynolds added: “There are several factors that could have led to the terns eating less fish. Part of the answer will lie in the rapid growth of industrial fishing for species like tuna over past decades – but ecosystems are complex, and other forms of global change, such as the warming of the oceans may also play a significant part in this story. As oceans warm, the movements of top predators and the fish on which they forage are changing, possibly making it more difficult for the terns to follow them in search of food.”

The wider significance of Atlantic seabirds

Dr Sam Weber, a co-author from the University of Exeter, explained: “Seabirds are often regarded as sensitive indicators of the health of marine ecosystems – or ‘sentinel species’ – so the findings of this study could be seen as a bellwether for broader ecological challenges facing the tropical Atlantic.”

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