European sea bass: the fish that is a home bird

European sea bass may look like fish and swim like fish, but they are also home birds. A new study to track the movement of the species has found that they are extraordinarily faithful to their home coastal patch. The fish are also "as charismatic as salmon", according to lead scientist Dr Tom Doyle of NUI Galway (NUIG), but far less adventurous.

A group of fish tagged in Cork harbour for the study, published in Scientific Reports, found that they were so parochial that even the east and west siders wouldn't mix.

The project involved anglers working with scientists from NUIG's Ryan Institute and University College Cork. It is the "first of its kind on the movements of the economically-important fish", Dr Doyle says.

European sea bass (Dicentrarchus labrax L) are known to inhabit coastal waters around Ireland, Britain and north Africa, and the Mediterranean during the summer months before migrating offshore to spawn and overwinter.

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They are long-lived, surviving up to 20 years, and feed on shore crabs, shrimp, juvenile plaice and flounder.

Stock depletion

Although they have been protected at sea for three decades here, due to stock depletion, some 11,000 anglers in Ireland target them on a catch and release basis. As the authors explain, comparatively little is known about the movements of individuals rather than the population of marine migratory fish.

The project team used acoustic telemetry to “tag” 30 fish and track the summer movements and seasonal migrations of individuals. They selected Cork harbour as a large tidally and estuarine-influenced coastal environment.

The researchers found that the vast majority of tagged sea bass stayed for 167 days on average in one place, and had a 93 per cent return rate to specific areas. Individual fish had “core” residential areas, swimming in a radius of 3km (1.8 miles) or less.

Same patch

“Knowing that sea bass return to the same little patch of coastal water each year is absolutely fascinating, and asks so many questions about how they navigate and recognise when they are ‘home’,”Dr Doyle says. “But it also has important implications for the conservation of this species.” Being so long-lived, and so parochial, means they are easy targets.

“Overfishing of these local populations may take tens of years or longer to recover as any recruitment to these coastal areas may be initially due to chance,” he says.

Ireland already has some robust measures, as there has been no commercial fishing allowed for sea bass within the 12-mile limit since 1990.

However, it may be important to examine protection measures for specific inshore areas, Dr Doyle says.

Co-authors were Damien Haberlin and Dr Mark Jessopp from UCC's MaREI Centre for Marine and Renewable Energy, and Jim Clohessy from Cork Angling Hub. The study was funded by the ESB and Science Foundation Ireland. Mr Clohessy said it represented a "phenomenal" marriage between science and angling.