Co-author of the study, Mr Jim Clohessy holding up a sea bass at the entrance to Cork Harbour.
Apr 05 2017 Posted: 09:19 IST

NUI Galway-led study finds that localised residency and inter-annual fidelity to coastal foraging areas may place sea bass at risk of local depletion

A collaboration between Irish researchers from NUI Galway, UCC and Cork Harbour Angling Hub, have become the first in the world to track the detailed movements of individual sea bass in Europe. The authors have found that sea bass in Cork Harbour were highly resident, remaining within one to three kilometres of where they were originally caught and tagged, a behaviour not known before this study. They also found that these localised fish returned to the same areas after their winter migration.

The study, published this week in Scientific Reports, was led and co-authored by Dr Tom Doyle from the Ryan Institute and MaREI Centre at NUI Galway, in close collaboration with researchers Mr Damien Haberlin, Mr Ashley Bennison and Dr Mark Jessopp from UCC’s MaREI Centre and expert angler, Jim Clohessy from Cork Harbour Angling Hub.

Sea bass is a large fish species only found in Irish and UK waters and south into the Mediterranean and along North Africa. It is a commercially important species as it fetches a high price on the markets compared to other fish species. Sea bass is also an important fish for recreational anglers and is worth up to €70 million to the Irish economy.

Despite very robust conservation measures in place in Ireland, sea bass populations in northern European waters have been declining since 2010, so much so that the EU has introduced a series of emergency measures to try and halt this decline. These include catch restrictions on various bass fisheries, a large closed area around Ireland and Celtic seas, and a limit to the amount of sea bass that recreational anglers can retain in a day (one fish). The International Council for the Exploration of our Seas (ICES) advised the EU Commission that there should be no catch of sea bass in 2017.

This study presents the first telemetry tracking movements of sea bass. Telemetry is the remote tracking of an animal using an electronic device (transmitter) and a series of listening posts (acoustic receivers), which were strategically placed all around Cork Harbour. The team used acoustic telemetry to track 30 individual fish for up to one year during 2013 to 2015 in the harbour. As the tagged fish swam around the harbour their movements were detected if they swam within 500 metres of a listening post. 

Speaking about the research, Dr Tom Doyle from the Ryan Institute at NUI Galway, said: “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’, but it also has important implications for the conservation of this species.”

Fish left the harbour in October and November and returned in May and June, accurately describing the timing of departure and return migrations. Remarkably, 93% of fish returned to Cork Harbour after their winter migration and 86% returned to the exact area they resided in before their migration, displaying high fidelity to these local areas. Given their longevity (fish can live up to 25 years) and the combination of inter-annual fidelity to localised foraging areas, sea bass may be very susceptible to local depletion.

Co-author of the study, Mr Jim Clohessy from Cork Harbour Angling Hub, said: “The marriage between science and angling in this study is fascinating. The results and some of the information coming out of this research has the potential to save the state a lot of money in terms of targeting their fisheries protection.”

Mr Damien Haberlin from UCC’s MaREI Centre, added: “It is really amazing that for many of our familiar marine fish we know very little about their movements beyond some very broad generalisations that they are found inshore during the summer months and during the winter they move offshore to reproduce. So in this context, our findings are very exciting. It’s really nice to have some detailed movement data on one of our most important marine fish species.”

The research was funded by ESB and Science Foundation Ireland (under MaREI Centre), with strong support from the local angling community in Cork Harbour, and in particular Richie Ryan and Andy Davies, who helped catch the fish to carry out the research.

To read the full paper in Scientific Reports visit: www.nature.com/articles/srep45841

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