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Giant Atlantic bluefin tuna usually visit the Irish coast in the summer, but marine heatwaves have made conditions uncomfortable.
Scientists who have been tracking their movements have found that they are avoiding Ireland and spending more time in higher latitudes where water temperatures are cooler.
The study, led by Grace McNicholas, is a doctoral research project in the School of Natural Sciences at Trinity College Dublin.
“These fish migrate thousands of kilometres every year and arrive along the Irish coast in both the summer and autumn,” she said.
“Our results provide early indications that fish are migrating further north than expected, and we believe this is due to ocean warming.”
Warmer sea temperatures are becoming more frequent, with last summer’s marine heatwave off the west coast of Ireland being classified as “ultra-extreme”.
At its peak, scientists recorded water temperatures as much as five degrees above normal.
Even a change of one or two degrees can greatly disrupt small marine life that depends on a stable environment, forcing organisms higher up the food chain to change their behavior as well.
Ms McNicholas said analysing recent events was crucial to determining future trends.
“It’s important to understand how climate change is changing the conditions that tuna encounter during their journey,” she said.
“It helps us predict future migration routes and ultimately guide management decisions for this ecologically and economically important species.”
Atlantic bluefin tuna can grow to more than four meters in length and weigh nearly one tonne, and can reach extremely high speeds when chasing prey, reaching up to 65 km/h.
They were once abundant in Irish waters, but overfishing has caused a dramatic decline in global numbers and are listed internationally as endangered.
They were completely wiped out from Ireland in the early 21st century, but conservation efforts over the past decade have seen them return to their traditional feeding grounds around Ireland. Experts fear they could disappear again if warming waters drive them away.
The study used tags and satellite tracking to record the movements of more than 50 tunas over a year.
Scientists from Stanford University and the University of California, the Irish Marine Institute and local anglers also assisted in the global exercise.
Dr Nick Payne, Assistant Professor in Trinity University’s School of Natural Sciences, emphasised the importance of the project.
“This study is yet another clear example of the dramatic impacts climate change is having on marine habitats,” he said.
“Atlantic bluefin tuna are a very important species for a number of reasons and it looks like they may move further north in the near future. This could have significant impacts on various coastal communities, including some in Ireland.”
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