Atlantic bluefin tuna with yellow floy tag visible in its back. Photo courtesy of Adrian Molloy.

Atlantic bluefin tuna (Thunnus thynnus)

The Atlantic bluefin tuna is distributed throughout the Atlantic Ocean in two main breeding populations. The eastern Atlantic stock spawns in the Mediterranean and is generally distributed between Norway and the Canary Isles, whereas the western Atlantic stock spawns in the Gulf of Mexico and is generally distributed between Newfoundland and Brazil. Bluefin are a highly migratory species that tends to range over thousands of kilometres between open ocean and coastal waters seasonally. In Irish waters, bluefin tuna appear in autumn, along the west and southwest coasts. 

Tunas are unusual among fish because they are warm-blooded and able to regulate their own body temperature. This enables them to quickly dive to depths of more than 1000m, subjecting them to exceptional differences in temperature in a short space of time. Bluefin are exceptionally powerful fish, capable of reaching speeds of 65 km per hour in their constant hunt for prey, especially schools of small fish or squid.

Bluefin are a long-lived species, with a life span of around 40 years. They grow to over 4m in length and can weigh up to 900 kg. Those recorded in Irish waters are typically around 2 m long. 

The conservation status of the Atlantic bluefin tuna is listed as endangered by the IUCN Red List. Although this high value species has suffered from overfishing, recent stock assessments have been more positive about bluefin abundance. ICCAT, the international conservation commission which regulates tuna fisheries, has ruled that Ireland may collect scientific data by allowing recreational angling to catch-and-release bluefin for tagging. Please visit our Tuna CHART webpage to read more about this citizen-science initiative in partnership with charter angling skippers.

Atlantic bluefin tuna breaching the water surface in Donegal Bay. Photo courtesy of David Morrissey.