Bluefin tuna off Britain and Ireland: Return of the giant tunny?

Abstract

General Intro: Over the late summer and autumn months, visitors to the western coasts of the British Isles might see frenzied splashing at the surface of the water. While dolphins, seals, ocean sunfish and basking sharks could be spotted, bluefin tuna are now being increasingly reported, bursting out the water whilst feeding on shoals of small silvery fish. Bluefin tuna are one of only a handful of fish (one out of a group of 30, out of ~25,000 fish species) that are “warm blooded”, or endothermic, meaning they can migrate to food-rich, but cold, regions like the northeast Atlantic. To stay warm, they need to feed often and on oil-rich food, such as herring, mackerel, sardines and sprat; digesting this food generates the metabolic heat they need to keep warm and affords them abilities that few fish have, including increased muscle performance, heightened senses and the ability to grow to sizes in excess of 3m long and 700kg – simply put they are a ‘superfish’. It is this constant need to feed that brings them to the waters of the northeast Atlantic between July and December and drives the frenzied feeding behaviour that makes them so exhilarating to watch in the wild. Despite their ‘superfish’ abilities, Atlantic bluefin tuna are the archetype for fisheries mis-management, and are still extensively fished despite stocks being below historical levels. Consequently, understanding them in order to successfully conserve this incredible species long into the future has been the topic of much dedicated research over the past century.