Bluefin Tuna

By Sarah Ward

Living Seas Officer

In September, officers at the Sussex IFCA were surprised to find an Atlantic Bluefin Tuna (Thunnus thynnus) which had washed up on the shores of Chichester Harbour. Although the fish was not alive, samples and examination by the officers suggested it had only recently died, meaning it had likely found its own way to the region, rather than having simply drifted in on the tide. Having been absent from UK waters for a long time, recent surveys and anecdotal sightings suggest that the species may be starting to return – that said, sightings tend to be in western waters so an individual this far east is still highly unusual.

Bluefin are the largest of the tunas, at around 2m in length and weighing 250 kilograms on average. Tuna have been eaten by humans for centuries, though their popularity grew internationally around the 1970s, particularly in Japan where their meat is sought-after for sushi and sashimi. A fish once sold for the huge sum of $1.75million! Driven by the high price of sales, the commercial fishing industry developed and refined techniques to locate and catch the species: this caused stocks to diminish and conservation efforts worldwide to protect the species, which is now listed as ‘endangered’ on the IUCN Redlist. Although management is in place internationally to help alliviate the pressure on tuna, the high market value is a strong incentive for illegal fishing and stocks continue to be relatively low.

Tuna are indeed an important source of food, but their importance doesn’t end there. As top predators, they play a significant role in the ocean food web. Adult bluefins are only eaten by very large animals, such as toothed whales and some sharks. Bluefin are slow growing: they aren’t mature to reproduce until around eight years of age. Adults live on average to 15 years of age, although older individuals of up to 35 years old have been recorded!

Opinion on the long-term sustainability of Bluefin Tuna is somewhat mixed: a Japanese long-line fishery gained MSC accreditation earlier this year (the blue tick you see on some fish products), however the Marine Conservation Society suggest avoiding all Bluefin Tuna products. Other tuna species, such as Albacore or Yellowfin, are often a more sustainable choice, particularly those which have been caught by pole-and-line.