Recently I stopped eating tuna and feeding animals any food with traces of it, due to this reason.
[quote]Tuna stocks in the world’s seas have more than halved in the past 50 years, with overfishing pushing many exotic varieties to dangerously low levels.
The rising popularity of sushi has been cited as one of the factors for declining numbers, with many tuna species now listed as either endangered or critically endangered.
Over-fishing of the fish, especially of the rare bluefin, bigeye and yellowfin varieties – which are prized as delicacies – is now ‘jeopardising their long-term sustainability’.
Researchers studied tuna and mackerel levels in the Atlantic, Pacific and Indian oceans between 1954 and 2006.
Maria Juan-Jorda, from A Coruna University in Spain, said: ‘Populations have declined, on average, by 60 per cent over the past half century, but the decline in the total adult biomass is lower (52 per cent), driven by a few abundant populations.
'The steepest declines are exhibited by two distinct groups: the largest, longest lived, highest value temperate tunas and the smaller, short-lived mackerels, both with most of their populations being over-exploited.
‘The remaining populations, mostly tropical tunas, have been fished down to approximately maximum sustainable yield levels, preventing further expansion of catches in these fisheries.’
Around 12.5 per cent of the tunas and their relatives are now caught each year globally, according to the findings, published in Proceedings of the National Academy of Sciences.
Wild tuna are captured and kept in floating cages where they are fed with fresh fish, and with farming unregulated the amount caught and exported is unknown.
Tuna provides a critical part of the diet for millions of poor people as well as being at the core of the world’s luxury sushi markets.
But many tuna species are now listed as either endangered or critically endangered.
Over the past few decades the world’s appetite for tuna has spurred a surge in the number and capacity of tuna-fishing vessels. Industrial tuna fleets from Japan, the European Union (EU), Taiwan, Korea, the US and increasingly China and the Philippines, fishing far from their home ports, are squeezing the last remaining financial benefits out of the planet’s tuna stocks.
The researchers said: 'Over-capacity of these fisheries is jeopardising their long-term sustainability.
‘To guarantee higher catches, stabilize profits, and reduce collateral impacts on marine ecosystems requires the rebuilding of over-exploited populations and stricter management measures to reduce overcapacity and regulate threatening trade.’
Even tuna fisheries that were considered healthy just a few short years ago, such as those of the Western Pacific Ocean, have joined the global depletion trend.
Tuna are highly migratory. Over their life cycles they travel vast distances, crossing the high seas and darting in and out of the waters of many coastal areas on their routes to breed and feed.
The researchers said: 'The annual catches of tuna and their relatives have risen continuously since the 1950s, reaching 9.5million tonnes in 2008.
‘The global adult biomass of tunas and their relatives has been halved over the past half century but not without yielding considerable catches, income and food for the benefit of humanity.’
Demand from Japan has seen the Mediterranean fishing fleet increase over the past decade. Many of these boats use illegal spotter planes to track the tuna.
Previous research has shown the average size of mature tuna fish, which can weigh over half a ton, had more than halved since the 1990s. This has had a large impact on the population since bigger fish produced many more offspring.
The study is published in Proceedings of the National Academy of Sciences.[/quote]