Fisheries[edit]
Capture of Atlantic bluefin tuna in tonnes from 1950 to 2009
Commercial capture[edit]
Aquaculture[edit]
Tuna farming began as early as the 1970s. Canadian fishermen in St Mary's Bay captured young fish and raised them in pens. In captivity, they grow to reach hundreds of kilos, eventually fetching premium prices in Japan. Farming enables farmers to exploit the unpredictable supply of wild-caught fish. Ranches across the Mediterranean and off South Australia grow bluefin offshore. Annual revenues are $220 million. A large proportion of juvenile and young Mediterranean fish are taken to be grown on tuna farms. Because the tuna are taken from the wild to the pens before they are old enough to reproduce, farming is one of the most serious threats to the species.[citation needed] The bluefin's slow growth and late sexual maturity compound its problems. The Atlantic population has declined by nearly 90 percent since the 1970s.[19]
In Europe and Australia, scientists have used light-manipulation technology and time-release hormone implants to bring about the first large-scale captive spawning of Atlantic and southern bluefin.[9] The technology involves implanting gonadotropin-releasing hormone in the fish to stimulate fertile egg production and may push the fish to reach sexual maturity at younger ages.[20]
However since bluefin require so much food per pound of weight gained-up to 10 times that of salmon-, if bluefin were to be farmed at the same scale as twenty-first century salmon-farming many of their prey species may become depleted if farmed bluefin were fed the same diet as their wild counterparts. As of 2010, 30 million tons of small forage fish were removed from the oceans yearly, the majority feed for farmed fish.[9]
Market entry by many North African Mediterranean countries, such as Tunisia and Libya in the 1990s, along with the increasingly widespread practice of tuna farming in the Mediterranean and other areas such as southern Australia (for southern bluefin tuna) depressed prices. One result is that fishermen must now catch up to twice as many fish to maintain their revenues.[citation needed]