Wild caught bluefin tuna is one of the most unsustainable seafood dishes in Hong Kong, with the Pacific bluefin tuna listed as vulnerable, Atlantic bluefin tuna listed as endangered and the southern bluefin tuna listed as critically endangered on the IUCN Red List. So what about farmed bluefin tuna? Is this a more sustainable option? While bluefin tuna farms, mainly located in Australia, the Mediterranean and Japan, might at first glance seem to be an acceptable replacement to the wild-caught alternative, closer examination shows otherwise.
Bluefin tuna is a carnivorous species that sits at the top of the food chain. In aquaculture, it has a high Fish In Fish Out ratio (FIFO). FIFO is an environmental performance benchmark used to measure the efficiency at which the aquaculture converts a weight-equivalent unit of wild fish into a unit of cultured fish. Bluefin tuna has an average FIFO ratio of 15:1. In other words, for every tonne of farmed bluefin tuna, a total of 15 tons of feed is required. By comparison, farmed salmon and trout have a FIFO ratio of 0.82:1, while species in the Cyprinidae family such as grass carp only has a FIFO rate of 0.02:1. In 2015, the average aquaculture FIFO ratio was 0.22:1.
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Bluefin tuna commands one of the most expensive per pound prices on the global seafood market, so it is in the interest of farmers to increase their size. By feeding bluefin tuna a mixture of sardine, sand eel, saury, chub mackerel, Japanese horse mackerel, and cuttlefish, aquaculture farmers can increase the weight of a single fish by 10-20kg. This makes farmed bluefin tuna environmentally inefficient and unsustainable.
In the WWF Seafood Guide, which covers over 70 of the most familiar seafood items in the city, both farmed and wild-caught bluefin tuna fall into the “avoid” category. The guide has three categories: green – recommended; yellow – think twice; red – avoid. The green category indicates well-managed fisheries where seafood is caught or farmed in an ecologically-friendly manner. The yellow category indicated fisheries that are at risk of becoming unsustainable. The red category indicates fisheries that are over-exploited, or seafood that is caught or farmed in an ecologically-unfriendly manner.
Sustainable replacements to bluefin tuna include yellowfin tuna caught with handlines in Indonesia and the Philippines. Handline fishing is highly selective and therefore has a low bycatch rate. Additionally, these yellowfin fisheries have a more solid management framework that prevents fishing during certain seasons, giving fish stocks a chance to recover.
Featured image by: Wikimedia Commons
This article was originally published on WWF-Hong Kong, and is republished here as part of an editorial partnership with Earth.Org.