Bigeye Tuna

(Thunnus obesus)

Albakoor, Albacore, Longfin tunny, Longfin tuna, Langvin tuna, bigeyes

1. What is it?

Bigeye tuna (Thunnus obesus) are predatory, migratory, schooling fish found in the tropical and subtropical waters of the Pacific, Atlantic and Indian Oceans. Juveniles and sub-adults can be found near the surface whilst adults tend to stay in deeper waters of around 300 m to 500 m. Spawning stock biomass has been decreasing since the late 10970s and adult mortalities increasing as catches started to exceed the estimated maximum sustainable yield. The species is listed as Vulnerable on IUCN’s list for threatened species and currently stocks are fished at maximum levels.

2. How was it caught or farmed?

Bigeye tuna are caught using a double-line system that is suspended at different depths and covered in baited hooks up to 10 kms long (called “pelagic longlines”). Pelagic longlining can have significantly high amounts of bycatch (up to 22% of total catch) which may contain threatened species such as sharks, seabirds and turtles. The issue of bycatch is being addressed in birds; however shark bycatch is still an issue and requires further attention. Pelagic longlines have little effect on the surrounding benthic habitat.

3. Where is it from?

In South Africa tuna is harvested in both the Atlantic and Indian Oceans. Due to its migratory nature (crossing international boundaries) and high demand, the stock is generally managed by Regional Fisheries Management Organizations (RFMOs) which fall under the larger fishery management organizations. South Africa has signed the United Nations Fish Stocks Agreement and is an active member of the International Commission for the Conservation of Atlantic Tuna (ICCAT) and a cooperating non-member of the Indian Ocean Tuna Commission (IOTC). Based on recommendations and resolutions provided by RFMOs, South Africa has implemented a number of legislative and permit conditions in order to regulate tuna stocks. However, lack of strong management from the RFMOs and ICCAT could have negative results for high-sea fisheries in the future.