Topic: Bluefin tuna

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    Bluefin tuna is a highly sought-after fish for consumption.

    Photo: Erlend Astad Lorentzen / Institute of Marine Research
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    The Atlantic bluefin tuna is the largest of the world’s tuna species and one of the largest fish species on the planet. It can reach 3 m length and weigh more than 700 kg.

    Photo: Øyvind Tangen / Institute of Marine Research

The Atlantic bluefin tuna is the most iconic fish species in the world. It is the largest of all tuna species and one of the largest fish species on our blue planet. They can reach sizes of more than 3 meters in length and weigh more than 700 kg. They can reach swimming speeds of up to 70 km/h, cross the Atlantic Ocean in 50 days and dive deeper than 1000 m depths.

Bluefin tuna is a highly sought-after fish for consumption, especially at the international markets for raw fish with sushi and sashimi. They have a large economic value in their most important areas of distribution. The world record for a single bluefin tuna was set in January 2020 with an astonishing 26 million NOK (95 000 NOK per kilo).

Taxonomy and biology

The Atlantic bluefin tuna (ABFT) is part of the mackerel family (Scombridae). It is the largest of the world’s tuna species and one of the largest fish species on the planet. The ABFT can reach sizes of more than 3 meters in length, weigh more than 700 kg and reach a life span of nearly 50 years of age. ABFTs can also maintain body temperature to remain up to 7–12 °C above surrounding water temperature. They inhabit pelagic waters including the entire North Atlantic Ocean and Mediterranean Sea. The ABFT is the most iconic fish species on our blue planet. It can reach swimming speeds of up to 70 km/h, cross the Atlantic Ocean in 50 days and dive to depths of more than 1000 meters, based on electronic satellite tags with depth sensors.

There are two stock-components of ABFT in the Atlantic Ocean. The western Atlantic stock is mainly spawning in the Gulf of Mexico and the eastern Atlantic stock is mainly spawning in the Mediterranean. The eastern Atlantic stock is spawning during spring in May–June in warm waters (> 24°C), and primarily at three different spawning sites in the Mediterranean. Eastern ABFT matures earlier (4–5 years of age and < 45 kg) than the western ABFT (8–10 years of age and > 135 kg).

ABFT are feeding notoriously on nutrient rich prey all along the Norwegian coastline and in the Norwegian Sea. The most important sources of food are herring, mackerel and other schooling fish, besides squid and crustaceans during earlier stages of life. 

Distribution

ABFT are widely distributed over the entire North Atlantic Ocean and Mediterranean Sea. It is predominantly bluefin tuna from the eastern Atlantic stock which are annually migrating to Norwegian waters. After spawning, they are performing an extensive feeding migration in the Mediterranean, but mainly into the North Atlantic Ocean. In recent years, there have been an increasing amount of ABFT into Norwegian waters. Based on satellite tags, visual observations and catches, we see that the ABFT have had a successful comeback into the northern part of the Northeast Atlantic and Norwegian waters from around 2012. They have been observed as far north as up to Svalbard at 76,2°N in 2018. 

Status and advice 

The stock is after more than a decade, showing signs of a positive development in size with reduced fish mortality both for adults and juveniles, in addition to descent recruitment by 2003- and 2009-year classes. The eastern stock of ABFT is at present managed in a sustainable way. There is scientific documentation from ICCAT giving repeated annual evidence of a positive development and increased stock size. The science committee (SCRS) at the International Commission for the Conservations of Atlantic Tunas (ICCAT), recommends a step by step increase in catches leading to a total quota of 36 000 tonnes for 2020. The potential long-term benefit for eastern ABFT is estimated to about 50 000 tonnes each year. 

Fishery

The international fishery on ABFT was about 32 000 tonnes in 2019. Bluefin tuna is mainly fished internationally with purse seine and line, but also with rods, driftnets and fish traps. Norway was a considerable fishing nation for ABFT during the 1950s and 1960s. Catches ranged from 1000 tonnes up to almost 15 000 tonnes each year. Mature bluefin tuna from 6–20 years, equivalent of fish at around 50 kg to more than 470 kg, have been visiting the Norwegian coast from the Oslofjord all the way up to Troms, from July to October. At this time, it was also mainly purse seine nets that was used along the entire coastline. The largest individuals swam faster and migrated further north along the Norwegian coastline. Until late 1970s, the ABFT gradually disappeared from high latitudes along the coast of Norway and were practically nowhere to be seen in Norwegian waters by the mid-1980s and onwards. ABFT have had a successful comeback into the northern part of the Northeast Atlantic and Norwegian waters from around 2012. Norway thus reopened the ABFT fishery inside the Norwegian Exclusive Economic Zone (EEZ) in 2014. The Norwegian quota in ICCAT increased tenfold from around 30 tonnes in 2014 to around 300 tonnes in 2020. 

Food

Bluefin tuna is a highly sought-after fish for consumption, especially at the international markets for raw fish with sushi and sashimi. They have a large economic value in their most important areas of distribution. The world record for a single bluefin tuna was set in January 2020 with an astonishing 26 million NOK (95 000 NOK per kilo). It is, however, very uncommon for single bluefin tuna to be sold at these astronomic high prices.

 

Makrellstørjefangst 1971
Bluefin tuna catch from the Norwegian coast 1971. Arild Aldeholm/Institute of Marine Research.

 

Bluefin Tune captured by "Vågly" in 1971.
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Bluefin Tuna catched by "Tofterøy".