Topic: Bluefin tuna

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

Atlantic bluefin tuna (BFT) has a wide geographical distribution, but live mainly in the temperate pelagic ecosystem of the entire North Atlantic and its adjacent waters; the Mediterranean Sea, Gulf of Mexico and Gulf of St. Lawrence. There are two separate stocks of BFT with mixed migration patterns; the East Atlantic and Mediterranean bluefin tuna stock and West Atlantic bluefin tuna stock. It is predominantly the East Atlantic and Mediterranean bluefin tuna stock which is annually migrating to Norwegian waters. After spawning, they are performing an extensive feeding migration from the Mediterranean, into the vast North Atlantic Ocean.

During the last 10 years, there has been a substantial increase of BFT migrating to and feeding in Norwegian waters. Based on satellite tags, visual observations and catches, we document that the BFT had a successful comeback into the northern part of the Northeast Atlantic and Norwegian waters from around 2012. They have lately been observed as far north as up to Svalbard at 76,2°N in 2018. The spatial distribution of BFT has steadily increased in Norwegian waters during the period 2012–2022. BFT is now migrating to and feeding here from July/August to November/December. Preliminary results from satellite tagging of BFT demonstrate that BFT may stay more than 3 months a year in Norwegian waters during summer and autumn. New knowledge suggests that some BFT may even overwinter in Norwegian waters through the autumn and winter.

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 BFT 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), recommended some years ago a step-by-step increase in catches from 9 774 tonnes in 2011 and leading to a total quota of 36 000 tonnes in 2020. ICCAT kept the total allowable catch (TAC) at 36 000 tonnes also in 2021 and 2022.

A brand new and complex Management Strategy Evaluation (MSE) was adopted by consensus to be applied both for East Atlantic and Mediterranean as well as West Atlantic BFT during the ICCAT commission meeting in November 2022. The MSE management strategy is based on the collaborative process between scientists and managers. The TAC, inclusive dead discards, was decided shall be set at 40 570 t for 2023 to 2025, in accordance with the selected Management Procedure (MP) from the Management Strategy Evaluation (MSE) process with corresponding harvest control rules (HCR). The potential long-term benefit for eastern BFT is estimated to about 50 000 tonnes each year.

ICCAT has followed the scientific advice on BFT for the last 15 years. Even though there has been made substantial progress in amount and quality of various data during the last years, there are still substantial BFT data gaps, limitations, and uncertainties, including during the extensive and long-lasting Management Strategy Evaluation (MSE) process conducted on eastern and western BFT, which was finalized and adopted at the ICCAT commission meeting in November 2022. Substantial overfishing and underreporting of BFT was previously pronounced, particularly from 1998 to 2007. The control regime for East Atlantic and Mediterranean BFT is at present one of the strongest worldwide in fisheries management, which has improved substantially during the last 15 years.

Fishery

The international fishery on eastern Atlantic and Mediterranean BFT was 35 070 tonnes in 2021, after being as low as 9 774 tonnes in 2011.

Bluefin tuna is mainly fished internationally with purse seine and longline, but also with rods, driftnets, and fish traps.

Norway was a considerable fishing nation for BFT during the 1950s and 1960s. Catches ranged from 1000 tonnes up to almost 15 000 tonnes each year, with an average catch of 5 430 t between 1950 and 1970. 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 were 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.

BFT had a successful and miraculous comeback into the northern part of the Northeast Atlantic and Norwegian waters from around 2012, after decades of absence. Norway thus reopened the ABFT fishery inside the Norwegian Exclusive Economic Zone (EEZ) in 2014. The Norwegian quota in ICCAT increased manyfold from 34 t in 2014 to 300 t in 2020. The Norwegian quota was 315 t in 2021 and 2022. Furthermore, the Norwegian quota increased with 23% to 383 t in 2023 based on outcomes from international negotiations at the ICCAT commission meeting in November 2022. 

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.