Turnaround owes much to science and collaboration, explains leading researcher and International Scientific Committee member Dr Michel Dreyfus

Unfortunately, we didn’t realise the amount of reduction in the Pacific bluefin population until 2013. There were some signs that there was overexploitation, especially in the Western Pacific, with Japan in particular seeing that even with higher regulatory efforts, they weren’t catching the amounts they used to. But, in the Eastern Pacific, Mexico specifically, and within the IATTC, we didn’t see any signs of overexploitation because our fisheries were catching all they wanted to. Then came the ISC meetings, where we assess Pacific bluefin. In 2013, we got the first assessment that scientists were satisfied with, and that’s when we realised the spawning biomass population was just 2%.

Basically, what caused the problem was an over-catch of small bluefin (10-15cm, weighing 2-3 kgs) by very large fleets of artisanal vessels. These were fishing for a number of species, but they caught lots of small bluefin as well, and often this was by-catch. ISC assessments show this was happening from the 1990s all the way to 2012, with 80% of the bluefin tuna caught being less than one year old juveniles. These small sizes and ages aren’t seen in the Eastern Pacific. It was the Western artisanal fisheries, catching vast quantities of small juveniles, that was the main problem for the species.

Following the initial ISC assessment in 2013 (these are now done every two years), we decided to form a group in which countries interested in Pacific bluefin could participate in discussions. These countries are represented on the east coast with the Inter-American Tropical Tuna Commission (IATTC) and on the west coast through the Western and Central Pacific Fisheries Commission (WCPFC). Pacific bluefin migrate across the entire ocean, so we wanted to cover the whole population. This is where we now make conservation decisions that are brought to both coast’s commissions.

The first challenge was to raise the 2% spawning biomass. Transpacific measures were quickly enforced, including catch limits for all of the Japanese, American and Mexican fleets, since they have a lot of bluefin fisheries, including longliners, purse seiners, etc. We started to see a really fast recovery. In 2020, the spawning biomass reached 10%, and the initial results from this year’s new assessment indicate we’ve already reached 23% spawning biomass. As such, the population no longer holds an overexploited status.

Some fisheries have already received raised catch limits based on the results of the 2020 assessment, and this year, there’s going to be a broader increase because of the population’s new “good status”. There are also a lot of measures in place so the population doesn’t go down again. We have to take care that there’s no return to overexploited juvenile bluefin of less than one year of age. Everything is in place so the population will continue to be in a safe zone.