Atlantic Bluefin Tuna Shift North as Mediterranean and Gulf Spawning Decline

An international study led by AZTI and published in Fish and Fisheries projects Atlantic bluefin tuna will shift progressively northward through the 21st century as ocean temperatures rise, producing habitat gains in northern Europe, waters around Greenland and the wider Northeast Atlantic while shrinking tropical and temperate ranges. Maite Erauskin-Extramiana, AZTI researcher and lead author of “Navigating Future Waters: The Resilience of the Atlantic Bluefin Tuna Under Climate Change,” reports that under the most pessimistic greenhouse-gas emissions scenario Mediterranean habitat suitability could decline by 27 percent and Gulf of Mexico suitability by as much as 70 percent, and that prey distributions will follow a similar poleward trend with overlap between tuna and prey in higher latitudes increasing by around 15 percent. Erauskin-Extramiana said, “Bluefin tuna show a strong capacity to adapt, but our projections indicate that climate change is altering the balance between feeding areas, spawning grounds and fishing activity. That is why it is essential to progressively integrate projected climate-change impacts into management systems, so we can anticipate change and manage resources more efficiently and sustainably.”

Tagging and observational studies already show bluefin moving north in real time. Grace E. McNicholas, Ph.D. candidate at the School of Natural Sciences, Trinity College Dublin, is lead author on a Diversity and Distributions paper, DOI 10.1111/ddi.13865, and a June 11, 2024 press release documents electronic tags confirming tuna spending more time at higher latitudes. McNicholas’s team reported a 2019 event in which six giant Atlantic bluefin peeled away from established migration routes between Ireland and the Bay of Biscay or the Mid-Atlantic Ridge and moved toward Iceland, a shift thought to be linked to a marine heatwave.

U.S. observations add a consistent short-term signal: the National Marine Fisheries Service found large and small Atlantic bluefin moving further north to waters off Massachusetts at a rate of 4 to 10 kilometers per year. The species’ biology underpins why small shifts in water temperature matter: bluefin reach 6 to 10 feet in length, can live up to 40 years and hunt schools of fish such as herring and mackerel while undertaking long migrations to spawn and feed.

Field experts are already noting new feeding areas and management headaches. Buzzi said, “We are seeing bluefin tuna feeding in unusual areas, for example in the North Sea, around Scandinavia and Iceland. We are already seeing changes in migration patterns.” Trueman warned juveniles’ nursery areas are expected to shift away from the Mediterranean “potentially into the Bay of Biscay,” and that juveniles might become bycatch in established anchovy and sardine fisheries in the Bay of Biscay, adding, “You need to think about how you might change your monitoring or change your fishing regulations to adapt to those changing distributions.”

Atlantic bluefin, Thunnus thynnus, is regarded as one of the world’s most economically valuable marine species, and analysts say redistribution will have consequences for ecosystems, quota systems, international fisheries agreements and coastal livelihoods. The AZTI authors and observed tagging trends together frame a clear management challenge: with projected spawning-ground suitability falling by 27 percent in the Mediterranean and up to 70 percent in the Gulf of Mexico under the worst emissions pathway, fisheries managers face altered access, shifting catch composition and increased bycatch risk unless monitoring and regulations are adapted to the changing distribution.