What’s happening? Atlantic bluefin tuna (ABT), the largest and most valuable fish found in the ocean, have returned to UK waters, researchers from the University of Exeter and the Centre for Environment, Fisheries and Aquaculture have confirmed. The fish disappeared from the country’s coastline in the 1960s due to population decline and overfishing. Almost 1,000 sightings of the species were recorded between 2013 and 2018. Why does this matter? The return of the tuna species is a win for ocean ecosystems and biodiversity off the UK and Ireland’s shorelines, as well as for local fish spotters and surfers alike. The newly published research, an output of the Defra-funded Thunnus UK project, documents the reappearance of ABT in UK and Ireland territorial waters from 2014 onwards using data from scientific surveys, ecotours and fisheries. The reasons for the return of the fish are unclear, but they could be linked to conservation efforts alongside warming waters as a result of climate change. The researchers indicate that fishing, management, environmental and prey dynamics have all contributed to the sightings. ABT fishing is currently outlawed in UK waters. The migratory species is managed at an international level by the International Commission for the Conservation of Atlantic Tunas (ICCAT), and while stock sizes are thought to be increasing, the UK has not had an EU quota for Bluefin tuna and the fish cannot be targeted by commercial or recreational fishers. However, the return of the fish has led to calls for a recreational fishery. Advocates for this have argued live release fishing could aid monitoring of the fish through tagging and DNA sampling. Others have argued such a fishery would take up a small amount of a post-Brexit UK tuna quota , and some point out it represents a significant commercial opportunity. While the UK’s ocean conservation measures introduced in recent years may not be behind the return of the species, they could potentially aid its prosperity. The UK’s “blue belt” zone of protected marine areas was expanded in 2019, when the government established 41 new conservation areas nearly double the size of England, bringing the total such protected areas around the nation’s coastline to 355. Earlier this year, the UK government also announced proposals to ban bottom trawling, a highly destructive fishing practice, across the Dogger Bank conservation area and three other English marine protected areas (MPAs). The MPAs are known as important breeding grounds for species including cod and sand eels. Trawl fishing has also been banned across 117 square miles of seabed along Sussex’s coastline to aid the restoration of seaweed forests – home to hundreds of marine species – which have been damaged by trawling, dredging and storm damage. Overfishing is still affecting the status of two-thirds of UK fish populations, according to charity Oceana. Efforts to aid this includes a recent agreement on 2021 catch limits over six jointly-managed fish stocks in the North Sea between the UK, EU and Norway, to promote the long-term health of key populations including cod, haddock and herring. While the future for ABT around the UK and Ireland is at this point still uncertain, careful consideration should now be given on how to manage the returned visitors to sustain their population.