International fisheries, international management decisions and the chance of seeing a bluefin tuna jump near Denmark

Bluefin tuna, Thunnus thynnus, is a charismatic large highly migratory fish species which now again visits Danish waters after a long period of rarity or absence. The species was a common seasonal resident until the early 1960s but then within a few years became extremely rare. This situation lasted for decades until they started coming back in large numbers in the early-mid 2010s. This species has high value both as a recreational and commercial fishing species, and for eco-tourism. While present in Danish and neighboring waters (e. g., North Sea, Norwegian Sea) the species is a predator of herring, mackerel, garfish and other species. The reasons for its disappearance and reappearance are speculative and have not been fully described or identified. In addition the timings of the disappearance and reappearance were not forecasted by scientists or managers so the events were unexpected. In this presentation I will summarize some of the hypotheses for these changes, including the roles of international (including Danish) fisheries and international management on these events. These factors have most likely had major roles on both events. In particular, a new international recovery plan implemented in 2008-2010 following years of unsustainable, unreported and illegal fishing has led to a rapid and major increase in biomass, geographic range and fishery yields. And now it is possible to see this species attacking and jumping for prey in Danish waters again. The recovery of biomass and range of this population, which was on a trajectory of collapse and which migrates across and through multiple national and international jurisdictions, demonstrates that some management actions can be successful if supported by societal and political will.