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| Rising ocean temperatures are causing marine fish species to shift spatial distributions and ranges, and are altering
predator-prey dynamics in food webs. Most documented cases of species shifts so far involve relatively small species
at lower trophic levels, and consider individual species in ecological isolation from others. Here, we show that a large
highly migratory top predator fish species has entered a high latitude subpolar area beyond its usual range. Bluefin
tuna, Thunnus thynnus Linnaeus 1758, were captured in waters east of Greenland (65°N) in August 2012 during
exploratory fishing for Atlantic mackerel, Scomber scombrus Linnaeus 1758. The bluefin tuna were captured in a single
net-haul in 9–11 °C water together with 6 tonnes of mackerel, which is a preferred prey species and itself a new
immigrant to the area. Regional temperatures in August 2012 were historically high and contributed to a warming
trend since 1985, when temperatures began to rise. The presence of bluefin tuna in this region is likely due to a combination
of warm temperatures that are physiologically more tolerable and immigration of an important prey species to
the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland
waters. | |
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