A study of demersal fish species in the North Sea over a 25 year period has shown that most fish are moving deeper and further north to escape rising sea temperatures.
The study, published online in the journal Science on 12 May, was led by conservation ecologists Allison Perry and John Reynolds at the University of East Anglia in Norwich, UK. They used records of fish catches from research vessels to measure the centres of distribution of the 36 commonest species of bottom-living fish in the North Sea between 1997 and 2001. Temperatures on the seafloor rose by 1°C during this time.
The researchers found that two-thirds of species moved toward cooler waters by going further north, or deeper, or both. Among 20 species whose range boundaries fall within the North Sea, half of them moved significantly with warming, most northwards. Blue whiting (Micromesistius poutassou), the target of the largest fishery in the Atlantic, showed the largest boundary movement, of 816 km.
The trends were seen in both commercially exploited and non-targeted fish species. Species that moved tended to be smaller and mature earlier than those that stayed put. The less mobile species may be hampered by their slower generation times or could be more closely tied to particular habitats, the researchers suggested.
The fact that some species are shifting and others aren’t could disrupt the ecosystem by altering relationships between predator and prey, the researchers suggested. “Further temperature rises are likely to have profound impacts on commercial fisheries through continued shifts in distribution and alterations in community interactions”, they wrote. For instance, they predict that blue whiting and redfishes (Sebastes spp.) will have retracted completely from the North Sea by 2050, based on average estimates of temperature rise.