A new study on climate change and its effect on the behaviour of certain species has been carried out by Denmark Technical University (DTU) Aqua.
The study comes as bluefin tuna were found hunting for mackerel in east Greenland waters in 2012. Scientists at DTU Aqua say warmer temperatures and prey species which are also moving north, could be reasons why the tuna were found in the Denmark Strait.
Three large bluefin tuna, each weighing around 100kg, were among the several tonnes of mackerel that were caught in August 2012.
Presence of bluefin tuna in the Denmark Strait are extremely rare, since they usually search for prey in areas where surface temperatures are warmer than 11?C. But, the water temperatures were so warm, and because one of tuna’s favourite prey species, mackerel, had already expanded its range to the region, the study reveals it’s likely bluefin tuna has expanded or is currently expanding its habitat to more northerly regions.
If summer temperatures continue to increase during this century, and if both bluefin tuna and its prey species are managed in sustainable ways, then it is likely that bluefin tuna could become a regular summer visitor in east Greenland waters, at least as far north as the Denmark Strait, said professor Brian MacKenzie.
The data we have available are too limited to estimate how many tuna came so far north, but because the species is a schooling species, with schools having around 10-100 individuals, and because the fishermen caught the three tuna in the same haul, it is likely there were many more present, he added.
The DTU Aqua scientists are now planning further investigations to determine whether this new migration behaviour toward more northern waters could be the result of an increase in the total population of bluefin tuna.
Regardless of whether the stock has increased or not, climate-related changes in distributions of commercial fish like these we have seen already for mackerel and herring, will mean that international management authorities will need to develop new fishery and ecosystem management plans, explained Helle Siegstad, head of the department for fish and shellfish, GNI.
DTU Aqua says it’s important that it can provide authorities with a solid scientific and data basis, on for example bluefin tuna, when they are making new fishery management decisions in future.
Mercator Media Ltd 2014