Return of Atlantic bluefin tuna signals conservation success say Hull scientists

Small numbers of the giant fish have returned to the North Sea in recent years, lured by abundant stocks of herring, a species that almost disappeared from east coast waters due to over-fishing.

A ten-year ban on the herring fishery from 1977 onwards has seen stocks of the 'silver darlings' recover in subsequent decades. Now a growing population of tuna, once heavily depleted, is moving into new waters in search of food.

Professor Rodney Forster, Director of Hull’s Marine Laboratory welcomes the return of the tuna but cautions that the North Sea may see further change: “The appearance of bluefin tuna in the North Sea may be a sign of stocks recovering in response to international conservation measures that now limit tuna catches.

“Work is under way to track the movements of the new arrivals but the provenance of the Whitby fish is not yet known. They may be from the eastern Atlantic stock, or they may have crossed the Atlantic to take advantage of abundant food resources off the UK’s east coast.”

Separately, Hull Marine Laboratory scientists are developing techniques to track herring movements, measuring chemical signals in the ear bones, matching those with sea areas to learn more about their spawning grounds. “We’re looking to find the chemical equivalent of a Humber birth certificate,” Professor Forster says.

“Tuna are a warm-blooded species; their presence or absence is independent of sea temperatures. But the same is not true for herring that favour cooler waters, along with the plankton that they feed on.

“This year and last, we have recorded the highest temperatures ever seen in the North Sea with Yorkshire's coastal waters warming some two degrees Celsius on average over the past forty years.

"As sea temperatures continue to rise, warm-water species such as octopus may become more common in the North Sea, competing directly with existing fisheries and creating new challenges for coastal communities."