European fisheries ministers might not relish the idea, but new research suggests that whales may be entitled to a stake in the management certain stocks in Irish waters.
The study by a team of Irish scientists shows that fin and humpback whales are attracted to the Irish coast by the superior taste of our scad and herring stocks, whereas these species feed on krill in other parts of “blue Europe”.
Krill are tiny plankton-eating crustaceans which fin and humpback whales consume in large quantities, with fin whales relying almost exclusively on them in the Mediterranean and Bay of Biscay .
When same fin whales arrive in the Celtic Sea, however, they cannot resist gorging on scad and herring, according to Dr Conor Ryan of Galway-Mayo Institute of Technology (GMIT).
Dr Ryan, who worked with the Marine Institute and the Irish Whale and Dolphin Group (IWDG) on the project, says that the visiting fin and humpbacks will follow the seasonal movements of sprat and herring as they congregate inshore to spawn between Slea Head, Co Kerry and Wexford's Hook Head peninsula.
Studying the diet of such large whales proved challenging for the scientists, as the mammals cover vast distances and dive for up to 15 minutes at a time. Carcases which beach and perish tend to be of limited value to the researchers, as these mammals tend to be sick and have often stopped feeding beforehand.
The team took skin samples, using biopsy darts fired from a cross-bow, to conduct isotope analysis under license from the National Parks and Wildlife Service.
Stable isotope analysis is “rapidly becoming an essential tool” for tracing food webs, Dr Ryan says.
Chemical tracers - as in stable carbon and nitrogen isotopes in the skin of the whales - were analysed. These same chemical signatures were measured in samples from sprat, herring and various krill species of different age classes, collected during annual fisheries surveys by the Marine Institute's research vessel Celtic Explorer .
“ By matching the best fitting stable isotope signatures, the researchers were able to calculate what proportion of each prey species the whales were consuming,”Dr Ryan explains.
The results showed that fin in whales in Irish waters have a diet comprising 50 per cent krill and 50 per cent young sprat and herring, which contrasts with the trend towards krill elsewhere in Europe.
Humpback whales also seem to prefer sprat and herring when feeding in Irish waters and their diet comprises less than 30 per cent krill, Dr Ryan says.
The team studied baleen plates - the flat sheets of tissue in the mouths of some large whales to filter food from seawater - to examine any changes in diet over the past century. Some of the baleen plates had been stored in museums in Ireland and Britain.
The main finding was that the long term diets of minke, fin and humpback whales are quite different from each other, Dr Ryan says, which is “surprising” as they tend to feed close together.
The last such dietary study here was carried out in 1913 on migratory fin whales, caught at two whaling stations run by Norwegians in Co Mayo.
“We now have clear evidence that sprat and herring are important species supporting whales in Irish waters, and we must manage our fisheries with this in mind,”Dr Ryan says.
“We are very worried that sprat is being fished with an open quota, despite a huge gap in our knowledge about the life history of this important species in the Celtic Sea, “he adds.
Dr Simon Berrow, GMIT marine science lecturer and IWDG executive officer, says that the data will be incorporated into a new environmental management plan commissioned by the Celtic Sea herring management advisory committee.
“Whale-watching is growing in Ireland and has the potential to expand much more if we manage these fish stocks for both fishers and whales and dolphins, which will further benefits to coastal communities,”Dr Berrow has commented.
The study findings have been published in several peer-reviewed scientific journals.
