This project, running from August 1994 to July 1996, had two main aims: to study the diets of marine mammals in NE Atlantic and to use these data to estimate potential impact on fisheries. Seasonal, regional, internannual and interespecific differences in diet were studied.
Diets of common and grey seals in Scotland were studied by collection of faeces at haul-out sites. Cetaceans strandings and by-catches in Scotland were studied in collaboration with Scottish Agriculture College Veterinary Services. Additional samples were collected in Galicia (NW Spain) in collaboration with Coordinadora para o Estudio dos Mamíferos Mariños, in Holland with M. Addink from the Nationaal Natuurhistorisch Museum in Leiden and in Denmark in collaboration with Dr. Carl Kinze from the Zoologisk Museum in Copenhagen. Prey remains were identified using reference material and guides. Diet composition was quantified based on counts and measurements of hard remains.
Seal diets have been described throughout the year in Orkney where sandeels are the main prey in the summer and other species such as Gadidae are eaten in the winter. Results have also being obtained from the East and West coasts of Scotland.
The harbour porpoise is the most frequently stranded cetacean in Scotland and, like the seals, takes mainly inshore fish species, with sandeel dominating the summer diet. Stomach contents of fourteen sperm whales from three mass strandings in Scotland and Denmark contained mainly the oceanic squid Gonatus sp. In Spain the common dolphin was the most commonly stranded species and fed mainly on offshore fish species. Most of the samples from Holland and Denmark that were examined were harbour porpoises and white-beaked dolphins. They had been feeding mainly on Gadidae and Gobiidae.
Most of the prey species are of at least some importance to commercial fisheries. Preliminary estimates of the impact on fisheries have been derived based on literature values of population estimates and energy requirements. For example, harbour porpoise in the NE Atlantic may take upwards of 359,000 tonnes of sandeel per year. Obviously, can not be assumed that the fish removed would necessarily have been available to fisheries. Similar calculations for seals in the Orkney area suggest that the two species may removed a combined total of approximately 15,000 tonnes of sandeel per year.
Pierce, G.J. & Santos, M.B., 1996. Trophic interactions of squid Loligo forbesi in Scottish waters. In Greenstreet, S.P.R. and Tasker, M.L. (eds), Aquatic Predators and their Prey, Fishing New Books, Oxford. pp. 58-64.
Further papers arose during and after the follow-up project, on Modelling The Impact of Marine Mammals on NE Atlantic Fisheries
Santos, M.B., Pierce, G.J., Ross, H.M. & Reid, R.J., 1994. Diets of small cetaceans from the Scottish coast. International Council for the Exploration of the Sea, C.M. 1994/N:11.
Santos, M.B., Pierce, G.J., Wijnsma, G., Ross, H.M. & Reid, R.J., 1995. Diets of small cetacean stranded in Scotland 1993-1995. International Council for the Exploration of the Sea. C.M. 1995/N:6.
Santos, M.B., Boyle, P.R., Pierce, G.J., Wijnsma, G., Ross, H.M. & Reid, R.J., 1995. Diets of sperm whales stranded in Scotland. International Council for the Exploration of the Sea. C.M. 1995/N:5.
Santos, M.B., Pierce, G.J., González, A.F., López, A. & Guerra, A., 1995. Diets of small cetaceans stranded on the Galician coast (NW Spain). International Council for the Exploration of the Sea. C.M. 1995/N:11.
Santos, M.B., Pierce, G.J., Carter, T.J., Hoskins, S., Ross, H.M., Reid, R.J. & McKenzie, C., 1996. Stomach contents of sperm whales stranded in the North Sea. International Council for the Exploration of the Sea. C.M. 1996/N:10.
Santos, M.B., Pierce, G.J., López, A., Barreiro, A. & Guerra, A., 1995. Diets of small cetaceans stranded on NW Spain. International Council for the Exploration of the Sea. C.M. 1996/N:11.
OTHER CONFERENCE PRESENTATIONS
Santos, M.B., Pierce, G.J., Ross, H.M. & Reid, R.J., 1994. Incidence of cephalopods in the diets of small cetaceans from the Scottish coast. International Conference of the Cephalopod International Advisory Council (CIAC) on "The Behaviour and Natural History of Cephalopods", Naples, Italy, June 4-11, 1994.
Pierce, G.J., Santos, M.B. & Wanghongsa, S., 1994. Diets of seals in Orkney (N. Scotland). International Symposium on the Biology of Marine mammals in the Northeast Atlantic, Tromsø, Norway, 29 November-1 December, 1994.
Santos, M.B., Pierce, G.J., Wijnsma, G., Ross, H.M. & Reid, R.J., 1995. Cephalopods in the diets of sperm whales stranded on the Scottish coast. Twelfth International Malacological Congress, Vigo, Spain, September 3-8, 1955.
Pierce, G.J., Santos, M.B., Wijnsma, G., Addink, M., López, A., Tollit, D., Reid, R.J. & Ross, H.M., 1995. Diets of seals and porpoises: interspecific competition and competition with European fisheries. Eleventh Biennial Conference on the Biology of Marine Mammals, Orlando, Florida, December 14-18, 1995.
For further information contact Graham Pierce or Begoña Santos.