Porpoises on European coasts maintain their populations but migrate southwards

An international team of scientists has found the exact abundance of the main species of small cetaceans on the European Atlantic continental shelf.

The SCANSII Project, led by the University of St Andrews (Scotland) in collaboration with twelve institutions -- including the Spanish Cetacean Society -- and organisations from eight European countries, is the second installment of the initial project undertaken in 1994, and demonstrates the trend over the last ten years.

As José Antonio Vázquez from the Spanish Cetacean Society explains: "The main result is that the porpoise population has remained the same but there has been a trend to move from the north to areas further south."

The main objectives were to obtain up-to-date, exact figures for the abundance of the harbour porpoise and other small cetaceans in the waters of the European Atlantic shelf and the North Sea, and to recommend suitable methods for monitoring and economic sustainability to evaluate temporal trends in relative abundance.

The expert continues, "Creating a robust management framework that enables us to assess the impact of bycatch and recommend safe bycatch limits for each species is another of the aims we sought for years to achieve."

Thirteen different cetacean species

The sample was taken in July 2005 in waters of the Northwest Atlantic continental shelf from the Straits of Gibraltar to Norway, and seven oceanographic research vessels and three light aircrafts were used for it.

A total of 1,370,114 km2 were surveyed, during which records were obtained for 13 species of cetacean: the harbour porpoise, the common bottlenose dolphin, the white-beaked dolphin, the short-beaked common dolphin, the common minke whale, the Atlantic white-sided dolphin, the striped dolphin, Risso's dolphin, the long-finned pilot whale, the killer whale, Cuvier's beaked whale, the fin whale and the sei whale.

"Absolute abundance estimates were obtained for the first five species in the area of study. The harbour porpoise, standing at 375,358, is the most numerous in these waters, followed by the common dolphin, the common minke whale and the white-beaked dolphin. The common bottlenose dolphin is the least numerous with only 16,485 recorded," the scientist affirms.

The absolute abundances obtained in this project were similar to those of 1994 for the harbour porpoise and lower for the common minke whale. In terms of spatial distribution, while for the common minke whale a slight displacement of the densest areas of the North Sea to the central part was recorded, in the case of the harbour porpoise a displacement from northern areas of the United Kingdom and Demark to the southeast of the United Kingdom is observed.

According to Vázquez, "this displacement may be due to movement of prey species." Another result to highlight from this campaign is the success in obtaining, for the first time ever, absolute abundance estimates for the bottlenose dolphin and the common dolphin over the entire North European Atlantic continental shelf.

"As such the absolute abundance estimates obtained allow us to contextualise quantitatively the effect of bycatches on current populations, as well as to create predictive models that enable us to include various hypothetical situations for the development of bycatches and how these affect size evolution in the population in the medium- and long-term future," the expert concludes.