28 April 2009

Killer whales and harbour seals

Harbour seals (Phoca vitulina) are one of Britain's largest and most charismatic marine predators but they are facing a dramatic decline in Scotland and eastern England. So far, this decline is unexplained.

Reasons behind this trend could be many: food competition with grey seals (Halichoerus grypus), reduced prey availability, man-made impacts such as legalised shooting of seals to protect fish farms and illegal use of fishing nets, and more.

Another reason could be the presence of killer whales (Orcinus orca) in the same area where seals are. These big cetaceans are blamed to have some responsibility.

Researchers from the University of Aberdeen made a study based on inshore sightings of killer whales around Scotland, and in Shetland especially. It showed a correspondence between the seal pupping season and a peak in orca sightings. The study suggests that these cetaceans may prey heavily on harbour seal pups at the pupping season.

However, the situation is complex and it is unlikely that only killer whales, or any other single factor, is responsible for the decline of harbour seals.


Photo: Harbour seal by www.flickr.com

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