The preliminary conclusions from the first comprehensive counting survey ever of cetaceans in the North Sea (the 1994 SCANS Survey ) shows that there are about 250,000 harbour porpoises in this area. However, the by-catch of harbour porpoises in the fisheries in this area is known to be quite substantial, and a lot of work remains to be done to determine the impact of this by-catch on stocks.

Most people were a bit surprised by this high estimate, says Christina Lockyer, secretary of ASCOBANS (Agreement on the Conservation of the Baltic and North Seas). The harbour porpoise was thought to be predominantly a coastal species, but the sighting survey showed that it is quite capable of being pelagic. It is more widely distributed than we thought. A revised final estimate will be presented at the International Whaling Commission in Dublin in May this year.

Research published in 1994 showed that the Danish gillnet fishery in the North Sea takes about 7,000 harbour porpoises a year as by-catch. This led to warnings that the harbour porpoise might be driven to extinction. This reaction was toned down after the size of the abundance estimate became known, says Morten Winter of the Danish Fisheries Research Institute, which was responsible for the by-catch study. Denmark has by far the biggest gillnet fishery in the North Sea, but England’s (though just half the size of Denmark’s) is still sizable. Danish vessels have been using gillnets in the North Sea for more than 20 years, targeting turbot, flounder and cod. The turbot fishery has been shrinking in recent years, but effort in the cod fishery has increased. Other nations with North Sea coastlines also have coastal gillnet fisheries.

It is not known what level of take the harbour porpoise stocks can stand without becoming depleted. The general consensus among experts contacted by the High North News is that the recruitment rate is probably in the region of 4%. Using this figure, the stock could sustain a take of about 10,000 a year.

But the calculation is not that simple, Lockyer points out. We have limited knowledge of the population structure, and we could have smaller individual populations in areas where the fisheries are concentrated.

In a resolution passed at the first meeting of ASCOBANS in Stockholm in September 1994, it was stated that the parties (to the agreement) should establish or be encouraged to continue independent observer schemes to assess most significant by-catches before 1996. By 1997, we will hopefully have a total estimate of by-catches of harbour porpoises in the North Sea and also better knowledge of the population structure, says Lockyer. The SCANS Survey was a cooperative project involving eight EU countries. Nine ships participated.