Clyde Nephrops: biology and fisheries

Abstract

SynopsisThe fishery for Norway lobsters Nephrops norvegicus began in the 1950s and has since become one of the most valuable assets of the Clyde Sea Area. Landings of Nephrops reached a peak of 26001 in 1972. Following a decline in landings up to 1975 there has been a further increase to over 45001 in 1983, valued at £4–5 million. Most of the landings are made by inshore trawlers working from Ayr, Troon, Girvan, Largs, Campbeltown and Tarbert. Recently a small creel fishery has developed in some sea lochs. The abundance of the stock appears to have been maintained; landings per unit of fishing effort have fluctuated without any obvious trend.Since September, 1979. several aspects of the biology of Nephrops have been studied in an area south of the Little Cumbrae at the north end of the east Arran Basin. Data are presented on the density, size composition, growth rate, reproductive biology and feeding of Nephrops in this area. The results are compared with those obtained for other Nephrops populations, revealing some unusual features of Clyde Nephrops. In the Clyde, densities were lower than in a number of other areas, while growth rate was much higher and animals grew to larger sizes. Sexual maturity was attained at a larger size in Clyde Nephrops and studies of ovary development revealed that considerable numbers of large females did not reproduce annually, in contrast to some other areas. Recent observations suggest that the biological characteristics of Nephrops populations in an area may be influenced by features of the local physical environment such as the particle size distribution and organic carbon content of the sediment. Differences between Clyde Nephrops and those from other areas are discussed in relation to this.