Acoustic estimates of saithe in the North Sea in 1984 and 1985

Abstract

This paper describes the results from a joint cruise in July 1984 with two vessels, and the results from two cruises in February - March 1985. In July the saithe were standing well above the bottom, but the saithe were often mixed with high densities of plankton which might result in too high integrator values for saithe. It is also a problem that big specimens are more difficult to catch than small ones. This may result in an overestimation of small fish. The estimate for July were 645 000 tonnes compared with a VPA estimate of 637 000 tonnes. In February - March the saithe were standing very close to the bottom, especially at the spawning grounds. The acoustic estimates therefore give only about 35% of the VPA estimate. The relative abundance of the year-classes are in good agreement in all estimates. The 1981 and 1982 year-classes seem to be good ones.