An estimate of the fish biomass in the North Sea

Abstract

Fish biomass estimates for the North Sea are made mainly by using ICES Virtual Population Analysis results for more than 10 important commercial species taken as “standard” species, by reference to which the catch rates of 65 non-standard species obtained from the MAFF North Sea groundfish surveys of 1977 and 1978 are interpreted as biomass. Naturally, the relative catchability of all these species must differ either very much or slightly. On account of this they are divided into five groups. The catchability coefficients of the non-standard species are assumed to be similar to the mean of the “standard” species within each group. For the other species the biomasses are computed in different ways. The estimated value of total fish biomass on 1 January in the North Sea was 10 million tonnes both in 1977 and 1978, that for 1977 being a little higher than that for 1978. The ratio of total catch to biomass of fish is approximately 1:3·4.