Chair of the North Sea advice drafting group (ADGNS) Ghislain Chouinard.
'The spawning stock biomass (SSB) is the combined weight of all individuals in a fish stock that are capable of reproducing. To calculate the spawning stock biomass, you need to have estimates of the number of fish by age group, estimates of the average weight of the fish in each age group and an estimate of the amount of fish in each age group that are mature. For example, if there are 1,000 fish of age three that weigh on average 0.5 kg and 50% of these fish are mature, the spawning biomass of this age group is 250 kg (1000 X 0.5 X 0.5).
The SSB is an indication of the status of the stock and the reproductive capacity of the stock. Where possible, reference points relative to SSB are established for each stock. These SSB reference points are different for each stock and are like signposts. One can compare the present SSB of a stock with these reference points and make a determination as to whether the stock is relatively in good shape or in bad shape. The estimate of the SSB and its position relative to the reference points are part of the framework that ICES uses to give advice on fishing opportunities for a given stock. For many stocks, there are no estimate of spawning stock biomass and advice has to rely on other indicators.'