Stock prediction using stochastic recruitment numbers with empirical stock-dependent distribution
MetadataVis full innførsel
OriginalversjonThis report is not to be cited without prior reference to the author
Probability distributions for the recruitment, conditional on the spawning stock biomass (SSB) were made using a kernel method. Predictions were made with recruitments according to these distributions for 10 years, using a Monte Carlo procedure, assuming constant weight at age, maturity ogive and natural mortality. Examples are given for 3 stocks, Western mackerel, North Sea sandeel and North Sea herring. Three management strategies were studied, a fixed F, a fixed yearly catch and a regime aiming at stabilizing the SSB. Due to the variable recruitment, attempts to stabilize the SSB increases the year to year variations in the yield. Attempting to take a fixed catch every year is hazardous, since the appearance of a few poor year classes may detoriate the stock so that the future recruitment suffers. This simple approach may be a useful tool for evaluating management strategies in terms of risks and possible outcome of the fisheries.