Stock prediction using stochastic recruitment numbers with empirical stock-dependent distribution
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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.