Publication Abstract

Fishing mortality and the variation of catches: a time series approach

D.N. MacLennan, J.G. Shepherd, J.G. Pope and H. Gislason

The effect of fishing mortality on the variation of yield is re-examined, wath particular attention to the changes of stock size from one year to the next. Using a SHOT model of the stock dynamics, we show that the year-on-year variability of the exploitable biomass increases roughly in proportion to the fishing mortality. The theory is further developed by means of an age-structured model which takes account of the exploitation pattern (the fishing mortality as a function of age). We determine the condition for minimum variability. The corresponding exploitation pattern is not unique but depends on the fishing mortality on the recruiting year-class. As an example, the theory is applied to the cod (Gadus morhua) stock in the North Sea. We show how the stability of the yield depends on the fishing effort through the number of year-classes contributing to the fishery.

Reference:

D.N. MacLennan, J.G. Shepherd, J.G. Pope and H. Gislason, 1992. Fishing mortality and the variation of catches: a time series approach. ICES Journal of Marine Science, 49: 425-430.