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Research Document 1997/123

Analyses of the catch at length and evaluation of the Maximum Sustainable Yield for the capelin (Mallotus villosus) of NAFO Division 4R

By F. Grégoire

Abstract

To evaluate the fishing effort associated with Maximum Sustainable Yield, Jones' Cohort Analysis Model and the Thompson and Bell Modified Yield Model were applied to annual catches at length from the capelin fishery on the west coast of Newfoundland. The main input parameters for these models are M, F and Z, which are defined as the instantaneous rates of natural, fishing and total mortality. The annual total mortality rates were derived using the following techniques: (1) the catch curve; (2) the Jones-van Zalinge equation; and (3) the Beverton-Holt equation. Certain Z values were selected and, with these held constant, different combinations of M and F were used in the cohort analysis. This analysis shows that, the higher the value of F compared to M, the smaller the estimated biomass. However, the calculated yield does not vary. Moreover, for a fixed value of M and a variable Z, the Yield Model shows that the projected biomass tends to decrease slightly when F increases. This increase in F also results in a rapid increase in yield. Finally, the Yield Model shows that the current level of F is well below a value corresponding to Maximum Sustainable Yield.

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