STABILITY PROPERTIES OF DISCRETE STOCK-PRODUCTION MODELS

The paper focuses on the stability analysis of a certain class of catc h- and effort-controlled discrete stock - production models for optima l management of exploited populations, which were used as official met hods for Cape hake assessments in the International Commission for the Southeast Atlantic Fishery (ICSEAF) during 1988 - 1990, and are still used for forecasting TACs of this species and other commercially fish ed stocks. Ln spite of the formal approach used, the problem is of the utmost practical importance as instability of a model raises the inac curacy of the resultant estimates, providing also failures at the stag e of the model fitting and total allowable catch (TAG) forecasting. So , clarification of the stability conditions of stock - production mode ls enables their more deliberate and effective use in management of ma rine living resources. The effort-controlled models exhibit higher sta bility as compared with the catch-controlled ones: the fishing effort acts as a recovering force which suppresses the perturbations initiate d in the model by the inevitable errors in estimating the initial popu lation level. Therefore, the optimal management strategies and the TAC forecasts derived from the effort-controlled models are less risky th an those obtained with the use of the catch-controlled ones.