Mixed Populations—the Analysis of Community Dynamics

Abstract

In this paper we have hitherto dealt with populations consisting of a single species, but many exploited areas contain more than one species of commercial importance, and often these are caught simultaneously by the particular gear in use. In such cases we are interested in the effect of different characteristics of fishing intensity on the combined yield of all species, weighted if necessary by their relative values, and in this section we discuss briefly the procedures applicable to fisheries based on mixed populations. Strictly speaking, the behaviour of all fish populations inhabiting the same water basin is to some extent interrelated, since all are ultimately dependent on the productivity of the primary producer organisms of that area. It is only when there is direct interaction between two or more populations (§11.2) that special methods of analysis are essential, and in many instances there may be populations in the same area which, at least from the point of view of their exploitation, may be treated as effectively independent of each other (§11.1).