Impact of Fishing Pressure on Mean Length of Fish

Abstract

In Chapters 2 and 3 we dealt with each population of a species in a fairly aggregate way. There was one state variable representing the stock of whales, and one for the sand lance. That level of disaggregation was sufficient to capture the main features of our system—the interaction between predators and prey. In Chapter 4 we treated juvenile and adult members of the population alike and did not distinguish differences in their propensities to contract a disease. In contrast, in this chapter we wish to distinguish within each population among those individuals that have different features, such as different ages, different lengths, and different rates of reproduction. With such a model at hand we can investigate, for example, how different environmental or anthropogenic pressures may influence the fate of an individual subgroup of the population. Specifically, we shall model here how the age and length distribution within a fish population changes as fishing selectively targets older and larger individuals.

Clearly, it is not possible to go back and redirect history. But now—not for long—there is a chance, a brief window of opportunity to restore and protect the remaining healthy ecosystems that support us. Most important, most urgent, we must protect the principal substance of the biosphere: the sea. Silvia Earle, from SeaChange