On The Dynamics Of Exploited Fish Populations PDF Download

A possible form of a theory of exploitation of fish populations was examined. The exploitation theory was derived from a theory of community dynamics that represents the interactions between populations in a biological community with complex interrelated systems of isoclines on phase planes. The isocline systems are deduced, with a graphical calculus, from response functions that represent the biological characteristics of each of the interacting populations. The time-invariant systems of isoclines and the response functions from which they are deduced underlie, determine, and so explain time-variant population performances. A fish population was defined as a member of a simple community. Isocline systems were deduced to represent and provide an integrated explanation of the effects of the following factors on the dynamics and persistence of the fish populations: changes in the levels of environmental factors such as light energy and fishing effort, competition for food with another fish population, and foraging by the fish population on two prey species. The impact of these factors on the magnitude and form of the recruitment, production, and yield curves of the fish population was also determined. In general increases in light energy input rate and other environmental factors such as plant nutrients, and the addition of another prey species to the diet of the fish population, were found to increase the magnitude of these curves. Competition reduced their magnitude. With the theoretical approach developed here, causal-deterministic explanations of the dynamics of exploited fish populations can be developed. These explanations couple the dynamics of the fish population to the dynamics of other populations in the biological community and to external environmental factors. This approach thus permits broad understanding of the performances of exploited fish populations as they interact with their co-extensive environmental systems.