On The Dynamics Of Exploited Fish Populations

Among the fishes, a remarkably wide range of biological adaptations to diverse habitats has evolved. As well as living in the conventional habitats of lakes, ponds, rivers, rock pools and the open sea, fish have solved the problems of life in deserts, in the deep sea, in the cold antarctic, and in warm waters of high alkalinity or of low oxygen. Along with these adaptations, we find the most impressive specializations of morphology, physiology and behaviour. For example we can marvel at the high-speed swimming of the marlins, sailfish and warm-blooded tunas, air-breathing in catfish and lungfish, parental care in the mouth-brooding cichlids, and viviparity in many sharks and toothcarps. Moreover, fish are of considerable importance to the survival of the human species in the form of nutritious, delicious and diverse food. Rational exploitation and management of our global stocks of fishes must rely upon a detailed and precise insight of their biology. The Chapman & Hall Fish and Fisheries Series aims to present timely volumes reviewing important aspects of fish biology. Most volumes will be of interest to research workers in biology, zoology, ecology and physiology but an additional aim is for the books to be accessible to a wide spectrum of non-specialist readers ranging from undergraduates and postgraduates to those with an interest in industrial and commercial aspects of fish and fisheries.

This book explores how we can solve the urgent problem of optimizing the use of variable, uncertain but finite fisheries resources while maintaining sustainability from a marine-ecosystem conservation perspective. It offers readers a broad understanding of the current methods and theory for sustainable exploitation of fisheries resources, and introduces recent findings and technological developments. The book is divided into three parts: Part I discusses fish stock dynamics, and illustrates how ecological processes affecting life cycles and biological interactions in marine environments lead to fish stock variability in space and time in major fish groups; small pelagic fish, demersal fish and large predatory fish. These insights shed light on the mechanisms underlying the variability in fish stocks and form the essential biological basis for fisheries management. Part II addresses the technologies and systems that monitor changes in fisheries resources and marine ecosystems using two approaches: fishery-dependent and fishery-independent data. It also describes acoustic surveys and biological sampling, as well as stock assessment methods. Part III examines management models for effectively assessing the natural variability in fisheries resources. The authors explore ways of determining the allowable catch in response to changes in stock abundance and how to incorporate ecological processes and monitoring procedures into management models. This book offers readers a broad understanding of sustainable exploitation as well as insights into fisheries management for the next generation.

This book really began in 1980 with our first microcomputer, an Apple II +. The great value of the Apple II + was that we could take the computer programs we had been building on mainframe and mini-computers, and make them available to the many fisheries biologists who also had Apple II + 's. About 6 months after we got our first Apple, John Glaister came through Vancouver and saw what we were doing and realized that his agency (New South Wales State Fisheries) had the same equipment and could run the same programs. John organized a training course in Australia where we showed about 25 Australian fisheries biologists how to use microcomputers to do many standard fisheries analyses. In the process of organizing this and sub sequent courses we developed a series of lecture notes. Over the last 10 years these notes have evolved into the chapters of this book.

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.