Fishing

Abstract: Series foreword AJ Pitcher Foreword D Pauly Part One: Fundamentals of the theory of fishing, illustrated by analysis of a trawl factoy Introduction:- theoretical methods in the study of fishery dynamics The basis of a theoretical model of an exploited fish population and definition of the primary factors Mathematical representation of the four primary factors Recruitment Natural mortality Fishing mortality Growth A simple model giving the annual yield in weight from a fishery in a steady state Adaptation of the simple model to give other characteristics of the catch and population Part Two: Some extensions of the simple theory of fishing Recruitment and egg-production Natural mortality Fishing mortality and effort Growth and feeding Spatial variation in the values of parameters movement of fish within the exploited area Mixed populations:- the analysis of community dynamics Part Three: Estimation of parameters Relative fishing power of vessels and standardisation of commercial statistics of fishing effort Estimation of the total mortality coefficient (F + M), and the maximum age, t* Seperate estimation of fishing and natural mortality coefficients Recruitment and egg-production Growth and feeding Part Four: The use of theoretical models in a study of the dynamics and reaction to exploitation of fish populations Application of population models of part one Application of population models of part two Principles and methods of fishery regulation Requirements for the regulation of the North Sea Demersal fisheries Appendices Bibliography and author index Subject index List of amendments compiled by the American Fisheries Society

Abstract: The mean trophic level of the species groups reported in Food and Agricultural Organization global fisheries statistics declined from 1950 to 1994. This reflects a gradual transition in landings from long-lived, high trophic level, piscivorous bottom fish toward short-lived, low trophic level invertebrates and planktivorous pelagic fish. This effect, also found to be occurring in inland fisheries, is most pronounced in the Northern Hemisphere. Fishing down food webs (that is, at lower trophic levels) leads at first to increasing catches, then to a phase transition associated with stagnating or declining catches. These results indicate that present exploitation patterns are unsustainable.

Abstract: Fisheries have rarely been 'sustainable'. Rather, fishing has induced serial depletions, long masked by improved technology, geographic expansion and exploitation of previously spurned species lower in the food web. With global catches declining since the late 1980s, continuation of present trends will lead to supply shortfall, for which aquaculture cannot be expected to compensate, and may well exacerbate. Reducing fishing capacity to appropriate levels will require strong reductions of subsidies. Zoning the oceans into unfished marine reserves and areas with limited levels of fishing effort would allow sustainable fisheries, based on resources embedded in functional, diverse ecosystems.

Abstract: After a long history of overexploitation, increasing efforts to restore marine ecosystems and rebuild fisheries are under way. Here, we analyze current trends from a fisheries and conservation perspective. In 5 of 10 well-studied ecosystems, the average exploitation rate has recently declined and is now at or below the rate predicted to achieve maximum sustainable yield for seven systems. Yet 63% of assessed fish stocks worldwide still require rebuilding, and even lower exploitation rates are needed to reverse the collapse of vulnerable species. Combined fisheries and conservation objectives can be achieved by merging diverse management actions, including catch restrictions, gear modification, and closed areas, depending on local context. Impacts of international fleets and the lack of alternatives to fishing complicate prospects for rebuilding fisheries in many poorer regions, highlighting the need for a global perspective on rebuilding marine resources.

Abstract: Summary The foregoing examples illustrate how the theory developed here may be employed to make estimates concerning the condition of a commercial marine fishery. The examples employed, although having perhaps as complete information as any available for this purpose, leave something to be desired. In particular, in both of these examples, very little or no data are available concerning intensity of fishing and abundance for the early period of development of the fishery, well before the maximum catches are reached. A great deal of precision would be added to the estimate if such information were available. We may emphasize, therefore, the desirability of obtaining detailed information on the total catch and catch-per-unit-of-effort from as early in the development of a commercial fishery as may be possible. Measurements of fishing mortality rates at more than one level of population would also be desirable, since they would make possible verification of the adequacy of the form of equation (13a) for describing the changes in population under the joint influences of growth and fishing. In order to apply the theory developed here to the tropical tuna fishery, it will be necessary to compile statistics of catch, abundance and intensity of fishing over a considerable series of years, beginning as early in the history of the fishery as possible. This task is well under way. It will also be necessary to obtain some estimate of the rate of fishing mortality, or to devise some other means of estimating the constant k 2 . Estimation of fishing mortality from tagging promises to be a difficult problem for the tunas. Exploration of other means of obtaining the relationship between U and P appears, therefore, to constitute an important line of investigation.