Management of Multiple Resources

• Published in: Journal of the Fisheries Research Board of Canada
• Main Author: Garrod, D. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1973
• Subjects: General Medicine; atlantic cod; North Atlantic
• Online Access: http://dx.doi.org/10.1139/f73-321; http://www.nrcresearchpress.com/doi/pdf/10.1139/f73-321

From the point of view of the exploiting industry, fisheries can be classified according to the breadth of its resource base, varying from single-species fisheries to integrated multiple-resource fisheries.All resources exhibit short-term fluctuations, which in the multiple-resource fishery necessarily lead to differential rates of exploitation of the component resources.The differential rates of exploitation in the components of a multiple resource, even by aimed activity of the same vessels, imply nonequilibrium conditions in the individual stocks. This contrasts with the basic objective of conventional stock assessments to establish yield under equilibrium conditions.A technique of investigating and comparing yield from resources in equilibrium or nonequilibrium is illustrated with reference to North Atlantic cod, the "equilibrium" fishery being one in which the distribution of fishing is independent of stock density, whereas the nonequilibrium characteristics of a multiple-resource base are associated with a distribution of fishing mortality weighted by the density of the component resources.Provided fishing mortality varies about an appropriate mean level, there is no marked difference in yield under equilibrium or nonequilibrium conditions. Fisheries are robust systems which can tolerate wide between-year variations in fishing mortality provided it fluctuates around an appropriate mean level. This implies that there is no advantage in trying to manage a fishery by a precise control of fishing mortality.Under certain circumstances, determined by the variability of the particular resource complex, a density-dependent regime of exploitation may be a more efficient method of exploitation of a given array of resources. This has the additional advantages of reducing the year-to-year variation in yield to the total fishery and of reducing the risk of overexploitation in cases where catchability can be expected to be inversely proportional to stock abundance.