Pacific whiting (Merluccius productus) is commercially and ecologically one of the most important fishery resources in the Pacific coast of the United States. The fishery is currently going through a period of rapid and profound transformation that could cause a substantial redistribution of benefits among domestic users. Benefits from the Pacific whiting fishery consist of conflicting biological, social, economic and regional objectives. A major management issue is the problem of resource allocation between the domestic offshore and shore-based fleets. Economic analysis of fishery policy based on the single objective of maximizing present value of net revenues (PVNR) fails to realistically confront the Pacific whiting fishery management problem. This work proposes the use of the less restrictive concept of Pareto optimality as a criterion for efficiency in the fishery. The main objective of this dissertation is to develop a multiobjective bioeconomic policy model of the Pacific whiting fishery in the United States. The purpose of the model is to analyze the implications (trade-offs) of resource allocation alternatives on the level of three policy objectives PVNR, production, and female spawning biomass. Pareto optimal solutions for the three policy objectives were generated under various specifications of the model by means of generating techniques. Three policy instruments were considered: harvest quotas, fleet/processing capacity limits, and allocation between the shore-based and offshore fisheries. Results were presented in the form of trade-off curves. The analysis suggests that policy objectives in the case of Pacific whiting are non-complementary. Instead of a unique "optimal" policy solution the Pacific whiting fishery policy problem possesses an infinite number of [Pareto] "optimal" policy solutions. The principal characteristic of Pareto optimal solutions is that in moving from one to another, the objectives must be traded-off among each other. In spite of the uncertainties regarding the dynamics of the Pacific whiting fishery, the preliminary nature of the data and the simplistic specification of the model, the analysis in this work demonstrates the potential benefits of vector optimization for fishery policy development and analysis. / Graduation date: 1993

No description available.

No description available.

Life-history traits in fish populations are highly correlated. A subset of these correlations are called allometric scaling, they refer to biological processes which can be described using body size as independent variable. Particularly, allometric scaling related with food consumption (Q) and biomass production (P) has gained the attention of ecologists for several decades. This thesis proposes a quantitative framework for food consumption, which allows both the identification of the mechanisms underlying the allometric scaling for Q and the development of a predictive model for consumption to biomass ratio (Q/B) in fish populations. This thesis is based on the fact that food consumption can be inferred from first principles underlying the von Bertalanffy growth model. In addition, it has been noticed in the literature that biomass production and food consumption show similar allometric scaling dependence, therefore, both can be derived from these first principles. Thus, a similar quantitative framework was used to produce models for P/B in fish populations. Once functional forms for production and food consumption were identified, a third model was developed for the ratio between production and consumption (P/Q). This ratio is usually named ecological efficiency because it determines how efficiently a population can transform ingested food into biomass. Several authors have noticed that P/Q remains invariant (independent of body size) across species. From a theoretical point of view, the results presented here allow the first quantitative explanation for the existence of the allometric scaling for Q/B and the invariance of P/Q across fish species. These results, together with the explanation for allometry in P/B reported in the literature, suggest that the regular across-species pattern for the trio {P/B,Q/B,P/Q} can be explained by basic principles that underpin life-history in fish populations. This quantitative framework for the trio {P/B,Q/B,P/Q} is based on an explicit dependence with body size, which simplifies the estimation of these quantities. Model complexity depends, in part, on which data are available. Models were applied to real data from commercially important species fished in Chile. Statistical properties of the new models were evaluated by an intensive resampling approach. The simplest possible model for the trio {P/B,Q/B,P/Q} rests on the assumption of a stable age distribution. These quantities have a key importance in ecosystem modelling because they determine population energetics in terms of food intake by predation and the transformation of this energy into population biomass of predators. Application of the new models produces results which were comparable to those given by standard methods. This thesis is a result of multidisciplinary research which attempts to make a contribution to the understanding of the mechanisms underlying the allometric scaling of food consumption and production in fish populations. It proposes models for the trio {P/B,Q/B,P/Q} and thus, has the potential to be widely applicable in fisheries science.

Erratum pages inserted onto front end papers. / Bibliography: leaves 226-244. / vi, 244 leaves ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis developed mathematical models of commercially exploited fish populations, addressing the question of how to harvest a predator-prey metapopulation. Optimal harvesting strategies are found using dynamic programming and Lagrange multipliers. Rules about harvesting source/sink populations, more/less vulnerable prey subpopulations and more/less efficient predator subpopulations are explored. Strategies for harvesting critical prey subpopulations are suggested. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied Mathematics, 2000?

In fisheries, advice for the management of fish populations is based upon management quantities that are estimated by stock assessment models. Fisheries stock assessment is a process in which data collected from a fish population are used to generate a model which enables the effects of fishing on a stock to be quantified. This study determined the effects of various data sources, assumptions, error scenarios and sample sizes on the accuracy with which the age-structured production model and the Schaefer model (assessment models) were able to estimate key management quantities for a fish resource similar to the Cape hakes (Merluccius capensis and M. paradoxus). An age-structured production model was used as the operating model to simulate hypothetical fish resource population dynamics for which management quantities could be determined by the assessment models. Different stocks were simulated with various harvest rate histories. These harvest rates produced Downhill trip data, where harvest rates increase over time until the resource is close to collapse, and Good contrast data, where the harvest rate increases over time until the resource is at less than half of it’s exploitable biomass, and then it decreases allowing the resource to rebuild. The accuracy of the assessment models were determined when data were drawn from the operating model with various combinations of error. The age-structured production model was more accurate at estimating maximum sustainable yield, maximum sustainable yield level and the maximum sustainable yield ratio. The Schaefer model gave more accurate estimates of Depletion and Total Allowable Catch. While the assessment models were able to estimate management quantities using Downhill trip data, the estimates improved significantly when the models were tuned with Good contrast data. When autocorrelation in the spawner-recruit curve was not accounted for by the deterministic assessment model, inaccuracy in parameter estimates were high. The assessment model management quantities were not greatly affected by multinomial ageing error in the catch-at-age matrices at a sample size of 5000 otoliths. Assessment model estimates were closer to their true values when log-normal error were assumed in the catch-at-age matrix, even when the true underlying error were multinomial. However, the multinomial had smaller coefficients of variation at all sample sizes, between 1000 and 10000, of otoliths aged. It was recommended that the assessment model is chosen based on the management quantity of interest. When the underlying error is multinomial, the weighted log-normal likelihood function should be used in the catch-at-age matrix to obtain accurate parameter estimates. However, the multinomial likelihood should be used to minimise the coefficient of variation. Investigation into correcting for autocorrelation in the stock-recruitment relationship should be carried out, as it had a large effect on the accuracy of management quantities.

Dissertation (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The efficient management of renewable resources may ensure sustainable income to communities and countries. In the past the mathematical modelling used in the management decisions, in South Africa, was based on biological considerations only. In this thesis we include economic factors in the models and aim to determine steady state harvesting levels such that a maximum present value of all future revenues may be reached. A bio-economical approach is followed throughout the study and applied to the South African Cape Rock Lobster (Jasus lalandii) resource. We first address the problem using the simplest surplus production models. The model is applied to the Cape Rock Lobster, finding that the economical factors do indeed influence the steady state results, emphasising that they should be incorporated in the modelling process. A more descriptive two-sex-delay-difference model is then applied, which includes delay times for juveniles to reach sexual maturity and distinguishes between sexes. Yet further involved stage-class models are also studied and we propose a solution to the non-linear programming problem reached. These models may assist decision makers in future as knowledge on, for example, the growth of the two sexes, proper size limits and the influence of price differences are gained. Finally, we propose a harvesting strategy where catch is taken from alternative spatial lanes and apply here results from reaction diffusion theory. This theoretical approach might provide guidelines to new and underdeveloped fisheries in future, but also influence current inshore fisheries towards new management strategies. / AFRIKAANSE OPSOMMING: Die doeltreffende bestuur van hernubare hulpbronne kan 'n volhoubare ekonomiese opbrengs aan gemeenskappe en lande verseker. In die verlede is die wiskundige modelle wat in die besluitnemingsproses gebruik is, in Suid Afrika, gebaseer op biologiese oorwegings alleen. In hierdie studie word ook ekonomiese faktore in die modelle ingesluit en word ewewigstoestande bepaal vir vangste, sodanig dat 'n maksimum huidige waarde van toekomstige inkomste uit 'n vissery bereik word. 'n Bio-ekonomiese benadering word deurgaans gevolg en modelle word toegepas op die Suid-Afrikaanse Weskus Kreefbron (Jasus lalandii). Die studie begin deur basiese surplus produksie modelle te gebruik. Die resultate van die toepassing op die Weskus Kreefbron toon dat die ekonomiese faktore 'n groot invloed op die voorgestelde ewewigstoestand van die populasie het. Dit benadruk dus die feit dat hierdie faktore in die modelleringsproses ingesluit behoort te word. Meer beskrywende twee-geslag-vertragings-verskil modelle word daarna toegepas, en sluit in 'n vertragings periode vir vis om 'n volwasse stadium te bereik. Hierdie tydfaktor verskil dikwels vir mannetjies en wyfies en daarom word hier 'n twee-geslag model gebruik. Meer gevorderde klasse modelle word ook bespreek. Ons stel 'n oplossing vir hierdie nie-lineêre programmeringsprobleem voor. Hierdie gevorderde modelle mag in die toekoms handige hulpmiddels wees wanneer inligting rakende 'n spesie gesoek word. Sulke inligting mag insluit die groeitempos van mannetjies en wyfies, geskikte grootte beperkings vir vangste en die invloed van prysverskille vir verskillende groottes vis. 'n Nuwe vangste strategie word ook voorgestel waar vangste slegs geneem word uit alternatiewe ruimtelike bane en pas ons hier resultate uit die reaksie-diffusie teorie toe. Hierdie teoretiese oplossings mag riglyne bied wanneer nuwe visserye in die toekoms ontgin word, maar ook huidige visserye beïnvloed in die rigting van 'n nuwe bestuur strategie.