Fishery dependent data--length distributions, sex ratios, maturity schedules, and species composition of landed catches--are necessary for stock assessments. These data are currently collected by state port biologists using a sampling design that randomly selects samples from a small percentage of a very large target population. Sampling programs may need to increase the sample size and possibly expand data collection times into evenings and weekends. This must also be accomplished in an economically reasonable manner, which is a significant challenge. Working cooperatively with the seafood processing plants is one way to meet these challenges. This study explored the feasibility of implementing a cooperative sampling program for Pacific West Coast groundfish, with the goal of improving the precision and accuracy of estimates derived from the fishery dependent samples. The study was a cooperative project utilizing seafood processing plant workers to collect fish length frequency data. There is evidence that the seafood plant workers can measure fish with reasonable accuracy. This cooperative effort has the potential to dramatically increase the sample size and the coverage of sampled catch landings. / Graduation date: 2001

No description available.

Stock assessments for many U.S. Pacific coast groundfish stocks are developed using the catch-at-age method known as Stock Synthesis. In this work a simulation package was developed and used to evaluate the sensitivity of the Stock Synthesis program. More specifically, the evaluation focused on the impacts of input data errors and stock characteristics on the accuracy and precision of Synthesis estimates. Factors examined included the length of the time series of data, the rate of natural mortality, the shape of the fishery and survey selectivity curves, the trend in the rate of fishing mortality, the recruitment pattern, and errors in the observed data for annual catch, fishing effort, fishery and survey age composition, and survey biomass indices. First, the study evaluated the sensitivity of the Stock Synthesis program applied to populations with simple multinomial age compositions. The length of the data series and sample size were the two most influential factors. Second, the study focused on populations with compound multinomial age composition, in which the age composition data were over-dispersed relative to simple multinomial samples. When the fishery age composition actually followed a compound multinomial distribution, the estimates produced by the Stock Synthesis program, which assumed simple multinomial distributions with maximum sample sizes of 400 fish, were moderately more biased and more variable. When applying Synthesis to populations whose age compositions follow compound multinomial distributions, the results from the experiments indicated that a common configuration, in which age sample sizes in the likelihood specification are limited to 400 fish per sample, probably gives age composition data too much emphasis. The experiments indicated that using 200 as the upper limit provided more accurate results than using 400. Third, the actual stock assessment of yellowfin sole (Limanda Aspera) was taken as a case study and it was found that more accurate assessment results could be achieved from a better balance in the amount of sampling effort allocated to age composition data versus survey biomass estimates. / Graduation date: 2002

Statistical modeling has evolved around building increasingly more complex models, even though it is common knowledge among statisticians that an optimal model size usually exists for any given data set. Having overly complex models leads to imprecise parameter estimates and tends to increase the subjective role of the modeler, which can distort the perceived characteristics of the system under investigation. One approach for controlling the tendency of contemporary models to increase in complexity and subjectivity is to use model selection criteria that account for these factors. The initial task of this thesis was to review existing model selection criteria. The second task involved testing the effectiveness of several model selection criteria. The Stock Synthesis program, which is often used on the U.S. west coast to assess the status of exploited marine fish stocks, was used for this evaluation because of its ability to handle multiple data sets and mimic highly complex population dynamics. In the review of existing model selection criteria the Akaike Information Criterion (AIC) and Schwarz's Bayesian Information Criterion (BIC) were identified as the criteria that most completely satisfied the fundamental principles of model selection: goodness-of-fit, parsimony, and objectivity. Their ability to select the correct model form and produce accurate parameter estimates was evaluated in Monte Carlo experiments with the Stock Synthesis program and were compared to a simple maximum log-likelihood criterion. The maximum log-likelihood criterion surprisingly outperformed both AIC and BIC in several of the experiments. / Graduation date: 1999

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 132-145).

A model of a fishery with an uncertain fish stock is proposed to compare alternative management systems with individual transferable quotas (ITQs). Assumptions of the model include: (1) the fish stock fluctuates randomly year by year; (2) in-season stock depletion is small; (3) the total allowable catch (TAC) set by the quota authorities has a definite relation with the fish stock level; (4) the true value of the stock level is revealed only at the middle of each season, when the authorities revise the TAC; (5) fishers form rational expectations on future quota prices. The principal results are: (a) If fishers are risk-neutral, the share quota (SQ) system and the quantity quota (QQ) system generate the same amount of fishery rent, although the division of the rent between fishers and the authorities under one system is different from the other. If the TAC is proportional to the stock level, the more price-inelastic the demand for fish is, the more likely it is that fishers are better off under the QQ system at the expense of the authorities. (b) A quota tax and a harvest tax that collect the same amount of revenue for the authorities result in the same division of the fishery rent among heterogeneous fishers. The quota tax and the profit tax differ in this respect. Which fishers will prefer a quota tax over a profit tax will depend on fishers' shares of the initial quota endowment and in total inframarginal profits afterward. (c) If fishers are risk-averse, the SQ system and the QQ system are not equivalent in their allocative efficiency. An example shows that the SQ system is potentially better than the QQ system when fishers prefer the latter and the authorities prefer the former. This conclusion has to be modified if risk-neutral traders participate in the quota market

Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, Discipline of Environmental Biology, 2006. / "January 2006" Bibliography: pages 188-209. Also available in print form.

A model of a fishery with an uncertain fish stock is proposed to compare alternative management systems with individual transferable quotas (ITQs). Assumptions of the model include: (1) the fish stock fluctuates randomly year by year; (2) in-season stock depletion is small; (3) the total allowable catch (TAC) set by the quota authorities has a definite relation with the fish stock level; (4) the true value of the stock level is revealed only at the middle of each season, when the authorities revise the TAC; (5) fishers form rational expectations on future quota prices. The principal results are: (a) If fishers are risk-neutral, the share quota (SQ) system and the quantity quota (QQ) system generate the same amount of fishery rent, although the division of the rent between fishers and the authorities under one system is different from the other. If the TAC is proportional to the stock level, the more price-inelastic the demand for fish is, the more likely it is that fishers are better off under the QQ system at the expense of the authorities. (b) A quota tax and a harvest tax that collect the same amount of revenue for the authorities result in the same division of the fishery rent among heterogeneous fishers. The quota tax and the profit tax differ in this respect. Which fishers will prefer a quota tax over a profit tax will depend on fishers' shares of the initial quota endowment and in total inframarginal profits afterward. (c) If fishers are risk-averse, the SQ system and the QQ system are not equivalent in their allocative efficiency. An example shows that the SQ system is potentially better than the QQ system when fishers prefer the latter and the authorities prefer the former. This conclusion has to be modified if risk-neutral traders participate in the quota market / Arts, Faculty of / Vancouver School of Economics / Graduate

No description available.

Thesis (Ph. D.)--College of William and Mary. / Vita. Includes bibliographical references.