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dc.contributor.authorHatch, Joshua M.en
dc.date.accessioned2014-12-05T07:01:04Zen
dc.date.available2014-12-05T07:01:04Zen
dc.date.issued2013-06-12en
dc.identifier.othervt_gsexam:314en
dc.identifier.urihttp://hdl.handle.net/10919/50988en
dc.description.abstractInherent uncertainties in the stock assessment for weakfish have precluded accurate and consistent advice concerning the management of commercial and recreational fisheries. Error within ageing techniques, used to assess relative age frequencies within commercial and recreational harvest, has been cited as a potential source for uncertainty during assessments of the weakfish fishery. The implications for age-reading error on weakfish stock assessment were explored using measurement-error growth models (i.e. Chapter 1), ageing error matrices within a statistical catch-at-age framework (i.e. Chapter 2), and Monte Carlo simulations to gauge robustness of ignoring this type of uncertainty during fisheries stock assessment (i.e. Chapter 3). Measurement-error growth models typically resulted in weakfish that grew to reach larger sizes, but at slower rates, with median length-at-age being overestimated by traditional von Bertalanffy growth curves, at least for the observed age range. Measurement-error growth models allow for incorporation of ageing uncertainty during nonlinear growth curve estimation, as well as the ability to estimate the ageing error variance. Age-reading error was further considered during statistical catch-at-age analysis of the weakfish fishery, mainly through permutations of true catch-at-age via ageing error matrices constructed from estimates of the ageing error variance, thus reflecting changes in relative age compositions as a consequence of ageing uncertainty. As a result, absolute levels of key population parameters were influenced, but general trends in those parameters tended to be similar, with strong congruency across models as to weakfish stock dynamics in most recent years. Finally, Monte Carlo simulations showed that implications for age-reading error on weakfish stock assessment are varied, depending upon the direction and magnitude of the ageing uncertainty. However, relative trends of parameter estimates over time tended to be similar, resulting in proper allocation of weakfish stock status, regardless of the type of ageing error considered. Furthermore, assuming negligible ageing uncertainty within fishery-independent surveys appears reasonable, as simulations incorporating ageing error within indices of relative abundance showed similar patterns to situations that only considered observation noise.en
dc.format.mediumETDen
dc.publisherVirginia Techen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectAgeing erroren
dc.subjectWeakfishen
dc.subjectBayesianen
dc.subjectStatistical catch-at-ageen
dc.subjectSimulationen
dc.titleThe Effects of Ageing Error on Stock Assessment for Weakfish Cynoscion regalisen
dc.typeThesisen
dc.contributor.departmentFisheries and Wildlife Sciencesen
dc.description.degreeMaster of Scienceen
thesis.degree.nameMaster of Scienceen
thesis.degree.levelmastersen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.disciplineFisheries and Wildlife Sciencesen
dc.contributor.committeechairJiao, Yanen
dc.contributor.committeememberOrth, Donald J.en
dc.contributor.committeememberO'Reilly, Robert Lauxen
dc.contributor.committeememberSmith, Eric P.en


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