Using catch-per-unit-effort data to solve spatial problems in Orange Roughy abundance estimates

<p>This thesis describes a thorough analysis of the Andes Complex orange roughy fishery, which started in 1991 and continues to date. The Andes Complex orange roughy fishery displays a rapid initial decline in catch rate, followed by a prolonged period of relatively stable catch rate. This trend is the classic feature of a hyperdepletion catch rate. The trends in the observed Andes Complex orange roughy catch rates were explored through the development of eight modified Schaefer Surplus Production Models (SPM). Each model applied a hypothesis about a mechanism catalysing the observed trend of the fishery. The SPM was modified by either adding new information to the model, or an additional parameter. The fits of the modified models were optimised to elucidate values of unknown parameters in the SPM, and these were used to create estimated abundance indicies for each model. Then I compared each index to the observed abundance index (catch rate), derived following an Exploratory Analysis. The best candidate models, which had the smallest likelihoods, BIC values, and best visual fits, were those assuming population growth rate changed midway through the fishery, or that the population size decreased following habitat damage (from trawling).</p>