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Type: Thesis
Title: Modelling the population and catchability of the southern rock lobster (Jasus edwardsii) in South Australia and Victoria using commercial fisheries catch rate data
Author: Feenstra, John Erik
Issue Date: 2018
School/Discipline: School of Mathematical Sciences
Abstract: The aim of this thesis is to contribute to the field of fisheries science and population modelling, having as subject matter the stocks of southern rock lobster (Jasus edwardsii) exploited by the commercial fisheries of the Southern Zone in South Australia (SZRLF) and the Western Zone in Victoria (WZRLF), Australia. The utility of a statistic known as “catch rate” is explored in regard to inferences drawn about the population and catchability of these southern rock lobster stocks. This thesis is in the form of “by publication” and contains three papers, two of which are published (“Paper One” and “Paper Three”) while one is submitted and under review (“Paper Two”). Studies on some crab and lobster fisheries have shown that natural anomalies in water temperature can substantially impact catch rates. Paper One involved a multivariate regression study of abiotic environmental influences considered to act through catchability on daily catch rates of the SZRLF stock, finding that moon phase, bottom temperature, and wave action were retained in the final model but explained relatively little variance or trend in catch rate. However, the study determined several qualitative outcomes regarding the nature of the influences on catch rates that were not previously reported in the literature for southern rock lobster. Mean catch rate was estimated to be 10% greater just prior to full moon than at new moon, wave height lagged at three days had a positive influence, while bottom temperature and (contemporary) wave height had a negative influence. Similar findings were determined for WZRLF except for moon phase. Paper One compared these outcomes to those from studies on other lobster species, and proposed several hypotheses as explanations. In Paper Two a GLM analysis was performed on WZRLF catch rates that included vessel identifier as a covariate, which represents a fishery influence on catchability, and found that it was substantially more influential on the trend in catch rate than was observed for the environmental influences reported in Paper One. Results suggest that the composition of the WZRLF vessel fleet changed over the years due to vessels exiting from the fishery being on average less efficient at fishing than the rest of the fleet, and hence driving an increase in net catchability and an overly optimistic assessment of the stock. Alternative forms of diagnostic indices were developed to study changes in vessel-driven catchability. The underlying mechanisms of vessel fleet dynamics were investigated and discussed in relation to other fisheries. In Paper Three, novel multi-year depletion models were developed based on extending the Leslie-Davis model. These were applied to data of the SZRLF, producing estimates not only of catchability and yearly trend in relative abundance, but also absolute exploitable abundance and yearly recruitment numbers. Although making strong assumptions about catchability and recruitment for a period in each year, during the rest of the fishing year it avoids the need for such assumptions nor requires fishing effort data. Results compared reasonably with those of a more sophisticated but data hungry integrated stock assessment model.
Advisor: Bean, Nigel
McGarvey, Richard
Linnane, Adrian
Punt, Andre
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 2018
Keywords: Southern rock lobster
catch rate
depletion model
environmental variables
fleet dynamics
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at:
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