Doctoral Thesis
Key factors influencing the population dynamics of economically important short-lived invertebrate species in Western Australia
Murdoch University
Doctor of Philosophy (PhD), Murdoch University
2026
DOI:
https://doi.org/10.60867/00000047
Abstract
My PhD research focusses on understanding impacts of environmental factors on the productivity of short-lived, economically important invertebrate species, and associated implications for their sustainability. As case studies, I investigated i) the blue swimmer crab, Portunus armatus, once commercially important in Cockburn Sound, a nearshore temperate marine embayment in south-western Western Australia (WA), and ii) two commercially important populations of white banana prawns, Penaeus merguiensis, in tropical nearshore marine areas of northern WA (Nickol Bay and the Kimberley).
First, using 18-years of fishery-independent monitoring data, I estimated size-at-age using using modal progression analyses, seasonal growth curves and generalised linear models to determine patterns of growth and variation with environmental and biological factors. I found substantial density-dependent temporal variation in the growth of P. armatus in Cockburn Sound associated with changes in primary productivity (chlorophyll-a), and juvenile crab density. I next developed and applied a state-space biomass dynamics model to available catch, CPUE and environmental data for P. armatus, and showed that primary productivity changes and depensatory stock dynamics have significantly impacted this population. Specifically, this modelling provided evidence that primary productivity declines in Cockburn Sound combined with historic heavy fishing pressure (leading to depensation), are responsible for its lack of population recovery.
I next extended this state-space biomass dynamics model to estimate the extent to which rainfall impacts population biomass and catchability of P. merguiensis in northern WA. This modelling demonstrated that whilst P. merguiensis biomass and catchability are positively related with summer rainfall, fishing mortality was substantially higher in some years where rainfall is higher than average. This likely reflects fishers focusing more effort towards catching prawns in years when they are aware that prawns are abundant, which has clear sustainability implications.
My study highlights the importance of accounting for environmental factors when modelling populations of short-lived species that occupy habitats which are sensitive to environmental change. The biomass dynamics models developed in my study provide valuable tools for assessing environmental impacts on short-lived, relatively data-deficient fished populations.
Details
- Title
- Key factors influencing the population dynamics of economically important short-lived invertebrate species in Western Australia
- Authors/Creators
- Rachel Marks
- Contributors
- James Tweedley (Supervisor) - Murdoch University, School of Environmental and Conservation SciencesNeil Loneragan (Supervisor) - Murdoch University, Centre for Sustainable Aquatic EcosystemsAlex Hesp (Supervisor)
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Publisher
- Murdoch University
- Identifiers
- 991005848589007891
- Murdoch Affiliation
- Centre for Sustainable Aquatic Ecosystems
- Resource Type
- Doctoral Thesis
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