Abstract
The West Coast Rock Lobster Managed Fishery (WCRLMF) moved from input to output controls in 2010. This change affected the relativity of fishery-based data sources (e.g., catch rates and landed size composition), making the assessment of the fishery problematic. A novel examination of the stock dynamics was required to ensure the robustness of the stock assessment and associated management arrangements. This study derived estimates of current biomass levels and harvest rates from the release of over 60,000 tagged western rock lobsters (Panulirus cygnus). A Brownie tag-recapture (BTR) model was initially implemented to provide an assessment on a fishery-wide basis. Estimates from this were compared to those derived from a novel purpose-built tag-recapture individual-based model (IBM) that accounted for sex, size, month, and location-specific changes in catchability. The two models produced similar estimates on a fishery-wide scale—harvest rate (HR 0.26 vs 0.30, respectively) and legal-sized biomass (about 24,500 vs 20,735 t, respectively)—while the IBM also provided estimates on a far finer spatial and temporal scale. Both models indicate that the WCRLMF is currently in a very sustainable condition and is being fished at a rate below maximum economic yield (HRmey is about 0.39). These findings were in concert with estimates derived for this fishery based on two separate catch-rate based population models, an integrated population model and a biomass-dynamics model. Such strong agreement among all models provides great certainty in the current assessment and management of this important marine resource.
Highlights
ABSTRACT.—The West Coast Rock Lobster Managed Fishery (WCRLMF) moved from input to output controls in 2010
This study aims to derive estimates of current biomass levels and harvest rates throughout the WCRLMF based on the multiple release and recapture of tagged lobsters in a spatially and temporally dynamic integrated model framework
Estimated legal biomass and harvest rate levels from these two models were compared to estimates from a biodynamics model (BMD; Online Supplementary Material) and an individual-based population model, neither of which use tag-recapture data for biomass estimation
Summary
ABSTRACT.—The West Coast Rock Lobster Managed Fishery (WCRLMF) moved from input to output controls in 2010. The movement of individuals into discrete size-specific spatiotemporal “bins” allows for the catchability of an animal to vary as it grows, moves, matures, and experiences different levels of harvest while maintaining other common parameters across groups (such as reporting rate; Phillips et al 2018) This ability to allow for individualistic catchability within the integrated model framework, whilst allowing for observations from different groups to collectively inform certain common characteristics, can increase the accuracy and robustness of parameter estimates (Maunder and Punt 2013, Goethel et al 2019, Senina et al 2020). This study aims to derive estimates of current biomass levels and harvest rates throughout the WCRLMF based on the multiple release and recapture of tagged lobsters in a spatially and temporally dynamic integrated model framework. If the IBM proves reliable in its assessment of the fishery—based only on tag-recaptures— the incorporation of this data into the IPM, in a framework like that of the IBM, will provide additional robustness to the annual fishery assessment
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