Climate driven shifts in benthic habitat composition as a potential demographic bottleneck for Western Rocklobster: understanding the role of recruitment habitats to better predict the under-size lobster population for fishery sustainability
University of Western Australia (UWA)
Tim J. Langlois
The marine heat waves (MHW) of 2010/11, 2011/12 and 2012/13 provide a benchmark with which to investigate changes in habitat composition and potential flow on effects to the fishery. A 2018 independent review of the science used for stock assessment of the fishery recommended that studies should be undertaken to a) investigate the impacts of the previous MHW on juvenile recruitment to the fishery and, b) to better understand the role of habitat composition in recruitment To understand the impact of habitat change on the fishery, either through warming events or changes in coastal processes, we need an increased understanding of the role of habitat on the survivorship and growth of puerulus, post-puerulus, juvenile and adult life stages of lobster. In the 40 year time-series of puerulus settlement index a very strong relationship has persisted between puerulus abundance and commercial lobster catches 3 - 4 years larter (de lestang et al., 2010). An undersize catch rate index, based on historical (1985 - present) catch-rate records, evidenced the existence of a strong correlation between puerulus and undersize catch rate (de Lestang pers. com.). However, two-four years after the MHW of 2010/11, this relationship degraded, with the observed catch rate of lobsters being far less than expected at northern locations of the fishery. Although the relationship has now started to return to its historical form, the severity and longevity of its departure are cause for concern and highlight the marked impact future MHW or changes in coastal processes could have on the fishery. Change in the extent and configurations of coastal habitats is already occurring in response to natural physical forcing (coastal processes) and accelerated by climate change related stressors. It is crucial to have a detailed knowledge of how habitat change affects survival and recruitment key life-stages of the western rock lobster, so these can be taken into consideration for management practices that ensure the sustainability of the fishery. Such information is currently lacking.
1. The overall objective is to evaluate the implications of habitat change for the western rock lobster fishery, by determining the relative importance of habitat for the survivorship and growth of critical western rock lobster life stages, to inform the interpretation of existing settlement and recruitment metrics where and when habitat change also occurs. This will be examined via four linked objectives:
2. Synthesise evidence of habitat change: use novel and historical habitat imagery and other remote sensing datasets to determine the spatial extent of habitat loss and recovery, either attributed to 2011/2012 marine heat wave or changes in coastal processes.
3. Investigate fine-scale correlations in anomalies between predicted and observed undersize catch rate index and areas of habitat loss and recovery, either attributed to 2011/2012 marine heat waves or changes in coastal processes.
4. Evaluate evidence of essential benthic habitat for juvenile lobster, by measuring how habitat quality (cover and composition) influences lobster survival.
5. Create a spatial index of essential habitats to inform the interpretation of existing settlement and recruitment metrics.