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Summary of East-of-Hangklip lobster-abalone-urchin models and abalone projections
(2005) Plagányi, Éva E
A complicated ecosystem interaction is impacting South African abalone Haliotis midae and rock lobsters Jasus lalandii along the East of Hangklip (EoH) coastline. The lobsters have dramatically reduced sea urchin Parechinus angulosus populations, thereby indirectly negatively impacting juvenile abalone, which rely on the urchins for shelter. This ecosystem change effect is incorporated in the spatial and age-structured assessment model for abalone, with model projections predicting steep declines in abalone spawning biomass in the lobster-infected areas. In practice, multi-species considerations have been incorporated in an ad hoc manner only in the assessment, because of the difficulties both in the conceptualisation and parameterisation of a more complicated multi-species model capable of explicitly representing the various interactions. However, a preliminary abaloneurchin-lobster multi-species model has been developed as a first step to explore the problem, to investigate the data needs and to test the potential sensitivity of model results to the choice of parameter values. Indications from preliminary investigations were that the predicted recovery of the abalone resource may be slower than that predicted by a model that does not explicitly take the various interactions into account.