Catch Predictions in Stock Assessment and Management of Invertebrate Fisheries Using Pre-Recruit Abundance-Case Studies from Western Australia

Catch predictions based on pre-recruit abundance have proven valuable in the stock assessment and management of major invertebrate fisheries in Western Australia for western rock lobster (Panulirus cygnus), pearl oyster (Pinctada maxima), abalone (Haliotis roei), prawn (Penaeus esculentus), scallop (Amusium balloti), and blue swimmer crab (Portunus armatus). Predictions are based on puerulus stage (post-larval) rock lobster from artificial collectors; 0+ and 1+ pearl oyster spat attached to commercial shell; dive survey of Roe's abalone; and trawl surveys of prawn (shrimp), scallop, and crab. These reliable predictions (R-2 = 0.67-0.97) are used in stock assessment and management harvest strategies to ensure that fishing effort or catch quotas are set so that adequate breeding stocks are maintained. This pro-active management based on predicted abundance avoids the pitfall of heavy fishing on poor recruit classes, which is a common cause of recruitment overfishing. The catch-pre-recruit relationship provides valuable information on density-dependent effects between the two life-history stages, with high levels evident in rock lobster and little evidence for prawns and crabs, which reflects the stage at which pre-recruits are measured. The review emphasizes the advantages of catch predictions based on pre-recruit abundance relative to environmental variables and the need for cost-effective pre-recruit monitoring to ensure long-term data. The pre-recruit abundance is valuable in investigating factors affecting year-class strength, including environmental factors and overfishing. The pre-recruit abundance is probably the most valuable information under climate change situations as it provides firm evidence of a change in abundance to justify management action before the change is reflected in the fishery.