Predicting the impacts of shifting recreational fishing effort towards inshore species
Recreational exploitation of inshore, marine fishes near Perth, WA, including King George Whiting, some other whiting species and Silver Trevally, is likely to increase markedly because of effort transfer from offshore to inshore species, due to new fishing regulations to protect offshore demersal species. No reliable stock assessment information is currently available for any of these species, which may already be overexploited. Furthermore, for King George Whiting and Silver Trevally, current assessment methods are inadequate because offshore movements with increasing body size, combined with different catchabilities and fishing pressures in nearshore and offshore habitats, make it impossible to obtain a representative age composition sample for an overall stock of these species. This problem can be addressed through developing a new stock assessment approach for such species, which is also applicable to other recreational, and commercial species, e.g. Estuary Cod.
The biological information published in reports and papers on commercial and recreational fish species in south-western Australia is often inaccessible to fishers and researchers may not be aware of all available information for those species. A book explaining the basics of fisheries science and outlining key information for important temperate WA fish species would be invaluable for engaging fishers and a valuable reference for researchers and managers.
The proposed project directly addresses an urgent need of the Department of Fisheries, WA, and the recreational sector, to assess likely impacts of recreational effort transfer from offshore to important inshore species. The assessment approach and guide is also very relevant to the commercial sector.
Final report
The project outputs have led to the following outcomes:
1. A model has been developed enabling reliable estimation of mortality of fish species that undertake size-related, unidirectional, offshore movements from age and length data. This new modelling approach is likely to be applicable to stocks of a number of fish species with this life history attribute, for which current stock status information may be very limited due to the difficulty of obtaining a representative sample for an overall stock.
2. Current age and length composition data and estimates of key stock assessment parameters, including selectivity, movement and fishing mortality, are now available for Silver Trevally and King George Whiting in coastal waters near Perth in Western Australia. Managers are aware that the study results have provided preliminary evidence that Silver Trevally and King George Whiting in waters near Perth are not currently experiencing overfishing.
3. This project has provided managers with information about the relative extents to which the stocks of Silver Trevally and King George Whiting in coastal waters near Perth might be expected to be impacted if fishing pressure were to increase by specified amounts. Managers are thus aware that King George Whiting stocks are likely to be more vulnerable than Silver Trevally to increases in fishing pressure in inshore waters.
4. Detailed summaries of the biology, stock assessment and management for 30 of Western Australia’s most important and/or well-known temperate fish species are now accessible to fishery stakeholders in the form of a species guide (published separately as Fisheries Research Report No. 242 by the Department of Fisheries, Western Australia). The guide provides a comprehensive “go to” source of information for anyone who wishes to find key facts and/or literature relating to these species.
Keywords: Silver Trevally, King George Whiting, size-related movement, fishing mortality, uncertainty, model assumptions
