Spatial management of estuarine fisheries resources: Do recreational-only fished estuaries provide conservation to harvested species?

摘要

Management of fisheries by preventing commercial, whilst allowing recreational-only fishing in some areas, is intended to increase stocks so that sustainable recreational fishing is conserved or enhanced. This study examined whether the relative abundances and length and age characteristics of five harvested species of fish differed between recreational-only fished (ROF) estuaries, and those open to both recreational and commercial fishing (non-ROF) in southeastern Australia. Specific predictions based on absolute and ranked values of a range of parameters were made so that conclusions could be reached about the effects of management. Fish were sampled using multimesh gillnets in a standard and stratified manner across two ROF and two non-ROF estuaries over three years, six to eight years post ROF implementation. Abundances of each species fluctuated among individual estuaries and sampling times with no indication of greater abundances in ROF estuaries. For four species (Sillago ciliata, Mugil cephalus, Acanthopagrus spp. and Girella tricuspidata), the mean lengths and the proportions of individuals of legal length, were mostly greater in the ROF compared to the non-ROF estuaries. However, for Platycephalus fuscus there were no discernible patterns. Three species (P. fuscus, S. ciliata and Acanthopagrus spp.) had a significantly greater proportion of older fish in the ROF estuaries, but for M. cephalus and G. tricuspidata this was only evident in one ROF estuary. It is hypothesised that the cessation of commercial fishing and subsequent reduction in fishing pressure in the ROF estuaries allowed a greater proportion of individuals of each species to survive to become larger and older. This study provides correlative evidence that ROF estuaries can protect some harvested species at the local scale of estuary. Examination of lengths and ages of fish, rather than simply their abundances, was necessary to identify the effects of removing commercial fishing. Further research is required to determine the potential broader-scale and long-term sustainability benefits on species as well as any spill-over effects on other organisms and estuarine ecosystems.