In NSW, inherent variation among the characteristics of different estuarine fisheries has resulted in a range of physical modifications designed to improve the selectivity of conventional gears. While some of these designs have been effective in reducing the bycatches of unwanted species by up to 95%, rates of reduction more commonly range between 30 and 70%. Such reductions have obvious benefits for the stocks of bycatch species. considering the magnitudes of bycatches in many estuarine fisheries, and especially those targeting prawns (i.e. often 1000s of fish per haul), it is apparent that despite the use of modified gears, in nearly all cases there still remains some capture and mortality of unwanted individuals.

To augment the post-release survival of unwanted bycatch throughout nearly all of NSW estuarine fisheries (including those involving static gears, where no BRDs have been developed), ancillary options within the second category of input controls (listed above in B2) need to be investigated. The sorts of modifications that warrant examination include, defined soak times for gears, devices to limit predation on discarded bycatch, netting materials in codends that reduce damage to bycatch, the use of gloves to handle bycatch, and the utility of separating target and bycaught species in water after capture.

The majority of these operational and/or post-capture handling procedures have NOT been examined, but have the potential to significantly reduce the remaining impacts of commercial fishing gears on non-target species and sizes in NSW’s estuaries. This is one of the main research priorities detailed in the Fishery Management Strategy for the NSW Estuary General Fishery and comprises a key category within the 2004-2007 Strategic Research Plan for Fisheries, Aquaculture and Aquatic Conservation in NSW. Quantification of the utility of this category of input controls would also have benefit and application throughout all other coastal fisheries in Australia.

The research will form the basis of a PhD candidature. This approach is justified because (i) the work is new and there is sufficient intellectual content to support a PhD student, (ii) there is a paucity of researchers with higher degrees working in the applied fields of gear technology and bycatch mitigation in Australia and (iii) previous, similarly-structured FRDC projects (e.g. 93/180 and 2001/031) have resulted in successful PhD candidatures by project staff. Specifying a PhD candidature formalizes what would already occur if funding was sought for a Fisheries Technician, but at approx. 1/3 the cost, while attracting a substantial in-kind contribution from affiliated institutions (the National Marine Science Centre and University of New England).

Reduction of by-catch has been an active area for research in Australia and around the world. The initial focus for research and management has been demersal trawl fishing, where the perception of waste and potential impact has been the greatest. However, the reasons for seeking to reduce unwanted catch apply to all fisheries, including those using demersal traps.

Demersal fish traps in NSW must be covered with mesh no smaller than 50 mm, and a galvanised hexagonal fencing wire is the most common material. However, many fishers use larger mesh and both 50 X 75 mm and 75 mm hexagonal mesh are in use. Those using and advocating larger mesh have done so to reduce the catch of undersize snapper and other small fish and to decrease sorting times. Other trappers are concerned about the effect of larger mesh dimensions on the catch of valuable species such as wrasses, sweep or bream which all have no minimum legal length (MLL) or have an MLL smaller than snapper.

An understanding of the differences in selectivity of different sizes of mesh on the species caught in fish traps will have a number of uses. This information is essential to determine the cost and benefit to fishers of changing mesh sizes. The selection probabilities for existing meshes can also be used to improve the assessments using age and length composition collected for snapper and bream in NSW. This is particularly important for snapper, where a very large proportion of the fishery is caught close to the MLL. Finally, because wire mesh can be made in a diversity of shapes and sizes, it may be possible to achieve desirable changes in selectivity for some species while not changing selectivity patterns for others.