Project number: 1998-138
Project Status:
Budget expenditure: $188,040.05
Principal Investigator: Doug Ferrell
Organisation: NSW Department Of Primary Industries
Project start/end date: 28 Jun 1998 - 12 Jun 2002


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.


1. Document throughout NSW, the current usage patterns of the various mesh types used in demersal fish traps.
2. Describe the size composition of retained and returned catch for species common in the NSW trap fishery for all mesh types as they are currently used.
3. Describe size composition of retained and returned catch for commercially available mesh and wire products in areas where they are not currently fished.
4. Determine the likely utility of possible mesh configurations not currently in use.

Final report

Author: Doug Ferrell
Final Report • 2002-04-30 • 1.76 MB


The New South Wales demersal trap fishery is a complex, multi-species fishery.  The most valuable species in the fishery is snapper, worth approximately half the value of the fishery, with bream, rubberlip morwong, ocean leatherjacket, silver trevally, sweep and pigfish accounting for a further 36% of the fishery.  Current regulations specify that traps must be covered with mesh having a measurement from one plain wire to the opposite plain wire of not less than 50 mm, and a 50 mm hexagonal fencing wire is the most commonly used trap mesh.  We know that 50 mm hexagonal wire mesh retains undersized snapper and some fishers advocate using panels of 50 x 75 mm welded mesh in their traps to reduce the catch of small, unwanted fish.  We needed knowledge concerning discarding of fish in the trap fishery, because it was apparent that the mesh selectivity of the currently used 50 mm hexagonal wire is inappropriate for snapper, and probably also for many other species captured in traps.

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