Stock assessment of the outer-shelf species in the Kimberley region of tropical Western Australia
Department of Primary Industries and Regional Development (DPIRD) WA
Stephen J. Newman
The Kimberley Fishery is developing rapidly and is now a complex fishery producing a high quality product. The small amount of information available at present causes concern at the state of exploitation of the stocks. Information is required as soon as possible to enable effective management of the fishery. The tools available are controls on size at first capture and overall fishing mortality. It is more practical in the first instance to obtain the information which will enable control of size at first capture, and to follow this with the information needed to control fishing mortality. The size selectivity of traps and lines needs to be examined to explore the possibility of using hook sizes and escape gaps in traps to reduce catches of smaller fish and hence increase long-term yields. Initial management controls can then be based on the outcome from size-at-first capture models. The size-at-first capture may be able to be controlled through the use of a mixture of fishing gear types (eg. fish traps in combination with lines and hooks of a specified size). The size-at-first capture of these fishes may also possibly be regulated through area controls, provided the distribution of adults and juveniles is known. These preliminary management controls will need to be followed up with a broad area fish trawl survey to provide estimates of stock size for use in more complex stock assessment models, enabling subsequent management controls to be implemented with the aim of directly regulating fishing mortality. A trawl survey would add greatly to knowledge of distribution of adults and juveniles. Direct controls on fishing mortality by area can be applied by zoning of fishing effort, monitored through the use of Vessel Monitoring Systems. For logistic reasons the trawl survey is not included in the current proposal. Specifically in this project there is a need to: (i) determine the population parameters of goldband snapper, and other key demersal species to facilitate the development of fishery assessment models. (ii) undertake a gear selectivity study (both traps and lines) to determine the feasibility of using gear controls such as hook size and escape gaps in traps. There is a further critical need in future projects to obtain: (1) direct stock size assessments via such methods as localised depletion experiments or broad area surveys; (2) to obtain information about the interaction of the Australian and Indonesian fishery (assessment of catch and effort data) for these species; (3) to obtain estimates of movement rates of the key species between regions and across borders (both national and international).
1. Estimate essential population parameters of goldband snapper and other key demersal species.
2. Estimation, by yield-per-recruit and egg-per-recruit analyses, of optimum combinations for size-at-first capture and fishing mortality.
3. Comparison of the size selectivity of commercial trap and line gear and to investigate methods of altering selectivity to enable targeting of fish of a specific size.
4. Advise fishery managers and industry on the combinations of gear and effort controls to produce optimal sustainable yields.
Principal Investigator: Dr. Stephen J. Newman, Dr. Michael J. Moran & Dr. Rodney C.J. Lenanton