Environmental and fisheries managers urgently need reliable data to underpin strategies to conserve or improve the ecosystems of normally-closed estuaries in the central region of the south coast of Western Australia. These managers thus need:

1. An understanding of the current status of the fish fauna of the highly-degraded Culham Inlet, and particularly of its population of black bream, and how that status has been influenced by extreme environmental perturbations in the recent past.

2. Reliable information on the extent to which the extreme environmental conditions experienced in certain of the last ten to fifteen years influenced either the spawning success and/or survival of the 0+ age class of black bream in Culham Inlet.

3. An understanding of the current status of the fish fauna of Stokes Inlet, which is less degraded than Culham Inlet but is still the subject of concern for local residents and visitors, and of Hamersley Inlet in whose catchment the vegetation has been the subject of only a relatively low level of clearing.

4. An ability to predict, qualitatively, the extent to which continuing degradation of any normally-closed estuary in the central region of the south coast of Western Australia will affect the fish faunas of those estuaries and, in particular, their recreational and commercial fish species. This information is required by the Department of Fisheries WA for developing its overall plan for managing the recreational and commercial fisheries in these estuaries (R. Lenanton, pers. comm.) and by other governmental authorities for developing strategies for conserving or restoring the quality of the important environments afforded by these estuaries.

Data from conventional tagging experiments have been and are becoming increasingly important for providing estimates of mortality rates in the stock assessment of large pelagic fishery resources as they provide a powerful, and perhaps only, alternative to relying on CPUE indices of abundance. There is an extensive scientific literature on tag-recapture experiments; however, a comprehensive framework for the analysis and design of tagging experiments in the pelagic fishery context does not exist. This has meant that in the design phase of tagging experiments, it has not been possible to provide scientifically rigorous advice on matters such as the relative tradeoffs between the number of tags to release, the spatial/temporal distribution of tags and the levels of observer coverage (required for estimation of reporting rates and for estimating the size/age distribution of the commercial catches). In addition, a comprehensive analysis of the extensive data from past SBT tagging experiments (particularly those conducted in the 1990s) taking into account all of the major potential sources of heterogeneity has not been completed because of the lack of a comprehensive estimation framework. Thus, the full benefit of the large research investment from these experiments has not been realized. It is also anticipated that conventional tagging programs will be a major future source of assessment information in both the eastern and western tuna fisheries. As such, an appropriate framework for the design and analysis of tagging experiments is needed to ensure that the full value from both past and future experiments is realized. Finally, there is increasing data accumulating from archival tags. There is a need to understand the role, and the relative cost/benefits, that archival tags can contribute to the overall estimation of mortality rates to past and future conventional tagging experiments.

Effective fishery management requires knowledge of the impact of fishing on stocks - good monitoring measures of harvest rates (U). However, there are NO reliable indices of U or of abundance for many fished species. Most methods are flawed; some (eg CPUE) may only indicate the impact of fishing when populations are depleted. Lack of effective monitoring means loss of catch, income and recreation and jeopardizes sustainability. Although an obvious method of measuring U, conventional tagging is strongly limited by post-release mortality, tag shedding and non-reporting of tags. We propose that genetic “tagging” - individuals identified from tissue collected with special lures or spears, and subsequent screening of the commercial catch to establish a “recapture rate” – largely overcomes the problems of conventional tags. We need this monitoring method. Even a modest increase in monitoring information quality translates to real economic and sustainability benefits. Anglers provide useful information on movements and growth (eg through SUNTAG tagging). But the information they provide for monitoring U is limited by the general tagging problems. By coupling conventional with genetic tagging, this project provides a direction for improvement of recreational tagging, by calibrating and quantifying problems, and developing them as a source of auxiliary information. This could substantially increase the value of recreational tagging.

There is currently NO effective monitoring method for Spanish mackerel: they are not amenable to survey, and because they school, CPUE is a poor abundance measure. They have poor post-tagging survival, with low return rates (5% ; Sawynock, pers. comm.). Lack of good monitoring information is of concern for all Australian mackerel fisheries; in several there are real concerns about harvest rates. It was concluded in stock assessment workshops conducted in Darwin in August 2000, led by Prof. Carl Walters and Dr Norm Hall, that the primary research direction for mackerel and several other fisheries should be the development of new tagging approaches. The method we propose meets that direction and could provide effective monitoring for a wide range of fisheries in which current status is otherwise very uncertain.

This project arises from the need within the SRL fishery to address a series of regional and fishery-wide questions including:

What areas contribute to successful recruitment within regions of the fishery?

Will increasing the spawning biomass in regions, where it is currently very low, be likely to increase recruitment to the fishery globally, only in certain restricted areas or not at all?

To what extent are management zones linked via larval transport from both west to east and east to west?

What drives puerulus settlement across the range of the fishery and how can regional and interannual differences in settlement be utilised to assess the health of the stock, and assist in the future with the prediction of catch rates?

These needs have been identified by managers, industry and research providers in South Australia, Victoria and Tasmania. In Tasmania, the Crustacean Research Advisory Group gave this issue their highest priority ranking due to its importance in targeting the current management objective aimed at rebuilding egg production.

Addressing these questions will help to ensure the sustainability of the fishery, assess the merits of alternative management strategies for improving recruitment (and hence yield) and provide the basis for possible future predictions of catch rates based on puerulus and or ocean monitoring.

The progressive rise in the number of recreational fishers in Western Australia is increasing the fishing pressure on the most sought-after recreational fish species in this State. The potential thus exists for these species to become exploited at levels that exceed those that are sustainable. The absence of biological data for mulloway, an icon recreational species, and silver trevally, the third most frequently-caught recreational fish species, has meant that the existing and proposed regulations, that were aimed at conserving and managing the stocks of these very important species, were not based on appropriate biological criteria. There is thus a strong need to develop a sound database for these species, which encompasses such crucial features as size and age compositions, growth, length and age at first maturity, fecundity and the location and time of spawning. Since the sand trevally, which is also fished recreationally, is morphologically so similar to silver trevally that it is very frequently confused with this species, and indeed is currently considered collectively with this species for management purposes, there is a need to understand the significance of those differences that are likely to exist between the habitats and biology of these two species.

The urgent need to acquire biological data on mulloway and silver trevally to underpin management plans has been highlighted by both RFAC and RecFishWest.