Fish habitat in coastal floodplains will continue to degrade unless practical guidelines for improvement of water quality and management of floodgates and other tidal barriers to allow passage of fish and invertebrates are developed. This is being increasingly recognised by many decision making agencies. However, landholders will not change current management practises unless as a minimum, there will be no adverse effects to their productivity. Guidelines for change must be developed in an integrated manner with a focus on land, water, agriculture and fisheries if all industry groups are to accept the changes.

Recent studies by NSW Fisheries (some funded by FRDC) show that a change in coastal floodplain and wetland habitats from freshwater to estuarine and recruitment of fish and invertebrates to these modified habitats can be achieved by increasing the degree of “leakiness” in the floodgate barriers (Gibbs et al. 1997). However, no data are available on the relationship between fish and invertebrate recruitment and the opening size or the frequency and timing of the opening of these floodgate barriers.

A second issue is the long term impact of chronic acid drainage, which does not cause major fish kills but which may have less obvious effects on the recruitment of migratory and catadromous fish such as Australian bass, striped mullet, freshwater herring, eels and school prawns. The life history, behaviour and demography of the catadromous Australian bass shows it is susceptible to such an impact (Harris 1983,1989). The Basscatch program (Harris 1989) has expanded in recent years and the population collapse through recruitment failure of Australian bass in NSW rivers such as the Hastings and Manning is partially attributed to acid drainage (Harris pers comm).

The management of floodgates and floodplains to allow passage of fish and invertebrates and the development of stable faunal communities in previously alienated habitat above the structures significantly enhances fish and invertebrate stocks. The consequent protection of fish habitats and fish and invertebrate species supports biodiversity conservation and the habitat restoration can assist in the development of management plans under the relevant Threatened Species Legislation.

Gibbs, P., McVea, T. and Louden, B. (1997). Utilisation of restored wetlands by fish and invertebrates. FRDC Project 95/150 Final Report (In Preparation).

Harris, J. H. (1983). The Australian bass, Macquaria novemaculeata. Ph. D. Thesis UNSW.

Harris, J. H. (1988). Demography of Australian bass, Macquaria novemaculeata (Perciformes, Percichthyidae), in the Sydney basin. Aust. J. Mar. Freshwater Res. 39: 355-369.

Harris, J. H. (1989). Basscatch - A co-operative fisheries project. Modern Fishing 80-83.

Internationally, the demand and resulting value of glass eels has increased tremendously in recent years. Live glass eels are now selling for over $15,000 per kilo. This international demand results from over-fishing of adult and glass eels in Asia, North America and Europe. This world experience indicates that recruitment over-fishing of long-lived freshwater eels can be catastrophic. Because of the increasing significance of adult eels in the estuarine fisheries of NSW, decreased catches in recent years and the prospect of increased future catches of glass eels for aquaculture, it is important to undertake research which will lead to an understanding of the current status of adult eel stocks in NSW. Stocks of adult eels must be managed properly to ensure continued production of the commercial fishery for adult eels, continued recruitment of glass eels and elvers for aquaculture and stability of coastal catchment ecosystems.

Limited research into the basic biology and ecology of longfinned eels has been carried out in Victoria and Tasmania, but there have been no biological studies conducted in NSW. The only published age and growth information for this species comes from one catchment in Tasmania and indicates that they are relatively long-lived (40 years), but this age data has not been validated. The available literature indicates that growth rates of freshwater eel species are highly variable among habitats and distributional ranges. Therefore, there is a need to determine the basic biological parameters of NSW longfinned eel stocks, including validated age structure, growth and mortality rates, and reproductive characteristics for use in stock assessment modelling.

Since there is a significant commercial fishery for adult eels in NSW, fishery-dependent techniques based on sampling of commercial catches represent the most cost effective stock assessment and monitoring methodology. Age and growth monitoring of many commercial finfish species in NSW is currently carried out by sampling fish at the Sydney Fish Markets and regional fishermen’s co-operatives. Most of the commercial eel catch in NSW is exported live through a few (currently four) specialised processors. Therefore, it will be necessary to establish a specialised monitoring regime and fishery-dependent model which will provide data on which to base advice for the future sustainable management of exploitation of the resource.

Australia has limited wild fisheries compared to other countries, and many species are fully or over-exploited. In addition, we import about 116,000 tonnes of edible fish products valued at $600 million annually. There is clearly a need to dramatically increase aquaculture production in Australia to replace lost production from wild fisheries, to replace imports, and to export high-quality products into substantial lucrative markets in Asia.

Aquaculture is in its infancy in Australia and prior to the mid 1980s was limited to the production of oysters, rainbow trout, and juvenile native freshwater fish and goldfish. However, over the last decade there has been a significant increase in interest, research, management and investment. Industries based on Atlantic salmon, penaeid prawns, barramundi, tuna, freshwater crayfish, freshwater fish, eels, microalgae and other species have developed. In 1994/95, approximately 40,000 tonnes and 13.8 million juveniles were produced for a total value of $465 million.

Culture techniques for most species have been predominantly or partly developed overseas. While Australia's production and overall value has increased significantly, many enterprises have struggled or failed due to a range of reasons including; a lack of technology, poor selection of species and sites, poor understanding of aquatic husbandry, water quality and diseases, a lack of research and extension, a lack of quality control and marketing and financial difficulties resulting from the high establishment and operational costs characteristic of new industries. Some developments have foundered because of the negative perception that either the community or government agencies have had of aquaculture.

Following a decision in 1990 to impose a minimum legal length of 60 cm (total length) on kingfish and the banning of pelagic traps in 1996, there has been considerable controversy concerning the appropriateness of the current management measures. Gillanders et al. (1997) demonstrated that the current minimum legal size is about 15 cm below the length at which 50% of females are mature. However, the absence of adequate size and age composition data for the commercial landings means it is not possible to determine the impact of possible changes in minimum legal size. Yield modelling, combined with information on composition of landings, is an appropriate and important first step in examining the suitability of minimum legal size settings.
The nature of the commercial fishery for kingfish presents significant difficulties for the design of unbiased and cost effective sampling of these fisheries. Kingfish are caught in significant quantities in small, localised fishing operations, mainly south of 30° S latitude. There appears to be considerable annual and seasonal variation in the catches by the various sectors, however it is known that when reasonable densities of kingfish are located, very high catches can be taken over short time periods. The dispersed yet intense nature of the fishery has great potential to cause bias in collections aimed at estimating the length and age composition of the total catch of kingfish. A major aim of this proposal is to develop cost effective sampling strategies which will minimise bias in ongoing monitoring of the kingfish fishery.
The collection of size and age composition estimates from the commercial catch will enable the evaluation of whether an age structured model would be an appropriate mechanism for assessing the status of the fishery. Variation in the relative strength of year classes can be evaluated in each of the three years and these will provide important information on the dynamics of this stock. Further, these data can be used to provide auxiliary inputs for the fitting of a synthetic model which will utilise catch-effort data that have been collected from the fishery.