Stable isotope tracing of the contribution of seagrass production to subtropical fisheries species occurring outside seagrass areas
An examination of which fisheries species are sustained by seagrass plant production has been highlighted as a major research priority in the recent reviews of fisheries habitat research gaps by Cappo et al. (1997) and Butler & Jernakoff (draft report to FRDC). The recommended method in Butler & Jernakoff for tracing seagrass production to fisheries species is stable isotope analysis. Coastal and fisheries managers currently consider seagrass to be valuable, nevertheless there are many seagrass meadows under threat and still being lost. An argument can be developed, supported by current scientific evidence, that many important fisheries species are not reliant on seagrass and that their numbers actually increase upon the decline of seagrass. Estuarine and offshore fisheries species that do not appear to be dependent on seagrass might actually be so, but indirectly; they may be deriving their food from animals in a trophic web that is sustained by energy (carbon) and nutrients (e.g. nitrogen) transported from seagrass meadows. Another estuarine habitat, mangrove forest, has previously been touted as generating plant production that drives food webs elsewhere in estuaries and offshore. Recent evidence from Australia and Asia suggests this is not so; mangroves seem to sustain only species living in mangrove areas. The question whether seagrass production is the major source of primary production sustaining fisheries production needs answering. The best method for tracing where fisheries species gain their nutrition is stable isotope analysis.
The proposed research will be done in Moreton Bay and Hervey Bay. These bays are of extraordinary importance to Queensland fisheries, with Moreton Bay alone comprising up to 30% of the total Queensland catch of inshore recreational and commercial species (Tibbetts & Connolly 1998). There are also important fisheries in deeper waters adjacent to these bays. Both bays have extensive areas of seagrass, but also mangroves, saltmarsh and occasional reefs offshore. They are also suffering ongoing seagrass loss.
Final report
Assessment of the impacts associated with the harvesting of marine benthic invertebrates for use as bait by recreational anglers
Coastal areas of Australia, especially those close to urban areas, are under increasing pressure from industrial and tourism developments, and the associated infrastructure to support them. These shallow-water coastal and estuarine areas will also continue to be the focus of attention by the recreational and commercial fishing sectors. An understanding of the impacts of damage to key intertidal habitats will allow managers to minimise the adverse impacts and developmental degradation on Australia's fisheries resources.
There is currently no detailed information available on the specific effects of loss or damage to intertidal estuarine habitats on the animal assemblages that utilise these habitats, despite the recognised importance of the habitats and the benthic invertebrates to fisheries resources. Studies which have examined the effects of damage to subtidal habitats have shown important links to fisheries utilising these habitats (e.g. Sainsbury et al., 1993). Similar studies should be a priority for critical intertidal estuarine habitats. Although this project focuses on damage to intertidal habitats caused by bait-harvesting, the results of this work will be applicable to other sources of damage to these habitats, providing an important database establishing causal relationships between effects on the physical structure of the habitat and impacts on the associated animals.
Final report
Habitat modification and its influence on prawn and crab fisheries
This project addresses a need for information on the effects of human-induced disturbance on important coastal habitats. Aims of the public and of the fishing industry have congruence in seeking to maintain healthy aquatic ecosystems. Ecological sustainable development is a frequently expressed aim of modern fisheries management but management objectives relating to the ecological consequences of commercial fishing are rarely underpinned by defensible quantitative information. It is therefore difficult, if not impossible, to determine if fisheries are being prosecuted in an ecological, sustainable manner. So little is known of processes structuring sub tidal ecosystems that is difficult to formulate coherent and meaningful policies governing activities in Australian aquatic habitats. More importantly, it is difficult to identify environmental performance indicators to assess the status of individual fisheries. In reality, the interactions of harvesting on marine species and co-occurring boita are poorly understood. This is particularly the case for inshore fisheries in which harvesting occurs within the euphotic zone and the potential for significant alteration in the food chain, mediated by fishing, is real. There is a clear need to identify human-induced processes that may damage coastal ecosystems and that may affect the viability of nearshore fisheries.
Fisheries in Gulf St Vincent claim that the productivity of fisheries is being affected by changes to the habitat.
This project is one of a suite of research programs aimed at evaluating the ecological consequences of fishing. Other research programs on prawn fishing discards and of the consequences of abalone fishing are proposed for South Australian ecosystems and address similar needs. The linkages and common focus on coastal ecosystems will reinforce the outcome and the utility of the proposed research. A key outcome will be the identification of quantitative yardsticks of performance in relation to reasonable standards of ecological sustainable fishing practices. This outcome is needed to reinforce management plans with the quantifiable performance indicators relating to ecological sustainable development that are presently lacking for Australian fisheries.
Final report