Neil Loneragan

This project investigates recreational and commercial fisher motivations for using a fishery and the beliefs, attitudes and perceived benefits of aquaculture-based enhancement programs and other management options. It also determines the total economic value for recreational fishing for Blue Swimmer Crabs (Portunus armatus) and Black Bream (Acanthopagrus butcheri) in a range of estuaries in south-western Australia and investigates the benefits of release programs in contributing to the optimisation of biological, social and economic objectives for those fisheries. Finally, it provides training for the next generation of fisheries and social scientists and fishery economists and project members engaged in community engagement and education.

Work was focused on two iconic small-scale estuarine fisheries in south-western Australia, i.e. those for Blue Swimmer Crabs and Black Bream. A two-phase approach to elicit common recreational fisher beliefs using semi-structured interviews (phase 1) and then sample a broader pool of respondents using closed-question online surveys (phase 2). Analyses demonstrated that motivations for recreational fishing were markedly different for the two fisheries, even when operating in the same system. Aquaculture-based enhancement was universally supported by the recreational sector as a fishery management approach as they believed it would enhance stocks and catches, and, although it may cause negative impacts, they were considered unlikely. Commercial fishers were less supportive of this management intervention. Enhancement of stocks was estimated to increase the economic value of recreational fishing through increased visitation. Biological modelling highlights that stocking could provide substantial benefits to the biomass of the target stocks, particularly Black Bream, but the parameters of any future stocking the need to carefully considered to ensure maximum benefits and the mitigation of density-dependent effects on wild stocks. Advice on the numbers and size-at-release for Blue Swimmer Crabs in the Peel-Harvey and Black Bream in the Blackwood River Estuary are provided to optimise the biological, social and economic dimensions of these fisheries.

This report provides the first comprehensive investigation into the biology and ecology of the Western School Prawn (Metapenaeus dalli) in the Swan-Canning Estuary in south-western Australia. It provides knowledge to help manage the fishery and evaluate release strategies for the aquaculture-based enhancement of this species. The study involved Murdoch University, the Department of Biodiversity, Conservation and Attractions (DBCA) (formerly Department of Parks and Wildlife and the Swan River Trust) and the Australian Centre for Applied Aquaculture Research (ACAAR). It was designed to complement a concurrent project to develop aquaculture techniques to produce and release M. dalli and re-engage the local community with prawning and the estuary (led by ACAAR, DBCA’s Parks and Wildlife Service and the West Australian Fish Foundation), funded by the Recreational Fishing Initiatives Fund. The Fisheries Research and Development Corporation provided matching funds for the current study. Biological data on M. dalli were collected from 20 sites in nearshore and 16 in the offshore waters of the Swan-Canning Estuary, ranging from the mouth of the system to ~40 and 30 km upstream in the Swan and Canning rivers, respectively, in every lunar month between October 2013 and March 2016. Laboratory studies were also completed to investigate the survival and growth of larval prawns in different salinity, water temperature and algal food conditions. Results were presented as part of the Prawn Watch program to engage the community in the research and encourage stewardship of the fishery and the estuary.

Summary This review summarises (i) the biology and behaviour of portunid crabs, focusing on the commercially and recreationally important species within the genera Callinectes, Portunus and Scylla, (ii) identifies previously successful aquaculture/restocking efforts for portunids and (iii) detail any successful aquaculture methods/techniques for these species. Portunids are highly fecund, fast growing, short-lived species, with high natural mortalities and whose populations are characterised by an abundance of immature individuals and fewer older, mature individuals. The dietary composition of these crabs, which are opportunistic, is influenced significantly by ontogeny, moult stage, habitat and season. Bivalves, gastropods, crustaceans and teleosts are the major prey categories consumed, with larger crabs consuming more mobile prey. Portunid crabs are more active during night than day, when many species bury. They have developed intricate mating and moulting behaviours that are influenced by water temperature and salinity. The females of many species undertake migrations associated with reproduction and the release of hatching eggs. Portunid fisheries occur globally, with the greatest capture rates occurring in the Indo-West Pacific. Global catches of portunid crabs are still increasing despite the relative stability in the catch rates of world finfish fisheries. High fishing pressure on many established portunid fisheries, exacerbated by environmentally driven fluctuations in recruitment, has led to several localised depletions. The management of portunid fisheries varies greatly between and within countries, but all employ input (i.e. licences, spatial and temporal closures) and/or output controls (size, sex and catch limits). Aquaculture-based enhancement has been suggested as a possible means is increasing stocks in depleted fisheries. A number of restocking and stock enhancement programs have been implemented around the world, including USA, Japan and South East Asia. These were all initiated in response to declines in stocks and, in each case, successful hatchery techniques were developed to enable small-scale production to occur. Releases were found to be most successful when the hatchery-reared individuals were released as crablets and not megalopae. Noting that far smaller numbers of individuals were produced due to cannibalism. Typically, release programs for brachyuran crabs appear to have been successful, albeit too different extents. For the most part, the evaluations of the effectiveness of these releases have been carried out at the pilot scale with only the culture of P. trituberculatus scaled up (~27-35 million juveniles per year). Species with fast growth rates, limited home ranges and a large economic value are likely to be the most appropriate species to culture and release. Any future release program for a portunid is likely to require extensive research and development, particularly to scale up production, and thus the biggest gains in this field to-date have come from increased knowledge rather than increased stocks. In terms of aquaculture, broodstock are typically collected from the wild using commercial fishers and to increase the success of the hatch, conditions in the culture environment should be similar to those in the waters the broodstock were collected from. If inseminated but not berried broodstock are collected, crabs require access to sandy substrate to spawn. Maintaining appropriate water quality is paramount and P. pelagicus larvae require relatively warm (25-30 °C) water at near-marine salinities (30-35 ppt) that is well oxygenated and of a slightly basic pH (8). The larvae require different feed throughout the transition from zoea to megalopa. Typically, zoea are fed a range of microalgae strains (which also enrich live feeds and provide a greenwater culture) and rotifers, with Artemia being provided once the larvae reach the later zoeal stages. At the crablet stage, diet in the hatchery comprises commercial shrimp/prawn feeds. Stocking density is important, with faster growth and greater survival occurring at lower densities. Cannibalism in portunids starts at the megalopa stages and lower stocking densities and the provision of greater substrate complexity reduce juvenile cannibalism. Portunid species have been shown to actively select more complex habitats, such as seagrass, macroalgae, pebbles and crushed shells over finer sand substrates and artificial habitats, such a nets, have also been successful in increasing survival.

The incidental capture of cetaceans (whales, dolphins and porpoises) in fishing gear is a serious threat to populations and species worldwide. In Australia, several dolphin populations are being impacted by mortalities through interaction with fisheries, in particular, gillnets, purse-seining, long-lining and trawl fisheries. The capture of dolphins has been a conservation issue in the Pilbara Fish Trawl Interim Managed Fishery (PFTIMF) that was first assessed in 2002 by the Department of Fisheries Western Australia (DoFWA). At that time, an estimated 50 to 100 dolphins were being caught each year. A number of bycatch mitigation techniques were trialed between 2004 and 2007, including pingers (acoustic deterrents) and different exclusion grids, meeting with varying degrees of success (FRDC 2004/068). Due to ongoing dolphin bycatch, successive Ministers for Fisheries have not been prepared to move the fishery beyond ‘Interim Managed’ status. In late 2007, Murdoch University was asked to provide expertise on cetacean behaviour and fisheries interactions in the Pilbara trawl fishery.

This project built on collaborative research in the Jurien Bay Marine Park to develop quantitative models of the ecosystem in this region (Ecopath, Ecosim and Ecospace) and qualitative models of different parts of the ecosystem. These models were used to evaluate the effects of different management options, such as controls on fishing effort and different spatial closures, on fished species (e.g. Western Rock Lobster, Dhufish, Pink Snapper) and the trophic interactions in the ecosystem. In addition to evaluating different management options, the process of developing the model through a series of workshops provided a mechanism for integrating research from previous studies and building understanding about the ecosystem and model among researchers, managers, fishers. The Ecopath model consisted of 80 functional groups (more than 200 species), including 31 fish groups, 26 invertebrates, 11 primary producers, two marine mammals, two seabirds and eight non-living groups. The Advisory group for the project, which had representatives from the Department of Fisheries WA, Department of Environment and Conservation, RecFishWest, RLIAC, and WAFIC, provided directions for developing the management scenarios for evaluation by the quantitative models, including recent changes to fishing regulations in the West Coast region. The final stage of the model can address key ecological questions in the system and explore the dynamics of target species such as Western Rock Lobster and top predators under different fishing regimes. The benefits from the spatial closures, evaluated by Ecospace, vary greatly between species – they were much more effective for relatively sedentary species such as Dhufish and Pink Snapper than migratory species such as sharks.

The overall objective of this research project is to add to the general understanding of coral reef ecology and more specifically, advance the existing knowledge of the role of sea urchins in coral reef ecology at Ningaloo Marine Park. This study will examine marine grazers (particularly sea urchins), investigating their habitats, home range, reproduction, distribution, larval recruitment and settlement, and trophic relationships at Ningaloo Marine Park. The indirect effects of different closure regimes (e.g. Marine Protected Areas (MPA’s) such as sanctuary zones) on urchin ecology within Ningaloo Marine Park will be examined at length, both temporally and spatially over the next two to three years and will provide important new information which will aid in the formulation of future management strategies for the conservation and stewardship of Ningaloo Marine Park.