A study of the movement and behaviour of the sand crab (Portunus pelagicus) using ultrasonic tags
Final report
Definition of effective spawning stocks of commercial tiger prawns in the NPF and king prawns in the eastern king prawn fishery: behaviour of post-larval prawns
In the Northern Prawn Fishery and the East Coast King Prawn Fishery managers have concerns about declining levels of recruitment to the fishery, and the lack of knowledge of the relationship between spawning stock and recruitment to the fishery. In both fisheries, the increase in effective fishing effort due to the use of GPS plotters and other modern technologies means that measures will inevitably have to be taken to reduce effort in the future. A more accurate definition of the real spawning stock would allow management to more effectively protect spawning stock and maximize catches by ensuring that critical areas were not overfished while allowing fishing in non-critical areas. Clear identification of the critical spawning areas would also allow managers to determine if changes in annual recruitment were due to changes in levels of spawning stocks.
The CSIRO hydrodynamic model of Albatross Bay (and models being developed for the entire Gulf of Carpentaria) have the potential to allow managers to more accurately define the effective spawning stocks for tiger prawns, but are limited by our lack of knowledge of a critical piece of postlarval behaviour: the timing of the change in vertical migration behaviour from being day-night cued to tidally cued.
The research proposed for eastern king prawns is particularly important, not only because it provides information relevant to improving the management of the East Coast King Prawn Fishery, but also because it will allow us to validate the techniques used in obtaining the behavioural data on tiger prawns for the Northern Prawn Fishery (see Methods).
Final report
To effectively manage most fisheries, including penaeid prawn fisheries in northern and eastern Australia, it is important to know the relationship between the size of the spawning population and the number of young adults that recruit to a fishery in the next generation. In the tiger prawn fishery in the Gulf of Carpentaria, it has been assumed for management purposes that the total adult population at a particular time is the effective spawning stock, i.e. all spawners contribute to the next generation's stock. This is not necessarily correct and is particularly unlikely for many species of penaeid prawns, whose larvae and postlarvae have to migrate from offshore spawning areas to coastal and estuarine nursery areas. The area that contains spawners that actually contribute offspring to subsequent adult populations has been termed the effective spawning area.
The main aim of our project was to investigate the vertical migration behaviour of postlarval penaeid prawns that enables them to recruit from offshore spawning areas to the coastal nursery areas. We used two strategies to achieve this aim: field sampling in estuaries in southern and northern Queensland and laboratory experiments.
Keywords: Effective spawning, prawns, postlarvae, behavior, vertical migration.
Use of archival tags for studying the movement and swimming behaviour of school sharks
Final report
There has been serious concern over the status of the school shark fishery for many years, and it has been the subject of numerous stock assessments (Punt & Walker 1998). It is a well researched species: Olsen (1954) showed that school shark can make extensive migrations, and that females moved to pupping grounds in the south-east of Australia to give birth. However, despite their apparent ability to move freely through the fishery, there are regional differences in size, age and reproductive condition, together with different catch-rate trends in different regions of the fishery. Originally stock assessment models were based on the assumption of a single freely-mixing stock, in light of the ability of the species to move long distances. However, Prince (1992) argued that the biological and catch data was incompatible with the assumption of a single stock, and was instrumental in having spatial structure in the fishery taken into account. Punt et al. (2000) developed a model that takes account of the spatial structure of the population, allows for multiple stocks and which uses catch-rate data and information from tagging studies to derive values for the parameters of the model.
In this study it was the longitudinal movements of the fish that were of greatest interest, and although daily longitude estimates from the archival tags were highly variable, weekly median estimates appeared reliable. Latitude estimates were based on bathymetry except around Tasmania where none were possible. One fish appeared to move to New Zealand, but the clock in the archival tag was found to be seriously defective when tested upon its return. Although conventional tagging shows movements of school shark between Australia and New Zealand, we conclude that there was no evidence of any movement of archival-tagged fish further east than 149–150° E. No school shark migrated across the entire range of the Australian fishery in the time they were at liberty (<1.5 y), and there was limited mixing between the eastern and western regions of the fishery in this time frame. The restricted movement shown by the archival-tagged sharks provides additional support for the move to spatially-structured stock assessments. Although these results seemed at odds with the impression of wide-ranging movements shown by earlier conventional tagging, re-analysis of tag returns from the 1947–56 tagging program (Olsen 1954) provided support for restricted longitudinal movements. For school sharks ≥ 95 cm total length at release tagged in Victoria and Tasmania, the percentage recaptured in South Australia did not peak until after 4–6 y at liberty for females (~70%) and 12–14 y for males (~40%). These results however depend upon the relative fishing effort in these two areas at the time.
Biological and life history studies of the yabbie, Cherax destructor, and its potential for aquaculture
Final report
A study of fishery-induced mortality of under-sized rock lobsters
Final report
Spawning and larval rearing research on King George whiting (Sillaginodes punctata) relevant to aquaculture and fisheries biology
After southern bluefin tuna, King George whiting is the most important fish species in South Australia. This species attracts a high market price on local and interstate markets and has biological attributes which suggest that is has good potential as a candidate for aquaculture. To allow commercialisation of this species, there is an immediate need to commence research to control egg production and conduct larval rearing trials to expose and solve culture problems so that a valid assessment of this species can be provided to aquaculturalists and investors.
FRDC funded research on the reproductive biology of wild King George whiting has identified a need to determine the spawning frequency of individual fish to get accurate estimates of fecundity.
There is a need to recognise that aquaculture is the only way to increase production of small volume coastal fisheries, such as that for King George whiting, without increasing fishing pressure on natural populations.
There is a need to develop aquaculture of coastal marine finfish species as an option which has potential to allow commercial fishers to diversify and reallocate effort to reduce pressure on wild stocks.