Theme E: Interactions between wild and released animals and their ecological and genetic implications
28. ECOLOGICAL AND GENETIC IMPACTS OF BARRAMUNDI (LATES CALCARIFER) STOCKING IN NORTHERN AUSTRALIA
John Russell1, D. Jerry2, PA Thuesen1, FE Thomson1 and C. Smith-Keune2
1Queensland Department Of Employment, Economic Development And Innovation, Northern Fisheries Centre, PO Box 5396, Cairns, Qld., 4870 Australia
2James Cook University, Queensland, Australia
john.russell@deedi.qld.gov.au
Baramundi (Lates calcarifer) have been stocked into northern Australian waterways since the mid 1980s for stock enhancement and to create new impoundment fisheries. Fisheries managers and other interest groups are now concerned that these stockings are impacting on aquatic ecology and on the genetic diversity of wild L. calcarifer stocks in coastal river systems. Particular concerns have been expressed about the potential effects these introductions are having on fauna of conservation concern. To address these issues, an experiment to determine the diet, movements and the genetic impacts of the release of stocked barramundi commenced in late 2009. This experiment involved the release of about 13000 marked 0+ barramundi into different habitats in a northern Australian coastal river and into a large impoundment. These stockings are being monitored using routine six weekly electrofishing surveys. Preliminary gut content analyses of these fish found those in the coastal river were consuming crustaceans (Macrobrachium spp. and atyid shrimp) while fish were the dominant prey of impoundment L. calcarifer. The stocked 0+ fish resident in the coastal river showed strong site fidelity, with no evidence of either these fish, or the impoundment barramundi, moving into lower order streams in environmentally sensitive areas. There was also no evidence that they were preying on fauna of conservation concern. Older fish from previous stockings moved downstream into estuarine and coastal areas with some fish making inter-riverine movements. DNA parentage analyses are also being used to assign stocked juveniles to their family of origin. This is being done to determine if differential family survival occurs thereby lowering the overall genetic diversity of stocked groups. Recaptured stocked fish mostly showed relatively even representation across hatchery family groups, although a dominant family group representing 35% of the fish that were originally stocked into the river was absent from subsequent recaptures.
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