Key habitat and home range of mulloway Argyrosomus japonicus in a south-east Australian estuary: finding the estuarine niche to optimise stocking

Abstract

The preferred habitats, home range and activity patterns of sub-adult mulloway Argyrosomus japonicus (Sciaenidae) in the Georges River, New South Wales, Australia, were investigated using ultrasonic telemetry. Tags were surgically implanted in 9 hatchery-reared and 12 wild-caught mulloway (330 to 730 mm total length, TL). Fish were tracked for 2 periods of continuous tracking over 72 h in a 15 km section of river, once daily for a 20 d period, and up to 3 times mo -1 for 11 mo. Key habitats were identified as discrete holes or basins up to 20 m deep. Mulloway preferred this deep hole habitat as small fish (hatchery-reared, 300 to 500 mm TL) remained in these deep holes both day and night, while large fish (wild, 500 to 800 mm TL) ventured outside the holes at night. . Small fish released in shallow water initially had significantly greater movements than those released directly over deep holes, with movement up to 10 km in 3 d. Activity patterns varied between small and large fish, with significantly larger movements by large fish during the night and early morning than daytime. Five wild-caught mulloway tracked over 11 mo showed strong fidelity to holes within their particular home range. Mulloway should be stocked directly into their deep holes to minimise movements. The use of key habitats by mulloway indicate that their survival will be sensitive to stocking density. Optimal stocking density could be estimated from the area of key habitat in the target estuary.

Movement of gray snapper Lutjanus griseus among subtropical seagrass, mangrove, and coral reef habitats

“…2). OR1 and OR2 are offshore coral reef sites in the forereef habitat located between the 2 acoustic receiver arrays described Jorgensen et al 2006, Taylor et al 2006, Meyer et al 2007). We deployed ultrasonic tags to monitor the diel and seasonal movements of gray snapper using stationary tracking techniques.…”

Active acoustic tracking suggests that soft sediment fishes can show site attachment: a preliminary assessment of the movement patterns of the blue-spotted flathead (Platycephalus caeruleopunctatus)

“…To indicate activity level, we used a minimum activity index (MAI m h −1 ) [18] which was calculated by the distance between two points divided by the time elapsed between observations, averaged across all points for each fish. The nature of the data collection meant that this was only possible for the first 4 days of intense tracking.…”

Riding the tide: estuarine movements of a sciaenid fish, Argyrosomus japonicus

“…For example, if foraging success varies temporally, then it would be advantageous for fish to sample multiple habitats, but if certain areas are safer or more productive, it would be more advantageous to exhibit 'stationary' behaviour. Taylor et al (2006) classified deeper areas with bottom structures and submerged cliffs as key habitats and holding sites for juvenile Argyrosomus japonicus, which are structured habitats that may reduce the predation risk. The Great Fish Estuary has a uniform bathymetry with few underwater structures or deep pools.…”

“…Griffiths (1997b) also suggested that the spatial distribution pattern of A. japonicus juveniles in the Great Fish Estuary was mainly determined by predator avoidance and optimised feeding. Dominant prey items of juvenile Argyrosomus ja ponicus include mysids, prawns and teleosts (Marais 1984, Griffiths 1997b, Taylor et al 2006). In the Great Fish Estuary, teleosts (Mugilidae and small pelagic estuarine round herring Gilchristella aestuaria) and mysids (Mesopodopsis slabberi and Rhopalophthalamus terranatalis) were the most dominant prey items (Griffiths 1997b).…”

“…The spawner biomass per recruit ratio of Argyrosomus japonicus has been re duced to between 1.0 and 4.5% of its unfished condition, probably caused by over-fishing during the juvenile estuarine-dependent phase (Griffiths 1997a). While much is known of the biology of A. japonicus (Griffiths 1996(Griffiths , 1997b, little information exists on its movements (Taylor et al 2006, Cowley et al 2008). An understanding of the driving forces for the movements of individuals is important to gain insights into the ecology of estuarine-dependent fishes and contribute to the corrective management of overexploited species.…”