Investigating fine-scale spawning habitat and reproductive dynamics of estuarine-dependent fishes
van der Meulen, D.E., Walsh, C.T., Gray, C.A. and Taylor, M.D., 2011. Investigating fine-scale spawning habitat and reproductive dynamics of estuarine-dependent fishes. Presentation given at the 1st International Conference on Fish Telemetry, 12 – 18 June, 2011, Sapporo, Hokkaido, Japan.
Determining the mechanisms related to spawning is essential for understanding the reproductive dynamics, as well as factors influencing recruitment, in estuarine-dependent fish populations. Utilising active tracking, the fine-scale spatial and temporal patterns in the spawning activity of several recreationally important fish species have, and continue to be monitored in a tidal river in south-eastern Australia. For example, twenty seven adult estuary perch Macquaria colonorum were actively tracked during the spawning season within a 3km reach of the lower Shoalhaven River. Monitoring was carried out over a 48 hour period during the new and full moon phases in July and August 2009 respectively. In conjunction, plankton tows were also done to independently determine the timing and location of these particular spawning events. Tagged estuary perch exhibited high site-fidelity, with movements restricted to areas of specific habitat. The main habitats associated with fish aggregations included structurally complex large wooden debris; a concrete ferry landing; and a section of submerged rock wall. All three habitat types were proximate to turbulent, deeper and faster moving sections of the river. Egg count distributions confirmed spawning events coincided with areas of high tagged fish utilisation, while egg abundances peaked at night during the first two hours of the run out tide. We postulate that spawning and recruitment success of estuary perch is attributable to their selective spawning habitats that are: 1) structurally complex to provide refuge and protection from predation, as well as congregate prey items; 2) adjacent to deep water of high velocities to maximise egg dispersal; and 3) in close proximity to river entrance to facilitate offshore dispersal and inter-estuarine connectivity.