ASFB Home > The effects of spatial and temporal factors on the abundance of seven key finfish species along south-western Australia.

In Situ Observations of the Swimming Ability and Behaviour of Settlement-Stage Larvae of a Temperate Marine Fish Re-Entrained in the Pelagic Environment

Jeremy Hindell, Gregory P Jenkins, Sean M Moran and Michael J Keough

MAFRI, QUEENSCLIFF, AUSTRALIA

THEME: ASFB

The relationship between larval supply and recruitment can be influenced by a variety of processes that occur after settlement, one of which is the re-entrainment of larvae into the pelagic environment. Secondary dispersal in the water column was studied in early settlement-stage Sillaginodes punctata in Port Phillip Bay, Australia. S. punctata were captured in shallow seagrass beds and released in different depth zones off-shore to mimic the re-entrainment of fish. The behaviour, vertical movement and horizontal displacement of fish were recorded in 3 depth zones (1.5, 3 and 7m) over patchy rocky-reef. The direction and speed of local currents were described using an S4 current meter and the movement of drogues. Fish immediately oriented toward the bottom, and into the current after release. In shallow water (1.5m), 86% of fish swam directly to the bottom, and their net horizontal mobement was largely unrelated to the speed and direction of currents. In the intermediate depth zone, the average depth reached by fish was midway between those reached in the shallow and deep zones, and their dispplacement was not always related to currents. In the deepest depth zone, 81% of fish remained within 1m of the surface and their horizontal displacement was significantly related to the direction and speed of currents. Settlement-stage larval dispersal in the water column appears to have the potential to modify initial recruitment patterns, but only if fish reach deeper water, where their displacement (direction and distance) resembles local hydrodynamic regimes more closely than in shallow water. In shallow water, fish behavious and vertical migration reduces settlement-stage larval dispersal.