DISTRIBUTIONAL ECOLOGY OF MILKFISH, CHANOS-CHANOS, LARVAE IN THE GREAT-BARRIER-REEF AND CORAL SEA NEAR LIZARD ISLAND, AUSTRALIA

Plankton hauls captured 682 milkfish larvae (2.1-12.3 mm) in the Great Barrier Reef Lagoon and Coral Sea during 1979-1986. Larvae were present from November to March, and absent in April, July and October. We analyzed concentration, abundance and size-frequency data and concluded that spawning took place in the Coral Sea or at the outer edge of the continental shelf, apparently following an adult spawning migration of at least 50 km. Larvae then moved inshore to at least our most inshore routine sampling site near midshelf. Some larvae may have remained for a period in the lee of reefs along the shelf edge. Larvae apparently occupied the upper few metres of the water column, thereby becoming susceptible to shoreward movement in the wind-driven surface layer. Movement from spawning sites to midshelf probably required active maintenance of vertical position by larvae which enabled passive movement with favourable currents, and perhaps horizontal swimming. By the time larvae reach midshelf, continued inshore movement by horizontal swimming alone is possible.