VARIATION IN SETTLEMENT AND LARVAL DURATION OF KING GEORGE WHITING, SILLAGINODES-PUNCTATA (SILLAGINIDAE), IN SWAN BAY, VICTORIA, AUSTRALIA

Otoliths were examined from late-stage larvae and juveniles of King Ge orge whiting, Sillaginodes punctata, collected from Swan Bay in spring 1989. Increments in otoliths of larval S. punctata are known to be fo rmed daily. A transition in the microstructure of otoliths from late-s tage larvae was apparently related to environmental changes associated with entry to Port Phillip Bay. The pattern of abundance of post-larv ae of S. punctata in fortnightly samples supported the contention that the transition was formed immediately prior to ''settlement'' in seag rass habitats. Backcalculation to the otolith transition suggested tha t five cohorts had entered Swan Bay, each approximately 10 days apart, from late September to early November. Stability of this pattern for juveniles from sequential samples indicated that otolith increments co ntinued to be formed daily in the juvenile stage. The pattern of settl ement was consistent for two sites within Swan Bay. The larval phase o f King George whiting settling in Port Phillip Bay was extremely long and variable, ranging from approximately 100 to 170 days. Age at settl ement was more variable than length, and growth rate at settlement was extremely slow, approximately 0.06 mm.d-1. Backcalculated hatching da tes ranged from April to July. Increment widths in the larval stage su ggest that growth slows after approximately 45 to 75 days; beyond whic h individuals are in a slow growth, competent stage of 40 to 100 days. Variable larval duration and settlement is discussed in terms of earl y-life-history strategies and hydrodynamic processes.