ROBUST STATISTICAL MODELING OF HAWKSBILL SEA-TURTLE GROWTH-RATES (SOUTHERN GREAT-BARRIER-REEF)

Growth rates recorded between 1974 and 1991 for 44 immature hawksbill sea turtles in the southern Great Barrier Reef foraging grounds were m odelled using nonparametric regression methods. The implicit sampling design in this long-term mark-recapture program was mixed longitudinal and included growth records for both female and male hawksbills rangi ng between 39 and 85 cm CCL (curved carapace length). Distinct sex-spe cific growth patterns were found, with immature female hawksbills grow ing at ca 0.5 cm yr(-1) faster than male immature hawksbills at all re corded sizes. The mean-size specific growth rate function for females was nonmonotonic, rising rapidly from recruitment size (>35 cm CCL) to a maximum growth rate of 2.2 cm yr(-1) at 60 cm CCL before declining to negligible growth approaching sexual maturity at a size greater tha n or equal to 80 cm CCL. The mean-size specific growth rate function f or males was also nonmonotonic, rising from the same recruitment size to a maximum growth rate of 1.7 cm yr(-1) at 60 cm CCL before declinin g to negligible growth approaching sexual maturity greater than or equ al to 80 cm CCL. No significant inter-annual variation in growth rates was found but the data set was too small to be conclusive. Size-speci fic growth rates were slower than observed for stocks from western Atl antic-Caribbean waters. Juvenile hawksbill growth spurts around 60 cm CCL, sex-specific growth and slow size-specific growth rates are disti nct growth characteristics for immature hawksbill sea turtles resident in southern Great Barrier Reef waters.