MEPS 149:23-34 (1997)  -  doi:10.3354/meps149023

Nonparametric regression modelling of green sea turtle growth rates (southern Great Barrier Reef)

Limpus C, Chaloupka M

Somatic growth rates recorded between 1974 and 1991 for green sea turtles Chelonia mydas resident in the southern Great Barrier Reef (sGBR) foraging grounds of the sGBR genetic stock were modelled using nonparametric regression. The sampling design in this long-term mark-recapture program was mixed longitudinal and included growth records for female and male turtles ranging between 39 and 116 cm CCL (curved carapace length). Distinct sex-specific growth patterns were found, adults displayed constant negligible growth while inter-annual variability in immature female growth attributable to major oceanographic events was evident. Females grew faster than the males from ca 62 to 65 cm CCL with divergent growth patterns following distinct juvenile growth spurts. The expected female size-specific growth rate function was nonmonotonic, rising from recruitment size (>35 cm CCL) to maximum growth of 2.1 cm yr-1 at ca 60 cm CCL before declining to negligible growth approaching sexual maturity at ca 95 to 100 cm CCL. The male size-specific growth rate function was nonmonotonic rising from the same recruitment size to maximum growth of 2.2 cm yr-1 at ca 63 cm CCL before declining faster than females to negligible growth approaching sexual maturity at a significantly smaller size, <=95 cm CCL. Assuming a post-hatchling pelagic phase of 5 yr, the mean age at sexual maturity for each sex was estimated at >=40 yr using numerical integration of the expected size-specific growth rate functions. Expected age-specific growth rate functions for each sex derived by numerical differentiation showed that the juvenile growth spurt for females resident in the sGBR foraging grounds occurs at around 9 yr at large since recruitment (60 cm CCL, >=14 yr old) and for males at ca 11 yr at large (63 cm CCL, >=16 yr old). Juvenile growth spurts, sex-specific growth, slow size-specific growth rates, inter-annual growth variability of immatures and many decades to sexual maturity are growth characteristics for green sea turtles resident in the sGBR foraging grounds of the sGBR genetic stock.

Somatic growth · Green sea turtles · Great Barrier Reef · Nonparametric regression

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