Growth Rates of Wild Green Turtles (Chelonia mydas) at a Temperate Foraging Area in the Gulf of California, México
Growth rates recorded between 1995 and 2001 for green turtles in the central Gulf of California were analyzed using nonparametric regression modeling. A mixed longitudinal sampling design provided 21 growth rate estimates from 19 turtles recaptured at intervals ≥ 11 months. Initial straight carapace length (SCL) of turtles ranged from 58.6–93.8 cm. Growth rates ranged from 0.2 cm/yr to 3.4 cm/yr. The size-specific growth rate function was nonmonotonic, rising steadily from slightly under 1.0 cm/yr in the smallest sizes (approximately 60 cm SCL) to a maximum growth rate of 1.5 cm/yr at about 85 cm SCL, then declining to just over 1 cm/yr for turtles > 90 cm SCL. Mean annual growth was 1.4 cm/yr. We estimate turtles require 9–21 yr in this neritic habitat to attain maturity. These data represent the first information on wild green turtle growth in temperate regions of the Eastern Pacific Ocean.Abstract
Graphical summary of GAM model growth covariates summarized in Table 1. Annual growth rate (response variable) is shown on the y-axis as a centered smoothed function scale to ensure valid pointwise 95% confidence bands. Covariates shown on the x-axis include (A) year (of growth record), (B) mean size between prior or first capture and recapture, and (C) recapture interval in years. Solid curves are the cubic smoothing spline fits for each continuous covariates conditioned on all other covariates in the GAM model (see Table 1). Dotted curves are the 95% confidence bands around the fits
Estimated size-specific growth rate function for SCL growth of Chelonia mydas resident in Bahía de los Angeles foraging grounds. (o) Fitted values from the GAM model summarized in Table 1; the solid curve is a cubic B-spline smooth fitted to the fitted GAM model values to highlight the underlying size-specific growth rate function
Comparison of size-specific growth rate functions for green turtles from the Bahamas (Bjorndal et al., 2000), southern Great Barrier Reef (sGBR, females; Limpus and Chaloupka, 1997), and Bahía de los Angles (BLA). The Australian study was based on curved carapace length (CCL), whereas the present study (BLA) and that from the Bahamas was based on straight carapace length measurements (SCL). Differences in CCL and SCL are minor (Bjorndal and Bolten, 1989) as are differences between sexes (Limpus and Chaloupka, 1997) and thus do not affect the qualitative comparisons presented in this paper