Estimation of Green Turtle (Chelonia mydas) Growth Rates from Length-Frequency Analysis

Abstract

Length-frequency analysis (using the computer program MULTIFAN) was used to estimate growth rates and number of age classes in a population of immature green turtles (Chelonia mydas) at Great Inagua in the southern Bahamas. Results from MULTIFAN were compared with growth rates estimated from nonlinear regression analysis on capture-recapture data and with calculated growth rates for 5-cm carapace length increments for the same population of green turtles. MULTIFAN underestimated growth rates of the smaller green turtles but yielded a better estimate of asymptotic size than did the nonlinear regression analysis. Estimates generated by MULTIFAN and by nonlinear regression analysis for the number of years it takes a green turtle at Great Inagua to grow from 30 to 70 cm carapace length fell within the 95% confidence limits of the calculated growth data from capture-recapture data. When the number of length-frequency samples was reduced sequentially from 10 years to two years, MULTIFAN was successful in estimating the number of age classes in the population for each of the nine sample sets. Length-frequency analysis shows promise as a method to rapidly estimate the number of year classes in a population of immature sea turtles and to estimate von Bertalanffy growth parameters.