Population characteristics, age structure, and growth dynamics of neritic juvenile green turtles in the northeastern Gulf of Mexico

Characterization of a population of green turtles inhabiting the northeastern Gulf of Mexico was made possible by the mortality of a subset of >4500 sea turtles that stranded during a mass cold stunning event in Florida, USA, during January 2010. In total, 434 dead, stranded green turtles Chelonia mydas were evaluated through necropsy and skeletochronological analysis to characterize morphology, sex, body condition, disease status, age structure, and growth patterns. Standard straightline carapace lengths ranged from 18.1 to 78.5 cm (mean +/- SD = 36.3 +/- 10.4 cm) and did not significantly differ from those of stranded green turtles that survived this event. Prevalence of fibropapilloma (FP) was low, at 6%, and sex ratio was significantly biased toward females (2.45F:1M). Age estimates ranged from 2 to 22 yr (mean +/- SD = 9 +/- 4 yr) and female age distribution was significantly greater than that of males. Mean stage durations, as calculated through summation of size class-specific growth rates and fitting smoothing spline models to length-at-age data, were similar and ranged from 17 to 20 yr. Generalized additive models and generalized additive mixed models were used to assess the potential influence of discrete and continuous covariates on growth rates. Somatic growth was significantly influenced by size, age, and calendar year; however, no effect of sex, FP status, or body condition was found. Increased understanding of population parameters will improve population models for the species and can also serve as a reference for assessing potential effects of the 2010 Deepwater Horizon oil spill in the Gulf of Mexico.