Morphometry and allometry of free-living olive ridley sea turtles (Lepidochelys olivacea) from the Mexican Central Pacific

Research on olive ridley sea turtle (Lepidochelys olivacea) has emphasized egg-laying females and neonates, using data collected on nesting beaches, but no systematic studies on morphological characteristics by size and sex have been published. This research describes the morphometry of free-living olive ridley sea turtles from coastal and oceanic waters of the Mexican Central Pacific captured and released from 2011 through 2013. A total of 3469 km was surveyed, and 142 sea turtles were evaluated by sex, size class, marine area, and geographic region for nine corporal measurements and their allometric relationships. The average curved carapace length (CCL) was 62.12 cm, range 42-94 cm. Significant differences were found by sex and size class with total tail length (TTL) (♂ = 26.33 cm, ♀ = 12.4 cm); similarly with vent to tail tip length (VTTL) (♂ = 6.38 cm, ♀ = 3.86 cm); and for rear flipper length (RFL) (♂ = 28.17 cm, ♀ = 38.62 cm, immatures = 23.80 cm). Turtles from the coastal region of Colima-Michoacán showed longer CCL = 62.46 cm and wider CW = 66.58 cm. Adult female RFLs showed positive allometry, b = 1.098, suggesting an accelerated growth of the posterior extremities, probably favoring reproductive behaviors, e.g. nest digging and egg-covering. Morphological differences were likely due to ontogenetic sexual distinctions rather than marine area or geographic differences.