Sexy Riddles of the Ridleys
By Conservancy Research Manager Dr. Jeff Schmid
The Conservancy of Southwest Florida was recently awarded a research grant from the Sea Turtle Grants Program. Conservancy Research Manager Dr. Jeff Schmid, Greg Curry of Rookery Bay National Estuarine Research Reserve, Drs. Camryn Allen and Jeff Seminoff with the National Marine Fisheries Service, and Jeff Schwenter of South Carolina Department of Natural Resources will apply some new techniques to determine the sex of the immature Kemp’s ridley turtles inhabiting the Ten Thousand Islands. The Kemp’s ridley is considered the most endangered sea turtle but also happens to be the most common species residing in the coastal waters of southwest Florida. Understanding the sex ratio (number of males to number of females) of these potential recruits to the breeding population is essential to the conservation and management of this endangered species.
The gender of a marine turtle is determined by the prevailing temperature in the nest during egg incubation. Warmer nest temperatures produce more females and cooler temperatures produce more males, hence the saying “hot mamas, cool daddies”. The Kemp’s ridley primarily nests in the western Gulf of Mexico on a stretch of beach near Rancho Nuevo, Mexico. Since 1978, Mexican and U.S. biologists have collected eggs laid by nesting females and reburied the eggs in protective corrals to prevent poaching and depredation. It was later found that his conservation measure resulted in warmer incubation temperatures and had been producing a long-term female biased sex ratio for Kemp’s ridley hatchlings. Despite this unintended consequence, female biased sex ratios may have been advantageous to this critically endangered species.
Adult marine turtles can be sexed by the length of the tail, whereby male turtles have a much longer tail than females. However, this characteristic is not apparent in the immature Kemp’s ridleys inhabiting our coastal waters. Other methods are used for sexing immature turtles such as the concentration of testosterone in the blood. Males have higher levels of this sex hormone than females. A study in the Ten Thousand Islands 15 years ago found significantly more immature female ridleys than males, 2 females to every male or a 2F:1M ratio, as would be expected given the female hatchling bias on the nesting beach.
The Kemp’s ridley population has undergone some dramatic changes in the past twenty years, increasing from the brink of extinction owing to bi-national conservation efforts but still well below historical estimates. The increasing number of nesting females has resulted in the protective corrals reaching capacity and some of the nests have been left to incubate naturally on the beach. This relatively recent practice could result in different hatchling sex ratios so more up-to-date studies are needed for sexing immature Kemp’s ridleys living in our coastal waters. Our study will be investigating any size-specific or seasonal differences in sex ratio and compare our sexing data to earlier efforts in the Ten Thousand Islands and other regions of west Florida.
This study is funded in part by a grant awarded from the Sea Turtle Grants Program which is supported by proceeds from the sale of the Florida Sea Turtle License Plate. Learn more at www.helpingseaturtle.org.
