Loggerhead turtle (Caretta caretta) nesting habitat on low-relief mangroveislands in southwest Florida and consequences to hatchling sex ratios

A four-year (1991-1994) survey documented regular nesting by loggerhead tur tles (Caretta caretta) on the narrow, discontinuous beaches of low relief m angrove islands in the northern half of the Ten Thousand Islands in southwe st Florida. The nesting habitat differed from that on beaches where loggerh ead nesting has been well documented such as the barrier-island beaches of the southeastern United States. In the Ten Thousand Islands, turtles emerge d and nested on open beaches, but they also crawled through mangroves to re ach nesting sites that were within dense vegetation, sometimes 10-15 m with in maritime forests. We estimate that at least 240-480 loggerhead nests wer e made each year along approximately 16 km of shoreline in the Ten Thousand Islands. This nest density (15-30 nests/km) was similar to that on nearby barrier-island beaches. Raccoons (Procyon lotor) depredated 80.1% of logger head nests in the survey area, and several patterns of depredation were not ed. Among nests that were protected with screens or cages, 68.6% of eggs pr oduced hatchlings that emerged from the nest. Sand temperatures at clutch d epth were lowest at nest sites that were near the water or were shaded. Bas ed on the results of previous research on loggerhead hatchling sex ratios a nd incubation temperatures, the mean incubation temperatures in the norther n half of the Ten Thousand Islands from 1992-1994 (approximately 29 C) may have resulted in an overall hatchling sex ratio of about 1:1. Therefore, be cause many loggerhead nesting beaches in the southern half of Florida are b elieved to produce a highly female-biased hatchling sex ratio, the producti on of equal proportions of male and female hatchlings may make the nesting of loggerheads in the Ten Thousand Islands important in ensuring the produc tion of some male hatchlings by the south Florida nesting population. On ot her loggerhead nesting beaches in south Florida, nests that are nearest the water may have the best chance of producing some male hatchlings. Conserva tion activities that involve moving loggerhead clutches from sites that are near the water (where hatching success and incubation temperatures are low er) to sites that are farther from the water (where hatching success and in cubation temperatures are higher) may counteract the benefits of a nesting pattern that reduces the risk of overly skewed hatchling sex ratios by expo sing clutches to a variety of incubation temperatures.