BULLETIN OF MARINE SCIENCE, 74(2): 325–335, 2004 325 Bulletin of Marine Science © 2004 Rosenstiel School of Marine and Atmospheric Science of the University of Miami PREDATION RISK TO LOGGERHEAD HATCHLINGS AT A HIGH-DENSITY NESTING BEACH IN SOUTHEAST FLORIDA Kelly R. Stewart and Jeanette Wyneken ABSTRACT It has been suggested that mortality is high for early life history stages of long-lived vertebrates such as sea turtles. However, few studies have quantified mortality rates for these stages. We assessed the risk to loggerhead sea turtle hatchlings at the commence- ment of their offshore migration from a natural high-density nesting beach (Juno Beach, Florida), and at high-density (managed) open-beach hatchery sites. We followed indi- vidual hatchlings by kayak, at night as they left the beach, to document the proportion of turtles that survived their initial 15 min in the water. Of the 217 hatchlings followed, 206 survived for an observed survival rate of 95%. Tarpon were the most common predator observed. This in-water survival rate is much higher than that previously ob- served in the waters adjacent to a Florida hatchery (72%) and may be due to reduced risk associated with temporal and spatial variation in nest location at the natural beach, but not at the hatchery. Sea turtles are iteroparous and produce numerous, small offspring in several clutches (Miller, 1997). These characteristics indicate that, over time, evolutionary pressures have selected for a life history strategy in which investment in individual offspring is minimal and survival of young is low (Frazer, 1992). Many authors agree that mortality in early life stages is probably extremely high in turtles (Richardson and Richardson, 1982; Stan- cyk, 1982; Frazer, 1986; Heppell et al., 1996). Egg loss and nest predation by mammalian, avian, and crustacean predators are well documented (Witzell and Banner, 1980; Stancyk, 1982; Gyuris, 1994a). Because sea turtles have high fecundity, some laying 200–600 eggs per nesting season (Hirth, 1980; Van Buskirk and Crowder, 1994; Miller, 1997), perhaps one in 10,000 hatchlings will survive to maturity (Frazer, 1986). Important information can be obtained from the nesting beach regarding the reproductive cycles, fecundity, and variables that determine nest success of sea turtles, however, disproportionately little is known about mortality after hatchlings have entered the water. Life for hatchling sea turtles is inherently risky. Besides their small body size (around 4 cm carapace length), hatchlings have few defenses against predators. During their offshore migration, they may dive to avoid aerial predators (Frick, 1976; Witherington and Salmon, 1992) or tuck in their flippers and float motionless to avoid detection (With- erington, 2002). Threats to survival include predation at the nest, during the crawl from the nest to the ocean, during the swim through nearshore waters, and during growth on pelagic nursery grounds. Predation risk decreases with size. Other sources of mortality for young turtles include incidental capture in fishing gear, entanglement in marine de- bris, and ingestion of foreign materials such as tar and plastics (Lutcavage et al., 1997). Baseline population sizes (e.g., for hatchlings, juveniles, adults), recruitment levels, and mortality/survival rates for loggerhead turtles [Caretta caretta (Linnaeus, 1758)] in the U.S. are estimated from limited empirical data (Frazer, 1986; Crouse et al., 1987; National Marine Fisheries Service, 2001; Heppell et al., 2003). Few studies have quanti- fied or partitioned mortality at various life stages. The pelagic stage of loggerheads may last for 6.5–11.5 yrs (Bjorndal et al., 2000), and begins when hatchlings enter the water after having traversed the beach from the nest. To date, no demographic baselines based on empirical data have been established for this early stage. Quantification of mortality