1. Introduction

In the hours after they enter thewater and swimoffshore, sea turtle
hatchlings can suffer high mortality from fish and avian predators
(Burger and Gochfeld, 2014; Frick, 1976; Gyuris, 1994; Pilcher et al.,
2000). They are therefore generally believed to swimoffshore as quickly
as possible (Whelan and Wyneken, 2007) and then, once in deeper
offshore water, they drift passively (Bolten and Balazs, 1995; Carr,
1987). Several studies have quantified the rate of aquatic predation
suffered by sea turtle hatchlings in the nearshore environment (Gyuris,
1994; Pilcher et al., 2000; Stewart and Wyneken, 2004; Whelan and
Wyneken, 2007; Witherington and Salmon, 1992; Wyneken et al.,
1997). Although recorded predation rates vary greatly among sites,
from 4.6% for loggerhead (Caretta caretta) hatchlings in South Florida
(Whelan andWyneken, 2007) to 85% for green (Chelonia mydas) hatchlings
at Heron Island, Australia (Gyuris, 1994), most authors identify
nearshore waters as highly threatening for hatchling turtles. Taking
into account that observation periods of these studies have typically
consisted of approximately 10–15 min, even the lowest observed rates
(4.6% by Whelan and Wyneken, 2007; 5% by Stewart and Wyneken,
2004; 7% by Wyneken et al., 1997) are likely to exact heavy losses if
hatchlings remain in nearshore environments for long periods of time
(Whelan and Wyneken, 2007). Several factors, such as depth, bottomstructures,
and release protocols have been shown to affect predation
risk, which is especially high in shallow (b10 m) waters (Pilcher et al.,
2000; Witherington and Salmon, 1992), and when hatchlings cross reef
structures (Frick, 1976; Gyuris, 1994; Pilcher et al., 2000; Witherington
and Salmon, 1992). Because high hatchling densities attract aquatic
predators (Wyneken et al., 2000), hatchlings released en masse from
hatchery sites suffer from 50% (Pilcher et al., 2000) to ten times
(Wyneken et al., 2000) higher predation rates than those released from
natural sites with a low density of nests. Other factors that may affect
predation rates are tidal and moon phases (Gyuris, 1994; Harewood
and Horrocks, 2008), water clarity, coast-specific predator assemblages,
and fish movement patterns (Whelan andWyneken, 2007)