Diel foraging behavior of gravid leatherback sea turtles in deep waters of the Caribbean Sea

Abstract

SUMMARYIt is generally assumed that leatherback turtles (Dermochelys coriacea), like other species of sea turtle, do not feed while offshore from nesting beaches, and rely instead on fat reserves to fuel reproductive activities. Recent studies, however, provide evidence that leatherbacks may forage during the internesting interval while offshore in the Western Atlantic Ocean and Caribbean Sea. Bio-logging technology was used to investigate the foraging behavior of female leatherback turtles at St Croix, US Virgin Islands. Leatherback gastrointestinal tract temperatures (T GT ) were analyzed for sudden fluctuations indicative of ingestions, and laboratory ingestion simulations were used to characterize temperature fluctuations associated with ingestion of prey versus seawater. Dive patterns associated with prey ingestion were characterized and the proportion of prey ingestion during the day (05:00-18:59h) and night (19:00-04:59h) were compared. A combined total of 111 prey ingestions for seven leatherback turtles were documented during the internesting interval. The number of prey ingestions ranged from six to 48 for individual turtles, and the majority (87.4%) of these events occurred during the daytime. Prey ingestions were most frequently associated with V-shaped dives, and the mean (±1s.d.) maximum dive depth with prey ingestion ranged from 154±51 to 232±101m for individual turtles. Although leatherbacks were found to opportunistically feed during the internesting interval, the low prey ingestion rates indicate that energy reserves acquired prior to the breeding season are critical for successful reproduction by leatherbacks from the St Croix, USVI nesting population.

Water mass characteristics and solar illumination influence leatherback turtle dive patterns at high latitudes

“…The diel cycle has been reported elsewhere for leatherbacks during southward migrations and v www.esajournals.org while resident in the tropics (Eckert et al 1989, James et al 2005a, James et al 2006a, Casey et al 2010. However, only with the HR archival data presented here is the consistency so clearly evident for turtles in their Canadian foraging domain, and so clearly triggered by solar illumination.…”

“…Heaslip et al (2012) demonstrated that foraging during daylight hours in Atlantic Canada is restricted to the photic zone. Moreover, while leatherbacks clearly dive throughout the night throughout their range, Casey et al (2010) provide evidence from stomach temperature telemetry that food ingestion rates in waters adjacent nesting beaches are significantly lower during the night than during the day.…”

“…The HR data we examined leads us to the simplest conclusion that the strictly diel dive depth periodicity is explained by leatherbacks being visual predators that are reliant on adequate ambient light to effectively forage (Casey et al 2010). This idea has been proposed before for diving marine predators, including penguins, which have been recorded diving more deeply during daylight hours and remaining in shallow waters, with infrequent feeding, throughout the night (Wilson et al 1993).…”

“…All three turtles exhibited shorter and deeper dives with smaller inter-dive translocation distances during the day (;05:00 to ;20:00 h local). In contrast, with low ingestion rates at night, simultaneous long, shallow dives during the night may be related to resting and a conservation of energy for times when prey detection and capture is more probable and profitable (Casey et al 2010).…”

“…Instruments deployed on nesting female leatherbacks in subtropical and tropical waters have revealed diel dive patterns (Eckert et al 1989, Ferraroli et al 2004, Hays et al 2004) and Casey et al (2010) propose that this constitutes an energy-saving strategy used by a visual predator to maximize foraging during daylight hours when prey might be most effectively captured. In contrast to the tropics, only general conclusions have been drawn regarding dive patterns at north temperate latitudes (e.g., James et al 2005bJames et al , 2006a.…”