Wild versus head-started hawksbill turtles Eretmochelys imbricata: post-release behavior and feeding adaptions

Abstract

To ensure the success of reintroduction programs, it is important to monitor the postrelease behavior and survival of released animals. In this study, the post-release movement and behavior of 5 wild and 5 head-started hawksbill turtles Eretmochelys imbricata were monitored using ultrasonic telemetry. Their dispersal directions and recaptures may indicate that wild turtles perform homing migrations. However, the head-started turtles showed non-uniform patterns in dispersal movements. Four head-started turtles moved out of the monitoring area in various directions, whereas one turtle stayed within the monitoring area for approx. 10 mo. These results might indicate that head-started turtles wander aimlessly in their new surroundings. Signal reception patterns indicated that wild turtles were active in the daytime and rested under the coral at night. Although the head-started turtles also rest at night, their resting places did not seem to be sheltered from hazardous sea conditions or adequate for efficient resting. Therefore, head-started hawksbill turtles appear to need pre-release training such as exposure to structures or ledges in the rearing tank so they can utilize similar structures in the wild for shelter during rest periods and maximize their dive duration by employing these as a roof to counteract the positive buoyant effect of inhaled air. Prey analysis of a head-started turtle captured incidentally demonstrates that these turtles can make feeding adaptations to adjust to the natural environment. These findings provide constructive information for the implementation and improvement of head-start programs.

Dive behaviour of adult hawksbills (Eretmochelys imbricata, Linnaeus 1766) in the eastern Pacific Ocean highlights shallow depth use by the species

“…Hawksbills have been documented undertaking prolonged bouts on the seabed with few mid-water dives in other ocean regions (Houghton et al, 2008;Okuyama et al, 2010) and our findings suggest the hawksbills tracked here also spent considerable time near the sea floor.…”

Movement patterns of juvenile hawksbill turtles Eretmochelys imbricata at a Caribbean coral atoll: long-term tracking using passive acoustic telemetry

“…Distinct diel variation in the number of detections received is most likely attributable to nocturnal resting under coral ledges, where receivers are unable to detect acoustic signals from transmitters (van Dam & Diez 1997, Blumenthal et al 2009b, Okuyama et al 2010, Witt et al 2010 Highly resident individuals were detected for the majority of their transmission period around 1 receiver, while sequential residents were detected for weeks or months around multiple receivers. Transient turtles were detected at multiple stations within the array and were only detected at each receiver for a few days (Ogden et al 1983.…”

“…These have ranged from engaging recreational divers and photo-identification (Dunbar et al 2014) to using towed underwater video (Walcott et al 2014). Tracking technologies have included radio tele metry (Berube et al 2012), active acoustic telemetry (van Dam & Diez 1998, Scales et al 2011, and passive acoustic telemetry (Blumenthal et al 2009b, Okuyama et al 2010, Hart et al 2012. Active acoustic telemetry, in which focal animals are repeatedly located using a small vessel-based directional hydrophone system, has previously revealed that juvenile hawksbill turtles inhabiting Lighthouse Reef Atoll, Belize, have more extensive home ranges than those inhabiting other developmental sites in the Caribbean (Scales et al 2011), although the nature of data acquisition necessitated short tracking durations (< 25 d).…”

A question of scale: Replication and the effective evaluation of conservation interventions

“…Some of the concerns raised about headstarting reflect a lack of post-release monitoring and reporting of individual turtle outcomes, resulting in speculation about the relative fitness of headstarted turtles and health of headstarted populations. Critics point out that habituation to captivity could affect predator avoidance (Frazer 1992;Meylan and Ehrenfeld 2000), foraging (East and Ligon 2013), and habitat selection behaviours (Okuyama et al 2010). Headstarts from temperate populations kept active year-round in captivity to maximize growth will lack overwintering experience prior to release, potentially compromising post-release over-wintering survivorship (Frazer 1992;Bjorndal et al 2003).…”