Scott A. Eckert

Embryo mortality and hatch success in In situ and translocated leatherback sea turtle Dermochelys coriacea eggs

Abstract At Sandy Point National Wildlife Refuge, St Croix, US Virgin Islands, natural beach erosion results in the loss of 45–60% of the leatherback sea turtle Dermochelys coriacea eggs laid there per annum. In a 4-year study (1982–1985), 31·4–68·1% of the eggs laid annually (312 of 582 total clutches) were collected at oviposition and reburied in stable beach zones in an effort to mitigate losses to erosion. Reburial did not significantly increase the proportion of eggs per clutch that failed to develop, the proportion of eggs that contained pre-term dead embryos, the occurrence of embryonic deformity, or the risk of depredation for eggs or hatchlings. However, a consistently larger proportion of pipped, dead hatchlings in clutches that had been moved reduced overall hatch success in translocated as compared to in situ clutches (53·7% versus 64·1%, respectively). Collection and reburial of otherwise doomed eggs resulted in a net gain of c . 6650 hatchlings over 4 years.

Internesting and Postnesting Movements and Foraging Habitats of Leatherback Sea Turtles (Dermochelys coriacea) Nesting in Florida

ABSTRACT We tracked 10 leatherback turtles by satellite from 2 Florida Atlantic Coast nesting beaches for a period ranging from 38 days to more than 454 days. Movement and foraging areas were often coastal, which contrasts with other satellite telemetry studies where leatherbacks are more pelagic. Using kernel home-range estimation we identified the primary internesting residence areas as well as Atlantic foraging areas. The primary internesting habitat was centered east–southeast of Cape Canaveral, Florida, from 2 to 60 km offshore and extending 215 km along the coast. Atlantic foraging areas were located primarily on the continental shelf from 30° to 50°N, and in an offshore area centered at 42°N, 65°W, as well as off Africa in the Mauritania upwelling. Seasonally, the location of these foraging areas changed, occurring on the North American continental shelf from March through November and off the shelf from December through February. One of the tracked turtles may have been killed with 17 other leatherbacks by coastal shrimp fishing located near the Georgia–Florida border. We illustrate how using remotely sensed data could be used to prevent such mortalities.

Movements of whale sharks (Rhincodon typus) in South‐east Asian waters as determined by satellite telemetry

Management of whale shark Rhincodon typus populations is hampered by a lack of information on the range travelled by individual whale sharks. This applies particularly in South-east Asia where the whale shark is increasingly used in commercial trade and for ecotourism. In this study an investigation of the movements of individual whale sharks from the greater Sulu Sea region was initiated using satellite telemetry. The movements of six sharks were monitored from 7 to 128 days. Two sharks travelled distances of 4567 and 8025 km. Both sharks moved through multiple political jurisdictions, confirming the need to manage the populations on a multilateral or regional level.

Identification of distinct movement patterns in Pacific leatherback turtle populations influenced by ocean conditions

Interactions with fisheries are believed to be a major cause of mortality for adult leatherback turtles (Dermochelys coriacea), which is of particular concern in the Pacific Ocean, where they have been rapidly declining. In order to identify where these interactions are occurring and how they may be reduced, it is essential first to understand the movements and behavior of leatherback turtles. There are two regional nesting populations in the East Pacific (EP) and West Pacific (WP), comprising multiple nesting sites. We synthesized tracking data from the two populations and compared their movement patterns. A switching state-space model was applied to 135 Argos satellite tracks to account for observation error, and to distinguish between migratory and area-restricted search behaviors. The tracking data, from the largest leatherback data set ever assembled, indicated that there was a high degree of spatial segregation between EP and WP leatherbacks. Area-restricted search behavior mainly occurred in the southeast Pacific for the EP leatherbacks, whereas the WP leatherbacks had several different search areas in the California Current, central North Pacific, South China Sea, off eastern Indonesia, and off southeastern Australia. We also extracted remotely sensed oceanographic data and applied a generalized linear mixed model to determine if leatherbacks exhibited different behavior in relation to environmental variables. For the WP population, the probability of area-restricted search behavior was positively correlated with chlorophyll-a concentration. This response was less strong in the EP population, but these turtles had a higher probability of search behavior where there was greater Ekman upwelling, which may increase the transport of nutrients and consequently prey availability. These divergent responses to oceanographic conditions have implications for leatherback vulnerability to fisheries interactions and to the effects of climate change. The occurrence of leatherback turtles within both coastal and pelagic areas means they have a high risk of exposure to many different fisheries, which may be very distant from their nesting sites. The EP leatherbacks have more limited foraging grounds than the WP leatherbacks, which could make them more susceptible to any temperature or prey changes that occur in response to climate change.

Photopic Spectral Sensitivity of Green and Loggerhead Sea Turtles

Abstract Flicker electroretinography (ERG) was used to examine the in situ photopic (cone-photoreceptor based) spectral sensitivities of Green and Loggerhead Sea Turtles. Both species were responsive to wavelengths from 440–700 nm, and both had peak sensitivity in the long wavelength portion of the spectrum (∼580 nm). For Loggerhead Sea Turtles, no measurable responses were obtained below about 440 nm, whereas reliable signals were seen for Green Sea Turtles at wavelengths down to 400 nm. Both species exhibited significant declines in sensitivity below 500 nm. The overall shapes of the spectral sensitivity functions were similar for the two species. These results support previous findings that sea turtles have well-developed photopic visual systems. The characteristics of these spectral sensitivity functions indicate that both species possess multiple cone photopigment types, and these, in conjunction with the presence of colored oil droplets, strongly imply a capacity for color discrimination. Comparative evaluation suggests that these turtles have modified their visual pigments from those of their terrestrial relatives to better suit the ambient conditions present in the shallow water, submarine environments that they typically inhabit.

Predicting bycatch hotspots for endangered leatherback turtles on longlines in the Pacific Ocean

Fisheries bycatch is a critical source of mortality for rapidly declining populations of leatherback turtles, Dermochelys coriacea. We integrated use-intensity distributions for 135 satellite-tracked adult turtles with longline fishing effort to estimate predicted bycatch risk over space and time in the Pacific Ocean. Areas of predicted bycatch risk did not overlap for eastern and western Pacific nesting populations, warranting their consideration as distinct management units with respect to fisheries bycatch. For western Pacific nesting populations, we identified several areas of high risk in the north and central Pacific, but greatest risk was adjacent to primary nesting beaches in tropical seas of Indo-Pacific islands, largely confined to several exclusive economic zones under the jurisdiction of national authorities. For eastern Pacific nesting populations, we identified moderate risk associated with migrations to nesting beaches, but the greatest risk was in the South Pacific Gyre, a broad pelagic zone outside national waters where management is currently lacking and may prove difficult to implement. Efforts should focus on these predicted hotspots to develop more targeted management approaches to alleviate leatherback bycatch.

Pre-reproductive Movements of Leatherback Sea Turtles (Dermochelys coriacea) Nesting in the Caribbean

The temporal pattern of colonization by epibionts on leatherback sea turtles (Dermochelys coriacea) nesting at Sandy Point, St. Croix, provides unique insight into the pre-reproductive movements of the turtles. Recruitment of the pantropical pelagic cirriped, Conchoderma virgatum, was rapid and continuous once the turtles arrived at the nesting grounds. The date at which individual turtles arrived at the nesting grounds was extrapolated from a von Bertalanffy growth model estimating the age of barnacles present during a turtles first nesting. The data suggest that gravid turtles do not arrive from temperate latitudes until just prior to nesting, and that they go directly to a preferred nesting beach rather than nesting opportunistically en route. The Sandy Point nesters apparently arrive at the nesting beach asynchronously over a period of 4 mo and, irrespective of date, individuals commence nesting within relatively few days of arrival. Mating presumably occurs prior to or during the migration and not in tropical waters. The occurrence of five additional species of epibiotic cirripeds and the presence of a parasitic isopod, Excorallana antillensis, are documented.

Field anaesthesia of leatherback sea turtles (Dermochelys coriacea)

Ten nesting leatherback sea turtles on Trinidad were anaesthetised for electroretinogram (erg) measurements, using ketamine and medetomidine, reversed with atipamezole. They weighed 242 to 324 kg and were given initial doses of 3 to 8 mg/kg ketamine and 30 to 80 μg/kg medetomidine administered into an external jugular vein; six of the turtles received supplementary doses of 2·6 to 3·9 mg/kg ketamine combined with 0 to 39 μg/kg medetomidine. The lower doses were used initially to ensure against overdosage and reduce the chances of residual effects after the turtles returned to the water, but successful ergs called for step-wise dose increases to the required level of anaesthesia. Respiratory rate, heart rate, electrocardiogram, cloacal temperature, and venous blood gases were monitored, and blood was collected for plasma biochemistry. At the end of the erg procedure, atipamezole was administered at 150 to 420 μg/kg (five times the dose of medetomidine), half intramuscularly and half intravascularly. The turtles were monitored and prevented from re-entering the water until their behaviour was normal. No apparent mortalities or serious anaesthetic complications occurred. The observed within-season return nesting rate of the anaesthetised turtles was comparable with that of unanaesthetised turtles.

Amphibious Hearing in Sea Turtles

Despite increasing levels of anthropogenic noise throughout the oceans, we know very little about the hearing capabilities of sea turtles or how they might behaviorally and physiologically respond to potentially harmful sources of noise. Sea turtles are among the evolutionarily oldest and most endangered marine species. Seven species of sea turtle exist worldwide, including Dermochelys coriacea (leatherback), Eretmochelys imbricata (hawksbill), Chelonia mydas (green), Caretta caretta (loggerhead), Lepidochelys kempi (Kemp’s ridley), Lepidochelys olivacea (olive ridley), and Natator depressus (flatback). With the exception of Natator depressus (for which we have insufficient data), all are classified as critically endangered or endangered by the International Union for the Conservation of Nature’s Red List of Threatened Species (2010). Sea turtles are found in nearly all temperate and tropical marine environments and are highly migratory, traveling great distances between developmental, foraging, and nesting habitats. Given their endangered status, understanding the effects of noise on sea turtles is both timely and critically important.

A technique for underwater anesthesia compared with manual restraint of sea turtles undergoing auditory evoked potential measurements.

ABSTRACT A safe and effective technique for underwater anesthesia of green sea turtles (Chelonia mydas) was developed to allow fully submerged in-water measurements of auditory evoked potentials (A...