The coast of Cape Verde hosts the third largest loggerhead nesting population in the world

[EN] Extensive sea turtle nesting monitoring has been conducted in several islands of the Archipelago of Cape Verde during the past years. The loggerhead turtle is the only species that nests in these islands though green and hawksbill turtle juveniles are very often found feeding around their coasts. Around 90% of loggerhead nests are deposited in the island of Boavista on approximately 50 km of white sandy beaches. This is one of the less populated islands with more inaccessible beaches, as all villages are far from the main nesting areas. Another 9% of nests are equally distributed among the islands of Sal, Maio and San Nicolau and the remaining 1% of nests are found among the other six major islands and several islets of the archipelago.

Evidence from genetic and Lagrangian drifter data for transatlantic transport of small juvenile green turtles

[EN] Green turtle hatchlings disperse away from their natal location to spend an early pelagic stage in the ocean, followed by a neritic stage where small juveniles settle in coastal areas. Here, we combined genetic and Lagrangian drifter data to investigate the connectivity between natal and foraging locations; particularly focussing on the evidence for transatlantic transport. Our results supported the general hypothesis that turtles tend to select foraging areas ‘closest-to-home’.

Quantifying wildlife-watching ecotourism intensity on an endangered marine vertebrate

Here, we show how seasonal changes in animal density drive strategic shifts in the activities of wildlife-watching operators. These shifts result in high viewing intensity when animal densities are low, highlighting the need for modifications to existing wildlife-watching guidelines. We used the endangered loggerhead sea turtle Caretta caretta as a model species that exhibits staggered departure from an important breeding area (Zakynthos, Greece, Mediterranean) over a 2-month period (July to August) when tourism is at a peak, to investigate changes in wildlife-watching strategies, zoning effectiveness and voluntary guideline compliance over time. We used a combination of direct land-based observations, global positioning system tracking (of wildlife-watching vessels and turtles) and models. The modelled number of turtles present in the breeding area decreased from >200 in July to <50 in August, while the intensity of turtle-viewing increased from a mean 1.5 to 6.1 wildlife-watching vessels per turtle-viewing event (i.e. concurrent and consecutive vessels observing a single turtle) over the same period, respectively. During this period, the wildlife-watching strategy changed and compliance to guidelines reduced (exacerbated by recreational vessels). However, wildlife-watching activity was limited to a highly restricted 0.95-km2 nearshore area, overlapping with just 9.5% of the core habitat area used by turtles. Our results have broad implications (whale watching etc.) by showing the importance of taking the number of animals available for viewing into consideration when assessing wildlife-watching activity and when designing viewing guidelines, particularly for populations where numbers noticeably fluctuate.

Using climatic suitability thresholds to identify past, present and future population viability

Often climatic niche models predict that any change in climatic conditions will impact species abundance or distribution. However, the accuracy of models that just incorporate climatic information to predict future species habitat use is widely debated. Alternatively, environmental conditions may simply need to be above some minimum threshold of climatic suitability, at which point, other factors drive population size. Using the example of nesting sites of loggerhead sea turtles (Caretta caretta) in the Mediterranean (n = 105), we developed climatic niche models to examine whether a climatic suitability threshold could be identified as a climatic indicator in order for large populations of a widespread species to exist. We then assessed the climatic suitability of sites above and below this threshold in the past (∼1900) and future (∼2100). Most large sites that are currently above the climatic threshold were above the threshold in the past and future, particularly when future nesting seasonality shifted to start 1–2 months earlier. Our analyses highlight the importance of future phenological shifts for maintaining suitability. Our results provide a positive outlook for sea turtle conservation, suggesting that climatic conditions may remain suitable in the future at sites that currently support large nesting populations. Our study also provides an alternative way of interpreting the outputs of climatic niche models, by generating a threshold as an index of a minimum climatic suitability required to sustain large populations. This type of approach offers the possibility to benefit from information provided by climate-driven models, while reducing their inherent uncertainties.

Incidental capture of loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) sea turtles by the pelagic longline fishery off southern Brazil

Incidental capture in fishing gear is one of the main sources of injury and mortality of juvenile and adult sea turtles (NRC, 1990; Lutcavage et al., 1997; Oravetz, 1999). Six out of the seven extant species of sea turtles — the leatherback (Dermochelys coriacea), the green turtle (Chelonia mydas), the loggerhead (Caretta caretta), the hawksbill (Eretmochelys imbricata), the olive ridley (Lepidochelys olivacea), and the Kemp’s ridley (Lepidochelys kempii) — are currently classified as endangered or critically endangered by the World Conservation Union (IUCN, formerly the International Union for Conservation of Nature and Natural Resources), which makes the assessment and reduction of incidental capture and mortality of these species in fisheries priority conservation issues (IUCN/Species Survival Commission, 1995).

Protracted rainfall decreases temperature within leatherback turtle (Dermochelys coriacea) clutches in Grenada, West Indies: Ecological implications for a species displaying temperature dependent sex determination

Protracted or intense rainfall may affect the reproductive success of reptilian species on a number of levels ranging from the availability of prey, the integrity of the nesting site and the subsequent survivability of offspring. For sea turtles (a species displaying temperature sex determination) nesting throughout the tropics and subtropics, rainfall has previously been shown to influence the development environment of clutches; in its extreme resulting in high levels of egg or hatchling mortality. Yet when compared to other abiotic variables affecting clutch success, rainfall has received relatively little attention. We therefore examined how fluctuations in local rainfall at a tropical nesting site for leatherback turtles (Dermochelys coriacea) affected the nest environment. Temperature data loggers placed within clutches (n = 8) revealed that protracted rainfall had a marked cooling effect on nests, so that seasonally improbable male-producing temperatures (

Increase of a Caribbean leatherback turtle Dermochelys coriacea nesting population linked to long-term nest protection

The leatherback turtle Dermochelys coriacea is considered to be at serious risk of global extinction, despite ongoing conservation efforts. Intensive long-term monitoring of a leatherback nesting population on Sandy Point (St. Croix, US Virgin Islands) offers a unique opportunity to quantify basic population parameters and evaluate effectiveness of nesting beach conservation practices. We report a significant increase in the number of females nesting annually from ca. 18-30 in the 1980s to 186 in 2001, with a corresponding increase in annual hatchling production from ca. 2000 to over 49,000. We then analyzed resighting data from 1991 to 2001 with an open robust-design capture-mark-recapture model to estimate annual nester survival and adult abundance for this population. The expected annual survival probability was estimated at ca. 0.893 (95% CL 0.87-0.92) and the population was estimated to be increasing ca. 13% pa since the early 1990s. Taken together with DNA fingerprinting that identify mother-daughter relations, our findings suggest that the increase in the size of the nesting population since 1991 was probably due to an aggressive program of beach protection and egg relocation initiated more than 20 years ago. Beach protection and egg relocation provide a simple and effective conservation strategy for this Northern Caribbean nesting population as long as adult survival at sea remains relatively high. (c) 2005 Elsevier Ltd. All rights reserved.

Some aspects of the ecology of the leatherback turtle Dermochelys coriacea at Laguna Jalova, Costa Rica

The ecology and reproductive biology of the leatherback turtle (Dennochelys coriacea) was studied on a high-energy nesting beach near Laguna Jalova, Costa Rica, between 28 March and 8 June 1985. The peak of nesting was between 15 April and 21 May. Leatherbacks here measured an average 146.6 cm straightline standard carapace length and laid an average 81.57 eggs. The eggs measured a mean 52.12 mm diameter and weighed an average of 85.01 g. Significant positive relationships were found between the carapace lengths of nesters and their clutch sizes and average diameter and weight of eggs. The total clutch weighed between 4.02 and 13.39 kg, and yolkless eggs accounted for an average 12.4% of this weight. The majority of nesters dug shallow (<24 cm) body pits and spent an average 81 minutes at the nest site. A significant number of c1utcbes were laid below the berm crest. In a hatchery 42.2% of the eggs hatched, while in natural nests 70.2% hatched. The average hatchling carapace length was 59.8 mm and weight was 44.6 g. The longevity of leatherback tracks and nests on the beach was affected by weather. One nester was recaptured about one year later off the coast of Mississippi, U.S.A. Egg poaching was intense on some sections of the Costa Rican coast. Four aerial surveys in four different months provided the basis for comparing density of nesting on seven sectors of the Caribbean coast of Costa Rica. The beach at Jalova is heavily used by green turtles (Chelonia mydJJs) after the leatherback nesting season. The role of the Parque Nacional Tortuguero in conserving the leatherback and green turtle is discussed.(PDF file contains 20 pages.)

Jellyfish aggregations and leatherback turtle foraging patterns in a temperate coastal environment

Leatherback turtles (Dermochelys coriacea) are obligate predators of gelatinous zooplankton. However, the spatial relationship between predator and prey remains poorly understood beyond sporadic and localized reports. To examine how jellyfish (Phylum Cnidaria: Orders Semaeostomeae and Rhizostomeae) might drive the broad-scale distribution of this wide ranging species, we employed aerial surveys to map jellyfish throughout a temperate coastal shelf area bordering the northeast Atlantic. Previously unknown, consistent aggregations of Rhizostoma octopus extending over tens of square kilometers were identified in distinct coastal

Movement patterns for a critically endangered species, the Leatherback Turtle (Dermochelys coriacea), linked to foraging success and population status

Foraging success for pelagic vertebrates may be revealed by horizontal and vertical movement patterns. We show markedly different patterns for leatherback turtles in the North Atlantic versus Eastern Pacific, which feed on gelatinous zooplankton that are only occasionally found in high densities. In the Atlantic, travel speed was characterized by two modes, indicative of high foraging success at low speeds (<15 km d−1) and transit at high speeds (20–45 km d−1). Only a single mode was evident in the Pacific, which occurred at speeds of 21 km d−1 indicative of transit. The mean dive depth was more variable in relation to latitude but closer to the mean annual depth of the thermocline and nutricline for North Atlantic than Eastern Pacific turtles. The most parsimonious explanation for these findings is that Eastern Pacific turtles rarely achieve high foraging success. This is the first support for foraging behaviour differences between populations of this critically endangered species and suggests that longer periods searching for prey may be hindering population recovery in the Pacific while aiding population maintenance in the Atlantic.

Climate change and sea turtles : a 150-year reconstruction of incubation temperatures at a major marine turtle rookery

Sea turtles show temperature dependent sex determination. Using an empirical relationship between sand and air temperature, we reconstructed the nest temperatures since 1855 at Ascension Island, a major green turtle (Chelonia mydas) rookery. Our results show that inter-beach thermal variations, previously ascribed to the albedo of the sand, which varies hugely from one beach to another, have persisted for the last century. Reconstructed nest temperatures varied by only 0.5 °C on individual beaches over the course of the nesting season, while the temperature difference between two key nesting beaches was always around 3 °C. Hence inter-beach thermal variations are the main factor causing a large range of incubation temperatures at this rookery. There was a general warming trend for nests, with a mean increase in reconstructed nest temperatures for different months of between 0.36 and 0.49 °C for the last 100 years.

Behaviour and buoyancy regulation in the deepest-diving reptile : the leatherback turtle

In the face of the physical and physiological challenges of performing breath-hold deep dives, marine vertebrates have evolved different strategies. Although behavioural strategies in marine mammals and seabirds have been investigated in detail, little is known about the deepest-diving reptile – the leatherback turtle (Dermochelys coriacea). Here, we deployed tri-axial accelerometers on female leatherbacks nesting on St Croix, US Virgin Islands, to explore their diving strategy. Our results show a consistent behavioural pattern within dives among individuals, with an initial period of active swimming at relatively steep descent angles (∼–40 deg), with a stroke frequency of 0.32 Hz, followed by a gliding phase. The depth at which the gliding phase began increased with the maximum depth of the dives. In addition, descent body angles and vertical velocities were higher during deeper dives. Leatherbacks might thus regulate their inspired air-volume according to the intended dive depth, similar to hard-shelled turtles and penguins. During the ascent, turtles actively swam with a stroke frequency of 0.30 Hz but with a low vertical velocity (∼0.40 ms–1) and a low pitch angle (∼+26 deg). Turtles might avoid succumbing to decompression sickness (‘the bends’) by ascending slowly to the surface. In addition, we suggest that the low body temperature of this marine ectotherm compared with that of endotherms might help reduce the risk of bubble formation by increasing the solubility of nitrogen in the blood. This physiological advantage, coupled with several behavioural and physical adaptations, might explain the particular ecological niche the leatherback turtle occupies among marine reptiles.