Movement patterns for a critically endangered species, the leatherback turtle (Dermochelys coriacea), linked to foraging success and population status (original) (raw)
Related papers
FLEXIBLE FORAGING MOVEMENTS OF LEATHERBACK TURTLES ACROSS THE NORTH ATLANTIC OCEAN
Ecology, 2006
Some marine species have been shown to target foraging at particular hotspots of high prey abundance. However, we show here that in the year after a nesting season, female leatherback turtles (Dermochelys coriacea) in the Atlantic generally spend relatively little time in fixed hotspots, especially those with a surface signature revealed in satellite imagery, but rather tend to have a pattern of near continuous traveling. Associated with this traveling, distinct changes in dive behavior indicate that turtles constantly fine tune their foraging behavior and diel activity patterns in association with local conditions. Switches between nocturnal vs. diurnal activity are rare in the animal kingdom but may be essential for survival on a diet of gelatinous zooplankton where patches of high prey availability are rare. These results indicate that in their first year after nesting, leatherback turtles do not fit the general model of migration where responses to resources are suppressed during transit. However, their behavior may be different in their sabbatical years away from nesting beaches. Our results highlight the importance of whole-ocean fishing gear regulations to minimize turtle bycatch.
Movement Ecology, 2013
Background: Leatherback turtles are renowned for their trans-oceanic migrations. However, despite numerous movement studies, the precise drivers of movement patterns in leatherbacks remain elusive. Many previous studies of leatherback turtles as well as other diving marine predators have analyzed surface movement patterns using only surface covariates. Since turtles and other marine predators spend the vast majority of their time diving under water, an analysis of movement patterns at depth should yield insight into what drives their movements. Results: We analyzed the movement paths of 15 post-nesting adult female Pacific leatherback turtles, which were caught and tagged on three nesting beaches in Mexico. The temporal length of the tracks ranged from 32 to 436 days, and the spatial distance covered ranged from 1,532 km to 13,097 km. We analyzed these tracks using a movement model designed to yield inference on the parameters driving movement. Because the telemetry data included diving depths, we extended an earlier version of the model that examined surface only movements, and here analyze movements in 3-dimensions. We tested the effect of dynamic environmental covariates from a coupled biophysical oceanographic model on patch choice in diving leatherback turtles, and compared the effects of parameters measured at the surface and at depth. The covariates included distance to future patch, temperature, salinity, meridional current velocity (current in the north-south direction), zonal current velocity (current in the east-west direction), phytoplankton density, diatom density, micro-plankton density, and meso-zooplankton density. We found significant, i.e. non-zero, correlation between movement and the parameters for oceanic covariates in 8 of the tracks. Of particular note, for one turtle we observed a lack of correlation between movements and a modeled index of zooplankton at the surface, but a significant correlation between movements and zooplankton at depth. Two of the turtles express a preference for patches at depth with elevated diatoms, and 2 turtles prefer patches with higher mezozooplankton values at depth. In contrast, 4 turtles expressed a preference for elevated zooplankton patches at the surface, but not at depth. We suggest that our understanding of a marine predator's response to the environment may change significantly depending upon the analytical frame of reference, i.e. whether relationships are examined at the surface, at depth, or at different temporal resolutions. Lastly, we tested the effects of accounting for ocean currents on the movement patterns and found that for 13 of the 15 turtles, the parameter governing distance to the next patch decreased.
2012
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 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.
Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle
2010
Understanding food web functioning through the study of natural bio-indicators may constitute a valuable and original approach. In the context of jellyfish proliferation in many overexploited marine ecosystems studying the spatio-temporal foraging patterns of the giant "jellyvore" leatherback turtle turns out to be particularly relevant. Here we analyzed long-term tracking data to assess spatio-temporal foraging patterns in 21 leatherback turtles during their pluri-annual migration in the Northern Atlantic. Through an analytical approach based on the animal's own motion (independent of currents) and diving behavior distinct zones of high and low foraging success were identified. High foraging success occurred in a sub-equatorial zone spanning the width of the Atlantic and at high (>30°N) latitudes. Between these zones in the centre of North Atlantic gyre there was low foraging success. This "ocean desert" area was traversed at high speed by leatherbacks on their way to more productive areas at higher latitudes. Animals traveled slowly in high foraging success areas and dived shallower (17.2 ± 8.0 km day − 1 and 53.6 ± 33.1 m mean ± SD respectively) than in low foraging success areas (51.0 ± 13.1 km day − 1 and 81.8 ± 56.2 m mean ± SD respectively). These spatio-temporal foraging patterns seem to relatively closely match the main features of the integrated mesozooplankton distribution in the North Atlantic. Our method of defining high foraging success areas is intuitive and relatively easy to implement but also takes into account the impact of oceanic currents on animal's behavior.
Canadian Journal of Zoology, 2006
Diel diving patterns have been widely documented among plankton-feeding marine vertebrates. In many cases, these patterns have been interpreted as a response to the diel vertical migrations of prey. The leatherback turtle, Dermochelys coriacea (Vandelli, 1761), is a large marine predator that exploits gelatinous plankton in disparate foraging areas. Individuals of this species spend extended periods at northern latitudes before moving southward through pelagic waters. To identify and compare potential diel patterns of diving behaviour in temperate areas, where foraging has been observed, versus during southward migration, 15 subadult and adult leatherbacks were equipped with satellite-linked time-depth recorders off Nova Scotia, Canada. We observed variation in nocturnal versus diurnal behaviour, both at northern latitudes and during migration; however, diel differences in both diving and surface activity were much less pronounced while leatherbacks were in the north. We interpret the difference in leatherback diel diving regimen to reflect a response to changing resource conditions at these times, with leatherbacks foraging throughout the day and night at high latitudes, then changing to a bimodal pattern of diving during southward migration, with generally longer, deeper diving occurring during the night versus during the day. By quantifying diel changes in leatherback behaviour, we provide the first surface time correction factors based on multiple individuals for use in estimating abundance from aerial surveys. Résumé : Les patrons journaliers de plongée chez les vertébrés marins planctonophages ont été bien étudiés. Souvent, les patrons sont interprétés comme des réactions aux migrations verticales journalières des proies. La tortue luth, Dermochelys coriacea (Vandelli, 1761), est un prédateur marin de grande taille qui exploite le plancton gélatineux dans des aires d'alimentation disparates. Les individus de cette espèce passent de longues périodes dans les latitudes nordiques avant de se déplacer vers le sud dans les eaux pélagiques. Dans le but d'identifier et de comparer les patrons journaliers potentiels du comportement de plongée dans les zones tempérées où on observe de l'alimentation (par rapport aux patrons observés durant la migration vers le sud), nous avons muni 15 tortues subadultes et adultes d'enregistreurs de temps et de profondeur reliés à des satellites au large de la Nouvelle-É cosse, Canada. Nous avons observé une variation entre les comportements nocturne et diurne, tant dans les latitudes nordiques que durant la migration; les variations journalières d'activité en plongée et en surface sont, cependant, beaucoup moindres lorsque les tortues sont dans le nord. Nous interprétons les différences dans le régime journalier de plongée des tortues luth comme des réactions aux conditions changeantes des ressources à ce moment; aux latitudes élevées, les tortues s'alimentent tout au long de la journée et de la nuit; durant la migration vers le sud, elles adoptent un patron bimodal de plongée, avec généralement des plongées plus profondes et plus prolongées durant la nuit que durant le jour. En quantifiant les changements journaliers du comportement des tortues luth, nous fournissons les premiers facteurs de correction du temps passé en surface basés sur l'observation de plusieurs individus pour servir à estimer l'abondance à partir d'inventaires aériens.
Animal Behaviour, 2004
We used Satellite Relay Data Loggers to obtain the first dive profiles for critically endangered leatherback turtles outside the nesting season. As individuals moved from the Caribbean out into the Atlantic, key aspects of their diving behaviour changed markedly, in line with theoretical predictions for how dive duration should vary with foraging success. In particular, in the Atlantic, where foraging success is expected to be higher, dives became much longer than in the Caribbean. The deepest-ever dive profile recorded for a reptile was obtained in the oceanic Atlantic, with a 54-min dive to 626 m on 26 August 2002. However, dives were typically much shallower (generally !200 m) and shorter (!40 min). These results highlight the suitability of this species for testing models of dive performance.
2011
Leatherback turtles are the largest and widest ranging turtle species, and spend much of their time in the offshore pelagic environment. However, the high seas have thus far received little management attention to protect their ecosystems and biodiversity. We tagged 46 female leatherback turtles with satellite transmitters at Playa Grande, Costa Rica from 2004 to 2007. In the present study, we analyzed the vertical and horizontal habitat preferences of these leatherback turtles in the South Pacific Ocean. The turtles exhibited short, shallow dives during their migration southward (mean depth: 45 m; mean duration: 23.6 min), followed by deeper, longer dives (mean depth: 56.7 m; mean duration: 26.4 min) in the South Pacific Gyre that probably indicated searching for prey. We integrated the horizontal movements with remotely sensed oceanographic data to determine the turtles' response to the environment, and applied this information to recommendations for conservation in the pelagic environment. A generalized additive mixed model applied to the daily turtle travel rates confirmed that slower travel rates occurred at cooler sea surface temperatures, higher chlorophyll a concentration and stronger vertical Ekman upwelling, all of which are considered favorable foraging conditions. The southern terminus (35 to 37°S) of the leatherback tracks was also in an area of increased mesoscale activity that might act as a physical mechanism to aggregate their prey, gelatinous zooplankton. However, this could also act as a thermal limit to their distribution. This characterization of leatherback habitat use could aid the development of management efforts within the South Pacific Ocean to reduce mortality of leatherback turtles from fisheries interactions.
Population characteristics and seasonal migrations of leatherback sea turtles at high latitudes
Marine Ecology Progress Series, 2007
Efforts to model populations of the leatherback sea turtle Dermochelys coriacea and design appropriate conservation measures for this endangered species have been hindered by a lack of information on in-water (vs. nesting) population characteristics. We present the first synthesis of population characteristics of leatherbacks at high latitudes. During 8 seasons of fieldwork (1999 to 2006) off Nova Scotia, Canada, we collected biological data from 152 turtles, including 127 livecaptured individuals. The size-class distribution mainly represented large sub-adult and adult individuals (mean curved carapace length = 148.1 cm). Mean body mass was 392.6 kg (range: 191.9 to 640 kg). We found a significantly female-biased sex ratio (1.86 females:1 male) among mature turtles. We expect that there may be geographical variation in sex ratios of foraging populations reflecting breeding periodicity, distance from nesting areas, and associated migration patterns. Tag recoveries from 25 leatherbacks captured off Canada reveal nesting origins throughout South and Central America and the Caribbean. Recapture data suggest that although some female turtles proceed to Canadian waters within several months of nesting (in the same calendar year), entry into high-latitude coastal waters of the western Atlantic may more regularly occur later in the nesting remigration interval. Comparison of data from leatherbacks off Canada with those from a foraging population at similar latitudes off France reveals unequal size-class distributions, which may reflect the different thermal regimes in these areas.
The western Pacific leatherback turtle (Dermochelys coriacea), one of three genetically distinct stocks in the Indo-Pacific region, has declined markedly during past decades. This metapopulation nests year-round at beaches of several western Pacific island nations and has been documented through genetic analysis and telemetry studies to occur in multiple regions of the Pacific Ocean. To provide a large-scale perspective of their movements, high-use areas, and habitat associations, we report and synthesize results of 126 satellite telemetry deployments conducted on leatherbacks at western Pacific nesting beaches and at one eastern Pacific foraging ground during 2000–2007. A Bayesian switching state-space model was applied to raw Argos-acquired surface locations to estimate daily positions and behavioral mode (either transiting or area-restricted search) for each turtle. Monthly areas of high use were identified for postnesting periods using kernel density estimation. There was a clea...
The role of infrequent and extraordinary deep dives in leatherback turtles (Dermochelys coriacea)
Journal of Experimental Biology, 2008
SUMMARY Infrequent and exceptional behaviours can provide insight into the ecology and physiology of a particular species. Here we examined extraordinarily deep(300–1250 m) and protracted (>1h) dives made by critically endangered leatherback turtles (Dermochelys coriacea) in the context of three previously suggested hypotheses: predator evasion, thermoregulation and exploration for gelatinous prey. Data were obtained via satellite relay data loggers attached to adult turtles at nesting beaches(N=11) and temperate foraging grounds (N=2), constituting a combined tracking period of 9.6 years (N=26,146 dives) and spanning the entire North Atlantic Ocean. Of the dives, 99.6% (N=26,051) were to depths <300 m with only 0.4% (N=95) extending to greater depths(subsequently termed `deep dives'). Analysis suggested that deep dives: (1)were normally distributed around midday; (2) may exceed the inferred aerobic dive limit for the species; (3) displayed slow vertical descent rates and ...