Energy expenditure of adult green turtles at their foraging grounds and during simulated oceanic migration (original) (raw)
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1. Measuring the energy requirements of animals under natural conditions and determining how acquired energy is allocated to specific activities is a central theme in ecophysiology. 2. Turtle reproductive output is fundamentally linked with their energy balance so a detailed understanding of marine turtle energy requirements during the different phases of their life cycle at sea is essential for their conservation. 3. We used the non-invasive accelerometry technique to investigate the activity patterns and energy expenditure (EE) of adult green turtles (Chelonia mydas) foraging year-round at a sea-grass meadow in Mayotte (n = 13) and during simulated oceanic migration (displacement from the nesting beach) off Moh eli (n = 1), in the southwestern Indian Ocean. 4. At the foraging site, turtles divided their days between foraging benthically on the shallow seagrass meadow during daylight hours and resting at greater depth on the inner side of the reef slope at night. Estimated oxygen consumption rates (s _ V O 2) and daily energy expenditures (DEE) at the foraging site were low (s _ V O 2 during the day was 1Á6 and 1Á9 times the respective resting rate at night during the austral summer and winter, respectively), which is consistent with the requirement to build up substantial energy reserves at the foraging site, to sustain the energy-demanding breeding migration and reproduction. 5. Dive duration (but not dive depth) at the foraging site shifted significantly with season (dive duration increased with declining water temperatures, T w), while overall activity levels remained unchanged. In parallel with a significant seasonal decline in T w (from 28Á9 AE 0Á1 °C to 25Á3 AE 0Á4 °C), there was a moderate (~ 19%) but significant decline in DEE of turtles during the austral winter (901 AE 111 kJ day À1), when compared with the austral summer (1117 AE 66 kJ day À1). 6. By contrast, the turtle moved continuously during simulated oceanic migration, conducting short/shallow dives in the day, which (predominately at night) were interspersed with longer and deeper 'pelagic' dives. Estimated oxygen consumption rates during a simulated migration (1Á25 AE 0Á16 mL O 2 min À1 kg À0Á83) were found to be significantly increased over the foraging condition, equal to ~ 3 times the resting rate at night (0Á42 AE 0Á02 mL O 2 min À1 kg À0Á83), and daily energy expenditure amounted to 2327 AE 292 kJ day À1 , underlining the tremendous energetic effort associated with breeding migration. 7. Our study indicates that the accelerometry technique provides a new and promising opportunity to study marine turtle energy relations in great detail and under natural conditions.
Seasonal diving behaviour and feeding rhythms of green turtles at Mayotte Island
Marine Ecology Progress Series, 2013
In long-distance migratory marine species foraging behaviour remains particularly difficult to study even though it has important consequences for individual life history. Indeed, studies assessing concurrent dive patterns and feeding behaviour remain rare. We investigated the daily and seasonal feeding rhythms of green turtles Chelonia mydas on a coastal seagrass meadow at Mayotte, in the South Western Indian Ocean. Between 2005 and 2008, the behaviour of 19 green turtles (body mass: 86.8 to 134.0 kg) was recorded using electronic time-temperature-depth recorders, concurrently validated by direct in-water observations. Additionally, fast-acquisition global positioning system units were deployed on 3 of these turtles. Green turtles showed a high fidelity to the foraging site and conducted predominately flat-bottom dives, in accordance with both local bathymetry and tidal regime. On a daily basis, 2 main dive categories were identified: shortshallow foraging dives (mean ± SE: 6.0 ± 0.0 min for 2.0 ± 0.0 m) occurred during the day on the seagrass meadow, and long-deep resting dives (50.9 ± 19.0 min for 10.3 ± 1.4 m) occurred at night in coral and rocky areas. On a seasonal basis, mean dive duration increased from summer to winter (from 9.5 ± 0.5 to 15.7 ± 1.1 min) and was negatively correlated with seasonal water temperature (range: 25.7°C in winter to 29.3°C in summer). However, the daily foraging duration (~11 h d -1 ) did not vary significantly with season. Investigating green turtle foraging patterns is crucial for an understanding of their contribution to coastal ecosystem functioning.
Journal of Experimental Biology, 2011
Marine turtles are globally threatened. Crucial for the conservation of these large ectotherms is a detailed knowledge of their energy relationships, especially their at-sea metabolic rates, which will ultimately define population structure and size. Measuring metabolic rates in free-ranging aquatic animals, however, remains a challenge. Hence, it is not surprising that for most marine turtle species we know little about the energetic requirements of adults at sea. Recently, accelerometry has emerged as a promising tool for estimating activity-specific metabolic rates of animals in the field. Accelerometry allows quantification of the movement of animals (ODBA/PDBA, overall/partial dynamic body acceleration), which, after calibration, might serve as a proxy for metabolic rate. We measured oxygen consumption rates (V O2 ) of adult green turtles (Chelonia mydas; 142.1±26.9kg) at rest and when swimming within a 13m-long swim channel, using flow-through respirometry. We investigated the effect of water temperature (T w ) on turtle V O2 and tested the hypothesis that turtle body acceleration can be used as a proxy for V O2 . Mean massspecific V O2 (sV O2 ) of six turtles when resting at a T w of 25.8±1.0°C was 0.50±0.09ml min -1 kg -0.83 . sV O2 increased significantly with T w and activity level. Changes in sV O2 were paralleled by changes in respiratory frequency (f R ). Deploying bi-axial accelerometers in conjunction with respirometry, we found a significant positive relationship between sV O2 and PDBA that was modified by T w . The resulting predictive equation was highly significant (r 2 0.83, P<0.0001) and associated error estimates were small (mean algebraic error 3.3%), indicating that body acceleration is a good predictor of V O2 in green turtles. Our results suggest that accelerometry is a suitable method to investigate marine turtle energetics at sea.
Fidelity and over-wintering of sea turtles
Proceedings of The Royal Society B: Biological Sciences, 2007
While fidelity to breeding sites is well demonstrated in marine turtles, emerging knowledge of migratory routes and key foraging sites is of limited conservation value unless levels of fidelity can be established. We tracked green (Chelonia mydas, nZ10) and loggerhead (Caretta caretta, nZ10) turtles during their post-nesting migration from the island of Cyprus to their foraging grounds. After intervals of 2-5 years, five of these females were recaptured at the nesting beach and tracked for a second migration. All five used highly similar migratory routes to return to the same foraging and over-wintering areas. None of the females visited other foraging habitats over the study period (units lasted on average 305 days; maximum, 1356 days), moving only to deeper waters during the winter months where they demonstrated extremely long resting dives of up to 10.2 h (the longest breath-holding dive recorded for a marine vertebrate). High levels of fidelity and the relatively discrete nature of the home ranges demonstrate that protection of key migratory pathways, foraging and over-wintering sites can serve as an important tool for the future conservation of marine turtles.
Long-term monitoring of leatherback turtle diving behaviour during oceanic movements
Journal of Experimental Marine Biology and Ecology, 2006
The diving behaviour of four leatherback turtles (Dermochelys coriacea) was recorded for periods of 0.5-8.1 months during their postnesting movements in the Indian and Atlantic Oceans, when they covered 1569-18,994 km. Dive data were obtained using satellite-linked transmitters which also provided information on the dive depths and profiles of the turtles. Turtles mainly dove to depths b 200 m, with maximum dive durations under 30-40 min and exhibited diel variations in their diving activity for most part of the routes, with dives being usually longer at night. Diurnal dives were in general quite short, but cases of very deep (N900 m) and prolonged (N 70 min) dives were however recorded only during daytime. The three turtles that were tracked for the longest time showed a marked change in behaviour during the tracking, decreasing their dive durations and ceasing to dive deeply. Moreover, diel variations disappeared, with nocturnal dives becoming short and numerous. This change in turtle diving activity appeared to be related to water temperature, suggesting an influence of seasonal prey availability on their diving behaviour. The turtle diving activity was independent on the shape of their routes, with no changes between linear movements in the core of main currents or looping segments in presence of oceanic eddies.
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
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 21 ) and transit at high speeds (20-45 km d 21 ). Only a single mode was evident in the Pacific, which occurred at speeds of 21 km d 21 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.
What makes marine turtles go: A review of metabolic rates and their consequences
Journal of Experimental Marine Biology and Ecology, 2008
Quantification of metabolic rates (MR) is fundamental to understanding an individual organism's physiology and life history, as well as overall population dynamics. Applications of MR measurements have increased both in quantity and quality across animal ecology over the past 50 years. Included in this trend, research on MRs of marine turtles and its consequences for these unique ectothermic vertebrates has matured significantly. We reviewed existing literature on marine turtle MRs in the context of the physiology, ecology, and life history of these animals. Metabolic rates have been obtained and published for 4 of 7 marine turtle species, but not for all life stages for all of these species. Studies of marine turtle metabolism have ranged from straightforward MR measurements of a few individuals to use of innovative techniques to estimate energy expenditure of natural activities and for applications to marine turtle energetics and diving physiology. Comparisons of allometric relationships between resting MR (RMR) and body mass for leatherbacks (Dermochelys coriacea), green turtles (Chelonia mydas), other reptiles, and mammals revealed no differences between leatherbacks and green turtles, nor between those species and other reptiles, but significant differences with mammals. In addition, we synthesized research on the thermal biology of the leatherback turtle, which ranges from temperate to tropical waters, and concluded that leatherbacks achieve and maintain substantial differentials between body and ambient temperatures in varied thermal environments through an integrated balance of adaptations for heat production (e.g., adjustments of MR) and retention. Finally, we recommend that future research should 1) address remaining data gaps in current knowledge of MRs of some species, 2) apply MR measurements to important physiological, ecological, and conservation topics, 3) investigate cellular metabolism of marine turtles, and 4) focus on quantification of at-sea energy expenditure incurred by marine turtles during natural activities.
Phenotypically Linked Dichotomy in Sea Turtle Foraging Requires Multiple Conservation Approaches
Current Biology, 2006
Marine turtles undergo dramatic ontogenic changes in body size and behavior, with the loggerhead sea turtle, Caretta caretta, typically switching from an initial oceanic juvenile stage to one in the neritic, where maturation is reached and breeding migrations are subsequently undertaken every 2-3 years . Using satellite tracking, we investigated the migratory movements of adult females from one of the world's largest nesting aggregations at Cape Verde, West Africa. In direct contrast with the accepted life-history model for this species [4], results reveal two distinct adult foraging strategies that appear to be linked to body size. The larger turtles (n = 3) foraged in coastal waters, whereas smaller individuals (n = 7) foraged oceanically. The conservation implications of these findings are profound, with the population compartmentalized into habitats that may be differentially impacted by fishery threats in what is a global fishing hotspot . Although the protection of discrete areas containing coastal individuals may be attainable, the more numerous pelagic individuals are widely dispersed with individuals roaming over more than half a million square kilometers. Therefore, mitigation of fisheries by-catch for sea turtles in the east Atlantic will likely require complex and regionally tailored actions to account for this dichotomous behavior.
A review of long-distance movements by marine turtles, and the possible role of ocean currents
Oikos, 2003
A review of long-distance movements by marine turtles, and the possible role of ocean currents.-Oikos 103: 293-302. Sea turtle movements often occur in open-sea unsheltered areas, and are therefore likely to be influenced by major oceanographic processes. Only recently has work started to examine the possible relationships of these movements with dynamic oceanic features, and consequently a clear picture of such interaction is only available in a few cases. Newborn sea turtles are thought to rely on oceanic currents to reach their pelagic nursery habitats. The actual extent and timing of these developmental migrations are known for only a few populations, but these movements probably last several years and range over thousands of km. Large juveniles that have been tracked during their pelagic stage were found to make long-distance movements, sometimes swimming against the prevailing currents. Older juveniles of most species leave the pelagic habitat to recruit to neritic developmental habitats. This is a very poorly documented phase of the sea turtle life-cycle, and the few available indications show that turtles may have to swim actively for enormous distances to counterbalance their previous drift with the current. The course and extent of adult postnesting migrations vary greatly among different turtle species, but two main patterns are evident. Some species, like green, hawksbill and loggerhead turtles, shuttle between the nesting beach and a specific feeding area used for the entire inter-reproductive period. In these cases, individuals swim, rather than drift, to complete their journeys, with possible advection due to currents sometimes helping them to quickly reach their target, but sometimes providing navigational challenges. Other species such as the olive ridley and the leatherback turtle, leave the coastal nesting areas to reach the pelagic environment where they forage, and perform wandering movements. Major oceanographic processes (such as main currents and eddies) have been recently shown to have a remarkable influence on leatherback movements, making it questionable whether these journeys are to be considered migrations or, rather, prolonged stays in vast feeding areas.