Article

Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle

May 2010
Journal of Marine Systems 81:225-234

May 2010
81:225-234

DOI:10.1016/j.jmarsys.2009.12.002

Authors:

Sabrina Fossette

Victoria J Hobson

University of Exeter

Beatriz Calmettes

Collecte Localisation Satellites

Show all 7 authorsHide

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 meso-zooplankton 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.

Isolation by environment in the highly mobile olive ridley turtle ( Lepidochelys olivacea ) in the eastern Pacific

Article

Full-text available

May 2018
Proc Biol Sci

Spatial and temporal scales at which processes modulate genetic diversity over the landscape are usually overlooked, impacting the design of conservation management practices for widely distributed species. We examine processes shaping population divergence in highly mobile species by re-assessing the case of panmixia in the iconic olive ridley turtle from the eastern Pacific. We implemented a biophysical model of connectivity and a seascape genetic analysis based on nuclear DNA variation of 634 samples collected from 27 nesting areas. Two genetically distinct populations largely isolated during reproductive migrations and mating were detected, each composed of multiple nesting sites linked by high connectivity. This patternwas strongly associated with a steep environmental gradient and also influenced by ocean currents. These findings relate to meso-scale features of a dynamic oceanographic interface in the eastern tropical Pacific (ETP) region, a scenario that possibly provides different cost–benefit solutions and selective pressures for sea turtles during both the mating and migration periods.We reject panmixia and propose a new paradigm for olive ridley turtles where reproductive isolation due to assortative mating is linked to its environment. Our study demonstrates the relevance of integrative approaches for assessing the role of environmental gradients and oceanographic currents as drivers of genetic differentiation in widely distributed marine species. This is relevant for the conservation management of species of highly mobile behaviour, and assists the planning and development of large-scale conservation strategies for the threatened olive ridley turtles in the ETP. © 2018 The Author(s) Published by the Royal Society. All rights reserved.

The leatherback turtle Dermochelys coriacea (Vandelli, 1761) in the bay of Biscay and the North East Atlantic

Article

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Jan 2013

The Gulf Stream frontal system: A key oceanographic feature in the habitat selection of the leatherback turtle?

Article

Full-text available

May 2017
DEEP-SEA RES PT I

Although some associations between the leatherback turtle Dermochelys coriacea and the Gulf Stream current have been previously suggested, no study has to date demonstrated strong affinities between leatherback movements and this particular frontal system using thorough oceanographic data in both the horizontal and vertical dimensions. The importance of the Gulf Stream frontal system in the selection of high residence time (HRT) areas by the North Atlantic leatherback turtle is assessed here for the first time using state-of-the-art ocean reanalysis products. Ten adult females from the Eastern French Guianese rookery were satellite tracked during post-nesting migration to relate (1) their horizontal movements to physical gradients (Sea Surface Temperature (SST), Sea Surface Height (SSH) and filaments) and biological variables (micronekton and chlorophyll a), and (2) their diving behaviour to vertical structures within the water column (mixed layer, thermocline, halocline and nutricline). All the turtles migrated northward towards the Gulf Stream north wall. Although their HRT areas were geographically remote (spread between 80–30 °W and 28–45 °N), all the turtles targeted similar habitats in terms of physical structures, i.e. strong gradients of SST, SSH and a deep mixed layer. This close association with the Gulf Stream frontal system highlights the first substantial synchronization ever observed in this species, as the HRTs were observed in close match with the autumn phytoplankton bloom. Turtles remained within the enriched mixed layer at depths of 38.5±7.9 m when diving in HRT areas, likely to have an easier access to their prey and maximize therefore the energy gain. These depths were shallow in comparison to those attained within the thermocline (82.4±5.6 m) while crossing the nutrient-poor subtropical gyre, probably to reach cooler temperatures and save energy during the transit. In a context of climate change, anticipating the evolution of such frontal structure under the influence of global warming is crucial to ensure the conservation of this vulnerable species.

The Gulf Stream frontal system: A key oceanographic feature in the habitat selection of the leatherback turtle?

Article

May 2017
DEEP-SEA RES PT I

Although some associations between the leatherback turtle Dermochelys coriacea and the Gulf Stream current have been previously suggested, no study has to date demonstrated strong affinities between leatherback movements and this particular frontal system using thorough oceanographic data in both the horizontal and vertical dimensions. The importance of the Gulf Stream frontal system in the selection of high residence time (HRT) areas by the North Atlantic leatherback turtle is assessed here for the first time using state-of-the-art ocean reanalysis products. Ten adult females from the Eastern French Guianese rookery were satellite tracked during post-nesting migration to relate (1) their horizontal movements to physical gradients (Sea Surface Temperature (SST), Sea Surface Height (SSH) and filaments) and biological variables (micronekton and chlorophyll a), and (2) their diving behaviour to vertical structures within the water column (mixed layer, thermocline, halocline and nutricline). All the turtles migrated northward towards the Gulf Stream north wall. Although their HRT areas were geographically remote (spread between 80-30°W and 28-45°N), all the turtles targeted similar habitats in terms of physical structures, i.e. strong gradients of SST, SSH and a deep mixed layer. This close association with the Gulf Stream frontal system highlights the first substantial synchronization ever observed in this species, as the HRTs were observed in close match with the autumn phytoplankton bloom. Turtles remained within the enriched mixed layer at depths of 38.5±7.9 m when diving in HRT areas, likely to have an easier access to their prey and maximize therefore the energy gain. These depths were shallow in comparison to those attained within the thermocline (82.4±5.6 m) while crossing the nutrient-poor subtropical gyre, probably to reach cooler temperatures and save energy during the transit. In a context of climate change, anticipating the evolution of such frontal structure under the influence of global warming is crucial to ensure the conservation of this vulnerable species.

Multispecies leatherback assemblage from the Chandler Bridge and Ashley formations (Oligocene) of South Carolina, USA

Article

Full-text available

Dec 2020

Paleogene dermochelyid species richness far exceeded that of today. Leatherback sea turtles were most species rich in the Paleogene, but their richness declined sharply during the Neogene with only one species existing today, Dermochelys coriacea. We describe the fossil remains of three leatherback genera (Natemys, Psephophorus, and Egyptemys) from the upper Oligocene Chandler Bridge Formation and two (Natemys and Psephophorus) from the lower Oligocene Ashley Formation of South Carolina, USA. The fossils consist of isolated and some associated carapacial ossicles. Several ossicles are referred to Natemys sp. because their scalloped edges are indicative of the carapacial sunflower pattern specific to this genus. Additionally, two Natemys morphotypes (Natemys sp. 1 and 2) are distinguished based on differences in ossicle thickness and internal structure. We refer two ossicles to cf. Psephophorus because of their internal diploic structure and because one has a dorsal radial pattern while the other has a prominent ridge that exhibits strong visceral concavity. Finally, we refer one ossicle to cf. Egyptemys because it has a shallow keel that shows little expression on the visceral surface, although we also acknowledge the ossicle’s similarity to some ridged ossicles of the genus Psephophorus. These ossicles represent the first multispecies assemblage of leatherback fossils reported worldwide. Furthermore, the specimens fill both temporal and geographic gaps for extinct leatherback genera and represent the first formally described dermochelyids from South Carolina and the Oligocene of the Atlantic Coastal Plain.

Accumulation of trace elements in leatherback turtle (Dermochelys coriacea) eggs from the south-western Caribbean indicates potential health risks to consumers

Article

Nov 2019
CHEMOSPHERE

Trace metal and metalloid levels were measured in eggs of the NW Atlantic leatherback turtle (Dermochelys coriacea) from nesting grounds in the Bocas del Toro province, Panama, to infer exposure and associated risks to local communities. Samples were analyzed for a set of 26 essential and non-essential elements using inductively coupled plasma techniques. Median concentrations of Fe, Zn, As, Se and Sr in D. coriacea eggs were higher than previously reported for this species, which likely reflects differential contamination levels of specimens during foraging. The evaluation of non-carcinogenic human health risks from ingesting leatherback eggs has revealed potential deleterious effects due to high concentrations of As, Se and Sr for all examined age and gender groups, while Hg and Zn levels were above international standards for children. Hazard index (HI) values exceeded unity in all cases indicating serious health impacts related to possible additive effects of multiple metals co-occurring in the eggs. Our findings suggest that exposure to high (inorganic) As and Cr(VI) levels is associated with an increased carcinogenic risk, significantly exceeding the acceptable lifetime risk of 10−6 for both adults and children. Despite some limitations, such as unclear As and Cr speciation, our results demonstrated that the ingestion of D. coriacea eggs poses considerable health risks to local communities, and their consumption should not exceed 3.4 × 10−4 g (5.0 × 10−6 eggs) kg BW d−1. Resource managers and conservationists should focus their attention to human health effects as an alternative tool to address egg poaching and consumption.

Observation of a leatherback sea turtle Dermochelys coriacea in the Gulf of Corinth, Greece.

Article

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Jan 2015
MTN

Information relevant to the identification of critical habitat for Leatherback Sea Turtles (Dermochelys coriacea) in Canadian Pacific waters

Technical Report

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Dec 2015

In 1981, Leatherback Sea Turtle populations in Canadian waters were assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as Endangered. This status was confirmed in 2001, and in 2003, the Leatherback Sea Turtle was listed as Endangered on Schedule 1 of the Species at Risk Act (SARA). In May 2012, the species was reassessed as two separate populations (Atlantic and Pacific). Both populations continue to be designated as Endangered. As part of the SARA recovery process, the “Recovery Strategy for the Leatherback Turtle populations in Pacific Canadian waters” was published on the SARA Registry in February 2007. For species listed as Threatened or Endangered, SARA requires identification of the habitat necessary for the survival or recovery of a listed wildlife species. Once this habitat is identified in the final recovery strategy or action plan, it is deemed the species’ “critical habitat” and afforded legal protection from destruction under the Act. Leatherback Sea Turtles feed on scyphozoan prey in temperate high latitude locales, such as the Canadian Pacific coast. We used an envelope model to locate suitable habitat for Leatherback Sea Turtle foraging, and describe the biophysical function and features of suitable habitat in Canadian Pacific waters.

Evidence of Leatherback Turtles (Dermochelys coriacea) in Brazilian Subtropical Coastal Waters

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May 2023

Toward a common approach for assessing the conservation status of marine turtle species within the european marine strategy framework directive

Article

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Oct 2022

Environmental policies, including the European Marine Strategy Framework Directive (MSFD), generally rely on the measurement of indicators to assess the good environmental status (GES) and ensure the protection of marine ecosystems. However, depending on available scientific knowledge and monitoring programs in place, quantitative GES assessments are not always feasible. This is specifically the case for marine turtle species, which are listed under the Biodiversity Descriptor of the MSFD. Relying on an expert consultation, the goal of this study was to develop indicators and a common assessment approach to be employed by European Union Member States to evaluate the status of marine turtle populations in the frame of the MSFD. A dedicated international expert group was created to explore and test potential assessment approaches, in coherence with other environmental policies (i.e. Habitats Directive, OSPAR and Barcelona Conventions). Following a series of workshops, the group provided recommendations for the GES assessment of marine turtles. In particular, indicators and assessment methods were defined, setting a solid basis for future MSFD assessments. Although knowledge gaps remain, data requirements identified in this study will guide future data collection initiatives and inform monitoring programs implemented by EU Member States. Overall this study highlights the value of international collaboration for the conservation of vulnerable species, such as marine turtles.

Ecological Trap or Favorable Habitat? First Evidence That Immature Sea Turtles May Survive at Their Range-Limits in the North-East Atlantic

Article

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Oct 2021

Unusual environmental events can push marine animals outside their physiological tolerances through changes in trophic and/or thermal conditions. Such events typically increase the risk of stranding. Rescue Centers offer a unique opportunity to report animals in distress and satellite track rehabilitated individuals to identify potential new habitats and support an effective conservation of these endangered species. By combining sightings (1988–2020) and tracking data (2008–2020) collected along the French Atlantic and English Channel coasts, our study assessed if the Bay of Biscay is an ecological trap or a favorable habitat for immature sea turtles. The largest tracked individuals migrated westward to pelagic waters, likely toward their natal beaches, while smaller individuals remained within the Bay of Biscay (BoB) and crossed colder (mean: 17.8 ± 3.0°C) but more productive waters. The turtles’ directions differed from the ones of ocean currents, excluding a passive advection to these unexpected habitats. Although the BoB might be thermally unsuitable in winter, the higher micronekton biomass predicted in this region could offer a productive foraging habitat for immature turtles. However, the majority of the sightings referred to individuals stranded alive (75%), suggesting this area could also act as an ecological trap for the smallest individuals that are mostly reported in winter suffering cold-stunning. Assumed to be outside the species range, our results reveal a potential foraging ground in the North-East Atlantic for these young turtles, confirming the crucial role of the rehabilitation centers and the need to continue prioritizing conservation of these endangered species, particularly vulnerable at this stage and at such temperate latitudes.

Identification of the Gulf of Mexico as an important high‐use habitat for leatherback turtles from Central America

Article

Full-text available

Aug 2021

Endangered leatherback sea turtles (Dermochelys coriacea) are wide‐ranging, long‐distance migrants whose movements are often associated with environmental cues. We examined the spatial distribution and habitat use for 33 satellite‐tracked leatherbacks from nesting beaches on the Caribbean coast of Costa Rica and Panama from 2004 to 2018, an important nesting population for the leatherback Northwest Atlantic Distinct Population Segment. Tracking revealed the use of two distinct regions, the Gulf of Mexico (GoM, n = 18) and the North Atlantic Ocean (NAO, n = 15). We developed density utilization maps to elucidate high‐use habitats, migration pathways, and seasonal movements. GoM leatherbacks were found in three concentrated high‐use habitats connected by a migration pathway, while NAO leatherbacks were primarily found in a single, large high‐use habitat. Leatherbacks in both regions have the potential to interact with Atlantic pelagic longline fisheries based on seasonal overlap with high fishing effort. Our findings suggest that the GoM is an important destination for leatherbacks from the Caribbean coast of Central America with seasonal movements between high‐use habitats within the GoM. While leatherbacks are utilizing high‐use habitats in both the NAO and the GoM, the proportion of individuals migrating into the GoM increased over the study period. Additionally, NAO leatherbacks have increased the distance they travel in the first 90 d. Regional differences in movement and spatial distribution of high‐use habitats are important considerations when developing conservation plans for the Northwest Atlantic leatherback population.

First record of a leatherback sea turtle (Dermochelyidae) from the Mio-Pliocene Purisima Formation of northern California, USA

Article

Jun 2019

The Azores: A Mid-Atlantic Hotspot for Marine Megafauna Research and Conservation

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Jan 2020

The increasing public perception that marine megafauna is under threat is an outstanding incentive to investigate their essential habitats (EMH), their responses to human and climate change pressures, and to better understand their largely unexplained behaviors and physiology. Yet, this poses serious challenges such as the elusiveness and remoteness of marine megafauna, the growing scrutiny and legal impositions on their study, and difficulties in disentangling environmental drivers from human disturbance. We argue that advancing our knowledge and conservation on marine megafauna can and should be capitalized in regions where exceptional access to multiple species (i.e., megafauna ‘hotspots’) combines with the adequate legal framework, sustainable practices, and research capacity. The wider Azores region, hosting EMHs of all key groups of vulnerable or endangered vertebrate marine megafauna, is a singular EMH hotspot on a migratory crossroads, linking eastern and western Atlantic margins and productive boreal waters to tropical seas. It benefits from a sustainable development model based on artisanal fisheries with zero or minor megafauna bycatch, and one of the largest marine protected area networks in the Atlantic covering coastal, oceanic and deepsea habitats. Developing this model can largely ensure the future integrity of this EMH hotspot while fostering cutting-edge science and technological development on megafauna behavior, biologging and increased ocean observation, with potential major impacts on the Blue Growth agenda. An action plan is proposed.

Re-examining trophic dead ends: stable isotope values link gelatinous zooplankton to leatherback turtles in the California Current. Marine Ecology Progress Series 632:205–219

Article

Full-text available

Dec 2019
MAR ECOL-PROG SER

Jeffrey A. Seminoff

Predator–prey interactions provide essential information for tracing energy flow through food webs and evaluating the structure and function of ecosystems. In pelagic environ- ments, these interactions are often difficult to discern, which is problematic for identifying specific energy pathways that support populations of protected species. We examined the trophic ecology of an endangered population of leatherback turtles Dermochelys coriacea and their gelatinous prey in the California Current-Large Marine Ecosystem (CC-LME). We combined carbon and nitrogen bulk stable isotope analysis and compound-specific isotope analysis of amino acids (CSIA-AA) with Bayesian statistical approaches to examine the diets of leatherbacks and their prey (scyphozoans and thaliaceans) sampled in the CC-LME. Our objectives were to evaluate (1) temporal changes in leatherback trophic position, (2) the contribution of different gelatinous prey to leatherback diets, and (3) trophic structure of the leatherback food web by estimating trophic posi- tions and isotopic niches of leatherbacks and their potential prey. Leatherback trophic positions did not change over time, although carbon isotope values suggest a temporary shift in leatherback habitat in 2005, coincident with anomalous upwelling conditions. Bayesian mixing models suggest that carnivorous sea nettles Chrysaora fuscescens were the largest contributor to leatherback diet, followed by filter-feeding thaliaceans. Isotope analyses provided useful and ecologically realistic estimates of trophic structure, where trophic positions were lowest for thaliaceans, intermediate for scyphozoans, and highest for leatherbacks. Overall, our findings provide information on leather- back foraging ecology over a 13 yr period and the trophic structure of gelatinous zooplankton that support the leatherback population in the CC-LME.

Leatherback bycatch in an eastern Caribbean artisanal longline fishery

Article

Full-text available

Dec 2019

Overlap of small-scale fisheries with sea turtle high-use areas is of growing concern, but the extent to which these endangered species interact with fishing gear is rarely known. Structured face-to-face interviews with 22 longline vessel captains were used to make a rapid assessment of sea turtle bycatch by the artisanal longline fleet of Barbados in the eastern Caribbean. Extrapolated estimates suggested that an average of 284 sea turtles yr-1 were caught on 1896200 hooks, a bycatch per unit effort of 0.15. Based on extrapolation of the percentage of the observed vessels to the entire fleet, an estimated average of 374 sea turtles yr-1 are caught. The majority of captains (86%) reported leatherback turtles Dermochelys coriacea to be the predominant species. The Barbados longline fleet operates in sea areas through which leatherbacks pass on their way to and from important nesting beaches in Trinidad and Tobago, Grenada, and the Guianas, and in which they reside during the pre-nesting period as well as throughout the nesting season. Although most sea turtles caught as bycatch were released alive, they often remained hooked with trailing lines. The majority of captains expressed their willingness to be trained in safe-handling and release of hooked and entangled turtles, to increase the probability of their survival.

Re-examining trophic dead ends: stable isotope values link gelatinous zooplankton to leatherback turtles in the California Current

Article

Full-text available

Dec 2019

Photographic identification and citizen science combine to reveal long distance movements of individual reef manta rays Mobula alfredi along Australia’s east coast

Article

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Jul 2019

Research into the movement ecology of terrestrial and marine animals is growing globally, especially for threatened species. Understanding how far an animal can move and the extent of its range can inform conservation planning and management. On the east coast of Australia, reef manta rays Mobula alfredi are the subject of a photographic identification study, Project Manta. In June 2018, videos of reef manta rays from the SS Yongala (19.31° S, 147.62° E), were submitted to the Project Manta east coast sightings database. The videos were of two individuals previously identified from North Stradbroke Island (27.42° S, 153.55° E), about 1150 km to the south of the SS Yongala. This represents the greatest point-to-point distance travelled by individual M. afredi and extends the latitudinal range for this sub-population on the east coast. This study highlights that citizen science input can provide valuable data to address knowledge gaps in the distribution and population range of marine species. Knowledge of the 1000+ km range movement potential of individual M. alfredi, highlights the possibility that regional sub-populations may span jurisdictional zones of more countries than previously considered likely, complicating conservation management of this species.

The importance of sample size in marine megafauna tagging studies

Article

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Jul 2019
ECOL APPL

Telemetry is a key, widely used tool to understand marine megafauna distribution, habitat use, behavior, and physiology; however, a critical question remains: “How many animals should be tracked to acquire meaningful data sets?” This question has wide‐ranging implications including considerations of statistical power, animal ethics, logistics, and cost. While power analyses can inform sample sizes needed for statistical significance, they require some initial data inputs that are often unavailable. To inform the planning of telemetry and biologging studies of marine megafauna where few or no data are available or where resources are limited, we reviewed the types of information that have been obtained in previously published studies using different sample sizes. We considered sample sizes from one to >100 individuals and synthesized empirical findings, detailing the information that can be gathered with increasing sample sizes. We complement this review with simulations, using real data, to show the impact of sample size when trying to address various research questions in movement ecology of marine megafauna. We also highlight the value of collaborative, synthetic studies to enhance sample sizes and broaden the range, scale, and scope of questions that can be answered.

Satellite tracking of hawksbill turtles nesting at Buck Island Reef National Monument, US Virgin Islands: Inter-nesting and foraging period movements and migrations

Article

Full-text available

Jan 2019
BIOL CONSERV

To conserve imperiled marine species, an understanding of high-density use zones is necessary prior to designing and evaluating management strategies that improve their survival. We satellite-tracked turtles captured after nesting at Buck Island Reef National Monument (BIRNM), St. Croix, US Virgin Islands to determine habitat-use patterns of endangered adult female hawksbills (Eretmochelys imbricata). For 31 turtles captured between 2011 and 2014, switching state-space modeling and home range analyses showed that inter-nesting (IN) core-use areas (i.e., 50% kernel density estimates [KDEs]) were 9.6 to 77.7 km² in area, occupied for 21 to 85 days, and in shallow water (21 of 26 centroids > −10 m). The IN zones overlapped with areas both within the protected borders of BIRNM, and outside BIRNM (32% of turtle-tracking days outside during IN). Turtles migrated to their foraging grounds between July and October with path lengths ranging from 52 to 3524 km; foraging areas included 14 countries. Core-use foraging areas (50% KDEs) where turtles took up residence were 6.3 to 95.4 km², occupied for 22 to 490 days, with mean centroid depth − 66 m. Our results show previously unknown habitat-use patterns and highlight concentrated areas of use both within and adjacent to a US protected area during the breeding season. Further, our results clearly demonstrate the need for international conservation to protect hawksbills, as migrating turtles crossed between two and eight different jurisdictions. Our results provide critical spatial and temporal information for managers charged with designing strategies to minimize human impact to and maximize survival for this globally imperiled species.

Understanding the 3D environment of pelagic seabirds from multidisciplinary oceanographic surveys, to advance ecosystem-based monitoring

Article

May 2019

Marine predators move through the seascape searching for foraging resources. Prey configuration and oceanographic processes could therefore shape their 3-dimensional (3D) oceanographic habitats. Taking advantage of multidisciplinary oceanographic JUVENA surveys targeting biomass estimation of pelagic fishes, observations of 2 highly migratory pelagic seabirds were collected during line-transects: sooty shearwaters (SOSHs) Ardenna grisea and great shearwater (GRSHs) A. gravis. Every autumn these species visit the pelagic ecosystem of the Bay of Biscay (BoB). We developed generalised additive models to disentangle the effects of the 3D ocean environment and preyscapes at different depth ranges, in addition to static variables, on driving the spatial abundance of these predators. The species differed in their vertical habitat use, with SOSHs and GRSHs influenced by habitat conditions above the depth of the maximum temperature gradient and at the surface, respectively. SOSHs were more abundant in deeper shelf areas with localised hotspots associated with upwelling and river discharges. In contrast, GRSHs were more abundant in shallow slope areas in the outer BoB sectors, followed by less dense areas with intermediate levels of juvenile anchovy biomass. Therefore, both species integrate marine resources at different vertical and spatial dimensions, influenced by topographic features, oceanographic conditions and preyscapes. Relative abundance estimations provided mean values of 3203 SOSHs (95% CI: 1753−5748) and 12 380 GRSHs (95% CI: 5797−28152) in the BoB during their annual migration; these numbers varied slightly inter-annually. This study provides an example of the combination of multiple pelagic components as a means to provide an integral assessment to advance ecosystem-based monitoring.

Movements of leatherback turtles (Dermochelys coriacea) in the Gulf of Mexico

Article

Full-text available

Sep 2018
MAR BIOL

Leatherback turtles are a migratory marine species that occur worldwide. Although known to inhabit the Gulf of Mexico (GoM), no quantitative studies have investigated the space use of leatherbacks in these waters. Satellite telemetry data of 16 leatherbacks tagged between 2005 and 2015 were analyzed with a switching state-space model to determine behavioral modes expressed while utilizing the GoM (15°N–32°N, 80.4°W–97.8°W). Foraging was found to be the predominant behavior expressed in the GoM, located mainly within three distinct areas, the northeast corner from Louisiana to Florida, the coastal shelf of southwest Florida, and the eastern side of Campeche Bay, Mexico. Leatherbacks were tracked within the GoM during all months of the year, and movements were associated with specific temperature and salinity ranges, salinity fronts, and sea surface height lows. Identifying leatherback habitat use is imperative to the successful management and survival of this marine species especially since the high-use areas coincide with intensive fishing pressure.

On feature selection and evaluation of transportation mode prediction strategies

Preprint

Full-text available

Feb 2019

Transportation modes prediction is a fundamental task for decision making in smart cities and traffic management systems. Traffic policies designed based on trajectory mining can save money and time for authorities and the public. It may reduce the fuel consumption and commute time and moreover, may provide more pleasant moments for residents and tourists. Since the number of features that may be used to predict a user transportation mode can be substantial, finding a subset of features that maximizes a performance measure is worth investigating. In this work, we explore wrapper and information retrieval methods to find the best subset of trajectory features. After finding the best classifier and the best feature subset, our results were compared with two related papers that applied deep learning methods and the results showed that our framework achieved better performance. Furthermore, two types of cross-validation approaches were investigated, and the performance results show that the random cross-validation method provides optimistic results.

Transportation Modes Classification Using Feature Engineering

Preprint

Full-text available

Jul 2018

Mohammad Etemad

Predicting transportation modes from GPS (Global Positioning System) records is a hot topic in the trajectory mining domain. Each GPS record is called a trajectory point and a trajectory is a sequence of these points. Trajectory mining has applications including but not limited to transportation mode detection, tourism, traffic congestion, smart cities management, animal behaviour analysis, environmental preservation, and traffic dynamics are some of the trajectory mining applications. Transportation modes prediction as one of the tasks in human mobility and vehicle mobility applications plays an important role in resource allocation, traffic management systems, tourism planning and accident detection. In this work, the proposed framework in Etemad et al. is extended to consider other aspects in the task of transportation modes prediction. Wrapper search and information retrieval methods were investigated to find the best subset of trajectory features. Finding the best classifier and the best feature subset, the framework is compared against two related papers that applied deep learning methods. The results show that our framework achieved better performance. Moreover, the ground truth noise removal improved accuracy of transportation modes prediction task; however, the assumption of having access to test set labels in pre-processing task is invalid. Furthermore, the cross validation approaches were investigated and the performance results show that the random cross validation method provides optimistic results.

Tracking anguillid eels: Five decades of telemetry-based research

Article

Jan 2017

Advances in telemetry technologies have provided new opportunities to reveal the often-cryptic spatial ecology of anguillid eels. Herein we review 105 studies published between 1972 and 2016 that used a variety of telemetry technologies to study the movements of eels in a variety of habitats. Eight anguillid species have been tracked in three main geographical locations: Western Europe, the north-eastern part of North America and Australasia. Telemetry has proven to be an effective method for determining patterns of yellow eel movements in continental waters. It has also been used extensively to investigate the migratory behaviour of maturing eels as they leave fresh water to reach the sea. Among recent findings is the observation that downstream migration in continental waters is quite discontinuous, characterised by extended stopovers. Reconstructed migration routes in the open ocean obtained from satellite tags have provided indications of spawning areas, extensive vertical migrations and initial clues about the orientation mechanisms at sea. Telemetry studies have also revealed apparent evidence of predation by marine mammals and fish at sea, suggesting a significant natural source of mortality during the eel spawning migration. Finally, we discuss some limitations of telemetry technology and future directions, as well as associated challenges, to the developing field of eel spatial ecology.

Pre-nesting Movements of Leatherback Sea Turtles, Dermochelys coriacea, in the Western Atlantic

Article

Full-text available

Jul 2017

Understanding high-use areas for highly migratory species and their movements within these areas may provide insight into behaviors such as foraging and mating. In the Western Atlantic, the leatherback sea turtle, Dermochelys coriacea, has a broad geographic range extending from nesting beaches at low latitudes to foraging areas off the coast of Eastern Canada. Biotelemetry has revealed much about the movements and habitats of leatherbacks. However, the timing and location of leatherback mating behavior remains unclear. We conducted spatial analyses of the movements of reproductive female leatherbacks prior to their first seasonal nesting events. Using kernel density estimates, high-use areas for seven female turtles originally tagged in Canadian waters were revealed from 50% volume contours depicting pre-nesting movements (120 days prior to confirmed nesting events) and inferred mating behavior (45 days prior to confirmed nesting events). All individuals initially remained offshore within a relatively small range of latitude (10–15° N) before transiting to and residing in coastal waters adjacent to nesting beaches in Colombia (n = 2), Trinidad (n = 3), Guyana (n = 1), and French Guiana (n = 1). Comparison of these movement patterns to those of mature male leatherbacks (n = 12) revealed similarities. Male and female residency within this offshore high-use area may be indicative of prey exploitation prior to the energetically costly nesting season. While the offshore residency period of three males and one female extended into the interval in which mating is expected to occur, most males and females transited to coastal waters where they resided throughout this period. High-use areas determined through kernel density analysis support and corroborate previous telemetry work indicating that mature male leatherbacks exhibit seasonal residency adjacent nesting beaches for the early portion of the nesting season, presumably to exploit mating opportunities. Fine-scale analyses of fisheries interactions in both coastal and offshore waters and estimation of accompanying mortality rates is required to evaluate fishery threats to this population during the pre-nesting interval.

A review of toxic metal contamination in marine turtle tissues and its implications for human health

Article

Jun 2017

Despite global awareness of trace-metal contamination in the ocean, its bioaccumulation through the food web, and resulting detrimental effects on health, the quantitative toxicology of marine turtles is still poorly known. Assessments are generally limited in number of species investigated, number of tissues analyzed, and geographical distribution of samples. The gaps in current knowledge prevent the use of that data in informing data-deficient regions of the potential exposure to toxic levels of heavy metals through sea turtle consumption, particularly from eggs given their widespread human consumption. We collated 95 studies reporting As, Cd, Hg, and/or Pb concentrations in edible sea turtle tissues and analyzed the data for differences among tissues and geographic locations. The majority (68%) of observations were from Caretta caretta or Chelonia mydas, with 59% of data from liver, kidney, muscle, or blood; and only 8.2% from eggs. We observed the expected tissue-selective distributions for all metals, but with significance only for As (muscle) and Cd (kidney). Cd posed the highest potential health concern, through consumption of kidney and liver, while Pb and Hg posed the highest concern through egg and muscle tissue, respectively. Data are sparse, however our conclusions show that heavy metal exposure through regular sea turtle consumption may pose a health concern. Future analyses, with priority given to eggs, adult olive ridleys, and adult hawksbills are needed to fully understand the human-health risks of global sea turtle consumption.

Crying a river: how much salt-laden jelly can a leatherback turtle really eat?

Article

Jan 2017

John Davenport

Leatherback turtles (Dermochelys coriacea) are capital breeders that accumulate blubber (33 kJ g −1 wet mass) by hyperphagia on a gelatinous diet at high latitudes; they breed in the tropics. A jellyfish diet is energy poor (0.1–0.2 kJ g −1 wet mass) so leatherbacks must ingest large quantities. Two published estimates of feeding rate [50% body mass day −1 (on Rhizostoma pulmo) and 73% body mass day −1 (on Cyanea capillata)] have been criticised as too high. Jellyfish have high salt and water contents that must be removed to access organic material and energy. Most salt is removed (as NaCl) by paired lachrymal salt glands. Divalent ions are lost via the gut. In this study, the size of adult salt glands (0.622 kg for a 450 kg turtle; relatively three times the size of salt glands in cheloniid turtles) was measured for the first time by computed tomography scanning. Various published values for leatherback field metabolic rate, body fluid composition and likely blubber accumulation rates are combined with known jellyfish salt, water and organic compositions to calculate feasible salt gland secretion rates and feeding rates. The results indicate that leatherbacks can produce about 10–15 ml secretion g −1 salt gland mass h −1 (tear osmolality 1800 mOsm kg −1). This will permit consumption of 80% body mass day −1 of C. capillata. Calculations suggest that leatherbacks will find it difficult/impossible to accumulate sufficient blubber for reproduction in a single feeding season. Rapid jellyfish digestion and short gut transit times are essential.

Crying a river: How much salt-laden jelly can a leatherback turtle really eat?

Article

Jan 2017

John Davenport

DAVENPORT, J. (2017). Crying a river: how much salt-laden jelly can a leatherback turtle really eat? Journal of Experimental Biology 220: 1737-1744.

Article

Feb 2017

John Davenport

Leatherback turtles (Dermochelys coriacea) are capital breeders that accumulate blubber (33 kJ g wet mass(-1)) by hyperphagia on a gelatinous diet at high latitudes; they breed in the tropics. A jellyfish diet is energy-poor (0.1-0.2 kJ g wet mass(-1)), so leatherbacks must ingest large quantities. Two published estimates of feeding rate (50% body mass d(-1) (on Rhizostoma pulmo), 73% body mass d(-1) (on Cyanea capillata)) have been criticised as too high. Jellyfish have high salt and water contents that must be removed to access organic material and energy. Most salt is removed (as NaCl) by paired lachrymal salt glands. Divalent ions are lost via the gut. In this study the size of adult salt glands (0.622 kg for a 450kg turtle; relatively 3 times the size of salt glands in cheloniid turtles) is measured for the first time by CT scanning. Various published values for leatherback field metabolic rate (FMR), body fluid composition and likely blubber accumulation rates are combined with known jellyfish salt, water and organic compositions to calculate feasible salt gland secretion rates and feeding rates. The results indicate that leatherbacks can produce about 10-15 ml secretion g salt gland mass(-1) h(-1) (tear osmolality 1800 mOsm kg(-1)). This will permit consumption of 80 % body mass d(-1) of Cyanea capillata Calculations suggest that leatherbacks will find it difficult/impossible to accumulate sufficient blubber for reproduction in a single feeding season. Rapid jellyfish digestion and short gut transit times are essential.

A leatherback tuttle’s guide to jellyfish in the North East Atlantic

Article

Full-text available

Jan 2013

Passive drift or active swimming in marine organisms?

Article

Full-text available

Dec 2016
Proc Biol Sci

Predictions of organismal movements in a fluid require knowing the fluid’s velocity and potential contributions of the organism’s behaviour (e.g. swimming or flying). While theoretical aspects of this work are reasonably welldeveloped, field-based validation is challenging. A much-needed study recently published by Briscoe and colleagues in Proceedings of the Royal Society B compared movements and distribution of satellite-tracked juvenile sea turtles to virtual particles released in a data-assimilating hindcast ocean circulation model. Substantial differences observed between turtles and particles were considered evidence for an important role of active swimming by turtles. However, the experimental design implicitly assumed that transport predictions were insensitive to (i) start location, (ii) tracking duration, (iii) depth, and (iv) physical processes not depicted in the model. Here, we show that the magnitude of variation in physical parameters between turtles and virtual particles can profoundly alter transport predictions, potentially sufficient to explain the reported differences without evoking swimming behaviour. We present a more robust method to derive the environmental contributions to individual movements, but caution that resolving the ocean velocities experienced by individual organisms remains a problem for assessing the role of behaviour in organismal movements and population distributions.

Resident areas and migrations of female green turtles nesting at Buck Island Reef National Monument, St. Croix, U.S. Virgin Islands

Article

Full-text available

Feb 2017

ABSTRACT: Satellite tracking studies can reveal much about turtles’ spatial use of breeding areas, migration zones, and foraging sites. We assessed spatial habitat-use patterns of 10 adult female green turtles Chelonia mydas nesting at Buck Island Reef National Monument (BIRNM), US Virgin Islands (USVI; 17° 47.4’ N, 64° 37.2’ W) from 2011 to 2014. Turtles ranged in size from 89.0 to 115.9 cm curved carapace length (CCL) (mean ± SD: 106.8 ± 7.7 cm). The inter-nesting period for all turtles ranged from 31 July to 4 November, and sizes of the 50% core-use areas ranged from 4.2 to 19.0 km2. We observed consistency of inter-nesting habitat-use patterns, with all turtles using near-shore (<1.5 km), shallow waters (<–20 m depth) within approximately 10 km of Buck Island. Seven of the 10 turtles remained locally resident after the nesting season; 5 turtles (50%) established resident foraging areas around Buck Island, 2 established resident foraging areas around the island of St. Croix, and the other 3 (30%) made longer-distance migrations to Antigua, St. Kitts & Nevis, and Venezuela. This is the first empirical dataset showing limited migration and use of ‘local’ resources after the nesting season in the USVI by this unique management unit of green turtles. Five of the turtles had resident foraging area centroids within protected areas; thus, inter-nesting and foraging areas at BIRNM that overlap with human use zones present an important management concern. Delineating spatial areas and identifying temporal periods of nearshore habitat use can be useful for natural resource managers with responsibility for overseeing vulnerable habitats and protecting marine turtle populations.

Balancing fishery and conservation: A case study of the barrel jellyfish Rhizostoma octopus in South Wales

Article

Sep 2016

In Wales, the barrel jellyfish Rhizostoma octopus is commercially harvested to produce high-value medical grade collagen. Although the fishery is presently not regulated, there are concerns how it may affect the leatherback turtle (Dermochelys coriacea), which preys on R. octopus in local waters. We combined monitoring data and morphometric and weight measurements in models to estimate the potential impact of R. octopus fishery on foraging turtles. We found a significant quadratic relationship between bell diameter and wet weight of R. octopus, with bell diameter explaining 88% of the variability in wet weight. R. octopus biomass in the Carmarthen Bay varied inter-annually between 38.9 and 594.2 tonnes y À1. The amount of R. octopus needed to satisfy a leatherback turtle's daily energetic requirements was estimated at 85.1– 319.1 kg. Using leatherback turtle sighting data, our models show that during a jellyfish 'low year " , the R. octopus population could be completely depleted by an average of two foraging turtles along with the current level of commercial harvesting (4.3 tonnes). During a jellyfish " high year " , the current level of commercial harvesting is predicted to have relatively little impact on food supply for even the maximum number of foraging leatherback turtle reported in the area. However, uncertainties related to the jellyfish's life cycle in the local waters need to be resolved for proper management of this emerging fishery.

Prey Density Threshold and Tidal Influence on Reef Manta Ray Foraging at an Aggregation Site on the Great Barrier Reef

Article

Full-text available

May 2016
PLOS ONE

Large tropical and sub-tropical marine animals must meet their energetic requirements in a largely oligotrophic environment. Many planktivorous elasmobranchs, whose thermal ecologies prevent foraging in nutrient-rich polar waters, aggregate seasonally at predictable locations throughout tropical oceans where they are observed feeding. Here we investigate the foraging and oceanographic environment around Lady Elliot Island, a known aggregation site for reef manta rays Manta alfredi in the southern Great Barrier Reef. The foraging behaviour of reef manta rays was analysed in relation to zooplankton populations and local oceanography, and compared to long-term sighting records of reef manta rays from the dive operator on the island. Reef manta rays fed at Lady Elliot Island when zooplankton biomass and abundance were significantly higher than other times. The critical prey density threshold that triggered feeding was 11.2 mg m-3 while zooplankton size had no significant effect on feeding. The community composition and size structure of the zooplankton was similar when reef manta rays were feeding or not, with only the density of zooplankton changing. Higher zooplankton biomass was observed prior to low tide, and long-term (~5 years) sighting data confirmed that more reef manta rays are also observed feeding during this tidal phase than other times. This is the first study to examine prey availability at an aggregation site for reef manta rays and it indicates that they feed in locations and at times of higher zooplankton biomass.

The influence of oceanographic features on the foraging behavior of the olive ridley sea turtle Lepidochelys olivacea along the Guiana coast

Article

Full-text available

Feb 2016
PROG OCEANOGR

The circulation in the Western Equatorial Atlantic is characterized by a highly dynamic mesoscale activity that shapes the Guiana continental shelf. Olive ridley sea turtles (Lepidochelys olivacea) nesting in French Guiana cross this turbulent environment during their post-nesting migration. We studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females, using satellite telemetry, remote sensing data (sea surface temperature, sea surface height, current velocity and euphotic depth), simulations of micronekton biomass (pelagic organisms) and in situ records (water temperature and salinity). The occurrence of foraging events throughout migration was located using Residence Time analysis, while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives. Olive ridleys migrated northwestwards using the Guiana current and remained on the continental shelf at the edge of eddies formed by the North Brazil retroflection, an area characterized by low turbulence and high micronekton biomass. They performed mainly pelagic dives, hunting for an average 77% of their time. Hunting time within a dive increased with shallower euphotic depth and with lower water temperatures, and mean hunting depth increased with deeper thermocline. This is the first study to quantify foraging activity within dives in olive ridleys, and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species. This study also provides novel and detailed data describing how turtles actively use oceanographic structures during post-nesting migration.

Sea turtle strandings along the Portuguese mainland coast: spatio‑temporal occurrence and main threats

Article

Full-text available

Jan 2016
MAR BIOL

The present study is a detailed analysis of sea turtle strandings over a 36-year period (1978–2013) along the Portuguese mainland coast. Out of the 806 stranded individuals, the loggerhead turtle Caretta caretta was the most frequent species (57.1 %) followed by the leatherback turtle Dermochelys coriacea (41.8 %), while green turtles Chelonia mydas and Kemp’s Ridley turtles Lepidochelys kempii were rare (respectively 1.0 and 0.1 %). Relative stranding densities of loggerheads showed an increase through time, whereas two leatherback stranding peaks were detected during the years 1994–1998 and 2009–2013. The highest loggerhead stranding density was observed on the southern coast during spring and summer when they are more susceptible to anthropogenic threats. The highest number of leatherback strandings was observed in the North-Central and Central-South western sectors during autumn and in the southern sector during summer, which may relate to seasonal food availability and water temperature considering those stranded animals that were subject to a post-mortem evaluation interaction with fisheries as the primary cause of stranding. Results show for the first time that waters off the Portuguese mainland coast is an important pathway for loggerheads and leatherbacks in the North Atlantic region. The present study serves as important baseline to the development of future sea turtle conservation efforts in the Portuguese mainland coast.

Linking Movement Ecology with Wildlife Management and Conservation

Article

Full-text available

Jan 2016

A common challenge in species conservation and management is how to incorporate species movements into management objectives. There often is a lack of knowledge of where, when, and why species move. The field of movement ecology has grown rapidly in the last decade and is now providing the knowledge needed to incorporate movements of species into management planning. This knowledge can also be used to develop management strategies that are flexible in time and space and may improve the effectiveness of management actions. Therefore, wildlife management and conservation may benefit by strengthening the link with movement ecology. We present a framework that illustrates how animal movement can be used to enhance conservation planning and identify management actions that are complementary to existing strategies. The framework contains five steps that identify (1) the movement attributes of a species, (2) their impacts on ecosystems, (3) how this knowledge can be used to guide the scale and type of management, (4) the implementation, and (5) the evaluation of management actions. We discuss these five steps in detail, highlighting why the step is important and how the information can be obtained. We illustrate the framework through a case study of managing a highly mobile species, the Atlantic salmon (Salmo salar), a harvested species of conservation concern. We believe that the movement-management framework provides an important, and timely, link between movement ecology and wildlife management and conservation, and highlights the potential for complementary, dynamic solutions for managing wildlife.

New Technologies for Monitoring and Upscaling Marine Ecosystem Restoration in Deep-Sea Environments

Article

Jan 2024

Clustering and classification of vertical movement profiles for ecological inference of behavior

Article

Full-text available

Jan 2023

Vertical movements can expose individuals to rapid changes in physical and trophic environments—for aquatic fauna, dive profiles from biotelemetry data can be used to quantify and categorize vertical movements. Inferences on classes of vertical movement profiles typically rely on subjective summaries of parameters or statistical clustering techniques that utilize Euclidean matching of vertical movement profiles with vertical observation points. These approaches are prone to subjectivity, error, and bias. We used machine learning approaches on a large dataset of vertical time series (N = 28,217 dives) for 31 post‐nesting leatherback turtles (Dermochelys coriacea). We applied dynamic time warp (DTW) clustering to group vertical movement (dive) time series by their metrics (depth and duration) into an optimal number of clusters. We then identified environmental covariates associated with each cluster using a generalized additive mixed‐effects model (GAMM). A convolutional neural network (CNN) model, trained on standard dive shape types from the literature, was used to classify dives within each DTW cluster by their shape. Two clusters were identified with the DTW approach—these varied in their spatial and temporal distributions, with dependence on environmental covariates, sea surface temperature, bathymetry, sea surface height anomaly, and time‐lagged surface chlorophyll a concentrations. CNN classification accuracy of the five standard dive profiles was 95%. Subsequent analyses revealed that the two clusters differed in their composition of standard dive shapes, with each cluster dominated by shapes indicative of distinct behaviors (pelagic foraging and exploration, respectively). The use of these two machine learning approaches allowed for discrete behaviors to be identified from vertical time series data, first by clustering vertical movements by their movement metrics (DTW) and second by classifying dive profiles within each cluster by their shapes (CNN). Statistical inference for the identified clusters found distinct relationships with environmental covariates, supporting hypotheses of vertical niche switching and vertically structured foraging behavior. This approach could be similarly applied to the time series of other animals utilizing the vertical dimension in their movements, including aerial, arboreal, and other aquatic species, to efficiently identify different movement behaviors and inform habitat models.

French Guiana. In: Nalovic, M.A., Ceriani, S.A., Fuentes, M.M.P.B., Pfaller, J.B., Wildermann, N.E., Uribe-Martínez, A., Cuevas, E. (eds.) (2021), Sea turtles in the North Atlantic & Wider Caribbean Region. MTSG Annual Regional Report 2021. Draft Report to the IUCN SSC Marine Turtle Specialist Group.

Chapter

Full-text available

Jan 2021

This Region comprises 48 parties, amongst countries and territories (Anguilla, Antigua & Barbuda, Aruba, Bahamas, Barbados, Belize, Bermuda, Bonaire, British Virgin Islands, Canada, Cape Verde, Cayman Islands, Colombia, Costa Rica, Cuba, Curacao, Dominica, Dominican Republic, French Atlantic & Channel coasts, French Guiana, Grenada, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Monserrat, Nicaragua, Panama, Portugal, Puerto Rico, Saba (Dutch West Indies), Saint Barthélemy, Saint Vincent & The Grenadines, Saint Eustach, Saint Maarten, Saint Kitts & Nevis, Saint Lucia, Saint Pierre & Miquelon, Suriname, Trinidad & Tobago, United Kingdom [U.K.], the United States [U.S.], U.S. Virgin Islands, Venezuela). The present report includes a total of 19 parties (39.5%, Belize, Canada, Colombia, Cuba, Curacao, France Atlantic, French Guiana, Guadeloupe, Guatemala, Martinique, Mexico, St. Bartholome, St. Eustach, St. Lucia, St. Martin, St. Pierre et Miquelon, UK-Ireland, the U.S., and Venezuela). It demands a large and constant effort to bring together the detailed information from all the parties, and although there are still several parties to include in this document, as it stands it is intended to provide panorama of the complete information on the reproductive ecology and status for sea turtle populations in the North Atlantic.

'Bahamas'. In: Nalovic, M.A., Ceriani, S.A., Fuentes, M.M.P.B., Pfaller, J.B., Wildermann, N.E., Uribe-Martínez, A., Cuevas, E. (eds.) (2021), Sea turtles in the North Atlantic & Wider Caribbean Region. MTSG Annual Regional Report 2021. Draft Report to the IUCN SSC Marine Turtle Specialist Group.

Technical Report

Full-text available

Apr 2022

Integrating marine megafauna into ecosystem-based management: a multidisciplinary approach applied to southern European waters

Thesis

Dec 2019

Isabel García-Barón

Long-term trends in the foraging ecology and habitat use of an endangered species: an isotopic perspective

Article

Full-text available

Dec 2018
OECOLOGIA

Evaluating long-term drivers of foraging ecology and population productivity is crucial for providing ecological baselines and forecasting species responses to future environmental conditions. Here, we examine the trophic ecology and habitat use of North Atlantic leatherback turtles (St. Croix nesting population) and investigate the effects of large-scale oceanographic conditions on leatherback foraging dynamics. We used bulk and compound-specific nitrogen isotope analysis of amino acids (CSIA-AA) to estimate leatherback trophic position (TP) over an 18-year period, compare these estimates with TP estimates from a Pacific leatherback population, and elucidate the pre-nesting habitat use patterns of leatherbacks. Our secondary objective was to use oceanographic indices and nesting information from St. Croix leatherbacks to evaluate relationships between trophic ecology, nesting parameters, and regional environmental conditions measured by the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation. We found no change in leatherback TP over time and no difference in TP between Atlantic and Pacific leatherbacks, indicating that differences in trophic ecology between populations are an unlikely driver of the population dichotomy between Pacific and Atlantic leatherbacks. Isotope data suggested that St. Croix leatherbacks inhabit multiple oceanic regions prior to nesting, although, like their conspecifics in the Pacific, individuals exhibit fidelity to specific foraging regions. Leatherback nesting parameters were weakly related to the NAO, which may suggest that positive NAO phases benefit St. Croix leatherbacks, potentially through increases in resource availability in their foraging areas. Our data contribute to the understanding of leatherback turtle ecology and potential mechanistic drivers of the dichotomy between populations of this protected species.

First report of metallic elements in loggerhead and leatherback turtle eggs from the Indian Ocean

Article

Feb 2018
CHEMOSPHERE

Bio-monitoring of pollutants in long-lived animals such as sea turtles is an important tool in ecotoxicology. We present the first report on metallic elements in sea turtle eggs from the Indian Ocean. Eggs of the leatherback and loggerhead turtle that breed on the Indian Ocean coast of South Africa were analysed for 30 elements. The eggshells and egg contents of the loggerhead turtle, the smaller of the two species, had higher or significantly higher concentrations than leatherbacks, except for strontium - the reason is unknown. Elemental concentrations in eggshells and contents were the same or lower compared with other studies. The differences in concentrations in the egg contents and eggshells between the two species are likely due to different trophic levels, migration patterns, life histories, age, and growth, as well as differences in pollution sources and the uptake, retention and elimination characteristics of the different elements by the different species. We found no congruence between patterns in eggshells and corresponding egg contents, for both species. However, eggshells and egg contents showed congruence between species. The lack of congruence between eggshells and contents within each species precludes using eggshell concentrations as a proxy for egg content concentrations. Copper, strontium, and selenium occurred at concentrations higher than available toxic reverence values. Further research is warranted, including the analyses of POPs, as well as possible deme discrimination based on compositional pattern differences. Turtles serve as 'active samplers' returning to the same location to breed-something that is not practical with marine mammals or elasmobranchs.

Reproductive Biology of Atlantic Leatherback Sea Turtles at Sandy Point, St. Croix: The First 30 Years

Article

Jun 2017

The nesting population of leatherback sea turtles at the Sandy Point National Wildlife Refuge (SPNWR), Sandy Point, St. Croix, US Virgin Islands, has been comprehensively studied since 1981. Nesting and hatching data are reported here for the first 30 yrs of the research and conservation project. Because of intense nest relocation and conservation efforts, the population initially showed a steady increase in numbers, with the most dramatic rise occurring between 1997 and 2001. In spite of continued efforts, however, this recovery began to stall in the decade from 2000 to 2010. Analysis of nesting data, including specific reproductive parameters such as recruitment rate, remigration interval, and productivity (number of nests laid, hatching success) during this time frame, in conjunction with historical data, provided an opportunity to assess the contribution of these factors to the population dynamics at Sandy Point. Annual reproductive data demonstrated that regardless of overall nesting numbers, odd years consistently exhibited higher nesting numbers (115.6±18.58) than even years (68.4±7.63) (p<0.01). The average annual remigration interval increased over the study period with a record high of 3.41±0.18 yrs observed in 2008. A steady decline in average nests laid was observed (R²=0.84) between 1992 and 2010, with a record low of 3.60±2.16 nests per turtle in 2010. Hatching success varied over the 30-yr period from a project low of 40.28%±23.20% in 2005 to a record high of 67.80%±20.31% in 1991. Mean overall hatching success for the first 30 yrs of the project was 58.50%±7.75%. Hatching success declined over the course of the project, and the number of hatchlings produced per turtle declined in the 2000s. These factors contributed to a decrease in population productivity and may ultimately have inhibited continued population growth. Over the study period, a stable percentage of remigrants continued to nest at Sandy Point. However, a decreased number and percentage of neophytes was observed, suggesting either a delayed or a decreased recruitment, possibly due to increased age to sexual maturity, an increased mortality of early life stages, or a change in food resources at foraging grounds. These results suggest a population that has slowed growth and that may begin to decline in the future. Further research needs to be conducted to understand possible maternal, physiological, and environmental factors that are impacting these reproductive parameters and, ultimately, affecting the population dynamics at SPNWR.

Influence of environmental parameters on movements and habitat utilization of humpback whales ( Megaptera novaeangliae ) in the Madagascar breeding ground

Article

Full-text available

Dec 2016

Assessing the movement patterns and key habitat features of breeding humpback whales is a prerequisite for the conservation management of this philopatric species. To investigate the interactions between humpback whale movements and environmental conditions off Madagascar, we deployed 25 satellite tags in the northeast and southwest coast of Madagascar. For each recorded position, we collated estimates of environmental variables and computed two behavioural metrics: behavioural state of ‘transiting’ (consistent/directional) versus ‘localized’ (variable/non-directional), and active swimming speed (i.e. speed relative to the current). On coastal habitats (i.e. bathymetry < 200 m and in adjacent areas), females showed localized behaviour in deep waters (191 ± 20 m) and at large distances (14 ± 0.6 km) from shore, suggesting that their breeding habitat extends beyond the shallowest waters available close to the coastline. Males' active swimming speed decreased in shallow waters, but environmental parameters did not influence their likelihood to exhibit localized movements, which was probably dominated by social factors instead. In oceanic habitats, both males and females showed localized behaviours in shallow waters and favoured high chlorophyll- a concentrations. Active swimming speed accounts for a large proportion of observed movement speed; however, breeding humpback whales probably exploit prevailing ocean currents to maximize displacement. This study provides evidence that coastal areas, generally subject to strong human pressure, remain the core habitat of humpback whales off Madagascar. Our results expand the knowledge of humpback whale habitat use in oceanic habitat and response to variability of environmental factors such as oceanic current and chlorophyll level.

Are we working towards global research priorities for management and conservation of sea turtles?

Article

Full-text available

Dec 2016

In 2010, an international group of 35 sea turtle researchers refined an initial list of more than 200 research questions into 20 metaquestions that were considered key for management and conservation of sea turtles. These were classified under 5 categories: reproductive biology , biogeography, population ecology, threats and conservation strategies. To obtain a picture of how research is being focused towards these key questions, we undertook a systematic review of the peer-reviewed literature (2014 and 2015) attributing papers to the original 20 questions. In total, we reviewed 605 articles in full and from these 355 (59%) were judged to substantively address the 20 key questions, with others focusing on basic science and monitoring. Progress to answering the 20 questions was not uniform, and there were biases regarding focal turtle species, geographic scope and publication outlet. Whilst it offers some meaningful indications as to effort, quantifying peer-reviewed literature output is ob viously not the only, and possibly not the best, metric for understanding progress towards informing key conservation and management goals. Along with the literature review, an international group based on the original project consortium was assigned to critically summarise recent progress towards answering each of the 20 questions. We found that significant research is being expended towards global priorities for management and conservation of sea turtles. Although highly variable, there has been significant progress in all the key questions identified in 2010. Undertaking this critical review has highlighted that it may be timely to undertake one or more new prioritizing exercises. For this to have maximal benefit we make a range of recommendations for its execution. These include a far greater engagement with social sciences, widening the pool of contributors and focussing the questions, perhaps disaggregating ecology and conservation.

Influence of environmental parameters on movements and habitat utilization of humpback whales in the Madagascar breeding ground

Article

Full-text available

Dec 2016

Assessing the movement patterns and key habitat features of breeding humpback whales is a prerequisite for the conservation management of this philopatric species. To investigate the interactions between humpback whale movements and environmental conditions off Madagascar, we deployed 25 satellite tags in the northeast and southwest coast of Madagascar. For each recorded position, we collated estimates of environmental variables and computed two behavioural metrics: behavioural state of ‘transiting’ (consistent/directional) versus ‘localized’ (variable/non-directional), and active swimming speed (i.e. speed relative to the current). On coastal habitats (i.e. bathymetry < 200 m and in adjacent areas), females showed localized behaviour in deep waters (191 ± 20 m) and at large distances (14 ± 0.6 km) from shore, suggesting that their breeding habitat extends beyond the shallowest waters available close to the coastline. Males' active swimming speed decreased in shallow waters, but environmental parameters did not influence their likelihood to exhibit localized movements, which was probably dominated by social factors instead. In oceanic habitats, both males and females showed localized behaviours in shallow waters and favoured high chlorophyll-a concentrations. Active swimming speed accounts for a large proportion of observed movement speed; however, breeding humpback whales probably exploit prevailing ocean currents to maximize displacement. This study provides evidence that coastal areas, generally subject to strong human pressure, remain the core habitat of humpback whales off Madagascar. Our results expand the knowledge of humpback whale habitat use in oceanic habitat and response to variability of environmental factors such as oceanic current and chlorophyll level.

Coastal leatherback turtles reveal conservation hotspot

Article

Full-text available

Nov 2016

Previous studies have shown that the world’s largest reptile – the leatherback turtle Dermochelys coriacea – conducts flexible foraging migrations that can cover thousands of kilometres between nesting sites and distant foraging areas. The vast distances that may be travelled by migrating leatherback turtles have greatly complicated conservation efforts for this species worldwide. However, we demonstrate, using a combination of satellite telemetry and stable isotope analysis, that approximately half of the nesting leatherbacks from an important rookery in South Africa do not migrate to distant foraging areas, but rather, forage in the coastal waters of the nearby Mozambique Channel. Moreover, this coastal cohort appears to remain resident year-round in shallow waters (<50 m depth) in a relatively fixed area. Stable isotope analyses further indicate that the Mozambique Channel also hosts large numbers of loggerhead turtles Caretta caretta. The rare presence of a resident coastal aggregation of leatherback turtles not only presents a unique opportunity for conservation, but alongside the presence of loggerhead turtles and other endangered marine megafauna in the Mozambique Channel, highlights the importance of this area as a marine biodiversity hotspot.

Animal-borne sensors successfully capture the real-time thermal properties of ocean basins

Article

Full-text available

Sep 2005

Climate change is perhaps the most pressing and urgent environmental issue facing the world today. However our ability to predict and quantify the consequences of this change is severely limited by the paucity of in situ oceanographic measurements. Marine animals equipped with sophisticated oceanographic data loggers to study their behavior offer one solution to this problem because marine animals range widely across the world's ocean basins and visit remote and often inaccessible locations. However, unlike the information being collected from conventional oceanographic sensing equipment, which has been validated, the data collected from instruments deployed on marine animals over long periods has not. This is the first long-term study to validate in situ oceanographic data collected by animal oceanographers. We compared the ocean temperatures collected by leatherback turtles (Dermochelys coriacea) in the Atlantic Ocean with the ARGO network of ocean floats and could find no systematic errors that could be ascribed to sensor instability. Animal-borne sensors allowed water temperature to be monitored across a range of depths, over entire ocean basins, and, importantly, over long periods and so will play a key role in assessing global climate change through improved monitoring of global temperatures. This finding is especially pertinent given recent international calls for the development and implementation of a comprehensive Earth observation system ( see http://iwgeo.ssc.nasa.gov/documents.asp?s=review) that includes the use of novel techniques for monitoring and understanding ocean and climate interactions to address strategic environmental and societal needs.

Biological and physical signatures in the tropical and subtropical Atlantic

Article

Full-text available

Aug 1999

The variability of sea surface chlorophyll concentration in the tropical and subtropical Atlantic during the first year of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery is examined. An Ocean General Circulation Model (OGCM) is used, along with TOPEX/Poseidon dynamic height observations and global gridded wind stress data sets, to explain the physical forcing of surface ocean color signals. Regions of high surface chlorophyll are strongly correlated with mesoscale and large-scale physical processes such as the strong upwelling off the west coast of Africa, the relatively high oceanic production within the Guinea Dome region, and the generation and propagation of large anticyclonic eddies along the coast of south America, north of the equator. The major river outflows (Amazon, Orinoco, and Congo) have strong signatures with plumes of apparently high Chl alpha in excess of 10 mg/3 near their deltas. The fall bloom in the eastern tropical Atlantic observed by the Coastal Zone Color Scanner (CZCS) was absent in 1997, whereas a bloom was observed in this region in July-September 1998, which was not observed by the CZCS. We attribute these apparent anomalies to the projection of the 1997-1998 El Nino event into the tropical Atlantic basin ; these signals are correlated with sea surface temperature anomalies known to be associated with ENSO. The SeaWiFS images show that there are seasonal blooms within the hydrographic provinces of the Guinea and Angola domes. These hydrographic provinces are characterized by the dynamic uplift of the thermocline at the North Equatorial Current southern boundary (Guinea Dome) and the Benguela Current eastern boundary (Angola Dome). Within these domes, the Ekman pumping and transport are significant due to the strong trade winds at the surface... (D'après résumé d'auteur)

Improved description of the ocean mesoscale variability by combining four satellite altimeters-art. no. L02611

Article

Full-text available

Jan 2006

Data from four satellite altimeters are combined with the aim of improving the representation of the mesoscale variability in the Global Ocean. All missions [Jason-1, ERS-2/ENVISAT, Topex/Poseidon interleaved with Jason-1 and Geosat Follow-On] are cross-calibrated previously to produce weekly gridded maps. In areas of intense variability, the rms differences between a classical configuration of two altimeters and the scenario merging four missions can reach 10 cm and 400 cm2/s2 in SLA and EKE, respectively, which represents an important percentage of the signal variance. A comparison with surface drifters shows that the four altimeter scenario improves the recovery of mesoscale structures that were not properly sampled with Jason-1 + ERS-2/ENVISAT. Finally, the consistency between altimetric and tide gauge data is improved by about 25% when coastal sea level is estimated with 4 satellites compared to the results obtained with 2 altimeters.

Identifying leatherback turtle foraging behaviour from satellite telemetry using a switching state-space model

Article

Full-text available

May 2007

Abstract 1 Identifying foraging habitat of marine predators is vital to understanding the ecology of 2 these species and for their management,and conservation. Foraging habitat for many marine 3 predators is dynamic and this poses a serious challenge for understanding how oceanographic 4 features may shape the ecology of these animals. To help resolve this issue, we present a 5 switching state-space model (SSSM) for discerning different movement,behaviours hidden 6 within error-prone satellite telemetry data. Along with modelling the movement dynamics, 7 the SSSM estimates the probability that an animal is in a particular discrete behavioural 8 mode, such as transitting or foraging. Using Argos satellite telemetry for leatherback sea tur- 9 tles we show that the SSSM readily identifies distinct classes of movement behaviour from the 10 noisy data. Moreover, patterns in simultaneously collected diving data, to which the model 11 is blind, match well with behavioural mode estimates. By combining behavioural mode esti- 12 mates from the model with the diving data we show that while transitting, leatherbacks make 13 longer, deeper dives, and while foraging, they encounter cooler waters that range from 13-22 14 , Keywords 20

Do leatherback turtles Dermochelys coriacea forage during the breeding season? A combination of data-logging devices provide new insights

Article

Full-text available

Sep 2006

Animals which undertake migrations from foraging grounds to suitable breeding areas must adopt strategies in these new conditions in order to minimise the rate at which body condition deteriorates (which will occur due to oogenesis or provisioning for young). For some animals this involves continuing foraging, whereas for others the optimal strategy is to fast during the breeding season. The leatherback turtle undertakes long-distance migrations from temperate zones to tropical breeding areas, and in some of these areas it has been shown to exhibit diving behaviour indicative of foraging. We used conventional time-depth recorders and a single novel mouth-opening sensor to investigate the foraging behaviour of leatherback turtles in the southern Caribbean. Diving behaviour suggested attempted foraging on vertically migrating prey with significantly more diving to a more consistent depth occurring during the night. No obvious prey manipulation was detected by the mouth sensor, but rhythmic mouth opening did occur during specific phases of dives, suggesting that the turtle was relying on gustatory cues to sense its immediate environment. Patterns of diving in conjunction with these mouth-opening activities imply that leatherbacks are attempting to forage during the breeding season and that gustatory cues are important to leatherbacks.

Swimming depth, ambient water temperature preference, and feeding frequency of young Pacific bluefin tuna (Thunnus orientalis) determined with archival tags

Article

Full-text available

Jul 2003
FISH B-NOAA

We investigated the migration and behavior of young Pacific bluefin tuna (Thunnus orientalis) using archival tags. The archival tag measures environmental variables, records them in its memory, and estimates daily geographical locations based on measured light levels. Of 166 archival tags implanted in Pacific bluefin tuna that were released at the northeastern end of the East China Sea from 1995 to 1997, 30 tags were recovered, including one from a fish that migrated across the Pacific. This article describes swimming depth, ambient water temperature, and feeding frequency of young Pacific bluefin tuna based on retrieved data. Tag performance, effect of the tag on the fish, and horizontal movements of the species are described in another paper. Young Pacific bluefin tuna swim mainly in the mixed layer, usually near the sea surface, and swim in deeper water in daytime than at nighttime. They also exhibit a pattern of depth changes, corresponding to sunrise and sunset, apparently to avoid a specific low light level. The archival tags recorded temperature changes in viscera that appear to be caused by feeding, and those changes indicate that young Pacific bluefin tuna commonly feed at dawn and in the daytime, but rarely at dusk or at night. Water temperature restricts their distribution, as indicated by changes in their vertical distribution with the seasonal change in depth of the thermocline and by the fact that their horizontal distribution is in most cases confined to water in the temperature range of 14-20°C.

Diving behaviour of jellyfish equipped with electronic tags

Article

Full-text available

Mar 2008

Jellyfish are one of the most abundant and conspicuous members of our coastal marine fauna and are now known to play major trophic roles in marine systems. However, little is known about the movements and behaviour of individuals. We equipped individual compass jellyfish (Chrysaora hysoscella) (n = 15) off the Dingle coast, Ireland, with miniature time-depth recorders to log their depth over periods of a few hours. Vertical movements were extensive, with all jellyfish changing their depth during tracking. A range of vertical movements were seen including initial diving from the surface down to a maximum of 29.6 m after device attachment, some jellyfish remaining near the bottom, some moving up and down in mid-water and some moving back near the surface. These results show that jellyfish actively reposition themselves in the water column over small time-scales and open the way for more extensive studies equipping jellyfish with electronic tags.

Estimation of global zooplankton biomass from satellite ocean colour

Article

Full-text available

Aug 2009

A changing Earth System requires knowledge on a global scale. The only way of obtaining detailed information at these scales is by using satellite remote sensing and/or modeling. In the marine environment, information on primary production (PP) is derivable from satellite data, whereas datasets of higher trophic levels are sparse. The challenge is to combine these two sources. A model relating the flow of energy from PP to zooplankton biomass, was used to address this problem. The model was parameterised with PP from the SeaWiFS satellite ocean colour record and a subset of a global dataset of zooplankton biomass. The model was then validated with the remaining zooplankton data. The model was used to: produce a map of annual global, zooplankton biomass, quantify the flow of carbon from PP to zooplankton and investigate the spatial variability of this flow. One of the more notable findings is that more energy is transferred to zooplankton when PP is low.

Leatherback turtles satellite-tagged in European waters

Article

Full-text available

Dec 2008

The North Atlantic is considered a stronghold for the critically endangered leatherback sea turtle. However, limited information exists regarding the movements of individuals to and from the seas off Europe’s northwesterly fringe, an area where leatherbacks have been historically sighted for the past 200 yr. Here, we used satellite telemetry to record the movements and behaviour of 2 individuals bycaught in fisheries off the southwest coast of Ireland. The turtle T1 (tagged 1 September 2005; female; tracked 375 d) immediately travelled south via Madeira and the Canaries, before residing in West African waters for 3 mo. In spring, T1 migrated north towards Newfoundland where transmissions ceased. T2 (29 June 2006; male; 233 d) travelled south for a short period before spending 66 d west of the Bay of Biscay, an area previously asserted as a high-use area for leatherbacks. This prolonged high latitude summer residence corresponded with a mesoscale feature evident from satellite imagery, with the implication that this turtle had found a rich feeding site. A marked change in dive behaviour was apparent as the turtle exited this feature and provided useful insights on leatherback diving behaviour. T2 headed south in October 2006, and performed the deepest-ever dive recorded by a reptile (1280 m) southwest of Cape Verde. Unlike T1, T2 swam southwest towards Brazil before approaching the major nesting beaches of French Guiana and Surinam. Importantly, these tracks document the movement of leatherbacks from one of the remotest foraging grounds in the North Atlantic.

Animal-borne sensors successfully capture the real-time thermal properties of ocean basins: Turtles as climatologists

Article

Full-text available

Sep 2005
LIMNOL OCEANOGR-METH

Changes in food web structure under scenarios of overfishing in the southern Benguela: Comparison of the Ecosim and OSMOSE modelling approaches

Article

Full-text available

Jan 2010

Ecosystem models provide a platform allowing exploration into the possible responses of marine food webs to fishing pressure and various potential management decisions. In this study we investigate the particular effects of overfishing on the structure and function of the southern Benguela food web, using two models with different underlying assumptions: the spatialized, size-based individual-based model, OSMOSE, and the trophic mass-balance model, Ecopath with Ecosim (EwE). Starting from the same reference state of the southern Benguela upwelling ecosystem during the 1990s, we compare the response of the food web to scenarios of overfishing using these two modelling approaches. A scenario of increased fishing mortality is applied to two distinct functional groups: i) two species of Cape hake, representing important target predatory fish, and ii) the forage species anchovy, sardine and redeye. In these simulations, fishing mortality on the selected functional groups is doubled for 10 years, followed by 10 years at the initial fishing mortality. We compare the food web states before the increase of fishing mortality, after 10 years of overfishing and after a further 10 years during which fishing was returned to initial levels. In order to compare the simulated food web structures with the reference state, and between the two modelling approaches, we use a set of trophic indicators: the mean trophic level of the community and in catches, the trophic pyramid (biomass per discrete trophic level), and the predatory/forage fish biomass ratio. OSMOSE and EwE present globally similar results for the trophic functioning of the ecosystem under fishing pressure: the biomass of targeted species decreases whereas that of their potential competitors increases. The reaction of distant species is more diverse, depending on the feeding links between the compartments. The mean trophic level of the community does not vary enough to be used for assessing ecosystem impacts of fishing, and the mean trophic level in the catch displays a surprising increase due to the short period of overfishing. The trophic pyramids behave in an unexpected way compared to trophic control theory, because at least two food chains with different dynamics are intertwined within the food web. We emphasize the importance of biomass information at the species level for interpreting dynamics in aggregated indicators, and we highlight the importance of competitive groups when looking at ecosystem functioning under fishing disturbance. Finally, we discuss the results within the scope of differences between models, in terms of the way they are formulated, spatial dimensions, predation formulations and the representation of fish life cycles.

An alternative technique for the long-term satellite tracking of Leatherback Turtles

Article

Full-text available

Jan 2008

The satellite transmitter fixed on a harness was, until a short time ago, the commonly used attachment technique to follow oceanic movements of the soft-shelled leatherback turtle Dermochelys coriacea. However, harnesses have recently been reported to have a potential welfare impact during long-term deployments in this species. Here, we present the first long-term (3 mo) monitoring of 2 leatherback turtles tracked with satellite transmitters directly attached to the carapace and compare tracking data with 3 other turtles, that were concurrently satellite-tracked with traditional harnesses. There were significantly more good quality locations recorded for carapace-equipped turtles than for turtles with harnesses, which suggests that the satellite transmitter is better directly fixed to the carapace. The mean locomotor travel rate (i.e. turtle’s own motion taking potential current drift into account) for turtles with harnesses was 16% slower (0.50 ± 0.01 and 0.59 ± 0.02 m s –1, respectively) and dives were 12% shorter (23.2 ± 0.8 and 26.3 ± 0.8 min, respectively) than for carapaceequipped turtles, but all were to a similar depth (87.0 ± 3.1 and 80.7 ± 2.9 m, respectively). Despite our small sample sizes, these first results suggest a marked hydrodynamic impact of the harness on the leatherback’s swimming and diving capabilities, and stress the need for further developments to improve long-term monitoring while reducing hydrodynamic constraints for this species.

Foraging habitat and food intake of satellite-tracked king penguins during the summer at Crozet Archipelago

Article

Full-text available

Apr 1997

The relationships between the foraging strategy of seabirds, hydrographic features and food availability are poorly understood. We investigated the movements at sea, time spent per oceanic sector, food intake, and diet of king penguins Aptenodytes patagonicus in the Crozet Islands (Southern Indian Ocean) during summer, as a function of the position of major frontal zones. Fifteen trips at sea were monitored using satellite transmitters over 3 austral summers (1992 to 1994). During each season, satellite transmitters were used in conjunction with stomach temperature recorders in order to investigate feeding activity. The at-sea distribution of king penguins was closely related to the localisation of major hydrographic frontal systems. Intense prospecting areas were observed mainly in zones corresponding to the northern limit of the Polar Front (50°to 51°S), southern limit of the Sub-Antarctic Front (44.50°to 45°S), and a zone between 47°and 48°S. During trips directed south, 2 distinct phases based on travelling speed were detected. The myctophids Electrona carlsbergi, Krefftichtys anderssoni and Protomyctophum tenisoni dominated the diet. The estimated average amount of food ingested per day at sea was 2.4 kg. Between 17 and 64 kg of food was captured during 7 to 25 d at sea. Approximately 80% of the food intake occurred during the first phase of the trip. Food intake was related to trip duration and relative amount of time spent in particular oceanic sectors. The sections 47°to 48°S and 48.5°to 50.50°S appeared particularly favorable for food intake, the latter coinciding with the northern limit of the Polar Front. King penguins fed intensively on several distinct patches when traveling towards the Polar Front. The foraging range seems to be related to the foraging success during the first phase of the trip. The foraging strategy of king penguins during the summer favors displacements toward frontal zones where food availability is optimal.

High-frequency reponse of wind-driven currents measured by drifting buoys and altimetry over the world ocean

Article

Full-text available

Aug 2003
J GEOPHYS RES

1] We investigate the wind-driven current response over the world ocean using SVP drifting buoys, ERS-1 and ERS-2, and TOPEX altimetry data and ECMWF wind stress fields. Wind-driven ageostrophic currents are estimated from drifting buoys by removing altimetry deduced geostrophic currents from observed drifting velocities. Removing the geostrophic signal enhances the coherence with wind stress at periods longer than 10 days. For superinertial periods lower than 20 days, a two-parameter (i.e., angle and amplitude) model is fitted to the isolated ageostrophic signal to study the upper ocean response to surface wind stress in that frequency band. The model, which can explain up to 30% of the variance in some areas, indicates that the currents spiral to the right (left) of the wind with depth in the Northern (Southern) Hemisphere, in agreement with the Ekman theory. The absolute value of the angle parameter is found to exhibit significant spatial and seasonal variability. The vertical eddy viscosity and the Ekman layer depth as deduced from Ekman theory are compared to previous results. Their seasonal variability is also studied. Model results are then used to compute the mean and standard deviation of ageostrophic currents in 5° boxes over the world ocean. The equatorial divergence and the subpolar and subtropical convergence zones are well reproduced. Citation: Rio, M.-H., and F. Hernandez, High-frequency response of wind-driven currents measured by drifting buoys and altimetry over the world ocean, J. Geophys. Res., 108(C8), 3283, doi:10.1029/2002JC001655, 2003.

Robust state-space modeling of animal movement data

Article

Full-text available

Dec 2005

Remotely sensed tracking data collected on animal movement is vastly un-derutilized due to a lack of statistical tools for appropriate analysis. Features of such data that make analysis particularly challenging include the presence of estimation errors that are non-Gaussian and vary in time, observations that occur irregularly in time, and com-plexity in the underlying behavioral processes. We develop a state–space framework that simultaneously deals with these features and demonstrate our method by analyzing three seal pathway data sets. We show how known information regarding error distributions can be used to improve inference of the underlying process(es) and demonstrate that our frame-work provides a powerful and flexible method for fitting different behavioral models to tracking data.

Habitat‐specific normal and reverse diel vertical migration in the plankton‐feeding basking shark

Article

Full-text available

Jul 2005
J ANIM ECOL

Megaplanktivores such as filter‐feeding sharks and baleen whales are at the apex of a short food chain (phytoplankton–zooplankton–vertebrate) and are sensitive indicators of sea‐surface plankton availability. Even though they spend the majority of their time below the surface it is still not known how most of these species utilize vertical habitat and adapt to short‐term changes in food availability. A key factor likely to control vertical habitat selection by planktivorous sharks is the diel vertical migration (DVM) of zooplankton; however, no study has determined whether specific ocean‐habitat type influences their behavioural strategy. Based on the first high‐resolution dive data collected for a plankton‐feeding fish species we show that DVM patterns of the basking shark Cetorhinus maximus reflect habitat type and zooplankton behaviour. In deep, well‐stratified waters sharks exhibited normal DVM (dusk ascent–dawn descent) by tracking migrating sound‐scattering layers characterized by Calanus and euphausiids. Sharks occupying shallow, inner‐shelf areas near thermal fronts conducted reverse DVM (dusk descent–dawn ascent) possibly due to zooplankton predator–prey interactions that resulted in reverse DVM of Calanus . These opposite DVM patterns resulted in the probability of daytime‐surface sighting differing between these habitats by as much as two orders of magnitude. Ship‐borne surveys undertaken at the same time as trackings reflected these behavioural differences. The tendency of basking sharks to feed or rest for long periods at the surface has made them vulnerable to harpoon fisheries. Ship‐borne and aerial surveys also use surface occurrence to assess distribution and abundance for conservation purposes. Our study indicates that without bias reduction for habitat‐specific DVM patterns, current surveys could under‐ or overestimate shark abundance by at least 10‐fold.

Reproduction and life history strategies of the common jellyfish, Aurelia aurita, in relation to its ambient environment

Article

Full-text available

May 2001

Cathy H Lucas

The scyphozoan Aurelia aurita (Linnaeus) is a cosmopolitan species, having been reported from a variety of coastal and shelf sea environments around the world. It has been extensively studied over the last 100 years or so, and examination of the literature reveals three striking features: (1) the presence of populations in a wide range of environmental conditions; (2) large inter-population differences in abundance and life history patterns over large and small spatial scales; and (3) inter-annual variability in various aspects of its population dynamics. A. aurita is clearly a highly flexible species that can adapt to a wide range of environmental conditions. While various physiological and behavioural characteristics explain how A. aurita populations can take advantage of their surrounding environment, they do not explain what governs the observed temporal and spatial patterns of abundance, and the longevity or lifespan of populations. Understanding these features is necessary to predict how bloom populations might form. In a given habitat, the distribution and abundance of benthic marine invertebrates have been found to be maintained by four factors: larval recruitment (sexual reproduction), migration, mortality and asexual reproduction. The aims of this review are to determine the role of reproduction and life history strategies of the benthic and pelagic phases of A. aurita in governing populations of medusae, with special attention given to the dynamic interaction between A. aurita and its surrounding physical and biological environment.

Lip-reading in remote subjects: An attempt to quantify and separate ingestion, breathing and vocalisation in free-living animals using penguins as a model

Article

Full-text available

Jan 2002

A new mandibular sensor is presented here based on the use of a Hall sensor, attached to one mandible, opposite a magnet, attached to the other mandible. Changes in sensor voltage, proportional to magnetic field strength, and thus inter-mandibular angle, are recorded in a logger. This system was tested on seven captive Adélie penguins (Pygoscelis adeliae) and three gentoo penguins (Pygoscelis papua) during: (1) feeding trials on land, where birds were given known quantities and types of food; and (2) trials in water where birds were allowed to swim and dive freely. In addition, six free-living Magellanic penguins (Spheniscus magellanicus) were equipped with the system for single foraging trips. Angular signatures were looked for in instances when both captive and free-living birds might open their beaks, and it was discovered that five major behaviours could be identified: ingestion, breathing, calling, head shaking and preening. Captive feeding trials showed that prey mass could be determined with reasonable accuracy (r 2=0.92), and there was some indication that prey type could be resolved if recording frequency were high enough. Vocalisations in Adélie penguins (arc calls) took <0.7 s for mean maximum beak angles of 4.2° (SD 1.3), and were distinguished by their relatively gradual change in beak angle and by their high degree of symmetry. Beak shakings were distinguishable by their short duration (multiple peaks of <0.5 s) and minimal maximum angle (<0.5°). Preening behaviour was apparent due to multiple decreasing peaks (angles <8°). Breathing could be subdivided into that during porpoising, where a characteristic double peak in beak angle was recorded, and that during normal surface rests between dives. During porpoising, only the primary peak (mean maximum beak angle 25.1°, SD 4.7) occurred when the bird was out of the water (mean maximum for second peak 5.9°, SD 4.1). During normal surface rests in free-living birds, breaths could be distinguished as a series of beak openings and closures, showing variation in amplitude and frequency according to an apparent recovery from the previous dive and preparation for the subsequent dive to come. The mandibular measuring system presented shows considerable promise for elucidating many hitherto intractable aspects of the behaviour of free-living animals.

Accuracy of satellite positions from free-ranging grey seals using ARGOS

Article

Full-text available

Aug 2002

We have undertaken an analysis of the locations derived from an ARGOS system using satellite relay data loggers mounted on free-ranging grey seals (Halichoerus grypus Fab.) in the Gulf of Bothnia, between Sweden and Finland. The accuracy of the classes reported within this study is similar to that reported by Service ARGOS and we suggest that it would be beneficial to receive the A and B location classes. Locations-derived location classes 0 and A can be used for studies involving long-range movements, 10 km or more, but would not be suitable for fine-scale analyses.

High-use oceanic areas for Atlantic leatherback sea turtles (Dermochelys coriacea) as identified using satellite telemetered location and dive information

Article

Full-text available

Aug 2006

Scott A. Eckert

The movements and behavior of nine female leatherback sea turtles, Dermochelys coriacea (L.) were monitored for up to 370days from their nesting beaches on the Caribbean island of Trinidad between 1995 and 2004 using satellite-linked time and depth recorders. During the inter-nesting period (typically March–July) turtles ranged widely, but frequented the area around Galera Point on the NE corner of Trinidad. Diving depths were typically <51m. Upon leaving Trinidad, the three longest tracked turtles moved to higher latitude foraging areas, NE of the Flemish Cap; along the continental shelf of the Iberian peninsula to the Bay of Biscay; and along the N. Atlantic subtropical front, where they remained until the end of November. Dives were initially deep (100–300m) and long (>26min) as the turtles left the Caribbean, but became very shallow (>50m) and short at high latitudes. Between mid-October and mid-November, the turtles left high latitudes for a presumed foraging area in the Mauritania upwelling where they resided until their tracking records ended. Diving remained relatively shallow. It is proposed that movements of these turtles from one foraging area to another are driven by the opportunity to forage in areas of distinct oceanic structure which serve to concentrate their gelatinous prey (e.g., salps, Scyphomedusae, Siphonophora) either at or below the surface.

Post-nesting migrations of loggerhead sea turtles in the Gulf of Mexico: Dispersal in highly dynamic conditions

Article

Full-text available

Apr 2009

This study is the first report of post-nesting migrations of loggerhead sea turtles (Caretta caretta) nesting in Sarasota County (Florida, USA), their most important rookery in the Gulf of Mexico (GOM). In total, 28 females (curved carapace length CCL between 82.2 and 112.0cm) were satellite-tracked between May 2005 and December 2007. Post-nesting migrations were completed in 3–68days (mean±SD=23±16days). Five different migration patterns were observed: six turtles remained in the vicinity of their nesting site while the other individuals moved either to the south-western part of the Florida Shelf (n=9 turtles), the Northeast GOM (n=2 turtles), the South GOM (Yucatán Shelf and Campeche Bay, Mexico, and Cuba; n=5 turtles) or the Bahamas (n=6 turtles). In average, turtles moved along rather straight routes over the continental shelf but showed more indirect paths in oceanic waters. Path analyses coupled with remote sensing oceanographic data suggest that most of long-distance migrants reached their intended foraging destinations but did not compensate for the deflecting action of ocean currents. While six out of seven small individuals (CCL<90cm) remained on the Florida Shelf, larger individuals showed various migration strategies, staying on the Florida Shelf or moving to long-distance foraging grounds. This study highlights the primary importance the Western Florida Shelf in the management of the Florida Nesting Subpopulation, as well as the need of multi-national effort to promote the conservation of the loggerhead turtle in the Western Atlantic.

Foraging ground fidelity and route-choice tactics of a marine predator: The Antarctic fur seal Arctocephalus gazella

Article

Full-text available

Nov 2001

This study examins the intra- and inter-individual changes in the foraging route-choice behaviour of 45 female Antarctic fur seals Arctocephalus gazella breeding at the Cap Noir colony in the Kerguelen Archipelago, southern Indian Ocean. Satellite transmitters were used to track seals during one or more consecutive foraging trips in 3 consecutive austral summers (1998 to 2000). In all years of study the seals showed a 'colony-preferred direction', concentrating their trips at sea in a 140degrees arc east of Kerguelen, indicating a preferred area for foraging. Within this area, lactating females travelled in 1 of 2 main directions: north east toward the edge of the Kerguelen plateau; and less commonly, east/south east. Each direction led seals to sub-areas characterised by different bathymetric features where animals appeared to use different tactics to search for food patches. Moreover, a fidelity index incorporating the mean direction of successive trips and the colony preferred direction indicated the existence of an individual directional fidelity. The organisation of foraging trips suggests 2 levels of learning by seals: a colony memory of the main foraging zone and an individual memory of profitable patches that are exploited by the same individual during successive trips.

Oceanographic features related to northern fur seal migratory movements

Article

Full-text available

Mar 2005
DEEP-SEA RES PT II

Northern fur seals breeding on the Pribilof Islands are characterized by pelagic migrations that begin each fall and last approximately eight months. Previous studies have examined the early phases of the migration with respect to timing, location, and effects of ocean surface currents on movement. We used satellite telemetry and remotely sensed satellite data to examine relationships between oceanographic features and the movements of adult female fur seals in the Bering Sea and North Pacific Ocean during early, middle and late portions of their winter migration. Physical locations of 13 female fur seals were monitored during 2002–2003, and diving data were collected on a subset of the animals. Remotely sensed data were obtained to assess sea-surface temperatures, chlorophyll a concentrations, and sea-surface height anomalies encountered by the fur seals. Data from historical pelagic collection of fur seals also were summarized to describe winter diet and the distribution of different age and sex classes of the general migration of fur seals to the eastern North Pacific. Seals departed from the Pribilof Islands in November and moved in a southeasterly direction over the continental shelf as they left the Bering Sea. Their travel routes did not follow coastal or bathymetric features as they crossed the North Pacific Ocean, but instead corresponded to complementary water movement of the Alaska Gyre and the North Pacific Current. Winter foraging areas varied geographically and were associated with eddies, the subarctic–subtropical transition region, and areas that undergo coastal mixing due to the California Current. The results indicate that fur seals may cue on a variety of oceanographic features that aid in reducing energetic expenditures and optimize foraging opportunities.

Identifying and comparing phases of movement by leatherback turtles using state-space models

Article

Full-text available

Mar 2008
J EXP MAR BIOL ECOL

Leatherback turtles (Dermochelys coriacea) are currently critically endangered and could be on the verge of extinction within the Pacific Ocean. In 2004–7, satellite transmitters were attached to 46 female turtles nesting at Playa Grande, Costa Rica, to further investigate their distribution and movements in the eastern Pacific to improve conservation measures. State-space models (SSM) provide a valuable tool for modelling movement data by simultaneously accounting for measurement error and variability in the movement dynamics. Track simulations and a measure of the uncertainty for each position estimate allowed model performance with large amounts of missing satellite data to be assessed, as this is common for marine animals. A switching SSM was applied to the tracks of the turtles, which also provided an estimate of the behavioural mode at each location. This enabled the internesting period to be objectively defined based on a shift between these two modes. This switch occurred later than the last observed nesting event, indicating turtles did not immediately move offshore and the length of time and area that turtles utilise during internesting could previously have been underestimated. The movement parameters, mean turning angle and autocorrelation in speed and direction, for each mode were similar to those in the Atlantic Ocean, but the foraging phase was more prolonged and widely dispersed suggesting that food patches are less predictable in the Pacific. This may explain the long period between nesting seasons.

Persistent Leatherback Turtle Migrations Present Opportunities for Conservation

Article

Full-text available

Jul 2008
PLOS BIOL

Effective transboundary conservation of highly migratory marine animals requires international management cooperation as well as clear scientific information about habitat use by these species. Populations of leatherback turtles (Dermochelys coriacea) in the eastern Pacific have declined by >90% during the past two decades, primarily due to unsustainable egg harvest and fisheries bycatch mortality. While research and conservation efforts on nesting beaches are ongoing, relatively little is known about this population of leatherbacks' oceanic habitat use and migration pathways. We present the largest multi-year (2004-2005, 2005-2006, and 2007) satellite tracking dataset (12,095 cumulative satellite tracking days) collected for leatherback turtles. Forty-six females were electronically tagged during three field seasons at Playa Grande, Costa Rica, the largest extant nesting colony in the eastern Pacific. After completing nesting, the turtles headed southward, traversing the dynamic equatorial currents with rapid, directed movements. In contrast to the highly varied dispersal patterns seen in many other sea turtle populations, leatherbacks from Playa Grande traveled within a persistent migration corridor from Costa Rica, past the equator, and into the South Pacific Gyre, a vast, low-energy, low-productivity region. We describe the predictable effects of ocean currents on a leatherback migration corridor and characterize long-distance movements by the turtles in the eastern South Pacific. These data from high seas habitats will also elucidate potential areas for mitigating fisheries bycatch interactions. These findings directly inform existing multinational conservation frameworks and provide immediate regions in the migration corridor where conservation can be implemented. We identify high seas locations for focusing future conservation efforts within the leatherback dispersal zone in the South Pacific Gyre.

Homing in green turtles Chelonia mydas: Oceanic currents act as a constraint rather than as an information source

Article

Full-text available

Sep 2006

As open sea navigators, green turtles Chelonia mydas have to deal with oceanic currents. These currents may have a mechanical influence, forcing turtles away from their desired course, but they may also provide information to navigating turtles by bringing chemical cues down-current from their target area. In the present paper, we have introduced new path analysis methods, coupling remote-sensing oceanographic data and satellite-tracking data in order to test these hypotheses. These methods were exemplified on the homing routes of 3 green turtles nesting on Europa, an isolated island in the southern part of Mozambique Channel. The turtles, displaced by ship east-southeast from Europa, returned to their nesting island in 13 to 59 d, following long, circuitous routes, and hence apparently displaying poor navigational abilities. Path analysis showed that turtles were unable to compensate for the deflecting action of currents, which moved them away from their intended course and lowered their orientation performance. At large distances from Europa, green turtles did not appear to find navigational information in water masses that had previously been in contact with their target area.

The jellyfish joyride: Causes, consequences and management responses to a more gelatinous future

Article

Full-text available

Apr 2009
TRENDS ECOL EVOL

Human-induced stresses of overfishing, eutrophication, climate change, translocation and habitat modification appear to be promoting jellyfish (pelagic cnidarian and ctenophore) blooms to the detriment of other marine organisms. Mounting evidence suggests that the structure of pelagic ecosystems can change rapidly from one that is dominated by fish (that keep jellyfish in check through competition or predation) to a less desirable gelatinous state, with lasting ecological, economic and social consequences. Management actions needed to stop such changes require tactical coping strategies and longer-term preventative responses based on fundamental and targeted research on this understudied group.

Are seabirds foraging for unpredictable resources?

Article

Feb 2007

Henri Weimerskirch

Circular Statistics in Biology

Article

Sep 1982

Intraspecific variation in movement patterns: Modeling individual behaviour in a large marine predator

Article

Apr 2004
OIKOS

In large marine predators, foraging entails movement. Quantitative models reveal how behaviours can mediate individual movement, such that deviations from a random pattern may reveal specific search tactics or behaviour. Using locations for 52 grey seals fitted with satellite-linked recorders on Sable Island; we modeled movement as a correlated random walk (CRW) for individual animals, at two temporal scales. Mean move length, turning angle, and net squared displacement (R2n: the rate of change in area over time) at successive moves over 3 to 10 months were calculated. The distribution of move lengths of individual animals was compared to a Lévy distribution to determine if grey seals use a Lévy flight search tactic. Grey seals exhibited three types of movement as determined by CRW model fit: directed movers – animals displaying directed long distance travel that were significantly underpredicted by the CRW (23% of animals); residents – animals remaining in the area surrounding Sable Island that were overpredicted by the model (29% of animals); and correlated random walkers – those (48% of animals) in which movement was predicted by the CRW model. Kernel home range size differed significantly among all three movement types, as did travel speed, mean move length, mean R2n and total distance traveled. Sex and season of deployment were significant predictors of movement type, with directed movers more likely to be male and residents more likely to be female. Only 30% of grey seals fit a Lévy distribution, which suggests that food patches used by the majority of seals are not randomly distributed. Intraspecific variation in movement behaviour is an important characteristic in grey seal foraging ecology, underscoring the need to account for such variability in developing models of habitat use and predation.

Are seabirds foraging for unpredictable resources? Deep-Sea Res II: Top Stud Oceanog

Article

Feb 2007
DEEP-SEA RES PT II

Henri Weimerskirch

It is generally assumed that the extreme life history traits of pelagic seabirds, such as low fecundity or slow growth of chicks, result from the difficulties obtaining energy at sea from unpredictable and patchily distributed resources. However, little information on seabird prey distribution and availability exists to sustain this widely accepted hypothesis. Using tracking studies of 68 sub-populations of flying seabirds, I examine whether it is possible to gain information on the predictability of their marine resources. Because prey are clustered from fine to large scale in nested unities, from swarms to patches and concentrations of patches, it is important to take into account spatial scale. In temperate and polar regions, at large and meso-scales, seabirds appear to have a good knowledge of the location and concentrations of patches and generally use a commuting type of trip to reach foraging zones. Predictability appears to be high at large and meso-scales, with individuals from each sub-population heading in a particular direction from the colony to reach favoured habitats of known enhanced productivity such as shelf edges, frontal zones, upwellings. Within these mesoscale features, the animals use an area-restricted search behaviour to search for patches and swarms at finer scales. Using information on foraging site fidelity of individual birds, I show that differences in predictability at coarse scales are related to the distance and time spent foraging, and in particular to the specific types of foraging habitat. Some habitats appear to be more predictable than others: birds return consistently to the same coarse-scale sectors on shelf edges, whereas predictability is low in oceanic waters, even in frontal zones. Preliminary results on tropical species suggest that the environment here is less predictable in tropic than in temperate or polar zones. This review highlights that patchiness and predictability of marine resources are complex notions: predictability is dependent on the spatial and temporal scale considered, and especially on the marine habitat of foraging interest. I discuss the potential consequences of these results for the breeding success and life history of seabirds.

How Wandering Albatrosses use weather systems to fly long distances. 1. An analytical method and its application to flights in the Tasman Sea

Article

Dec 2002

Rigorous analytical procedures for appraising how Wandering Albatrosses, Diomedea exulans gibsoni, use weather systems to achieve long-distance flights are described. They were applied initially to study the movements of two Wandering Albatrosses in the Tasman Sea where weather systems, though complex, display many of the general features found in the Southern Hemisphere between 30° and 50°S. It was found that no flight can be explained as a passive response to wind, as all flights revealed an 'intent' to fly in a given direction for at least several hundred kilometres, even through complex weather systems.

Feeding of Dermochelys coriacea on Medusae in the Northwest Atlantic

Article

Nov 2000

Regionally and seasonally differentiated primary production in the North Atlantic

Article

Oct 1995
DEEP-SEA RES PT I

A bio-geochemical classification of the N. Atlantic Basin is presented according to which the basin is first divided into four primary algal domains: Polar, West-Wind, Trades and Coastal. These are in turn sub-divided into smaller provinces. The classification is based on differences in the physical environment which are likely to influence regional alga dynamics. The seasonally-differentiated parameters of the photosynthesis-light curve (P-I curve) and parameters that define the vertical structure in chlorophyll profile are then established for each province, based on an analysis of an archive of over 6000 chlorophyll profiles, and over 1800 P-I curves. These are then combined with satellite-derived chlorophyll data for the N. Atlantic, and information on cloud cover, to compute primary production at the annual scale, using a model that computes spectral transmission of light underwater, and spectral, photosynthetic response of phytoplankton to available light. The results are compared with earlier, satellite-derived, estimates of basin-scale primary production.

Weimerskirch, H., Gault, A. & Cherel, Y. Prey distribution and patchiness: factors in foraging success and efficiency of wandering albatrosses. Ecology 86, 2611-2622

Article

Oct 2005

Seabirds are considered to rely on prey that are patchily distributed and whose abundance differs greatly according to physical processes or water masses. However, very little information is available about the environmental factors and individual factors that affect the foraging success of marine predators. We studied the distribution of prey encounters, foraging success, and efficiency in different water masses and during two stages of the breeding season when energy requirements differed in Wandering Albatrosses (Di-omedea exulans) of known experience and sex. The birds were simultaneously fitted with satellite transmitters, stomach temperature sensors, and activity recorders. Only 27% of prey were captured in patches (distance between two prey 1 km); the rest were caught at an average distance of 64 km. Prey in patches were smaller than isolated prey and were caught mainly at night. Diet analysis indicated that albatrosses preyed mainly upon adult squid: squid taken at night were smaller (bioluminescent species), whereas those taken during the day were larger (nonbioluminescent species). Birds spent more time foraging farther from the colony during incubation than during brooding, when their energy re-quirement was highest, but foraging effort (landings per hour, or kilometers per hour), foraging success (grams of prey per hour), and efficiency (grams of prey per landing per hour) were similar during the two stages. The rate of prey encounter and foraging efficiency did not differ between water masses or between oceanic and shelf-slope waters. We found no differences between the sexes in terms of foraging success and efficiency. Young, in-experienced individuals had foraging success and efficiency similar to those of older, ex-perienced birds but had a different strategy: they foraged more actively and caught more prey at night than did experienced birds. These results suggest strongly that Wandering Albatrosses rely on prey that are highly dispersed, catch few prey within the same patch, and do not adjust foraging effort according to energy requirements. The unpredictability of the location of prey and the type of prey caught by Wandering Albatrosses indicate that the species has a unique foraging strategy compared to most seabirds, which generally concentrate in more predictable foraging areas.

Monitoring a Marine Ecosystem Using Responses of Upper Trophic Level Predators

Article

Dec 2001
J ANIM ECOL

This study examined the changing status of the marine ecosystem at the island of South Georgia (Southern Ocean) using up to 27 variables measured over 22 years from three upper trophic level predators that specialize in foraging upon krill ( Eupuasia superba Dana). These variables included population size, breeding performance, offspring growth rate, foraging behaviour and diet. A method was developed for reducing these multivariate time‐series to a single vector, called a combined standardized index (CSI). Sensitivity analyses showed that missing values had a large effect upon the accuracy of the CSI but this effect was reduced if the individual variables were highly correlated. The level of correlation and proportion of missing values within the empirical data set were within the acceptable range. Individual variables had widely varying influence upon the CSI but, in general, those with longer time‐series had the greatest influence. Principal components analysis showed that variables representing offspring growth tended to explain the greatest proportion of the variability in the CSI and this was followed by variables representing diet. There were 3 years in which the CSI showed extreme and significantly low values. There was a significant non‐linear functional response (similar to the Holling Type II functional response) between the overall CSI and krill biomass and a similar relationship existed when the CSI was calculated for each species individually. Separate analysis of variables that were likely to be representative of changing population size showed the presence of a significant decline between 1977 and 1998. There was no trend in the CSI from variables representative of foraging conditions during the summer breeding season. The study has shown that the marine ecosystem at South Georgia shows acute but transient variability that is amplified in the response of upper trophic‐level predators. There is less certainty that trends in populations are a consequence of shifts in the degree to which the ecosystem can support krill‐feeding seals and penguins.

Determining feeding events and prey encounter rates in a southern elephant seal: A method using swim speed and stomach temperature

Article

Jan 2008

The foraging behavior of marine predators is largely determined by the interaction between their physiological characteristics and the abundance and distribution of their prey (Boyd 1996, Bradshaw et al. 2004a). Prey distribution in the marine environment is often patchy and to some extent unpredictable, as are the underlying biological and physical features of the ocean (Bradshaw et al. 2002, Constable et al. 2003, Field et al. 2004). Establishing where and when marine mammal predators forage is fundamental to obtaining a broader understanding of foraging ecology at an individual and species level (Boyd 1996). Identifying the location and timing of foraging by upper trophic level predators can also provide information on the characteristics and behavior of prey species as well as insights into how the predators might respond to, and reflect, changes in ecosystem structure and function (Austin et al. 2006, Kuhn and Costa 2006). Spatial and temporal patterns of feeding in southern elephant seals have been inferred from migration tracks (Jonker and Bester 1998; Field et al. 2001, 2004; Hindell et al. 2003; Bradshaw et al. 2004b), dive profiles (Hindell et al. 1991, Cam-pagna et al. 1999, Biuw et al. 2003), and the examination of stomach contents (Slip 1

A review of long-distance movements by marine turtles, and the possible role of ocean currents

Article

Nov 2003
OIKOS

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.

A comparison of indirect measures of feeding behavior based on ARGOS tracking data

Article

Feb 2007
DEEP-SEA RES PT II

ARGOS tracking data are frequently used to infer feeding locations of marine predators. Most track-based methods rely on the assumption that feeding takes place within regions of area-restricted search (ARS); however, it is unclear whether the spatial accuracy and temporal resolution of ARGOS-quality data are sufficient to extract the location of ARSs at the resolution of individual feeding bouts. Using ARGOS tracking data from northern elephant seals (Mirounga angustirostris) and Laysan albatrosses (Phoebastria immutabilis), we tested several track-based estimators of feeding locations against independent feeding proxies (dive type or shape and number of landing events). The track-based methods were: turn angle, transit rate, first-passage time, and fractal dimension. None of these methods provided a reliable estimate of putative feeding activity at the species level, as measured by dive-type analysis or landing events. At the individual level, variation in agreement between track-based estimates and feeding proxies highlighted the importance of considering the effect of spatial scale. Biological justification of track-based metrics should be more carefully assessed before assigning particular functions to individual tracks (feeding/foraging/searching/transit) or groups of tracks (biological hotspots).

Mouthing off about fish capture: Jaw movement in pinnipeds reveals the real secrets of ingestion

Article

Feb 2007
DEEP-SEA RES PT II

Determination of when and where animals feed and how much they consume is fundamental to understand their ecology and role in ecosystems. However, the lack of reliable data on feeding habits of wild animals, and particularly in marine endotherms, attests to the difficulty in doing this. A promising recent development proposes using a Hall sensor-magnet system, the inter-mandibular angle sensor (IMASEN) attached to animals’ jaws to elucidate feeding events. We conducted trials on captive pinnipeds by feeding IMASEN-equipped animals with prey to examine the utility of this system. Most feeding events were clearly distinguishable from other jaw movements; only small prey items might not be resolved adequately. Based on the results of this study we examined feeding events from free-ranging pinnipeds fitted with IMASENs and dead-reckoners and present data on prey capture and ingestion in relation to the three-dimensional movement patterns of the seals.

Seasonal cooling and blooming in tropical oceans

Article

Nov 1993
DEEP-SEA RES PT I

Alan Longhurst

The relative importance of tropical pelagic algal blooms in not yet fully appreciated and the way they are induced not well understood. The tropical Atlantic supports pelagic blooms together equivalent to the North Atlantic spring bloom. These blooms are driven by thermocline tilting, curl of wind stress and eddy upwelling as the ocean responds to intensified basin-scale winds in boreal summer. The dimensions of the Pacific Ocean are such that seasonal thermocline tilting does not occur, and nutrient conditions are such that tilting might not induce bloom, in any case. Divergence at the equator is a separate process that strengthens the Atlantic bloom, is more prominent in the eastern Pacific, and in the Indian Ocean induces a bloom only in the western part of the ocean. Where western jet currents are retroflected from the coast off Somalia and Brazil, eddy upwelling induces prominent blooms. In the eastward flow of the northern equatorial countercurrents, positive wind curl stress induces Ekman pumping and the induction of algal blooms aligned with the currents. Some apparent algal bloom, such as that seen frequently in CZCS images westwards from Senegal, must be due to interference from airborne dust.

Basin-scale variability of phytoplankton biomass, production and growth in the Atlantic Ocean

Article

May 2000
DEEP-SEA RES PT I

The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50 degrees N to 50 degrees S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75-125 mg Chl m(-2)) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chi a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m(-2). The estimated concentration of surface phytoplankton carbon

Why do Argos satellite tags deployed on marine animals stop transmitting? J Exp Mar Biol Ecol

Article

Sep 2007
J EXP MAR BIOL ECOL

Identifying the reasons for the loss of signals in satellite tracking studies is important for directing future improvements in transmitter technology and attachment systems, as well as defining the status of the tracked animals (alive or dead) at the end of the tracking period, which is integral to assessing survival rates through established methods. We highlight the importance of transmitted diagnostic data that reveal the status of a tag. We show in marine wildlife satellite tracking that the reasons behind transmitter signal loss can often be identified. Exhaustion of batteries, salt-water switch failure, antenna breakage, animal mortality and premature detachment of tags were all identified as causes of signal loss from transmitters routinely attached to turtles, fish and marine mammals. In principle, battery management systems should allow tracking of individuals for several years, even with existing transmitter technology, although in such long-term deployments in a marine setting, failure of the salt-water switch may persist as the Achilles heel of existing tags.

Expanded thermal niche for a diving vertebrate: A leatherback turtle diving into near-freezing water

Article

Aug 2006
J EXP MAR BIOL ECOL

The global distribution of extant reptiles is more limited than that of mammals or birds, with low reptilian species diversity at high latitudes. Central to this limited geographical distribution is the ectothermic nature of reptiles, which means that they generally become torpid at cold temperatures. However, here we report the first detailed telemetry from a leatherback turtle (Dermochelys coriacea) diving in cold water at high latitude. An individual equipped with a satellite tag that relayed temperature–depth profiles dived continuously for many weeks into sub-surface waters as cold as 0.4 °C. Global warming will likely increase the foraging range of leatherback turtles further into temperate and boreal waters.

The dispersal of the Amazon and Orinoco River water in the tropical Atlantic and Caribbean Sea: Observation from space and S-PALACE floats

Article

May 2004
DEEP-SEA RES PT II

The temporal evolution of spatial patterns of the colored water mass associated with the discharges of the Amazon and Orinoco Rivers between 1997 and 2002 was examined using concurrent in situ and satellite observations in the region bounded by 01N?241N and 701W?401W. Patches of low-salinity ($32?34) surface waters were frequently observed with Salinity Pro?ling Autonomous LAgrangian Current Explorer (S-PALACE) ?oats as far as 2000 km away from the mouths of the Amazon and Orinoco Rivers. Ocean-color data collected with the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) show that these patches originate with these rivers. Chlorophyll (Chl) and colored dissolved organic matter (CDOM) distribution estimated with SeaWiFS data are well correlated with low sea-surface salinity (SSS) throughout the observation period (average correlation coef?cients for monthly observations of �0.6 for the SSS?CDOM relationship and �0.5 for the SSS?Chl relationship). The color of the water in the river plumes is dominated by CDOM rather than Chl light absorption, in contrast to adjacent open-ocean and equatorial upwelling regions, where optical properties are primarily controlled by Chl. The mean CDOM absorption coef?cient for the area covered by the Amazon?s plume showed a peak in July for the 1998?2001 period, which lagged the Amazon?s hydrograph by one month. The timing of the CDOM peak along different sections of the Amazon River plume implies an estimated advection speed of $35 cm s�1 within the plume. Anti-cyclonic rings (eddies) with diameters of 400?500 km were observed moving along the northeastern coast of South America every year and in all seasons, at a frequency of about one every 30?60 days. These eddies moved to the northwest at a speed of 8?20 cm s�1, with higher speeds observed during the ?rst half of each calendar year. The average depth of the Amazon plume for SSS ranging from 32 to 35 was 20?30 m, and the total fresh-water volume contained in the plume was consistent with discharge rates. Due to uncertainties in the Chl and CDOM absorption coef?cient estimates in river plumes, accurate estimation of the rivers? impact on regional primary production remains a challenge. The paired SeaWiFS and S-PALACE ?oat observations validate the hypothesis that the coherent surface color patches seen annually far offshore in the tropical North Atlantic are caused by dispersal of Amazon and Orinoco River water. In contrast, wind-driven upwelling near the edge of the North Brazil Current retro?ection, another mechanism causing color enhancement, is not suggested by these data sets.

Feeding ecology of wild migratory tunas revealed by archival tag records of visceral warming

Article

Nov 2008
J ANIM ECOL

1. Seasonal long-distance migrations are often expected to be related to resource distribution, and foraging theory predicts that animals should spend more time in areas with relatively richer resources. Yet for highly migratory marine species, data on feeding success are difficult to obtain. We analysed the temporal feeding patterns of wild juvenile southern bluefin tuna from visceral warming patterns recorded by archival tags implanted within the body cavity. 2. Data collected during 1998-2000 totalled 6221 days, with individual time series (n = 19) varying from 141 to 496 days. These data span an annual migration circuit including a coastal summer residency within Australian waters and subsequent migration into the temperate south Indian Ocean. 3. Individual fish recommenced feeding between 5 and 38 days after tagging, and feeding events (n = 5194) were subsequently identified on 76.3 +/- 5.8% of days giving a mean estimated daily intake of 0.75 +/- 0.05 kg. 4. The number of feeding events varied significantly with time of day with the greatest number occurring around dawn (58.2 +/- 8.0%). Night feeding, although rare (5.7 +/- 1.3%), was linked to the full moon quarter. Southern bluefin tuna foraged in ambient water temperatures ranging from 4.9 degrees C to 22.9 degrees C and depths ranging from the surface to 672 m, with different targeting strategies evident between seasons. 5. No clear relationship was found between feeding success and time spent within an area. This was primarily due to high individual variability, with both positive and negative relationships observed at all spatial scales examined (grid ranges of 2 x 2 degrees to 10 x 10 degrees ). Assuming feeding success is proportional to forage density, our data do not support the hypothesis that these predators concentrate their activity in areas of higher resource availability. 6. Multiple-day fasting periods were recorded by most individuals. The majority of these (87.8%) occurred during periods of apparent residency within warmer waters (sea surface temperature > 15 degrees C) at the northern edge of the observed migratory range. These previously undocumented nonfeeding periods may indicate alternative motivations for residency. 7. Our results demonstrate the importance of obtaining information on feeding when interpreting habitat utilization from individual animal tracks.

An estimate of global primary production in the ocean from satellite radiometer data

Article

Jun 1995

An estimate of global net primary production in the ocean has been computed from the monthly mean near-surface chlorophyll fields for 1979–1986 obtained by the Nimbus 7 CZCS radiometer. Our model required information about the subsurface distribution of chlorophyll, the parameters of the photosynthesis-light relationship, the sun angle and cloudiness. The computations were partitioned among 57 biogeochemical provinces that were specified from regional oceanography and by examination of the chlorophyll fields. Making different assumptions about the overestimation of chlorophyll by the CZCS in turbid coastal areas, the global net primary production from phytoplankton is given as 45–50 Gt C year−1. This may be compared with current published estimates for land plants of 45–68 Gt C year−1 and for coastal vegetation of 1.9 Gt C year−1.

Seasonal and interannual variability of chlorophyll a and primary production in the Equatorial Atlantic: In situ and remote sensing observations

Article

Nov 2004

The seasonal variability of phytoplankton in the Equatorial Atlantic was analysed using Sea-viewing Wide Field-of-view Sensor (SeaWiFS)-derived chlorophyll a (Chl a ) concentration data from 1998 to 2001, together with in situ Chl a and primary production data obtained during seven cruises carried out between 1995 and 2000. Monthly averaged SeaWiFS Chl a distributions were in agreement with previous observations in the Equatorial Atlantic, showing marked differences between 10° W in the Eastern Tropical Atlantic (ETRA) and 25° W in the Western Tropical Atlantic (WTRA) provinces (Longhurst et al . 1995. J. Plankton Res. , 17, 1245–1271). The seasonal cycle of SeaWiFS-derived Chl a concentration calculated for 0–10° S, 0–20° W (ETRA) is consistent with in situ Chl a measurements, with values ranging from 0.16 mg m−3, from February to April, to 0.52 mg m−3 in August. Lower variability was observed in 10° N−10° S, 20–30° W (WTRA) where minimum and maximum concentrations occurred in April (0.15 mg m−3) and in August (0.24 mg m−3), respectively. A significant empirical relationship between depth-integrated primary production and in situ measured sea surface Chl a was found for ETRA, allowing us to estimate the seasonal cycle of depth-integrated primary production from SeaWiFS-derived Chl a . As for Chl a , this model was verified in a small area of the Eastern Equatorial Atlantic (0–10° S, 0–20° W), although in this instance it was not completely able to describe the magnitude and temporal variability of in situ primary production measurements. The annual euphotic depth-integrated primary production rate estimated for ETRA by our empirical model was 1.4 Gt C year−1, which represents 16% of the open ocean primary production estimated for the whole Atlantic Ocean.

Classifying movement behaviour in relation to environmental conditions using hidden Markov models

Article

Jul 2009
J ANIM ECOL

1. Linking the movement and behaviour of animals to their environment is a central problem in ecology. Through the use of electronic tagging and tracking (ETT), collection of in situ data from free-roaming animals is now commonplace, yet statistical approaches enabling direct relation of movement observations to environmental conditions are still in development. 2. In this study, we examine the hidden Markov model (HMM) for behavioural analysis of tracking data. HMMs allow for prediction of latent behavioural states while directly accounting for the serial dependence prevalent in ETT data. Updating the probability of behavioural switches with tag or remote-sensing data provides a statistical method that links environmental data to behaviour in a direct and integrated manner. 3. It is important to assess the reliability of state categorization over the range of time-series lengths typically collected from field instruments and when movement behaviours are similar between movement states. Simulation with varying lengths of times series data and contrast between average movements within each state was used to test the HMMs ability to estimate movement parameters. 4. To demonstrate the methods in a realistic setting, the HMMs were used to categorize resident and migratory phases and the relationship between movement behaviour and ocean temperature using electronic tagging data from southern bluefin tuna (Thunnus maccoyii). Diagnostic tools to evaluate the suitability of different models and inferential methods for investigating differences in behaviour between individuals are also demonstrated.

Fine-scale foraging behaviour of a medium-ranging marine predator

Article

May 2009
J ANIM ECOL

Movement patterns of predators should allow them to detect and respond to prey patches at different spatial scales, particularly through the adoption of area‐restricted search (ARS) behaviour. Here we use fine‐scale movement and activity data combined with first‐passage time (FPT) analysis to examine the foraging strategy of northern gannets Morus bassanus in the western North Sea, and to test the following hypotheses: (i) birds adopt a hierarchical foraging strategy characterized by nested ARS behaviour; (ii) the locations and characteristics of ARS zones are strongly influenced by physical oceanography; (iii) the initiation of ARS behaviour is triggered by the detection and pursuit of prey; (iv) ARS behaviour is strongly linked to increased foraging effort, particularly within nested ARS areas. Birds on 13 of 15 foraging trips adopted ARS behaviour at a scale of 9·1 ± 1·9 km, and birds on 10 of these 13 trips adopted a second, nested ARS scale of 1·5 ± 0·8 km, supporting hypothesis 1 above. ARS zones were located 117 ± 55 km from the colony and over half were within 5 km of a tidal mixing front ~50 km offshore, supporting hypothesis 2 above. The initiation of ARS behaviour was usually followed after only a short time interval (typically ~5 min) by the commencement of diving. Gannets do not dive until after they have located prey, and so this pattern strongly suggests that ARS behaviour was triggered by prey detection, supporting hypothesis 3 above. However, ~33% of dives in mixed coastal water and 16% of dives in stratified water were not associated with any detectable ARS behaviour. Hence, while ARS behaviour resulted from the detection and pursuit of prey, encounters with prey species did not inevitably induce ARS behaviour. Following the initiation of ARS behaviour, dive rates were almost four times higher within ARS zones than elsewhere and almost three times higher in zones with nested ARS behaviour than in those without, supporting hypothesis 4 above and suggesting that the foraging success of birds was linked to their ability to match the hierarchical distribution of prey.

Spatio-temporal foraging patterns of a giant zooplanktivore, the leatherback turtle

Abstract

No full-text available

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