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Diverse migratory strategies for a hawksbill sea turtle population
Abstract
Outside of short, infrequent visits to reproductive habitats, sea turtle lifespans are largely spent in foraging areas. Supporting imperilled populations in an era of biodiversity declines and environmental change requires improvements in the understanding of foraging distributions, plus the migratory corridors that connect foraging and reproductive habitats.
This study evaluates the migratory strategies and foraging geography of hawksbill sea turtles ( Eretmochelys imbricata ) in the Western Atlantic. The post‐nesting migrations of 22 females were tracked via satellite telemetry from Long Island, Antigua, during 2016–2019, and a state‐space model was utilized to estimate true turtle locations from Argos satellite fixes. Model output was used to characterize migratory routes and home ranges occupied during non‐migratory inter‐nesting and foraging periods.
Hawksbill migrations ( N = 19) resulted in displacements to foraging areas ranging 7–2300 km. Foraging geography varied considerably—whereas eight turtles remained in the immediate vicinity of Antigua and Barbuda (<30 km), there were also longer‐distance migrations (>470 km) to locations such as The Bahamas and Nicaragua. Inter‐nesting core home ranges (50% utilization distributions) ranged from 7 to 72 km ² , while foraging core areas ranged from 7 to 46 km ² .
These results add to evidence suggesting that, broadly, post‐nesting hawksbills forage in neritic habitats throughout the Wider Caribbean, including several high‐use areas. Short displacements to foraging habitats relatively nearby to nesting beaches appear to be the most common migratory behaviour, but individuals in a single population may exhibit various migratory strategies, resulting in basin‐wide connectivity between nesting and foraging sites. Given that a single individual or nesting population may inhabit several management jurisdictions, an idealized scenario for regional hawksbill conservation would entail data sharing between managers at linked nesting areas, foraging habitats and migratory corridors such that policies to protect key habitats and mitigate human impacts are designed and evaluated based on best‐available science.
... The intensive annual monitoring of this rookery paired with observed high nest site fidelity through natal homing facilitates recapture of nearly all individuals successfully nesting on the beach and identification of all newcomers to the Jumby Bay nesting site (Richardson et al. 1999;Kendall et al. 2019;Levasseur et al. 2019). In addition to reproductive life history, recent studies have aimed to identify Caribbean hawksbill foraging grounds using satellite telemetry, including specific study of this Jumby Bay hawksbill population (Hart et al. 2019;Maurer et al. 2022Maurer et al. , 2024Evans et al. 2024). While the Jumby Bay nesting population is genetically distinct (Levasseur et al. 2019), Caribbean hawksbills appear to use an array of "hot spot" foraging grounds within the Wider Caribbean. ...
... All of the females sampled for this study belong to the same reproductive population (Levasseur et al. 2019), but this population and other Caribbean hawksbill populations use numerous, distinct geographic foraging habitats across the Caribbean basin, as determined through satellite tracking (Hart et al. 2019;Maurer et al. 2022Maurer et al. , 2024. Therefore, the among-individual variance in δ 13 C values likely reflects differences in stable isotope composition of local carbon pools supporting food webs used by individuals in varying foraging grounds. ...
... Potential ontogenetic switches have been observed in small numbers in hawksbills in the Pacific (Wedemeyer-Strombel et al. 2021;Turner Tomaszewicz et al. 2022;Van Houtan et al. 2023), and at least two young (< 10 years reproductive age) individuals displayed shifts toward the mode of δ 13 C and δ 15 N values in this study. This population of hawksbills has been shown to use a range of depths for foraging (2-81-m), a range of foraging ground sizes with utilization distributions of 7-72-km 2 , and geographic foraging grounds across the Caribbean basin (Maurer et al. 2024). ...
Understanding an organism’s niche and ecological role in its ecosystem is critical for conservation, especially for species that use multiple habitats at different life stages. The hawksbill sea turtle (Eretmochelys imbricata) is one such migratory animal that plays an ecologically important role in imperiled coral reef habitats. Hawksbill resource use strategies (e.g., generalism vs. specialism) in these foraging grounds are poorly understood, yet stable isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N) can provide information on the trophic niche and foraging location of consumers. Additionally, when a single sample is taken from a tissue that accretes through time, such as keratin, analyses can reveal information on the long-term foraging patterns of individuals. Here, we evaluate resource use strategies for 98 females within a nesting aggregation of hawksbills on the island of Antigua (17.159, -61.756) in the Eastern Caribbean. Stable isotope analysis of scute tissue collected from 2017 to 2019 revealed population-level generalism and varying degrees of individual specialization. Additionally, reproductive age was significantly related to niche width, with younger turtles showing higher variability in their isotopic record. Older turtles displayed overall smaller ranges in isotope values, indicating a narrowing of resource use with increased reproductive age amongst breeding adult females. These findings provide evidence of high variability in hawksbill diet, illustrate differences in ecological niche use across different ages, and highlight the necessity of evaluating multiple life stages to inform the conservation of this critically endangered species.
... areas, sometimes by hundreds or thousands of kilometers (Evans et al. 2019;van Dam et al. 2008). Hawksbill turtles are often characterized as having some of the shortest (<500 km) reproductive migrations compared to other sea turtle species (Troëng et al. 2005;Horrocks et al. 2011;Gaos et al. 2012;Moncada et al. 2012;Hays and Scott 2013;Martinez-Estevez et al. 2021;Maurer et al. 2024) and have been thought of as a local or regional resource (Horrocks et al 2011;Moncada et al. 2012). However, satellite tracking has documented long distance (>1,000 km) migrations by Caribbean hawksbills (van Dam et al. 2008;Hawkes et al. 2012;Becking et al. 2016;Nivière et al. 2018;Hart et al. 2019;Maurer et al. 2022Maurer et al. , 2024, highlighting the importance of international cooperation and management of the species. ...
... Hawksbill turtles are often characterized as having some of the shortest (<500 km) reproductive migrations compared to other sea turtle species (Troëng et al. 2005;Horrocks et al. 2011;Gaos et al. 2012;Moncada et al. 2012;Hays and Scott 2013;Martinez-Estevez et al. 2021;Maurer et al. 2024) and have been thought of as a local or regional resource (Horrocks et al 2011;Moncada et al. 2012). However, satellite tracking has documented long distance (>1,000 km) migrations by Caribbean hawksbills (van Dam et al. 2008;Hawkes et al. 2012;Becking et al. 2016;Nivière et al. 2018;Hart et al. 2019;Maurer et al. 2022Maurer et al. , 2024, highlighting the importance of international cooperation and management of the species. Flipper tag returns provided the first insight into the movement of Nevis turtles and suggested that while most stayed within close proximity of Nevis, there was some movement to foraging areas outside of the Eastern Caribbean (Horrocks et al. 2011). ...
... Similar to Maurer et al. (2022), one hawksbill did not move far from the internesting area, but only migrated to the east side of Nevis to a primary foraging area 0.9 km offshore. Turtles with an international migration crossed through 29 EEZs, similar to the 21 EEZs for turtles from Antigua reported by Maurer et al. (2024). Hawkes et al. (2012) reported tracking turtles from Dominican Republic through only seven EEZs, though the number is Content courtesy of Springer Nature, terms of use apply. ...
Little is known about the post-nesting migration and foraging areas of hawksbill turtles (Eretmochelys imbricata) nesting on St. Kitts and Nevis, an important nesting site for hawksbills in the eastern Caribbean. To elucidate internesting, migration and foraging patterns of hawksbills from Nevis, we satellite tagged 28 post-nesting turtles between 2006 and 2022. Internesting, migrating and foraging activity periods were determined using a switching state–space model to estimate the behavioral state of the turtle’s locations. Twenty-five turtles (83–2,171 tracking days) established a foraging area, migrating between 5.3 and 2,799.5 km from the nesting beach. Twenty-one turtles were tracked during internesting movements with internesting areas ranging between 1.9 and 28.2 km². Nearly half of the internesting centroids were located closer to a different beach than the beach where the turtle was originally encountered nesting. Hawksbills crossed through 29 different Exclusive Economic Zones (EEZs), including zones with legal sea turtle fisheries or traditional subsistence use. Core foraging areas (KDE 50%) ranged between 3.8 and 69.0 km². Nearly a third of foraging centroids were within a Marine Protected Area (MPA), while nearly a quarter were within a legal sea turtle fishery EEZ. Hawksbills nesting on Nevis disperse to local, regional, and Caribbean wide foraging grounds, emphasizing the necessity of cooperative efforts to protect turtles and their habitats to ensure support of the recovery of hawksbill turtles throughout the wider Caribbean.
Satellite tracking is a key tool for studying sea turtles in the wild. Most tracking has been performed on adult females however, leaving knowledge gaps regarding other population segments, such as adult males. By satellite tracking 12 male green turtles (Chelonia mydas) at a breeding site in West Africa, we describe their movements from the breeding to the foraging grounds and compare migrations with those of 13 females tracked in the same season. During the mating period, some males remained near the focal nesting site, while others performed exploratory movements, apparently to visit other nearby rookeries. Males migrated on average shorter distances to foraging grounds (377 km, range 50–1081, n = 9) compared to females (1038 km, range 957–1850, n = 11]). Importantly, male foraging areas overlapped with previously described areas for females, suggesting sex-specific migration distances are not derived from differences in habitat selection. Strong support for differential migration by sex in sea turtles has hitherto been found in just one other species, but indications are that it may be a general feature in this group. These findings have important implications for our understanding of the interplay between reproductive roles and movement ecology of these emblematic animals.
Historic over-exploitation and the more recent threats caused by fisheries by-catch, disease and climate change have left sea turtle populations in the Wider Caribbean at risk of extinction.. In 1995, following regional declines in nesting and foraging populations, the island of Anguilla implemented a moratorium on the hunting of turtles. At the request of the Government of Anguilla for scientific data to either support or remove the moratorium, comprehensive population estimates were obtained, and foraging, nesting and migratory movements were examined. In addition, community perspectives on turtles and their protection were assessed. Between 2015 and 18 surveys of 30 nesting beaches estimated low nesting activity with a maximum of 41 hawksbill, 15 green, and 1–2 leatherback turtles nesting in Anguilla annually. The inter-nesting range of hawksbills exhibited high levels of geographic overlap and occurred within 1.5 km of nesting beaches. Migratory tracks of hawksbill turtles traversed through seven exclusive economic zones, two of which allow a legal turtle fishery. Site fidelity was observed in foraging areas of green turtles and genetic analysis revealed population differentiation between green turtle foraging sites in Anguilla and between hawksbill rookeries in Anguilla compared to other Leeward Islands, indicating the individual importance of each foraging and nesting site. The Anguillan public (n = 302) overwhelmingly agreed with the current ban on harvesting sea turtles and considered turtles important for ecotourism. Our work provides a case-study, that can be applied globally, of how scientific research combined with community perspectives can effectively inform policy and ultimately protect endangered species, and highlights that local Governments provided with high quality data in a timely fashion for their policy making timetable are more likely to integrate findings into their decision-making process.
Anthropogenic disturbances affect the health of coral reefs worldwide and may also impact hawksbill (Eretmochelys imbricata) foraging areas, potentially decreasing sponge numbers, while increasing macroalgae. Few studies have been conducted to understand energy content of hawksbill prey. We investigated observed (Geodia neptuni and Kallymenia limminghii) and potential (Xestospongia muta and Halimeda opuntia) hawksbill prey abundances and their energy contents in the Sandy Bay West End Marine Reserve, and related prey distribution to hawksbill distribution within the reserve. We analysed prey abundances by conducting in‐water habitat transects followed by point count analyses. In‐water hawksbill observations were recorded to provide total times turtles foraged on prey. We then measured energy content of prey types using microbomb calorimetry. Habitat assessments indicated sponges were most abundant in West Bay and West End, whereas macroalgae were most abundant in West End. Foraging observations indicated juvenile hawksbills spent more time foraging on G. neptuni (x̅ = 236.5 s) than K. limminghii (x̅ = 98.0 s) and no time foraging on either X. muta or H. opuntia. Energy content was higher for G. neptuni (4.09 kJ g−1) and K. limminghii (12.88 kJ g−1) than X. muta (2.48 kJ g−1) and H. opuntia (1.27 kJ g−1). Hawksbills were frequently observed feeding in West Bay where sponges were abundant and were also observed foraging on K. limminghii throughout this area. Fewer hawksbills were observed in West End and Sandy Bay than in West Bay, and these areas had fewer sponges compared with West Bay. Hawksbills benefit from foraging on the abundant observed sponge and macroalgae within their home ranges, allowing them to conserve energy and increase potential net energy gains from high energy prey.
One characteristic of global change is an increase in the frequency and magnitude of algae blooms. Although a large body of work has documented severe ecological impacts, such as mortality due to toxins or hypoxia, less research has described sublethal effects that may still affect population dynamics. Here, we focus on blooming Sargassum macroalgae in the North Atlantic and describe effects on nesting sea turtles. Since 2011, large masses of the algae have been inundating Atlantic nesting habitats. We documented the accumulation of Sargassum at Long Island, Antigua, and quantified effects on a rookery of hawksbill sea turtles (Eretmochelys imbricata). Using monitoring data from 2010–2019, we analyzed population- and individual-level patterns in nesting. Our results suggest that sea turtles respond to Sargassum at nesting beaches by shifting space use away from heavily impacted areas. We also tested for an effect on nesting success, but found no change in the years and areas most impacted by Sargassum. The algae may not increase the energetic costs of nesting after a turtle has emerged onto the beach, but we speculate that costs are imposed in algae-filled waters as turtles initially seek to emerge. As the Sargassum “invasion” continues, sea turtles at impacted sites will need to exhibit plasticity when choosing nesting sites, and nest densities may increase in areas with less Sargassum present. Individuals may also be required to expend more energy per nesting season. More broadly, this work demonstrates that algae blooms can have sublethal effects on fauna that affect population dynamics.
Sea turtles present a model for the potential impacts of climate change on imperiled species, with projected warming generating concern about their persistence. Various sea turtle life-history traits are affected by temperature; most strikingly, warmer egg incubation temperatures cause female-biased sex ratios and higher embryo mortality. Predictions of sea turtle resilience to climate change are often focused on how resulting male limitation or reduced offspring production may affect populations. In the present article, by reviewing research on sea turtles, we provide an overview of how temperature impacts on incubating eggs may cascade through life history to ultimately affect population viability. We explore how sex-specific patterns in survival and breeding periodicity determine the differences among offspring, adult, and operational sex ratios. We then discuss the implications of skewed sex ratios for male-limited reproduction, consider the negative correlation between sex ratio skew and genetic diversity, and examine consequences for adaptive potential. Our synthesis underscores the importance of considering the effects of climate throughout the life history of any species. Lethal effects (e.g., embryo mortality) are relatively direct impacts, but sublethal effects at immature life-history stages may not alter population growth rates until cohorts reach reproductive maturity. This leaves a lag during which some species transition through several stages subject to distinct biological circumstances and climate impacts. These perspectives will help managers conceptualize the drivers of emergent population dynamics and identify existing knowledge gaps under different scenarios of predicted environmental change.
Climate change is a threat to marine turtles that is expected to affect all their life stages. To guide future research, we conducted a review of the most recent literature on this topic, highlighting knowledge gains and research gaps since a similar previous review in 2009. We suggest a number of research priorities for an improved understanding of how climate change may impact marine turtles, including: improved estimates of primary sex ratios, assessments of the implications of female-biased sex ratios and reduced male production, assessments on the variability in upper thermal limits of clutches, models of beach sediment movement under sea level rise, and assessments of impacts on foraging grounds. Lastly, we suggest that it is not yet possible to recommend manipulating aspects of turtle nesting ecology as the evidence-base with which to understand the results of such interventions is not robust enough, but that strategies for mitigation of stressors should be helpful, providing they consider the synergistic effects of climate change and other anthropogenic-induced threats to marine turtles, and focus on increasing resilience.
In the Gulf of Mexico, the bulk of published studies for sea turtles have focused on northern (United States) waters where economic resources are centered, with fewer studies in the southern portion of the basin, resulting in significant knowledge gaps in these underrepresented areas. Similarly, publications on adult sea turtles are dominated by research on females that come ashore to nest and can be readily studied (e.g., through the collection of biological samples and the application of satellite-telemetry devices), whereas information on adult male sea turtles is scarce. The goal of this paper is to begin filling these knowledge gaps by synthesizing available data on adult male sea turtles in the southern Gulf of Mexico. We used satellite-telemetry, boat- and drone-based surveys, and stranding records combined with ocean circulation modeling to better understand the spatial distribution of male loggerhead (Caretta caretta), green (Chelonia mydas), hawksbill (Eretmochelys imbricata), and Kemp’s ridley (Lepidochelys kempii) sea turtles in the southern Gulf of Mexico. These spatially explicit analyses will provide context for opportunistically collected data on male sea turtles and better contribute to the management and restoration of sea turtle populations that use the Gulf of Mexico. Moreover, this synthesis can serve as a launching point for directed studies on male sea turtles in this region.
The geographic specificity of natal philopatry (how precisely breeding individuals return to their natal origins) influences breeding biology, genetic diversity and habitat range, and therefore has important implications for species resiliency and management. Also, the age at which individuals reach sexual maturity and enter the breeding population is a vital parameter for demographic analyses. Empirical research on philopatry and maturation, however, is challenging for long‐lived animals that are difficult to observe, such as marine turtles that have complex oceanic life histories. Regional natal philopatry is well established for marine turtles, but the geographic specificity of philopatry is unclear. Similarly, estimates of age at maturity vary widely, and direct evidence is lacking. Here, we targeted these information gaps by assessing kinship among 256 females from Antigua’s Jumby Bay (JB) hawksbill turtle rookery, a population with demonstrated nest‐site fidelity and neophyte assimilation. We estimated mother–daughter and full sibling relationships with a maximum‐likelihood full‐pedigree reconstruction approach, incorporating genotypic (12 microsatellites), maternal genealogy (mitochondrial DNA) and age structure (long‐term mark–recapture) data. We validated relationships with parentage assignment and pairwise relatedness estimators. Fourteen veteran nesters were the mothers of 42 younger nesters, and 94 nesters formed 35 full sibships. Time between the first nesting records of mothers and their daughters indicated maximum time to maturity as short as 14 years in Caribbean hawksbills. Thirteen of the 14 mothers showed consistently high fidelity to JB for two decades, providing compelling evidence that 41 of these daughters originated from JB nests and returned to this 1‐km‐long natal site to breed. Rookeries with strongly philopatric individuals might have limited colonization potential and be at a disadvantage in the event of habitat loss. This study demonstrates the utility of long‐term mark–recapture data in kinship analyses for answering questions relevant to endangered species conservation.
For decades, fisheries have been managed to limit the accidental capture of vulnerable species and many of these populations are now rebounding. While encouraging from a conservation perspective, as populations of protected species increase so will bycatch, triggering management actions that limit fishing. Here, we show that despite extensive regulations to limit sea turtle bycatch in a coastal gillnet fishery on the eastern United States, the catch per trip of Kemp's ridley has increased by more than 300% and green turtles by more than 650% (2001–2016). These bycatch rates closely track regional indices of turtle abundance, which are a function of increased reproductive output at distant nesting sites and the oceanic dispersal of juveniles to near shore habitats. The regulations imposed to help protect turtles have decreased fishing effort and harvest by more than 50%. Given uncertainty in the population status of sea turtles, however, simply removing protections is unwarranted. Stock-assessment models for sea turtles must be developed to determine what level of mortality can be sustained while balancing continued turtle population growth and fishing opportunity. Implementation of management targets should involve federal and state managers partnering with specific fisheries to develop bycatch reduction plans that are proportional to their impact on turtles.
Patterns of animal movement associated with foraging lie at the heart of many ecological studies and often animals face decisions of staying in an environment they know versus relocating to new sites.
The lack of knowledge of new foraging sites means there is risk associated with a decision to relocate (e.g. poor foraging) as well as a potential benefit (e.g. improved foraging).
Using a unique long‐term satellite tracking dataset for several sea turtle species, combined with capture–mark–recapture data extending over 50 years, we show how, across species, individuals generally maintain tight fidelity to specific foraging sites after extended (up to almost 10,000 km) migration to and from distant breeding sites as well as across many decades.
Migrating individuals often travelled through suitable foraging areas en route to their ‘home’ site and so extended their journeys to maintain foraging site fidelity.
We explore the likely mechanistic underpinnings of this trait, which is also seen in some migrating birds, and suggest that individuals will forgo areas of suitable forage encountered en route during migration when they have poor knowledge of the long‐term suitability of those sites, making relocation to those sites risky.
Reliable population estimates are fundamental to the conservation of endangered species. We evaluate here the use of photo-identification (photo-ID) and mark-recapture techniques for estimating the population size of the endangered Saimaa ringed seal (Phoca hispida saimensis). Photo-ID data based on the unique pelage patterns of individuals were collected by means of camera traps and boat-based surveys during the molting season in two of the species’ main breeding areas, over a period of five years in the Pihlajavesi basin and eight years in the Haukivesi basin. An open model approach provided minimum population estimates for these two basins. The results indicated high survival rates and site fidelity among the adult seals. More accurate estimates can be obtained in the future by increasing the surveying effort both spatially and temporally. The method presented here proved effective for evaluating population size objectively, whereas the results of the current snow lair censuses are dependent on varying winter conditions, for instance. We therefore suggest that a photo-ID-based non-invasive mark-recapture method should be used for estimating Saimaa ringed seal abundances in order to ensure reliable, transparent population monitoring under changing climatic conditions.
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.
Over 25 years ago the first satellite tracking studies of sea turtles were published. The technology and attachment methods have now come of age with long-term tracks over a year being commonplace and the ability to relay high resolution GPS locations via the Argos satellite system along with behavioral (e.g., diving and activity) and environmental (e.g., temperature) data. Early studies focused on breeding females because they come ashore to nest, allowing individuals to be restrained relatively easily for tag attachment. However, today the development of methods for the capture of turtles at sea are increasingly allowing studies on both adult male turtles as well as immature turtles as small as 11 cm carapace length. Here we review the extent of work after many thousands of individual turtles have been tracked. We consider the state-of-the-art equipment for satellite tracking turtles and how this technology is being used to tackle key questions. We highlight some of the emerging opportunities arising from improved spatial resolution of tracking, increased robustness and miniaturization of tags as well as increasing availability of environmental data. We highlight the huge potential for big-data studies to make use of the thousands of tracks that exist, although we discuss the long-standing challenges surrounding data accessibility.
Understanding population dynamics, and how it is influenced by exogenous and endogenous factors, is important to the study and conservation of species. Moreover, for migratory species, the phenology and duration of use of a given location can also influence population structure and dynamics. For many species, breeding abundance, survival, and reproductive performance, as well as phenology of nesting, are often the most accessible, and therefore, practical elements of their life history to study. For a population of hawksbill sea turtles (Eretmochelys imbricata), we modeled population change for nesters and total adult females, survival, and breeding probability, from 25 yr of intensive tagging data. We modeled breeding probability as a function of the number of years since last breeding and tested for differences between neophyte and experienced nesters. For each year, we also estimated the number of clutches deposited per female, and phenology of use, for neophytes and experienced nesters. To implement the analysis, we developed a novel generalized multistate open robust design mark–recapture modeling framework, with parameters for survival and transition probabilities, and for each primary period, state structure and arrival, persistence, and detection probabilities. Derived parameters included abundance of observable and unobservable components of the population, residence time, expected arrival and departure periods, and per‐period intensity of study area use. Abundance of nesters increased over most of the time series. Survival probability was 0.935 ± 0.01 (estimate ± SE). Virtually all hawksbills skipped at least one year of nesting. Breeding probability increased by skipping a second year, but then decreased thereafter. Subsequent breeding probability was lower for neophyte nesters than for experienced nesters, but the effect was weaker than the effect of years since breeding. Clutch frequency varied by year, with no discernable pattern of differences between neophytes and experienced nesters. Mean arrival and departure dates also varied, with a slight shift of nesting activity to earlier in the season. The multistate open robust design model developed here provides a flexible framework for modeling the dynamics of structured migratory populations and the phenology and duration of their seasonal use of study areas.
Anthropogenic stressors are impacting ecological systems across the world. Of particular concern are the recent rapid changes occurring in coral reef systems. With ongoing degradation from both local and global stressors, future reefs are likely to function differently to current coral-dominated ecosystems. Determining key attributes of future reef states is critical to reliably predict outcomes for ecosystem service provision. Here we explore the impacts of changing sponge dominance on coral reefs. Qualitative modelling of reef futures suggests that changing sponge dominance due to increased sponge abundance will have different outcomes for other trophic levels compared with increased sponge dominance as a result of declining coral abundance. By exploring uncertainty in the model outcomes we identify the need to: i) quantify changes in carbon flow through sponges, ii) determine the importance of food limitation for sponges, iii) assess the ubiquity of the recently described 'sponge loop', iv) determine the competitive relationships between sponges and other benthic taxa, particularly algae, and v) understand how changing dominance of other organisms alters trophic pathways and energy flows through ecosystems. Addressing these knowledge gaps will facilitate development of more complex models that assess functional attributes of sponge-dominated reef ecosystems. This article is protected by copyright. All rights reserved.
Determining patterns of migratory connectivity for highly-mobile, wide-ranging species, such as sea turtles, is challenging. Here, we combined satellite telemetry and stable isotope analysis to estimate foraging locations for 749 individual loggerheads nesting along the east central Florida (USA) coast, the largest rookery for the Northwest Atlantic population. We aggregated individual results by year, identified seven foraging hotspots and tracked these summaries to describe the dynamics of inter-annual contributions of these geographic areas to this rookery over a nine-year period. Using reproductive information for a subset of turtles (n=513), we estimated hatchling yields associated with each hotspots. We found considerable inter-annual variability in the relative contribution of foraging areas to the nesting adults. Also reproductive success differed among foraging hotspots; females using southern foraging areas laid nests that produced more offspring in all but one year of the study. These analyses identified two high priority areas for future research and conservation efforts: the continental shelf adjacent to east central Florida and the Great Bahama Bank, which support higher numbers of foraging females that provide higher rates of hatchling production. The implementation of the continuous-surface approach to determine geographic origins of unknown migrants is applicable to other migratory species.
We document a tendency for published estimates of population size in sea turtles to be increasing rather than decreasing across the globe. To examine the population status of the seven species of sea turtle globally, we obtained 299 time series of annual nesting abundance with a total of 4417 annual estimates. The time series ranged in length from 6 to 47 years (mean, 16.2 years). When levels of abundance were summed within regional management units (RMUs) for each species, there were upward trends in 12 RMUs versus downward trends in 5 RMUs. This prevalence of more upward than downward trends was also evident in the individual time series, where we found 95 significant increases in abundance and 35 significant decreases. Adding to this encouraging news for sea turtle conservation, we show that even small sea turtle populations have the capacity to recover, that is, Allee effects appear unimportant. Positive trends in abundance are likely linked to the effective protection of eggs and nesting females, as well as reduced bycatch. However, conservation concerns remain, such as the decline in leatherback turtles in the Eastern and Western Pacific. Furthermore, we also show that, often, time series are too short to identify trends in abundance. Our findings highlight the importance of continued conservation and monitoring efforts that underpin this global conservation success story.
The management of small rookeries is key to conserving the regional genetic diversity of marine turtle populations and requires knowledge on population connectivity between breeding and foraging areas. To elucidate the geographic scope of the populations of marine turtles breeding at Bonaire and Klein Bonaire (Caribbean Netherlands) we examined the post-breeding migratory behavior of 5 female loggerheads Caretta caretta, 4 female green turtles Chelonia mydas, and 2 male and 13 female hawksbill turtles Eretmochelys imbricata during the years 2004-2013. After leaving Bonaire, the 24 tracked turtles frequented foraging grounds in 10 countries. The distances swum from Bonaire to the foraging areas ranged from 608 to 1766 km for loggerhead turtles, 198 to 3135 km for green turtles, and 197 to 3135 km for hawksbill turtles, together crossing the waters of 19 countries. Males represented the minority in this study, but we made 2 key observations that require further research: males remained in the vicinity of the breeding area for 3-5 mo, which is 2-5 times longer than females, and males migrated greater distances than previously recorded. Although the turtles dispersed widely across the Caribbean, there appeared to be 2 benthic foraging areas of particular importance to all 3 species of marine turtles breeding at Bonaire, namely the shallow banks east of Nicaragua and Honduras (n = 8 tracked turtles) and Los Roques, Venezuela (n = 3). Marine turtles breeding at Bonaire face threats from legal turtle harvesting, illegal take, and bycatch in the waters that they traverse across the Caribbean
State-space models provide a powerful way to scale up inference of movement behaviours from individuals to populations when the inference is made across multiple individuals. Here, I show how a joint estimation approach that assumes individuals share identical movement parameters can lead to improved inference of behavioural states associated with different movement processes. I use simulated movement paths with known behavioural states to compare estimation error between nonhierarchical and joint estimation formulations of an otherwise identical state-space model. Behavioural state estimation error was strongly affected by the degree of similarity between movement patterns characterising the behavioural states, with less error when movements were strongly dissimilar between states. The joint estimation model improved behavioural state estimation relative to the nonhierarchical model for simulated data with heavy-tailed Argos location errors. When applied to Argos telemetry datasets from 10 Weddell seals, the nonhierarchical model estimated highly uncertain behavioural state switching probabilities for most individuals whereas the joint estimation model yielded substantially less uncertainty. The joint estimation model better resolved the behavioural state sequences across all seals. Hierarchical or joint estimation models should be the preferred choice for estimating behavioural states from animal movement data, especially when location data are error-prone.
Worldwide, migratory species are undergoing rapid declines but understanding the factors driving these declines is hindered by missing information about migratory connectivity and the lack of data to quantify environmental processes across the annual cycle. Here, we combined range-wide information about migratory connectivity with global remote-sensing data to quantify the relative importance of breeding and non-breeding environmental processes to persistent long-term population declines of a migratory songbird, the wood thrush (Hylocichla mustelina). Consistent with theoretical predictions about population limitation of migratory birds, our results suggest that habitat loss and climate have contributed to the observed declines in wood thrush breeding abundance, yet the relative importance of breeding versus non-breeding factors is population-specific. For example, high-abundance core breeding populations appear to be more limited by habitat loss, whereas low-abundance, peripheral populations appear to be limited by climate-driven seasonal interactions. Further, our analysis indicates that the relative impact of breeding habitat loss is at least three to six times greater than the impact of equivalent nonbreeding habitat loss and therefore the steepest regional declines have likely been driven by the loss of breeding habitat. These results underscore the need for population-specific conservation strategies implemented throughout the annual cycle to reverse long-term declines. © 2016 The Author(s) Published by the Royal Society. All rights reserved.
For seasonal migrants, logistical constraints have often limited conservation efforts to improving survival and reproduction during the breeding season only. Yet, mounting empirical evidence suggests that events occurring throughout the migratory life cycle can critically alter the demography of many migrant species. Herein, we build upon recent syntheses of avian migration research to review the role of non-breeding seasons in determining the population dynamics and fitness of diverse migratory taxa, including salmonid fishes, marine mammals, ungulates, sea turtles, butterflies, and numerous bird groups. We discuss several similarities across these varied migrants: (i) non-breeding survivorship tends to be a strong driver of population growth; (ii) non-breeding events can affect fitness in subsequent seasons through seasonal interactions at individual- and population-levels; (iii) broad-scale climatic influences often alter non-breeding resources and migration timing, and may amplify population impacts through covariation among seasonal vital rates; and (iv) changes to both stationary and migratory non-breeding habitats can have important consequences for abundance and population trends. Finally, we draw on these patterns to recommend that future conservation research for seasonal migrants will benefit from: (1) more explicit recognition of the important parallels among taxonomically diverse migratory animals; (2) an expanded research perspective focused on quantification of all seasonal vital rates and their interactions; and (3) the development of detailed population projection models that account for complexity and uncertainty in migrant population dynamics.
Despite being critically endangered, the at-sea behaviour of hawksbill turtles (Eretmochelys imbricata) remains insufficiently understood to support a global conservation strategy. Habitat location and spatial use are poorly documented, which is particularly true for the globally important Australian hawksbill population. We equipped 10 adult female hawksbill turtles nesting on Groote Eylandt, northern Australia, with Fastloc GPS and Argos satellite transmitters. We quantified fine-scale habitat use and area-restricted search behaviour, and located potential feeding and developmental habitats by simulating hatchling turtle dispersal patterns by using a particle-tracking hydrological model. During the breeding season, females mostly remained near their nesting site. Post-breeding, all turtles migrated to foraging sites on the Australian continental shelf, primarily in the Gulf of Carpentaria in coastal seagrass pastures, but also offshore near coral-reef platforms. The distribution of adult foraging grounds was similar to simulated dispersal patterns of hatchling turtles from distant rookeries, thus highlighting the ecological significance of the Gulf of Carpentaria for hawksbill turtles. Although this hawksbill turtle population is likely to be endemic to Australian waters, national and international conservation initiatives are required to mitigate sources of anthropogenic mortality (e.g. illegal tortoise-shell trade, incidental captures in fishing gear, marine debris, seabed mining exploitation).
Female sea turtles have rarely been observed foraging during the nesting season. This suggests that prior to their migration
to nesting beaches the females must store sufficient energy and nutrients at their foraging grounds and must be physiologically
capable of undergoing months without feeding. Leptin (an appetite-suppressing protein) and ghrelin (a hunger-stimulating peptide)
affect body weight by influencing energy intake in all vertebrates. We investigated the levels of these hormones and other
physiological and nutritional parameters in nesting hawksbill sea turtles in Rio Grande do Norte State, Brazil, by collecting
consecutive blood samples from 41 turtles during the 2010–2011 and 2011–2012 reproductive seasons. We found that levels of
serum leptin decreased over the nesting season, which potentially relaxed suppression of food intake and stimulated females
to begin foraging either during or after the post-nesting migration. Concurrently, we recorded an increasing trend in ghrelin,
which may have stimulated food intake towards the end of the nesting season. Both findings are consistent with the prediction
that post-nesting females will begin to forage, either during or immediately after their post-nesting migration. We observed
no seasonal trend for other physiological parameters (values of packed cell volume and serum levels of alanine aminotransferase,
aspartate aminotransferase, alkaline phosphatase, γ-glutamyl transferase, low-density lipoprotein, and high-density lipoprotein).
The observed downward trends in general serum biochemistry levels were probably due to the physiological challenge of vitellogenesis
and nesting in addition to limited energy resources and probable fasting.
Hawksbill sea turtles, Eretmochelys imbricata, reside around the main Hawaiian Islands but are not common. Flipper-tag recoveries and satellite tracking of hawksbills worldwide have shown variable distances in post-nesting travel, with migrations between nesting beaches and foraging areas ranging from 35 to 2,425 km. Nine hawksbill turtles were tracked within the Hawaiian Islands using satellite telemetry. Turtles traveled distances ranging from 90 to 345 km and took between 5 to 18 days to complete the transit from nesting to foraging areas. Results of this study suggest that movements of Hawaiian hawksbills are relatively short-ranged, and surveys of their foraging areas should be conducted to assess status of the habitat to enhance conservation and management of these areas.
Understanding spatial and temporal habitat-use patterns to protect both foraging and breeding grounds of species of concern is crucial for successful conservation. Saona Island in Del Este National Park (DENP), southeastern Dominican Republic (DR), hosts the only major hawksbill (Eretmochelys imbricata) nesting area in the DR (100 nests/year, SD = 8.4, range = 93-111), with the population having been critically reduced through hunting. We satellite tracked nine female hawksbill turtles and present analyses of their core-use areas with respect to Marine Protected Areas both in their internesting and foraging areas. Kernel utilization distributions indicated that during the internesting period all turtles remained close to their nesting beaches in small home ranges in the territorial waters of DR, mostly over the continental shelf (<200 m depth). Common core-use areas were located inside the DENP and 82.7 % of all locations were within the DENP. At foraging areas, only 23 % of locations were inside MPAs either in waters of the DR and in waters of Bahamas, Nicaragua and Honduras. Our results highlight that the protected areas of the DR are key for hawksbill conservation, and enforcement of existing legislation of the protected areas in the country is key. The present study also corroborates that the waters off Nicaragua and Honduras are exceptionally important foraging areas for hawksbills in the Caribbean, showing the turtle’s vulnerability in these waters.
Satellite transmitters were deployed on three green turtles, Chelonia mydas, and two hawksbill turtles, Eretmochelys imbricata, nesting in the Lesser Antilles islands, Caribbean, between 2005 and 2007 to obtain preliminary information about the inter-nesting, migratory and foraging habitats in the region. Despite the extremely small dataset, both year-round residents and migrants were identified; specifically, (1) two green turtles used local shallow coastal sites within 50 km of the nesting beach during all of their inter-nesting periods and then settled at these sites on completion of their breeding seasons, (2) one hawksbill turtle travelled 200 km westward before reversing direction and settling within 50 km of the original nesting beach and (3) one green and one hawksbill turtle initially nested at the proximate site, before permanently relocating to an alternative nesting site over 190 km distant. A lack of nesting beach fidelity was supported by flipper tag datasets for the region. Tagging datasets from 2002 to 2012 supported that some green and hawksbill individuals exhibit low fidelity to nesting beaches, whereas other females exhibited a high degree of fidelity (26 turtles tagged, 40.0 km maximum distance recorded from original nesting beach). Individual turtles nesting on St Eustatius and St Maarten appear to exhibit behavioural plasticity in their inter-nesting behaviour and post-nesting migration routes in the eastern Caribbean. The tracking and tagging data combined indicate that some of the green and hawksbill females that nest in the Lesser Antilles islands are year-round residents, whilst others may nest and forage at alternative sites. Thus, continued year-round protection of these islands and implementation of protection programmes in nearby islands could contribute towards safeguarding the green and hawksbill populations of the region.
We present the first data on hawksbill turtle post-nesting migrations and behaviour in the Arabian region. Tracks from 90 post-nesting turtles (65 in the Gulf and 25 from Oman) revealed that hawksbills in the Arabian region may nest up to 6 times in a season with an average of 3 nests per turtle. Turtles from Qatar, Iran and the UAE generally migrated south and southwest to waters shared by the UAE and Qatar. A smaller number of turtles migrated northward towards Bahrain, Saudi Arabia and one reached Kuwait. Omani turtles migrated south towards Masirah island and to Quwayrah, staying close to the mainland and over the continental shelf. The widespread dispersal of hawksbill foraging grounds across the SW Gulf may limit habitat protection options available to managers, and we suggest these be linked to preservation of shallow water habitats and fishery management. In contrast, the two main foraging areas in Oman were small and could be candidates for protected area consideration. Critical migration bottlenecks were identified at the easternmost point of the Arabian Peninsula as turtles from Daymaniyat Islands migrate southward, and between Qatar and Bahrain. Overall, Gulf turtles spent 68% of the time in foraging ground with home ranges of 40–60 km2 and small core areas of 6 km2. Adult female turtles from Oman were significantly larger than Gulf turtles by ~ 11 cm x¯=81.4CCL and spent 83% of their time foraging in smaller home ranges with even smaller core areas (~ 3 km2), likely due to better habitat quality and food availability. Gulf turtles were among the smallest in the world x¯=70.3CCL and spent an average of 20% of time undertaking summer migration loops, a thermoregulatory response to avoid elevated sea surface temperatures, as the Gulf regularly experiences sustained sea surface temperatures > 30 °C. Fishery bycatch was determined for two of the 90 turtles. These spatio-temporal findings on habitat use will enable risk assessments for turtles in the face of multiple threats including oil and gas industries, urban and industrial development, fishery pressure, and shipping. They also improve our overall understanding of hawksbill habitat use and behaviour in the Arabian region, and will support sea turtle conservation-related policy decision-making at national and regional levels.
We evaluated selective feeding in hawksbill turtles Eretmochelys imbricata by comparing ingested prey species with their availability at 2 sites in the SW Dominican Republic. Hawksbills fed on 6 benthic species: 5 demosponges (Chondrilla nucula, Geodia neptuni, Myriastra kalitetilla, Spirastrella coccinea, and Tethya crypta) and 1 corallimorpharian (Ricordea florida). Hawksbills showed positive selection for 4 species (from highest to lowest): S. coccinea, R. florida, and C. nucula at Bahia de las Aguilas, and M, kalitetilla and C. nucula at Cabo Rojo. S. coccinea and M. kalitetilla are rare in the environment and highly selected by hawksbills, which supports a previous observation that their distribution on reefs could be greatly affected by spongivores. The 2 remaining selected species were the dominant prey species in lavage samples (R. florida = 59% and C. nucula = 34% of total volume). Since they were the most abundant species at each site, this illustrates that diet choice is based on a combination of selectivity for certain species and local abundance. The dominance of R. florida in the diet challenges the prevailing view that Caribbean hawksbills are strict spongivores. Finally, our results indicate that hawksbills can have a positive indirect effect on corals by grazing on coral competitors, as well as affect overall reef benthic biodiversity. Both C. nucula and R. florida harbor photosynthesizing symbionts and are aggressive competitors for space on tropical reefs. Thus, at natural population levels, grazing by hawksbills may well have played an important role in Caribbean reef structure and dynamics. Because hawksbill populations have been substantially reduced (to at most 10% of pre-Columbian population levels) their effect has been considerably diminished.
Detailed post-breeding movement data is presented for hawksbill turtles tracked by satellite telemetry from Mona Island, Puerto Rico. Seven nesting females and 8 breeding males were tracked. Females traveled for 3 to 53 d to reach their foraging grounds, swimming distances of 84 to 2051 km (mean 867 km, n = 7) at average speeds of 23.5 to 38.7 km d-1(n = 7). Males traveled for <1 to 22 d, covering distances of <2 to 476 km (mean 101 km, n = 8) at average speeds of 13.0 to 24.7 kmd-1 (n = 5). One of the tracked males remained at the Mona Island breeding grounds for 11 mo before being recaptured there. The migration of 2 other male hawksbill turtles returning to Mona Island the following year from their foraging grounds was also documented. Descriptions of the foraging habitats used by these adult turtles are provided. The significant difference observed in migratory range between males and females are interpreted in an evolutionary context of food abundance predictability, an alternative hypothesis of geographic variation in mortality rates is also considered.
Energy storage is an important component of life-history variation. Some organisms ("income breeders") fuel reproductive expenditure by simultaneous feeding, whereas others ("capital breeders") fuel reproduction from energy gained earlier, and stored prior to use. Most published discussions of this topic have focused primarily on endothermic animals (birds and mammals), and have interpreted the costs and benefits of these alternative breeding tactics in the context of endothermy. The far more diverse array of ectothermic animals has received less attention in this respect. Many features associated with ectothermy preadapt organisms to store energy for long periods prior to use (i.e. to rely on "capital" rather than "income"). For example, birds and mammals experience high costs (in terms of mobility and thermoregulatory efficiency) if they store large body reserves. By contrast, the energetic and demographic costs associated with storage, maintenance, and utilisation of body reserves are low in many ectotherms. Thus, capital breeding (which may also be more efficient energetically in many situations) is extremely common in these low energy systems. Ectotherms comprise the most extreme examples of capital breeders, with a strong tendency towards semelparity where the capital of reserves is massively invested into a single reproductive event. Overall, theoretical and empirical studies of the evolution of capital versus income breeding as alternative strategies of resource use should take account of the important role played by alternative thermoregulatory and metabolic systems. The acquisition of endothermy in avian and mammalian lineages has involved a massive shift towards reliance on "income breeding", and the full spectrum of life-history variation in this respect cannot be appreciated without detailed examination of ectothermic organisms.
Four post-nesting hawksbill turtles (Eretmochelys imbricata) in Barbados were fitted with satellite transmitters during the 1998 nesting season as part of a Caribbean-wide hawksbill research satellite tracking project to investigate whether adult females may undertake long-distance migrations between their nesting and foraging sites. The four study animals left Barbados waters immediately following their final nesting activity for the season and travelled for periods of between 7 and 18 days to reach foraging grounds in Dominica, Grenada, Trinidad, and Venezuela, respectively. Straight-line travel distances ranged from 200 to 435 km. All animals seemed to be influenced by water depth and geostrophic currents along their migration routes. The turtles generally travelled through shallower waters provided this did not result in travel against significant currents. In places where the turtles encountered currents moving in the desired direction of travel, their travel speeds increased markedly. Foraging home range sizes varied between 1.96-49.5 km2 and were positively correlated with the average water depth, suggesting that turtles residing in deep water foraging areas may have to forage over larger areas to obtain sufficient food resources. All turtles settled at locations where sea conditions made them relatively inaccessible to fishermen, and this may be a key to their survival in countries where turtle fishing is permitted. The data indicate that adult females nesting in Barbados, where they are fully protected, may spend the majority of their lives in waters where they are only partially protected or unprotected.
Effective management of migratory sea turtles requires informed and sustained collaboration among range states. The primary objective of the Wider Caribbean Sea Turtle Conservation Network's regional Marine Turtle Tagging Centre at the University of the West Indies, Barbados, has been to encourage and enable such collaboration, uniting otherwise isolated sea turtle tagging programs to benefit from information on the geographic range of sea turtles tagged in one country and captured, sighted, or stranded in another country. We present the first summary of information gleaned from international tag returns of adult female hawksbill sea turtles (Eretmochelys imbricata) marked with Marine Turtle Tagging Centre tags. Twenty-one sea turtle projects in 19 countries and overseas territories received Inconel 1005–681 tags from the Marine Turtle Tagging Centre between January 2002 and June 2009, and 12 of these projects have reported tagging adult female hawksbills, for a combined total of 2261 tagged individuals. Sixty-three of these individuals (2.8%), sighted at least once in another country since being tagged, have been reported to the Marine Turtle Tagging Centre; the majority of them (96.8%) were originally tagged while they were nesting in Barbados. Based on minimum straight-line distance traveled, the point of capture averaged 343.9 ± 69.7 km standard error (SE), (median 175 km) from the nesting beach. The average number of days between tagging and the first recapture was 835 ± 67.9 days SE, median 860 days). Although the majority of returns came from within a few hundred kilometers of the tagging site, tagged animals often passed through multiple exclusive economic zones and were exposed to conflicting management regimes, which include legal and illegal sea turtle fisheries. The shallow continental shelf off the coasts of Nicaragua and Honduras was confirmed as a foraging ground for Eastern Caribbean hawksbills.
Management of the critically endangered hawksbill turtle in the Wider Caribbean (WC) has been hampered by knowledge gaps regarding stock structure. We carried out a comprehensive stock structure re-assessment of 11 WC hawksbill rookeries using longer mtDNA sequences, larger sample sizes (N = 647), and additional rookeries compared to previous surveys. Additional variation detected by 740bp sequences between populations allowed us to differentiate populations such as Barbados-Windward and Guadeloupe (F (st) = 0.683, P < 0.05) that appeared genetically indistinguishable based on shorter 380bp sequences. POWSIM analysis showed that longer sequences improved power to detect population structure and that when N < 30, increasing the variation detected was as effective in increasing power as increasing sample size. Geographic patterns of genetic variation suggest a model of periodic long-distance colonization coupled with region-wide dispersal and subsequent secondary contact within the WC. Mismatch analysis results for individual clades suggest a general population expansion in the WC following a historic bottleneck about 100 000-300 000 years ago. We estimated an effective female population size (N (ef)) of 6000-9000 for the WC, similar to the current estimated numbers of breeding females, highlighting the importance of these regional rookeries to maintaining genetic diversity in hawksbills. Our results provide a basis for standardizing future work to 740bp sequence reads and establish a more complete baseline for determining stock boundaries in this migratory marine species. Finally, our findings illustrate the value of maintaining an archive of specimens for re-analysis as new markers become available.
Data on hawksbill Eretmochelys imbricata migratory patterns are virtually unknown for nesting populations in the South Atlantic Ocean. The most significant nesting ground for hawksbills in the South Atlantic is located in Brazil, specifically in the northern state of Bahia. From February to March 2005, 15 adult female hawksbills were equipped with satellite transmitters on beaches of northern Bahia. During the internesting period, satellite-tracked hawksbills remained in the coastal waters of northern Bahia for 12 to 60 d before embarking on their postnesting migrations. Internesting areas occupied by the turtles varied between 43.1 and 447.9 km². Turtles’ postnesting migrations were performed mostly over the continental shelf: 5 headed south, and 8, north. Results from genetic analyses of tracked turtles showed that 6 of the individuals, characterized morphologically as hawksbills, were actually hawksbill-loggerhead hybrids. Foraging destinations of hawksbills were situated along the eastern coast of Brazil (9 to 17.5°S). Conversely, except for 1 hybrid that stayed along the eastern coast, hybrid turtles migrated to distant foraging areas located on the northern coast of Brazil (0 to 5°S). Foraging home range areas of satellite-tracked turtles ranged from 225.7 to 2192.3 km², and there were no significant differences in size between areas used by hawksbills and those used by hybrids. The location of hawksbill foraging areas partially overlapped with established marine protected areas (MPAs) distributed along the main reef areas in Brazil. These results underscore the importance of strengthening MPA monitoring and enforcement to protect critical hawksbill habitats in Brazil.
Cite this article as: Marcovaldi MÂ, Lopez GG, Soares LS, López-Mendilaharsu M (2012) Satellite tracking of hawksbill turtles Eretmochelys imbricata nesting in northern Bahia, Brazil: turtle movements and foraging destinations. Endang Species Res 17:123-132
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We generalize the method proposed by Gelman and Rubin (1992a) for monitoring the convergence of iterative simulations by comparing between and within variances of multiple chains, in order to obtain a family of tests for convergence. We review methods of inference from simulations in order to develop convergence-monitoring summaries that are relevant for the purposes for which the simulations are used. We recommend applying a battery of tests for mixing based on the comparison of inferences from individual sequences and from the mixture of sequences. Finally, we discuss multivariate analogues, for assessing convergence of several parameters simultaneously.
Adult female sea turtles are highly migratory, moving between foraging and nesting areas that can be thousands of kilometers apart. Conserving sea turtles and their habitats therefore depends on knowledge of space use across these migration-linked environments. Here, we describe migratory behavior of hawksbill sea turtles (Eretmochelys imbricata), a globally imperiled species. We used satellite telemetry to characterize the movements of females from nesting areas in Jamaica (n = 4) and Antigua (n = 4), West Indies, over 1998–2001. We mapped migrations and summarized space use during inter-nesting and foraging periods with kernel utilization distributions (UDs) and minimum convex polygons. Seven of eight turtles made post-nesting migrations, with paths ranging 56–1324 km in length, representing straight-line displacements of 68–1206 km. Two turtles sampled in southern Jamaica made short-range migrations within southern Jamaican waters, whereas two from northern Jamaica migrated further to foraging areas in the waters of Belize and Honduras. Three migrants sampled at Long Island, Antigua migrated to St. Eustatius, St. Kitts, and Redonda, respectively, with a fourth individual remaining resident in northeastern Antigua. Inter-nesting movements observed for three turtles produced 50% UDs ranging 12–44 km2, with centroid depths between 4–13 m. Foraging UDs for seven turtles spanned 8–111 km2 and 2–161 m in depth. Our results reveal variable migratory strategies, demonstrate international connectivity between hawksbill foraging and nesting habitats, and provide important information for Caribbean conservation efforts such as the design of protected areas or fisheries policies.
Global environmental change has featured a rise in macroalgae blooms. These events generate immense amounts of biomass that can subsequently arrive on shorelines. Such a scenario has been playing out since 2011 in the tropical and subtropical Atlantic, where Sargassum spp. have been causing periodic ‘golden tides’ in coastal habitats. Here we describe impacts on sea turtle nesting ecology, with a focus on the below-ground thermal environment for incubating eggs. Sargassum may blanket the surface of beaches due to natural wave or wind energy and can be redistributed via anthropogenic beach cleaning. When it covers egg clutches, it may alter incubation temperatures and therefore affect both embryonic survival and primary sex ratios. To evaluate the thermal impacts of Sargassum, we measured sand temperatures with data loggers buried under Sargassum cover treatments on a beach in Antigua, West Indies. Our split-plot experiment also tested for effects from shade, season (summer versus autumn), and high rainfall events. We modeled temperatures with a mixed-effects model and, surprisingly, our most compelling finding suggested that Sargassum's effects on below-ground temperatures were contingent on season. Greater Sargassum cover was associated with a cooling effect in the summer but warming in the autumn. We assume that the model term for season integrates several climate-related factors that vary seasonally in the Eastern Caribbean and modulate Sargassum's impact, including windspeeds. Comparing estimated marginal means for the high-cover treatments versus the controls, Sargassum cover led to a 0.21 °C increase in the autumn and a 0.17 °C decrease in the summer; these thermal changes can significantly impact developmental outcomes for sea turtle embryos. Atlantic nesting beach managers should monitor this macroalgal phenomenon and can use these data to begin to infer impacts on sea turtle populations and develop potential management strategies.
ContextHawksbill sea turtles (Eretmochelys imbricata) are conservation-dependent species in many areas of the world. A key component to ensuring successful conservation initiatives for the species is understanding their distribution and habitat use, in particular, knowing the nesting sites, migration routes and foraging areas for each genetic stock, and how these might overlap with threats. AimsInvestigate the post-nesting movements of hawksbill sea turtles nesting in the Torres Strait, including migration movements and foraging ground size and distribution. Methods
Nine nesting hawksbill turtles of the north-eastern Australian genetic stock were satellite-tagged between the 2010 and 2019 nesting seasons for 182 ± 143 days (mean ± s.d.). Key resultsThree turtles continued to nest on adjacent islands before commencing their post-nesting migrations. From the nine tracked turtles, the following three migration movement strategies were identified: (1) direct migration between the nesting beach and foraging ground, (2) non-direct movements with a period of meandering, and (3) establishment of two foraging areas separated by direct movement pathways. Foraging grounds were distributed across the Torres Strait and north-eastern Australia and varied in size between 0.54 km2 and 3.31 km2 (95% UD). None of the turtles migrated outside of Australian waters. Conclusions
The localisation of these movements and habitats within Australian waters provides a unique conservation opportunity, whereby protection efforts involve multiple life stages and potentially preserve turtles from multiple genetic stocks. The variety of inter-nesting, migration and home range strategies used by the tracked turtles in the present study highlight the broad scope of hawksbill movements. ImplicationsOur findings are useful for the implementation of future marine conservation areas and shed light into the nesting, migratory and foraging behaviours of hawkbills from this genetic stock. An understanding of the movement tracks and habitats used by a genetic pool is essential for well grounded implementation of conservation areas and management regulations.
Environmental conditions experienced by animals constrain their energy acquisition and its subsequent allocation to growth and reproduction, which ultimately contributes to population dynamics. Understanding how environmental conditions affect these physiological processes is therefore important for predicting how threatened species will respond to altered food and temperature conditions. Here we use a mechanistic modelling approach based on Dynamic Energy Budget (DEB) theory to demonstrate that changing food availability has a strong impact on growth and reproduction for a Western Australian population of green sea turtles (Chelonia mydas), particularly in scenarios with simulated marine heatwaves. Models predicted increasing time between nesting years in scenarios of decreasing food availability. Furthermore, increased frequency of marine heatwaves reduced reproductive output with the number of eggs a female produced in its lifetime predicted to be approximately 20% lower when heatwaves occurred every five years compared to every 20 years. Our predictions suggest that frequent marine heatwaves could have similar adverse effects to long-term decreases in food availability. In all scenarios, direct impacts of changes in temperature were less pronounced and suggest that the strongest impacts of the increasing temperatures of climate change will be mediated through food availability. The approach demonstrated here provides a strong foundation for understanding how the Ningaloo C. mydas population will respond to climate change, and can be refined as new physiological, behavioural, and environmental data become available.
Marine turtles migrate back to their natal region during reproduction, but the precision of this homing behavior and how the precision varies among populations and across biogeographic regions are unclear. We hypothesize that marine turtles nesting on insular landmasses navigate to their rookeries with greater precision than those nesting on continuous coastlines. We analyzed new mitochondrial and microsatellite marker data from hawksbill turtles Eretmochelys imbricata at nesting sites across Antigua and Barbuda, West Indies, to assess the scale of natal homing in the highly insular Leeward Islands. We then used published data from 15 western Atlantic rookeries to examine regional patterns of rookery structure. Mitochondrial control region data showed weak to no partitioning among nesting sites within Antigua and strong partitioning between Antigua and Barbuda, suggesting natal homing at a scale of 50 km. Microsatellite data showed weak to no partitioning between sites, indicating male-mediated gene flow. Regionally, we found stronger population structuring among rookeries of insular landmasses than among those of larger landmasses with continuous coastlines, despite shorter average rookery separation for the former. We also found a positive relationship between a rookery’s isolation index (a metric incorporating distances from larger landmasses) and its genetic divergence from proximate rookeries. These findings support our hypothesis, and we caution that insular rookeries that host marine turtles with extreme homing behavior have limited ability to colonize new nesting habitat. The unprecedented rates of development and increasing instability of present-day nesting habitat might therefore pose a greater and increasing threat to insular rookeries.
New observations are summarized that lead to the first comprehensive description of the mean inflow distribution in the passages connecting the Atlantic Ocean with the Caribbean Sea. The total Caribbean inflow of is shown to be partitioned approximately equally between the Windward Islands Passages (∼ ), Leeward Islands Passages (∼ , and the Greater Antilles Passages (∼ . These results are compared to a numerical model study using a 6-layer, 1/4° resolution Atlantic Basin version of the NRL Layered Ocean Model. Results from two simulations are described, including a purely wind-forced model driven by Hellerman and Rosenstein (J. Phys. Oceanogr. 13 (1983) 1093) monthly winds, and a model with an additional 14 Sv meridional overturning cell driven by inflow/outflow ports at the northern (65°N) and southern (20°S) model boundaries. The purely wind-driven version of the model exhibits a total Caribbean inflow of , consistent with expectations from steady, non-topographic Sverdrup theory. Nearly all of the wind-driven inflow occurs north of Martinique at latitude ∼15°N. The net transport through the Lesser Antilles passages south of 15°N (Grenada, St. Vincent, and St. Lucia passages) is nearly zero when the model is forced by winds alone. The addition of a meridional cell in the model increases the net Caribbean inflow to , with nearly all of the additional 11 Sv of inflow entering through the southern Lesser Antilles passages. The modeled inflow distribution resulting from the combined wind and overturning forced experiment is found to compare favorably with the observations.
Feeding-ground captures of green (Chelonia mydas) and loggerhead (Caretta caretta) turtles tagged while
nesting at eastern Australian rookeries over a 21-year period are summarised.
These turtles which nest in the Great Barrier Reef region range widely throughout the Arafura and
Coral seas. The tag recoveries include many from turtles that live in neighbouring countries and migrate
to breed in Australia. The breeding female shows a high fidelity to her home feeding ground as well
as to her nesting beach. Most recaptures of the green turtles occurred during hunting for food by
indigenous people while most recaptures of loggerhead turtles were incidental captures in commercial
fishing activities. Migratory behaviour, imprinting and navigation are discussed.
Adult female hawksbill turtles, Eretmochelys imbricata, return periodically and with surprising predictability to nest on a single beach in Antigua, West Indies. This consistent behavior has provided a window of opportunity for measuring several elusive parameters such as survival and recruitment, essential for population modeling. A total of 126 females have been identified after 11 seasons of saturation tagging surveys (1987-97). Seasonal nesting cohorts ranged from 22 to 38 individuals. The mean remigration interval for an individual was 2.69 years. The total number of reproductively active females in the population was estimated to be 78 animals, out of which 29 animals (37%) remigrated to nest each season on average. The appearance of 6.9 (range 4-11) new animals each season was considered to be recruitment, representing approximately 9% of the estimated adult female population. The permanent disappearance of 4.8 individuals per year was taken as a best estimate of mortality, represent- ing approximately 6% of the adult female population. An average female laid 5 clutches of 155 eggs per clutch during a nesting season, depositing 775 eggs with roughly 75% emergence success. This equates to an average production of 288 eggs/female per year. Mean survival of adult females was estimated to be 8.1 years of reproductive activity, during which an average female produced 3100 eggs during 4.1 nesting seasons. Recruitment predicted from estimates of fecundity was 5.4 new animals per season, close to the 6.9 new animals observed per season. With a reproductive rate of 288 eggs/year, an adult female must be allowed to reproduce for at least 9 years (4.1 nesting seasons/individual) to replace herself, and some animals must continue to be reproductively active for several decades or more to balance the early mortality of other individuals. The hawksbill's Critically Endangered status is logically the result of adult females not being provided the long term protection they evidently need to maintain population numbers.