Turtle Natator Depressus Research Articles

Predation rates on flatback turtle Natator depressus eggs and hatchlings at an island rookery

Predation can significantly threaten the vulnerable egg and hatchling stages of sea turtles, yet for most populations this remains poorly quantified for use in conservation. We provided the first quantified predation rates of flatback turtle eggs and hatchlings at Thevenard Island, a medium-sized rookery on the northwest coast of Australia, with a focus on ghost crabs as potential predators. Burrow densities were used as proxy for ghost crab densities, while start- and end-of-season nest inventories and infrared videography were used to quantify egg and hatchling predation, respectively. Inventories of 27 nests suggested a mean hatching success of 74.2 ± 4.6% with zero predation of eggs, while videography at 17 nests indicated that 30.1 ± 8.1% of emerged hatchlings were predated, mainly by ghost crabs. Females selecting nest locations not easily accessible to ghost crabs, or the composition of flatback’s eggshells may explain the lack of egg predation. A 44.0% egg-to-surf survival rate was estimated, almost double the rate estimated for C. caretta on the Ningaloo coast (24.4%) using similar techniques. Further work is needed to understand if those predation rates are sustainable for recovering threatened species and if mitigation efforts tailored to each species and each life stage are needed.

Identifying impactful sea turtle conservation strategies: a mismatch between most influential and most readily manageable life-stages

Sea turtles worldwide face a range of threats including sea level rise and warming associated with climate change, predation by invasive species, plastic and light pollution, coastal development, and human interference. Conservation managers have a long history of aiding sea turtle populations, from protecting nests to head-starting hatchlings. Due to these challenges faced by turtles, there is a constant focus on assessing the likely success of proposed conservation interventions to help inform decision-making processes. We develop an age-based, spatially implicit population model for the north-west shelf stock of Australia’s endemic flatback turtle Natator depressus that estimates the long-term outcomes of a range of onshore and offshore conservation interventions. Analysis of the model shows that young adults contribute most to population growth (i.e. have highest expected future reproductive success); however, this is often the most difficult life stage to manipulate in the field. Observable outcomes of interventions are often delayed for many years, especially for on shore activities (e.g. protecting eggs and hatchlings), due to late age to maturity. The potential impact of warming-induced female bias on population dynamics was also investigated. Although such bias increases population growth rates in the short term, negative effects of the bias (e.g. reduced female mating success) and negative environmental effects (e.g. reduced survival rates, habitat loss) can lead to sustained declines. Population models can rapidly assess climate change and conservation impacts on turtle dynamics and can guide monitoring efforts for real-world application.

Flatback futures—evaluating conservation interventions to reduce threats to an endemic Australian turtle

Australia’s endemic flatback turtle Natator depressus is the focus of a long-term conservation program aimed at securing the persistence of healthy populations in the northwest of Australia into the future. Primary threats to flatback turtles include (1) sea level rise, (2) predation from introduced species, (3) temperature increases, (4) onshore and nearshore light, (5) marine debris, and (6) modification to beaches. Population declines resulting from these threats have been reported or are anticipated, and a range of intervention options are possible that may limit their negative impact. Following methods previously developed and applied to iconic marine species and habitats, we generated a range of intervention options, and asked experts to prioritise those actions using an intervention prioritisation tool (IPT) and the public to prioritise based on social acceptability assessment (SAS). The IPT allows different conservation interventions to be assessed based on their economic cost, implementation feasibility, social acceptability, and perceived effectiveness in maintaining or increasing future turtle populations while simultaneously accounting for expert confidence in their assessment. Results generated by the IPT and SAS can be explored further to resolve uncertainty, a process that can help managers and experts alike in their decision-making process associated with flatback conservation. While this paper is focused on interventions relating to flatback turtles, we propose that our IPT can be applied in different settings to enable consideration of interventions for a range of threatened species and habitats to guide research and conservation investment decisions by managers.

Haematologic and plasma biochemical reference intervals for flatback turtles Natator depressus

Blood reference intervals (RIs) provide an indication of systemic health and are central to any baseline health survey. RIs are available for all sea turtle species, except for the flatback turtle Natator depressus. We developed the first nesting and foraging flatback turtle RIs from a healthy reference population of 211 individuals. We found flatback turtle RIs were generally similar to other published sea turtle RIs. For flatback turtles, we detected significant differences in blood reference values (RVs) by life stage (nesting vs. foraging), sex, and location, as well as by measurement technique (laboratory vs. field). Clinically significant differences justified the establishment of separate RIs for nesting and foraging flatback turtles and for laboratory and field techniques. Clinical application of these blood RIs for individuals in rehabilitation includes disease diagnosis, health monitoring, and the development of prognostic indicators. As sea turtles are regarded as sentinels of environmental health, flatback turtle baseline health data will also be useful for population health monitoring and as a reference for future studies where changes in RIs may indicate an environment in decline.

Social acceptability of conservation interventions for flatback turtles: comparing expert and public perceptions

Sea turtles are facing significant threats, including anthropogenic warming, predation from feral animals, and sea level rise. While a range of intervention options are available, resource constraints and increasing time pressures means managers face the difficult task of prioritising options. To achieve successful conservation outcomes, managers are increasingly seeking to understand the social acceptability, as well as biological plausibility and economic feasibility, of these intervention options. Previous studies have used expert opinion as predictors of social acceptability, given their technical knowledge and experience implementing the interventions; however, the assumption that the social acceptability of interventions is the same for both the general public and experts is largely untested. We tested this assumption using surveys to assess the social acceptability of 24 interventions proposed for a population of flatback turtles Natator depressus in northwest Australia. Survey responses were collected from community members (residents) and experts (resource managers and researchers). Experts were asked to provide their own opinion of acceptability and how they perceived community members would rate intervention options. In general, residents ranked interventions that directly intervene with human behaviour or the environment as more acceptable than those that directly target turtles, while experts tended to favour direct turtle interventions. Experts incorrectly predicted that the community would not be influenced by the target of the intervention. Our findings highlight the importance of understanding social acceptability of interventions before implementation to inform management decisions and engagement and communication strategies, particularly when interventions might be controversial or restrict human behaviour directly.

Behaviour‐specific spatiotemporal patterns of habitat use by sea turtles revealed using biologging and supervised machine learning

Abstract Conservation of threatened species and anthropogenic threat mitigation commonly rely on spatially managed areas selected according to habitat preference. Since the impact of threats can be behaviour‐specific, such information could be incorporated into spatial management to improve conservation outcomes. However, collecting spatially explicit behavioural data is challenging. Using multi‐sensor biologging tags containing high‐resolution movement sensors (e.g. accelerometer, magnetometer, GPS) and animal‐borne video cameras, combined with supervised machine learning, we developed a method to automatically detect and geolocate typically ambiguous behaviours for the poorly understood flatback turtle Natator depressus. Subsequently, we evaluated behaviour‐specific spatiotemporal patterns of habitat use. Boosted regression trees successfully identified the presence of foraging and resting in 7074 dives (AUC > 0.9), using dive features representing characteristics of locomotory activity, body posture, and three‐dimensional dive paths validated by ancillary video data. Foraging was characterised by dives with longer duration, variable depth, tortuous bottom phases; resting was characterised by dives with decreased locomotory activity and longer duration bottom phases. Foraging and resting showed minimal spatial segregation based on 50% and 95% utilisation distributions. Expected diel patterns of behaviour‐specific habitat use were superseded by the extreme tides at the near‐shore study site. Turtles rested in areas close to the subtidal and intertidal boundary within larger overlapping foraging areas, allowing efficient access to intertidal food resources upon inundation at high tides when foraging was ~25% more likely. Synthesis and applications. Using supervised machine learning and biologging tools, we show the potential for dynamic spatial management of flatback turtles to mitigate behaviour‐specific threats by prioritising protection of important locations at pertinent times. Although results are a species‐specific response to a super‐tidal environment, our approach can be generalised to a broad range of taxa and study systems, facilitating a conceptual advance in spatial management.

A focus on flatback turtles: the social acceptability of conservation interventions in two Australian case studies

Human-induced climate change is a threat to marine species and ecosystems worldwide, including sea turtles. As climate changes are projected to intensify, directed management and intervention is required to safeguard the future of vulnerable species and ecosystems. Prioritisation tools that explore the cost-benefit-risk can help in the choice of interventions. However, an often-overlooked element underpinning the success of directed interventions is the extent to which they are perceived as acceptable by local communities (i.e. social acceptability). We assess the social acceptability for a range of adaptation interventions for flatback turtles Natator depressus (FBTs) in north-western Australia. A survey of residents in Port Hedland and Broome showed that FBTs are important to the identity of both towns and local FBT decline or extinction would have negative local social and economic impacts. In both locations, survey respondents expressed strong support for intervening to protect FBTs and there was broad agreement between respondents from both locations on the most and least acceptable interventions. For example, in both locations the most acceptable intervention was to restrict 4-wheel-drive beach access for locals and visitors and the least acceptable was to intervene genetically in the FBT populations. In the case of FBT conservation in Port Hedland and Broome, (1) interventions that limit human behaviour, as opposed to interfering with the species themselves, are likely to be most socially acceptable, and therefore (2) are also most likely to be implemented successfully and avoid conflicts within the community.

Predicting core areas of flatback turtle hatchlings and potential exposure to threats

The lack of data on distribution of juvenile marine species can limit conservation efforts. As hatchlings, marine turtles are too small to track using satellite telemetry, so their at-sea distribution remains unknown. This knowledge gap is critical, as hatchlings already experience high mortality in coastal zones. In addition, further risks to their survival may occur beyond these areas, linked to threats associated with in-water artificial infrastructure and/or attraction to artificial lights and thus increased mortality from higher risk of predation or exhaustion from disorientation. To fill this gap, we used particle tracking forced by an ocean circulation model to predict the dispersal of flatback turtle Natator depressus hatchlings from 12 nesting sites off the coast of Western Australia. We used the model outputs to calculate the distribution of these ‘virtual hatchlings’ and infer the core area of hatchling use over 3 dispersal phases (1-4, 10-15 and 25-30 d). We then calculated the overlap between core areas and 2 anthropogenic threats (in-water artificial infrastructure and light pollution). Core areas were predominately located on the continental shelf during all dispersal phases, supporting the hypothesis that flatback turtles remain in neritic areas. Most (70-80%) of the core area during early dispersal (Days 1-4 and 10-15) contained at least one threat. However, less than half of the area used between Day 25 and 30 was exposed to threats. In the absence of empirical data on hatchling distribution, our results have predicted the core areas used by early life stage flatback turtles to assist in conservation management of these threatened species.

Sky glow disrupts the orientation of Australian flatback turtles Natator depressus on nesting beaches

Sky glow disrupts the orientation of Australian flatback turtles Natator depressus on nesting beaches

Streptococcus iniae associated mass marine fish kill off Western Australia.

Streptococcus iniae causes high mortality in cultured and wild fish stocks globally. Since the first report in captive Amazon river dolphins Inia geoffrensis in 1976, it has emerged in finfish across all continents except Antarctica. In March 2016, an estimated 17000 fish were observed dead and dying along a remote 70 km stretch of the Kimberley coastline north of Broome, Western Australia. Affected species included finfish (lionfish Pterois volitans, angelfish Pomacanthus sp., stripey snapper Lutjanus carponotatus, sand bass Psammoperca waigiensis, yellowtail grunter Amniataba caudavittata, damselfish Pomacentridae sp.), flatback sea turtles Natator depressus, and olive (Aipysurus laevis) and black-ringed (Hydrelaps darwiniensis) sea snakes. Moribund fish collected during the event exhibited exophthalmia and abnormal behaviour, such as spiralling on the surface or within the water column. Subsequent histopathological examination of 2 fish species revealed bacterial septicaemia with chains of Gram-positive cocci seen in multiple organs and within brain tissue. S. iniae was isolated and identified by bacterial culture, species-specific PCR, Matrix-Assisted Laser Desorption Ionisation Time-Of-Flight (MALDI-TOF) and biochemical testing. This is the first report of S. iniae associated with a major multi-species wild marine fish kill in Australia. Extreme weather events in the region including a marked decrease in water temperatures, followed by an extended period of above-average coastal water temperatures, were implicated as stressors potentially contributing to this outbreak.

Optimising sample sizes for animal distribution analysis using tracking data

Abstract Knowledge of the spatial distribution of populations is fundamental to management plans for any species. When tracking data are used to describe distributions, it is sometimes assumed that the reported locations of individuals delineate the spatial extent of areas used by the target population. Here we examine existing approaches to validate this assumption, highlight caveats, and propose a new method for a more informative assessment of the number of tracked animals (i.e. sample size) necessary to identify distribution patterns. We show how this assessment can be achieved by considering the heterogeneous use of habitats by a target species using the probabilistic property of a utilisation distribution. Our methods are compiled in the r package SDLfilter. We illustrate and compare the protocols underlying existing and new methods using conceptual models and demonstrate an application of our approach using a large satellite tracking dataset of flatback turtles Natator depressus tagged with accurate Fastloc‐GPS tags (n = 69). Our approach has applicability for the post hoc validation of sample sizes required for the robust estimation of distribution patterns across a wide range of taxa, populations and life‐history stages of animals.

Variation in thermal traits describing sex determination and development in Western Australian sea turtle populations

Abstract Both the development rate and sex of sea turtle embryos depend on incubation temperature, as all species of sea turtle are ectotherms and show temperature‐dependent sex determination (TSD). Theory predicts that selection should act on populations to optimize developmental times and primary sex ratios. In this study, we use a consistent methodology to measure development rates and model the reaction norm that defines TSD in three populations of flatback turtles Natator depressus and two populations of green turtles Chelonia mydas that nest in Western Australia. We show that development rates vary between and within species, likely reflecting adaptation to local beach microclimates. Similarly, the parameters that define the TSD reaction norm vary between the two species, and among N. depressus populations, with pivotal temperatures (TPIV) varying by 1.5°C (29.6–31.1°C), and the transitional ranges of temperatures (TRT) varying by 1.4–3.3°C. In contrast, we found a similar TPIV for the two C. mydas populations, but a wider TRT at the northernmost tropical rookery. Our findings support the view that thermal parameters in geographically separated populations of sea turtles are broadly similar, but the variation we describe will be highly relevant for predicting how populations will respond to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.

Nesting ecology of flatback sea turtles Natator depressus from Delambre Island, Western Australia

Nest site selection is likely to be important for the fitness of sea turtle populations, but data on the environmental drivers of nest site selection and other important parameters like nest site fidelity and inter-nesting and remigration intervals are limited. We address these questions using data on flipper tag resightings and track counts from flatback turtles (Natator depressus) from Delambre Island in Western Australia collected over 2–3 weeks each nesting season across six nesting seasons. The median inter-nesting interval was 13 days (range 9–17 days) and the mean±s.d. remigration interval was 1.99±0.95 years. Turtles had around 10% probability of returning to the same sector of the beach (150-m-long sections). The median distance between subsequent emergences (whether false crawls were included or not) was ~450m. The number of turtles both emerging and successfully nesting was higher when air temperature and humidity were lowest and emergences increased slightly with tide height. Sector of the beach was by far the strongest predictor of nest site, with turtles showing preference for the less exposed side of the island. The results of this study will assist with future monitoring of this population and the management of threats related to coastal development and activities.

Artificial light disrupts the nearshore dispersal of neonate flatback turtles Natator depressus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 600:179-192 (2018) - DOI: https://doi.org/10.3354/meps12649 Artificial light disrupts the nearshore dispersal of neonate flatback turtles Natator depressus Phillipa Wilson1,2,*, Michele Thums2, Charitha Pattiaratchi1, Mark Meekan2, Kellie Pendoley3, Rebecca Fisher2, Scott Whiting4 1Oceans Graduate School and The UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia 2Australian Institute of Marine Science, Indian Ocean Marine Research Centre, The University of Western Australia (M096), 35 Stirling Highway, Crawley, WA 6009, Australia 3Pendoley Environmental, 12A Pitt Way, Booragoon, WA 6154, Australia 4Marine Science Program, Department of Biodiversity, Conservation and Attractions, 17 Dick Perry Avenue, Kensington, WA 6151, Australia *Corresponding author: phillipa.wilson@research.uwa.edu.au ABSTRACT: After emerging from nests, neonate sea turtles entering the water are thought to orientate away from shore using wave cues to guide them out to sea. Artificial light may interfere with this process, but the relative importance of natural and anthropogenic cues to the dispersal of hatchlings is unknown. Here, we used acoustic telemetry to track the movement of flatback turtle Natator depressus hatchlings dispersing through nearshore waters. Turtles dispersed in the presence and absence of artificial light through a receiver array where a range of oceanographic variables were measured. Turtle tracks were analysed using a full subsets generalised additive mixed model approach to identify the most important cues influencing the bearing, variance in bearing (a measure of the ability to orientate directly), rate of travel and time spent in the array. Artificial light reduced their swim speed by up to 30%, increased the amount of time spent in nearshore waters (by 50 to 150%) and increased the variance in bearing (100 to 180% more variable), regardless of oceanographic conditions. Under ambient conditions, ocean currents affected the bearing of hatchlings as they left the shore, but when light was present, this effect was diminished, showing turtles actively swam against currents in their attempts to move towards light. After accounting for the effects of currents on hatchlings dispersing under ambient conditions, turtles swam offshore by moving perpendicular to the coastline and did not appear to orient into incident wave direction. Overall, light disrupted the dispersal of hatchlings, causing them to linger, become disoriented in the nearshore and expend energy swimming against ocean currents. KEY WORDS: Light pollution · Ocean currents · Acoustic telemetry · In-water movement · Hatchling · Vemco Positioning System Full text in pdf format Supplementary material PreviousNextCite this article as: Wilson P, Thums M, Pattiaratchi C, Meekan M, Pendoley K, Fisher R, Whiting S (2018) Artificial light disrupts the nearshore dispersal of neonate flatback turtles Natator depressus. Mar Ecol Prog Ser 600:179-192. https://doi.org/10.3354/meps12649 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 600. Online publication date: July 30, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Environmental predictors of foraging and transit behaviour in flatback turtles Natator depressus

This research was partially supported by Browse LNG Development Joint Venture Participants through the operator Woodside Energy Limited. M.T. was supported by an Indian Ocean Marine Research Centre (AIMS/CSIRO/UWA) Collaborative Post-doctoral Fellowship. Part of this work was undertaken for the Marine Biodiversity Hub, a collaborative partnership supported through funding from the Australian Government's National Environmental Science Programme.

Estimating long-term trends in abundance and survival for nesting flatback turtles in Kakadu National Park, Australia

Flatback turtles Natator depressus are endemic to Australia and Papua New Guinea's tropical oceans and, although the species has an extensive distribution around northern Australia, there are few published long-term abundance trends of nesting populations. We conducted a longterm capture-mark-recapture program on nesting flatback turtles on Field Island in Kakadu National Park, a World Heritage Area that is jointly managed by Aboriginal landowners and the Australian Government, from 2002 to 2013 for between 12 and 20 monitoring days per year. We used a Cormack-Jolly-Seber (CJS) model that accounted for transience and recapture heterogeneity to estimate apparent survival and recapture probability, and estimated abundance using a Horvitz-Thompson type estimator. A total of 257 flatback turtles attempted nesting during that period, averaging 3.68 ± 0.28 (mean ± SE) nesting attempts per night of monitoring. Annual apparent survival of nesting flatback turtles was 0.97 (95% CI = 0.94 to 0.98) and increased relative to body size. Recapture probability averaged 0.38 (95% CI = 0.34 to 0.42) and was influenced by inter-annual climatic variability. The size of the Field Island nesting flatback turtle population ranged from 97 (95% CI = 87 to 106) to 183 (95% CI = 165 to 200) and there was a non-significant trend over 12 yr of monitoring. Understanding long-term population trends of nesting marine turtles is fundamental for management and recovery of these at-risk species.

Inter-nesting distribution of flatback turtles Natator depressus and industrial development in Western Australia

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 26:25-38 (2014) - DOI: https://doi.org/10.3354/esr00628 Inter-nesting distribution of flatback turtles Natator depressus and industrial development in Western Australia Paul A. Whittock1,2,*, Kellie L. Pendoley1, Mark Hamann2 1Pendoley Environmental Pty Ltd, 12a Pitt Way, Booragoon, WA 6154, Australia 2School of Earth and Environmental Sciences, James Cook University, Townsville, QLD 4811, Australia *Corresponding author: paul.whittock@penv.com.au ABSTRACT: Offshore interactions of inter-nesting flatback turtles Natator depressus with resource industry activities are potentially frequent, yet the associated impact is largely unquantified. Consequently, there is a need to understand the degree of interaction and to provide data that can assist with effective conservation and management. We used satellite tracking to highlight the potential interaction of inter-nesting flatback turtles (n = 56) from 4 rookeries in Western Australia with regional resource industry activities. Flatback turtles demonstrated varying inter-nesting movements, with displacement distances ranging from 3.4 to 62.1 km. Some turtles at all 4 rookeries remained <10 km from the nesting beach. Core home range areas for inter-nesting flatback turtles ranged from 1.4 to 601.1 km2. The proportion of core home range areas for Thevenard and Barrow Island turtles that overlapped offshore petroleum title areas was 85.7 and 88.6%, respectively. The proportion of median daily positions that overlapped petroleum title areas was also high, 80.8% (Thevenard) and 87.3% (Barrow). There was no overlap of home range areas and median daily positions with petroleum title areas for Mundabullangana and Port Hedland turtles, although some inter-nesting movements of Port Hedland turtles were in close proximity to a proposed port expansion. The wide-ranging inter-nesting movement patterns highlight a need for the Australian Government and industry to expand the scope of Environmental Impact Assessments, ensuring adequate protection is provided to inter-nesting flatback turtles. The similar nearshore inter-nesting movement pattern recorded by some flatback turtles at each rookery provides an opportunity to establish boundaries for small-scale spatial and temporal protection measures. KEY WORDS: Flatback · Inter-nesting · Satellite tracking · Australia · Industry · Environmental Impact Assessment · EIA Full text in pdf format PreviousNextCite this article as: Whittock PA, Pendoley KL, Hamann M (2014) Inter-nesting distribution of flatback turtles Natator depressus and industrial development in Western Australia. Endang Species Res 26:25-38. https://doi.org/10.3354/esr00628 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 26, No. 1. Online publication date: November 20, 2014 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2014 Inter-Research.

Reproductive biology of the flatback turtle Natator depressus in Western Australia

In contrast to the circumglobal nesting distributions and well-described reproductive biology of most marine turtle species, all known records of flatback turtle Natator depressus nest- ing have occurred within Australia and are relatively underreported; the species is listed as 'Data Deficient' by the International Union for the Conservation of Nature (IUCN). We report important baseline data on the breeding biology of flatback turtles at 3 rookeries in the Pilbara region of Western Australia, an area subject to increasing coastal development due to rapid expansion of the resources sector. Barrow Island and Mundabullangana support substantial reproductive pop- ulations; over the 6 season sampling period from 2005/06 to 2010/11, ~4000 and ~3500 turtles were tagged at each location, respectively. Over 2 seasons of monitoring in 2009/10 and 2011/12 at Cemetery Beach, a smaller rookery in Port Hedland, ~350 flatback turtles were tagged. We detected variation in parameters of reproductive biology between island and mainland rookeries. Mean remigration interval at Barrow Island (1.9 yr) was significantly shorter than at mainland Mundabullangana (2.2 yr) and may reflect differences in location and characteristics of remote foraging habitats in turtles returning to mainland versus offshore rookeries. Clutch size was simi- lar (~47 eggs) among rookeries and smaller than mean clutch sizes recorded for all other Aus- tralian flatback rookeries (~53 eggs). Hatching success at Barrow Island (83.4%) was within the reported range for the species; however, at Mundabullangana and Cemetery Beach (68.2% and 57.3%, respectively) these values were the lowest published to date for this species and may be attributable to higher temperatures at mainland rookeries.

Swimming performance and metabolic rate of flatback Natator depressus and loggerhead Caretta caretta sea turtle hatchlings during the swimming frenzy

Swimming performance influences the dispersal success of sea turtle hatchlings when they first enter the water and engage in a 'swimming frenzy' which moves them rapidly offshore. We simultaneously measured swim thrust (in millinewtons, mN) and metabolic rate (in milliwatts, mW) of loggerhead Caretta caretta and flatback turtle Natator depressus hatchlings during the first 18 h of the swimming frenzy and compared the results with previous data from green turtle Chelonia mydas hatchlings. Metabolic rate was correlated with swim thrust in all species. In all species, swim thrust decreased sharply during the first 2 h of swimming, continued to slowly decrease until 12 h and remained constant at this lowest level until experiments ended at 18 h. Metabolic rate had a similar pattern, with a steep drop during the first 2 h followed by a less steep decrease before becoming relatively constant. Swim thrust and metabolic rate were highest in green turtle hatchlings. Flatback hatchling metabolic rate was similar to green turtle hatchlings but they weighed almost twice as much, while loggerhead hatchlings had the lowest metabolic rate. Flatback hatchling swim thrust decreased the fastest, falling below that of green turtle hatchlings within the first hour of swimming and falling below loggerhead turtle hatchlings after 12 h of swimming. These findings suggest that flatback hatchlings have a different dispersal behaviour compared to green and loggerhead hatchlings. The shorter highly vigorous swimming period of flatback turtles might be explained by the fact that they do not swim into off-shore oceanic dispersing currents, and managing their energy resources might be a strategic adaptation to survive predators in a relatively constant environment.

Early swimming activity of hatchling flatback sea turtles Natator depressus: a test of the ‘predation risk’ hypothesis

Marine turtle hatchlings emerge from nests on oceanic beaches, crawl to the surf zone and migrate offshore. Predators in shallow water can take many hatchlings, but once the turtles reach deeper water, both encounters with predators and mortality rates probably decline. Behavioral stud- ies have demonstrated that hatchlings show changes in swimming activity as they migrate offshore. During the first 24 h of migration, most species swim continuously (the 'frenzy'), thereby minimizing their time in shallow waters; however, swimming activity later declines in duration and vigor, espe- cially at night (the 'postfrenzy'). One interpretation of these differences is that hatchling migratory behavior evolved in response to the threat of predators (the 'predation risk' hypothesis). To further test this hypothesis, we quantified the daily swimming activity shown by the flatback Natator depres- sus, the only marine turtle that lacks an oceanic phase in its development. Instead, the hatchlings remain in relatively shallow Australian (continental shelf) waters where they may frequently encounter predators. We speculated that because of these encounters, flatback hatchlings might have evolved activity patterns that show little, if any, decline during migration. Over 4 d of laboratory observations, flatback activity at night declined by <13%. Over the same time period, nocturnal activity declined by 60 to 95% (depending on species) in other marine turtles with an oceanic phase in their life history. Our data therefore support the hypothesis that predation played an important role in shaping the evolution of hatchling migratory behavior, although they do not provide direct evi- dence of a cause and effect relationship.