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Orientation and swimming behavior of hatchling loggerhead turtles Caretta caretta L. during their offshore migration
Abstract
Loggerhead turtle Caretta caretta L. hatchlings emerging from nests on the eastern coast of Florida swim offshore toward the Florida Current. Part of the trip is accomplished during an initial 20-h period of swimming (the “frenzy”); the remainder may take a day or more of oriented swimming. Swimming speeds are slower than those of green turtles Chelonia mydas L. Hatchlings are well oriented in an offshore direction when released into the ocean during the day or night. Completion of a crawl down the beach or a plunge into the surf are unnecessary for proper orientation. Immediately after entering the ocean at night, responses to light appear essential for oriented swimming. However, present hypotheses based upon phototropotaxis may not account for orientation later in the migration.
... In order to produce high quality hatchlings, the swimming performance of hatchlings was measured along with hatchling self-righting ability as an index of hatchling quality. Many previous studies (Salmon and Wyneken, 1987;Wyneken and Salmon, 1992;Jones et al., 2002;Burgess et al., 2006;Jones et al., 2007;Wyneken et al., 2008;Booth, 2009;Ischer et al., 2009;Pereira et al., 2012) have described the swimming ability and swimming behaviour of hatchling sea turtle across several species. This is because their ability to swim and swim speed is the key to their survival. ...
... It is advantageous for hatchlings to be fast swimmers with large energy reserves, allowing them to quickly swim through predatory rich nearshore waters. In this study, we focus on early swimming effort, which has been termed as 'swimming frenzy' (Salmon and Wyneken, 1987). As most predation of sea turtle hatchlings occurs during this period, it is crucial to understand how variations in reserved energy in a hatchlings body might influence their early survivability. ...
... Power-stroke bouts are produced by the up and down movement of the hatchlings front flippers to generate forward thrust, and lasted for 2 to 20 seconds (Carr and Ogren, 1960;Davenport et al., 1984;Salmon and Wyneken, 1987;Wyneken, 1997;Burgess et al., 2006;Pereira et al., 2011). During hatchling dispersal, powerstroke bouts are inter-dispersed with a dog-paddling style of swimming for 1 to 5 seconds during which hatchlings heads break the surface to breath air (Salmon and Wyneken, 1987;Wyneken, 1997;Burgess et al., 2006). ...
... This period, known as the swim frenzy, enables hatchlings to move quickly from nearshore to offshore waters . During the swim frenzy the hatchlings are using multiple cues to enable their directional swimming -these include swimming towards the low, light, horizon, and swimming perpendicular to wave fronts (Lohmann et al., 2017;Salmon & Wyneken, 1987;Wilson et al., 2021). ...
... According to Salmon and Wyneken (1987) light cues are important for at sea dispersal, however, there is likely to be a distance offshore where the cue is either not available or not used. Although this distance is currently unknown, there is a growing empirical basis demonstrating that offshore dispersal for marine turtle hatchlings is compromised by light pollution originating from landbased or marine structures, such as infrastructure like jetties (Cruz et al., 2018;Truscott et al., 2017;Wilson et al., 2018). ...
The globally widespread adoption of Artificial Light at Night (ALAN) began in the mid‐20th century. Yet, it is only in the last decade that a renewed research focus has emerged into its impacts on ecological and biological processes in the marine environment that are guided by natural intensities, moon phase, natural light and dark cycles and daily light spectra alterations. The field has diversified rapidly from one restricted to impacts on a handful of vertebrates, to one in which impacts have been quantified across a broad array of marine and coastal habitats and species. Here we review the current understanding of ALAN impacts in diverse marine ecosystems. The review presents the current state of knowledge across key marine and coastal ecosystems (sandy and rocky shores, coral reefs and pelagic) and taxa (birds and sea turtles), introducing how ALAN can mask seabirds and sea turtles navigation, cause changes in animals predation patterns and failure of coral spawning synchronization, as well as inhibition of zooplankton Diel Vertical Migration. Mitigation measures are recommended, however, while strategies for mitigation were easily identified, barriers to implementation are poorly understood. Finally, we point out knowledge gaps that if addressed would aid in the prediction and mitigation of ALAN impacts in the marine realm.
... As most hatchlings survive solely on residual yolk reserves during dispersal, maintaining high activity levels and high energy consumption rates may place hatchlings at greater risk of fatigue and resource depletion before reaching foraging grounds compared to hatchlings with lower energy demands [2,18,20]. Hatchling activity levels are highest during the initial dispersal across the beach and through neritic waters where predator-densities are highest [8,21], and once hatchlings enter deeper, pelagic waters, the total time that they spend swimming per day gradually decreases [8,21]. Sea turtle species differ in the rate at which they shift their swimming activity and behaviour [8,9,22], and these differences are often attributed to variation in life history among species. ...
... As most hatchlings survive solely on residual yolk reserves during dispersal, maintaining high activity levels and high energy consumption rates may place hatchlings at greater risk of fatigue and resource depletion before reaching foraging grounds compared to hatchlings with lower energy demands [2,18,20]. Hatchling activity levels are highest during the initial dispersal across the beach and through neritic waters where predator-densities are highest [8,21], and once hatchlings enter deeper, pelagic waters, the total time that they spend swimming per day gradually decreases [8,21]. Sea turtle species differ in the rate at which they shift their swimming activity and behaviour [8,9,22], and these differences are often attributed to variation in life history among species. ...
Background
Sea turtle hatchlings must avoid numerous predators during dispersal from their nesting beaches to foraging grounds. Hatchlings minimise time spent in predator-dense neritic waters by swimming almost continuously for approximately the first 24 h post-emergence, termed the ‘frenzy’. Post-frenzy, hatchling activity gradually declines as they swim in less predator-dense pelagic waters. It is well documented that hatchlings exhibit elevated metabolic rates during the frenzy to power their almost continuous swimming, but studies on post-frenzy MRs are sparse.
Results
We measured the frenzy and post-frenzy oxygen consumption of hatchlings of five species of sea turtle at different activity levels and ages to compare the ontogeny of mass-specific hatchling metabolic rates. Maximal metabolic rates were always higher than resting metabolic rates, but metabolic rates during routine swimming resembled resting metabolic rates in leatherback turtle hatchlings during the frenzy and post-frenzy, and in loggerhead hatchlings during the post-frenzy. Crawling metabolic rates did not differ among species, but green turtles had the highest metabolic rates during frenzy and post-frenzy swimming.
Conclusions
Differences in metabolic rate reflect the varying dispersal stratagems of each species and have important implications for dispersal ability, yolk consumption and survival. Our results provide the foundations for links between the physiology and ecology of dispersal of sea turtles.
... Ocean currents are known to influence juvenile turtle dispersal in this region (Bass et al., 2006;DuBois et al., 2021;Shamblin et al., 2016). Hatchling sea turtles swim toward the nearest offshore currents in part to facilitate dispersal (Salmon & Wyneken, 1987;Wyneken & Salmon, 1992) and immature green turtles ride currents when recruiting to neritic foraging areas before returning to foraging areas closer to their natal beach as adults (DuBois et al., 2021;Okuyama et al., 2009;Witham, 1980). An examination of currents in the Caribbean and Atlantic may explain the genetic composition of foraging turtles at Bimini and Great Inagua (Figure 1). ...
Conservation of green sea turtles (Chelonia mydas) benefits from knowledge of population connectivity across life stages. Green turtles are managed at the level of genetically discrete rookeries, yet individuals from different rookeries mix at foraging grounds; therefore, rookeries may be impacted by processes at foraging grounds. Bimini, Bahamas, hosts an important foraging assemblage, but rookery contributions to this assemblage have never been resolved. We generated mitochondrial DNA sequences for 96 foraging green turtles from Bimini and used Mixed Stock Analysis to determine rookery contributions to this population using 817 and 490 base pair (bp) rookery baseline data. The MSA conducted with 817 bp data indicated that Quintana Roo, Mexico, and Central Eastern Florida contributed most to the Bimini population. The MSA conducted with 490 bp data indicated that Southwest Cuba and Central Eastern Florida contributed the most to Bimini. The results of the second MSA differ from a previous study undertaken with 490 bp data, conducted in Great Inagua, Bahamas, which suggested that Tortuguero, Costa Rica, contributed the most to that foraging assemblage. Large credible intervals in our results do not permit explicit interpretation of individual rookery contributions, but our results do indicate substantial relative differences in rookery contributions to two Bahamian foraging assemblages which may be driven by oceanic currents, rookery sizes, and possibly juvenile natal homing. Our findings may implicate a shift in contributions to the Bahamas over two decades, highlighting the importance of regularly monitoring rookery contributions and resolving regional recruitment patterns to inform conservation.
... Servomechanisms keep them on course by modifying their oscillating swimming motion [10,55]. Turtles swim by using power strokes of their front flippers oscillating in synchrony, as in a butterfly stroke [56]. This oscillating system is adjusted in the face of experimental displacements in yaw, pitch, or roll [55]. ...
Navigational mechanisms have been characterized as servomechanisms. A navigational servomechanism specifies a goal state to strive for. Discrepancies between the perceived current state and the goal state specify error. Servomechanisms adjust the course of travel to reduce the error. I now add that navigational servomechanisms work with oscillators, periodic movements of effectors that drive locomotion. I illustrate this concept selectively over a vast range of scales of travel from micrometres in bacteria to thousands of kilometres in sea turtles. The servomechanisms differ in sophistication, with some interrupting forward motion occasionally or changing travel speed in kineses and others adjusting the direction of travel in taxes. I suggest that in other realms of life as well, especially in cognition, servomechanisms work with oscillators.
... Our results suggest that temperature induced mortality rates are low (median of 19% ± 2.7 SD) throughout the decades, in line with evidence from the Azores which suggests relatively stable recruitment when accounting for nesting numbers (Vandeperre et al. 2019 can imperil young turtles, e.g. when they encounter eddies at the edge of the GS, these events might be avoided by active swimming, lowering the expected mortality rate further. Virtual turtles released west of the GS were more prone to experiencing cold temperatures, which underlines the importance of the initial 'swimming frenzy' which helps hatchlings escape predator-rich coastal waters and reach favorable offshore currents for transport to developmental habitats (Salmon & Wyneken 1987, Whelan & Wy neken 2007, Putman et al. 2012a). Future studies could use a subset of the available strandings data (e.g. the more recent years) to assess smaller scale effects and surface ocean processes such as Stoke's drift and their interactions on turtle strandings in Europe using local circulation models. ...
Juvenile sea turtles can disperse thousands of kilometers from nesting beaches to oceanic development habitats, aided by ocean currents. In the North Atlantic, turtles dispersing from American beaches risk being advected out of warm nursery grounds in the North Atlantic Gyre into lethally cold northern European waters (e.g. around the UK). We used an ocean model simulation to compare simulated numbers of turtles that were advected to cold waters around the UK with observed numbers of turtles reported in the same area over ~5 decades. Rates of virtual turtles predicted to encounter lethal (10°C) or detrimental (15°C) temperatures (mean 19% ± 2.7 SD) and reach the UK were consistently low (median 0.83%, lower quartile 0.67%, upper quartile 1.02%), whereas there was high inter-annual variability in the numbers of dead or critically ill turtles reported in the UK. Generalized additive models suggest inter-annual variability in the North Atlantic Oscillation (NAO) index to be a good indicator of annual numbers of turtle strandings reported in the UK. We demonstrate that NAO variability drives variability in the dispersion scenarios of juvenile turtles from key nesting regions into the North Atlantic. Coastal effects, such as the number of storms and mean sea surface temperatures in the UK, were significant but weak predictors, with a weak effect on turtle strandings. Further understanding how changing environmental conditions such as NAO variability and storms affect the fate of juvenile turtles is vital for understanding the distribution and population dynamics of sea turtles.
... Starting at the largest scale, sea turtles roam the oceans using geomagnetic, light, and wave cues. Every stroke of their movement, however, comes from rhythmic power strokes of the front flippers flapping up and down together (Salmon & Wyneken 1987). As we reviewed, servomechanisms modulate this oscillatory system to keep the direction of swimming goal oriented, coping with disturbances in pitch, yaw, and roll (Avens et al. 2003). ...
Animals navigate a wide range of distances, from a few millimeters to globe-spanning journeys of thousands of kilometers. Despite this array of navigational challenges, similar principles underlie these behaviors across species. Here, we focus on the navigational strategies and supporting mechanisms in four well-known systems: the large-scale migratory behaviors of sea turtles and lepidopterans as well as navigation on a smaller scale by rats and solitarily foraging ants. In lepidopterans, rats, and ants we also discuss the current understanding of the neural architecture which supports navigation. The orientation and navigational behaviors of these animals are defined in terms of behavioral error-reduction strategies reliant on multiple goal-directed servomechanisms. We conclude by proposing to incorporate an additional component into this system: the observation that servomechanisms operate on oscillatory systems of cycling behavior. These oscillators and servomechanisms comprise the basis for directed orientation and navigational behaviors.
Expected final online publication date for the Annual Review of Psychology, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Birkaç gün süren bu sürecin ardından yavrular birbirleri ara-irleri aracılığıyla yüzeye ulaşır (Dodd, 1988). Yavrular genellikle gece saatlerinde yuvadan çıkış yapar ve aksi yönde bulunan bir ışık kaynağı gibi olumsuz bir durum söz konusu değilse denize doğru hareket ederler (Salmon ve Wyneken, 1987). ...
... In each series of swimming trials for LW, LA and DA, hatchlings displayed their highest swimming performance during their first trial either directly after emergence (LW) or following periods of retention in air (LA, DA), then displayed lower performance during all subsequent trials over the next 72 h. This behavior is likely representative of the swimming performance exhibited during an initial swim frenzy period within the first 24 h upon reaching the sea followed by a post-frenzy period of decreased swimming activity once hatchlings reach safer waters offshore (Salmon and Wyneken 1987). These results suggest that the onset of the swim frenzy phase is flexible. ...
Retaining hatchling sea turtles following emergence may compromise their swim frenzy, a period of active swimming that is critical to their survival. To inform the best handling practices for sea turtles raised in hatcheries, we determined the interactive effects of retaining Loggerhead Turtle (Caretta caretta) hatchlings under different conditions (dark vs. light and air vs. water) and for different durations (24, 48, and 72 h) on swimming thrust measured at 24-h intervals during the swim frenzy period (72 h). The mean thrust of hatchlings placed in water immediately after emergence (control) was not significantly higher than the mean thrust of hatchlings retained in air (light or dark) for 24, 48, or 72 h. The mean thrust of hatchlings retained in water for 24, 48, and 72 h, however, was significantly lower than the mean thrust of hatchlings in the control treatment. This study indicates that the swim frenzy period of hatchlings can be delayed by retaining them in air for up to 72 h after emergence, such that hatchlings display uncompromised swimming following retention. Conversely, retaining hatchlings in water for the same duration of time can severely compromise their swimming performance following retention, which would put hatchlings at risk of predation upon entering the sea.
The study of comparative cognition bloomed in the 1970s and 1980s with a focus on representations in the heads of animals that undergird what animals can achieve. Even in action-packed domains such as navigation and spatial cognition, a focus on representations prevailed. In the 1990s, I suggested a conception of navigation in terms of navigational servomechanisms. A servomechanism can be said to aim for a goal, with deviations from the goal-directed path registering as an error. The error drives action to reduce the error in a negative-feedback loop. This loop, with the action reducing the very signal that drove action in the first place, is key to defining a servomechanism. Even though actions are crucial components of servomechanisms, my focus was on the representational component that encodes signals and evaluates errors. Recently, I modified and amplified this view in claiming that, in navigation, servomechanisms operate by modulating the performance of oscillators, endogenous units that produce periodic action. The pattern is found from bacteria travelling micrometres to sea turtles travelling thousands of kilometres. This pattern of servomechanisms working with oscillators is found in other realms of cognition and of life. I think that oscillators provide an effective way to organise an organism’s own activities while servomechanisms provide an effective means to adjust to the organism’s environment, including that of its own body.
Eleven hatchlings equipped with sonic transmitters and three equipped with chemical lights were tracked following their departure from beaches facing different points of the compass. The work was carried out off Bermuda with turtles hatched from eggs brought from Tortuguero, Costa Rica. Unless confronted with opposing shorelines, the turtles’ travel paths either approximated straight lines or took the form of gradual curves. These courses did not change to any great degree when land was below the horizon from turtle eye-level. The data suggest that hatchling C. mydas possess no inborn directional preference other than ‘away from land.’ The adaptive significance of this behavior may be that it serves to move the turtles rapidly beyond the reach of inshore predators.
Loggerhead turtle hatchlings in laboratory tanks had a sustained swimming speed of approximately 20 cm/sec at temperatures between 25.6 and 28.9 C. Test temperatures of 30.0 and 33.0 C significantly reduced this speed. The swimming speed of hatchlings exposed to fluctuating temperatures varied with the temperature. A temperature of 33.0 C eliminated phototactic orientation.
An adequate understanding of young sea turtle dispersal patterns is necessary for effective management of threatened or endangered species. Such patterns are poorly understood, and the term “lost year” has been adopted to emphasize this gap in sea turtle life history information. Tag returns from pen-reared yearling sea turtles indicate ocean current dispersal. Evidence indicates hatchlings would be similarly dispersed by ocean currents. Feeding studies with tank-held animals suggest that food resources are available in ocean currents for long-term sea turtle survival. Green turtle ( Chelonia mydas ) growth appears slow in nature.