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Abstract

Adult sea turtles of several species migrate across vast expanses of ocean to arrive at specific nesting areas and feeding sites. Two hypotheses have been proposed to account for this remarkable navigation. The first is that chemical cues emanating from target areas guide turtles to their destinations. The second is that turtles can approximate their position relative to target regions using fea-tures of the earth's magnetic field. Because animals often rely on multiple cues while migrating, the two hypotheses are not mutually exclusive. Satellite tracking experiments have revealed that migrating turtles often swim directly to distant goals, even when traveling perpendicularly to water cur-rents. Because animals usually change course frequently while seeking the source of a chemical plume, the consistency of headings casts doubt on the hypothesis that turtles follow such plumes over great distances. Chemical cues may nevertheless play a role in enabling turtles to recognize a target area in the final stages of a long migration. The magnetic navigation hypothesis is based on the finding that hatchling loggerhead turtles can detect two different features of the geomagnetic field (inclination angle and intensity) that vary across the earth's surface. Hatchlings from Florida, U.S.A., respond to magnetic features found along their migratory route by swimming in directions that may help keep them safely within the North Atlantic gyre, a circular warm-water current system favorable for growth and development. These results suggest that young turtles can derive positional information from features of the earth's field, and that such information may play an important role in guiding trans-oceanic migrations. Adults might also exploit geomagnetic features in long-distance navigation. In principle, turtles nesting on coastlines might locate the appropriate region by returning to an area marked by the intersection of the shoreline and a magnetic isoline (e.g., a particular inclination angle or intensity). Turtles that migrate to remote islands may be able to exploit bicoordinate magnetic maps for position-finding, although secular variation and other factors may limit the conditions under which such a system can be used.
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... These two parameters vary in somewhat different directions across much of the globe and thus form a bicoordinate magnetic grid of sorts Lohmann 1996a, 1996b). Suddenly, the concept of magnetic maps seemed very plausible (Lohmann et al. 1999). ...
... The concept of long-distance natal homing based on a magnetic map sense and imprinting was initially developed in the context of sea turtles and salmon (Lohmann and Lohmann 1994;Lohmann et al. 1999Lohmann et al. , 2008c. In its simplest form, the hypothesis proposes that young animals imprint on the magnetic field of their natal area (Box 3), then use this information to navigate back to the region using a magnetic map as adults (Lohmann et al. 2008c. ...
... The learning process might or might not meet the strict ethological definition of imprinting, depending on the animal. For example, long-lived animals such as sea turtles and birds, which reproduce in multiple years, might update their knowledge of the magnetic field of a nesting area each time they visit (Lohmann et al. 1999(Lohmann et al. , 2008cGould, 2015), rather than learning the field only on a single occasion when they are young. ...
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In addition to providing animals with a source of directional or ‘compass’ information, Earth’s magnetic field also provides a potential source of positional or ‘map’ information that animals might exploit to assess location. In less than a generation, the idea that animals use Earth’s magnetic field as a kind of map has gone from a contentious hypothesis to a well-established tenet of animal navigation. Diverse animals ranging from lobsters to birds are now known to use magnetic positional information for a variety of purposes, including staying on track along migratory pathways, adjusting food intake at appropriate points in a migration, remaining within a suitable oceanic region, and navigating toward specific goals. Recent findings also indicate that sea turtles, salmon, and at least some birds imprint on the magnetic field of their natal area when young and use this information to facilitate return as adults, a process that may underlie long-distance natal homing (a.k.a. natal philopatry) in many species. Despite recent progress, much remains to be learned about the organization of magnetic maps, how they develop, and how animals use them in navigation.
... 2b). Two of these parameters, inclination angle and total intensity, vary in different directions over much of the globe, so that the two form a large-scale bi-coordinate grid over many oceanic regions (Lohmann et al. 1999(Lohmann et al. , 2007. Evidence indicates that several fishes, as well as sea turtles and possibly other animals, exploit this pattern of magnetic variation as a kind of magnetic map (Lohmann et al. 2007(Lohmann et al. , 2012Putman et al. 2014c;Naisbett-Jones et al. 2017;Keller et al. 2021). ...
... A novel analysis of fisheries data has provided strong circumstantial evidence that young salmon do indeed imprint on the magnetic field of their home area, and that magnetic navigation plays a role in natal homing (Putman et al. 2013). The analysis exploited the fact that Earth's magnetic field changes gradually over time and that isolines of inclination and intensity shift slightly each year (Skiles 1985;Lohmann et al. 1999). Thus, the inclination and/or intensity existing at a particular location 1 year might drift northward the next year and possibly southward the year after that. ...
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As the largest and most diverse vertebrate group on the planet, fishes have evolved an impressive array of sensory abilities to overcome the challenges associated with navigating the aquatic realm. Among these, the ability to detect Earth’s magnetic field, or magnetoreception, is phylogenetically widespread and used by fish to guide movements over a wide range of spatial scales ranging from local movements to transoceanic migrations. A proliferation of recent studies, particularly in salmonids, has revealed that fish can exploit Earth’s magnetic field not only as a source of directional information for maintaining consistent headings, but also as a kind of map for determining location at sea and for returning to natal areas. Despite significant advances, much about magnetoreception in fishes remains enigmatic. How fish detect magnetic fields remains unknown and our understanding of the evolutionary origins of vertebrate magnetoreception would benefit greatly from studies that include a wider array of fish taxa. The rich diversity of life-history characteristics that fishes exhibit, the wide variety of environments they inhabit, and their suitability for manipulative studies, make fishes promising subjects for magnetoreception studies.
... In addition to humans, animals can also intelligently use magnetic fields to complete field navigation and positioning [23][24][25]. For example, sea turtles utilize geomagnetic navigation without the actual geomagnetic map during migration. ...
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Accumulating evidence suggests that migrating animals store navigational “maps” in their brains, decoding location information from geomagnetic information based on their perception of the magnetic field. Inspired by this phenomenon, a novel geomagnetic inversion navigation framework was proposed to address the error constraint of a long-distance inertial navigation system. In the first part of the framework, the current paper proposed a geomagnetic bi-coordinate inversion localization approach which enables an autonomous underwater vehicle (AUV) to estimate its current position from geomagnetic information like migrating animals. This paper suggests that the combination of geomagnetic total intensity (F) and geomagnetic inclination (I) can determine a unique geographical location, and that there is a non-unique mapping relationship between the geomagnetic parameters and the geographical coordination (longitude and latitude). Then the cumulative error of the inertial navigation system is corrected, according to the roughly estimated position information. In the second part of the framework, a cantilever beam model is proposed to realize the optimal correction of the INS historical trajectory. Finally, the correctness of the geomagnetic bi-coordinate inversion localization model we proposed was verified by outdoor physical experiments. In addition, we also completed a geomagnetic/inertial navigation integrated long-distance semi-physical test based on the real navigation information of the AUV. The results show that the geomagnetic inversion navigation framework proposed in this paper can constrain long-distance inertial navigation errors and improve the navigation accuracy by 73.28% compared with the pure inertial navigation mode. This implies that the geomagnetic inversion localization will play a key role in long-distance AUV navigation correction.
... Sea turtles use a variety of keen sensory modalities for longrange migrations that can span entire ocean basins during their ontogeny and for reproduction (Lohmann et al., 2008;Endres et al., 2016). Magnetoreception is a key sensory component for a variety of turtle species (e.g., Lohmann et al. (2012), Luschi et al. (2007) and Lohmann and Hester (1999)). However, gaining a mechanistic understanding of how magnetoreception enables migratory and goal-finding capabilities is an active area of research. ...
Article
Sea turtles complete migrations across vast distances, covering entire ocean basins. To track these migrations, satellite tracking tags are attached to their shells. The impact of these tags must be considered to ensure that turtles’ natural behavior is not artificially and adversely impacted through tag-related drag, and that the data collected by a small sample of sea turtles accurately represents the larger population. Additionally, it can be difficult to study animal energetics in the field over large migration distances. In this work, we modify a computational behavior model to study how satellite tracking tags affect turtle migration behavior. Our agent based model contains synthetic magnetic field environments that are used for navigation cues, an ocean current, resource distributions that represent locations of food, and an agent that attempts to migrate to several different goals. The agent loses energy as it progresses, and searches for the resource distributions to replenish itself. Our novel simulation framework demonstrates the relationship between an agent’s available energy capacity, its energy consumption based on mechanical power expended, and its ability to navigate to all migratory goal points. This study can be utilized to (1) probe the impacts of an animal’s energy capacity and foraging behavior on its resulting navigation and ecology, (2) guide future satellite tag designs, and (3) develop usage recommendations for a suitable tracking tag based on the type of experiment being conducted. Our model can be expanded beyond sea turtles to study other marine species (e.g., sharks, whales). Additionally, this model could be expanded to other domains within the marine environment. For example, it could be modified to examine design trade-offs in remotely operated vehicles (ROVs), which share many of the same operational constraints as sea turtles and other migratory species.
... Ovulation occurs only after the successful transmission of sperm by one or more males 41 . After the mating season is over, females migrate to their natal beach area; males return to foraging areas 19,[42][43][44][45][46] . ...
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Maternal risk-management, an extension of r/K selection, is an indispensable tool for understanding the natural selection pressures that shape the evolution of reproduction. Central to the construct of maternal risk-management is its definition of reproductive success as replacement fitness ( w = 2), the survival of one breeding daughter to replace the female and one outbreeding son to replace her mate. Here, I apply maternal risk-management as a theoretical framework to explain multiple reproductive adaptations by loggerhead sea turtles nesting on a barrier island off the southern coast of Florida, US, from 1988 to 2004. Extrapolated over a 30-year reproductive span, nesting females averaged 4000–4500 eggs. I show that, rather than “putting all their eggs in one basket,” females divided eggs into 40 clutches of variable size (50–165 eggs). To deposit clutches, females migrated to the barrier island 10–12 times at unpredictable intervals of 2–8 years. Each nesting season, females deposited 1–7 clutches over diversified time intervals at diversified locations on the beach. Despite devastating clutch losses caused by ten catastrophic hurricanes, hundreds of erratic thunderstorms and dozens of predation events during this study, 72% of clutches produced by nesting females on this barrier island were undisturbed—median hatching success for these clutches was an astonishing 92%. I conclude that diversified maternal investments over time and space by nesting females are reproductive adaptations that have successfully offset clutch losses, thus enabling populations of loggerhead females to meet or exceed their reproductive goal of replacement fitness.
... In biological systems, magnetic reception appears to be a sensory modality that, alongside other sensory cues, helps several animals achieve remarkable feats that parallel the goals of engineered systems (e.g. sea turtles migrating across oceans [9][10][11], insects navigating on the scale of continents [12,13], and birds in transcontinental migrations [14][15][16][17]). However, magnetic reception and its interaction with other sensing modalities remains poorly understood (e.g. the special edition on magnetic reception by the Journal of the Royal Society Interface (2010), [5,18,19]). ...
Article
Diverse taxa use Earth’s magnetic field in combination with other sensory modalities to accomplish navigation tasks ranging from local homing to long-distance migration across continents and ocean basins. Several animals have the ability to use the inclination or tilt of magnetic field lines as a component of a magnetic compass sense that can be used to maintain migratory headings. In addition, a few animals are able to distinguish among different inclination angles and, in effect, exploit inclination as a surrogate for latitude. Little is known, however, about the role that magnetic inclination plays in guiding long-distance migrations. In this paper, we use an agent-based modelling approach to investigate whether an artificial agent can successfully execute a series of transequatorial migrations by using sequential measurements of magnetic inclination. The agent was tested with multiple navigation strategies in both present-day and reversed magnetic fields. The findings (i) demonstrate that sequential inclination measurements can enable migrations between the northern and southern hemispheres, and (ii) demonstrate that an inclination-based strategy can tolerate a reversed magnetic field, which could be useful in the development of autonomous engineered systems that must be robust to magnetic field changes. The findings also appear to be consistent with the results of some animal navigation experiments, although whether any animal exploits a strategy of using sequential measurements of inclination remains unknown.
... Il existe parfois des corridors océaniques de migration chez les tortues marines. Beaucoup de migrations de longue distance des adultes permettent une liaison entre habitats de reproduction (accouplement, nidification) et habitats d'alimentation, parfois en utilisant le champ magnétique terrestre (Lohmann et al., 1999 ;Lohmann et al., 2008 ;Lohmann & Lohmann, 2019). ...
Chapter
Location is crucial in the life of an animal; in this chapter we cover the mechanisms used by animals to find food, shelter, mates, and the right microclimate. Animals may find good habitat by moving randomly, but more often movements are oriented to external stimuli. After determining the location of a stimulus, an animal moves toward that stimulus if it is attractive, or away from it if it is repulsive. Compass orientation gives animals the ability to move at an angle with respect to the location of the sun, moon, stars, or the earth’s magnetic field; homing and migration typically depend on compass orientation. In addition, path integration is important to many animals. When using path integration, an animal calculates an efficient route to its nest or den based on its outward journey. Migration allows animals to find seasonally appropriate habitats but requires complex navigation that can span thousands of kilometers.
Article
Certain animal species use the earth's magnetic field (i.e., magnetoreception) in conjunction with other sensory modalities, to navigate long distances. It is hypothesized that several animals use combinations of magnetic inclination and intensity as unique signatures for localization, enabling migration without a pre-surveyed map. However, it is unknown how animals use magnetic signatures to generate guidance commands, and the extent to which species-specific capabilities and environmental factors affect a given strategy's efficacy or deterioration. Understanding animal magnetoreception can aid in developing better engineered navigation systems that are less reliant on satellites, which are expensive and can become unreliable or unavailable under a variety of circumstances. Building on previous studies, we implement an agent-based computer simulation that uses two variants of a magnetic signatures-based navigation strategy. The strategy successfully migrates to eight specified goal points in an environment that resembles the northern Atlantic Ocean. In particular, one variant reaches all goal points with faster ocean current velocities while the other variant reaches all goal points with slower ocean current velocities. We also employ dynamical systems tools to examine the stability of the strategy as a proxy for whether it is guaranteed to succeed. The findings demonstrate the efficacy of the strategy and can help to develop new navigation technologies that are less reliant on satellites and pre-surveyed maps.
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Animals can move thousands of kilometres in the ocean before returning with pinpoint accuracy to specific locations. How animals accomplish this feat continues to puzzle scientists. New research provides evidence for how turtles re-orientate during their migrations.
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Molecular markers based on mitochondrial (mt) DNA control region sequences were used to test the hypothesis that juvenile loggerhead sea turtles (Caretta caretta) in pelagic habitats of the eastern Atlantic are derived from nesting populations in the western Atlantic. We compared mtDNA haplotypes from 131 pelagic juvenile turtles (79 from the Azores and 52 from Madeira) to mtDNA haplotypes observed in major nesting colonies of the Atlantic Ocean and Mediterranean Sea. A subset of 121 pelagic samples (92%) contained haplotypes that match mtDNA sequences observed in nesting colonies. Maximum likelihood analyses (UCON, SHADRACQ) estimate that 100% of these pelagic juveniles are from the nesting populations in the southeastern United States and adjacent Yucatan Peninsula, Mexico. Estimated contributions from nesting populations in south Florida (0.71, 0.72), northern Florida to North Carolina (0.19, 0.17), and Quintana Roo, Mexico (0.11, 0.10) are consistent with the relative size of these nesting aggregates. No contribution was detected from nesting colonies in the Mediterranean (Greece) or South Atlantic (Brazil), although samples sizes are insufficient to exclude these locations with finality. The link between west Atlantic nesting colonies and east Atlantic feeding grounds provides a more complete scientific basis for assessing the impact of subadult mortality in oceanic fisheries. Demographic models for loggerhead turtles in the western Atlantic can now be improved by incorporating growth and mortality data from juvenile turtles in pelagic habitats. These data demonstrate that the appropriate scale for loggerhead turtle conservation efforts is vastly larger than the current scale of management plans based on political boundaries.
Chapter
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Chapter
A review of field studies indicates that the homeward migrations of maturing Pacific salmon from the open ocean are well timed and oriented. It is hypothesized that salmon can determine their location relative to home and that this map sense is based on the inclination and declination of the earth’s magnetic field. In order to test this hypothesis experimental techniques which successfully documented compass orientation in small fishes may be modified to allow adult salmon to display directional orientation. The existence of a map sense could be evaluated by testing salmon after displacement. Subtle, systematic changes in the magnetic field around the arena simulating displacement could provide data with which to evaluate the role of the magnetic field in the map sense.
Chapter
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