Important areas at sea for adult loggerhead sea turtles in the Mediterranean Sea: satellite tracking corroborates findings from potentially biased sources

Sea turtle populations worldwide suffer from reduced survival of immatures and adults due to fishery bycatch. Unfortunately, information about the whereabouts of turtles outside the breeding habitat is scarce in most areas, hampering the development of spatially explicit conservation plans. In the Mediterranean, recoveries of adult females flipper-tagged on nesting beaches suggest that the Adriatic Sea and Gulf of Gabès are important foraging areas for adults, but such information could be heavily biased (observing and reporting bias). In order to obtain unbiased data, we satellite-tracked seven loggerhead sea turtles after they completed nesting in the largest known Mediterranean rookery (Bay of Laganas, Zakynthos, Greece). Three females settled in the north Adriatic Sea, one in the south Adriatic Sea and two in the Gulf of Gabès area at the completion of their post-nesting migrations (one individual did not occupy a distinct foraging area). The concordance of tracking results with information from recoveries of flipper-tagged turtles suggests that the north Adriatic Sea and the Gulf of Gabès represent key areas for female adult Mediterranean loggerhead sea turtles.     

Migration of green turtles <Emphasis Type="Italic">Chelonia mydas</Emphasis> from Tortuguero,Costa Rica

During 1955–2003, flipper tags were attached to 46,983 green turtles and ten turtles were fitted with satellite transmitters at Tortuguero, Costa Rica. Eight satellite-tracked turtles stayed within 135 km of the beach and probably returned to nest after release. The internesting area is more extensive than previously documented. Post-nesting migration routes of satellite-tracked turtles varied. Seven turtles swam close to the coast and three turtles swam through oceanic waters before moving toward nearshore areas. Sea surface height anomaly maps indicate that oceanic movements were consistent with the southwestern Caribbean gyre. Circling and semi-circling turtles could have been disoriented but submergence and surface times suggest they may have been feeding in Sargassum sp. concentrations. Rapid post-nesting migrations (mean 2.2 km hr⁻¹) ended on benthic feeding grounds in shallow waters (<20 m) off Belize (n=1), Honduras (n=1) and Nicaragua (n=8). The spatial distribution of migration end points (n=10) and tag returns (n=4,669) are similar. Fishermen in Nicaragua target green turtles along migratory corridors and on foraging grounds. Management efforts are urgently needed in Nicaragua, particularly in the high-density feeding areas south and east of the Witties (N14°09 W82°45). The proximity of foraging grounds to the nesting beach (mean 512 km) may permit female turtles to invest more energy in reproduction and hence the Tortuguero population may have greater potential for recovery than other green turtle nesting populations. Recovery of the Tortuguero green turtle population will benefit countries and marine ecosystems throughout the Caribbean, especially Nicaragua.     

Origins of green turtle (<Emphasis Type="Italic">Chelonia mydas</Emphasis>) feeding aggregations around Barbados,West Indies

Although green turtles (Chelonia mydas Linnaeus) do not nest in Barbados, the easternmost island in the Caribbean archipelago, juveniles are regularly seen foraging in nearshore waters. To examine the stock composition of this foraging population, mitochondrial (mt) DNA control region sequences were analysed from 60 juvenile (31–70 cm curved carapace length) green turtles and compared with data published for key nesting populations in the Atlantic, as well as other feeding grounds (FGs) in the Caribbean. Eight distinct haplotypes were recognised among the 60 individual green turtles sampled around Barbados. Three of the haplotypes found have only previously been reported from western Caribbean nesting beaches, and two only from South Atlantic beaches. The nesting beach origin of one of the Barbados FG haplotypes is as yet unidentified. Stock mixture analysis based on Bayesian methods showed that the Barbados FG population is a genetically mixed stock consisting of approximately equal contributions from nesting beaches in Ascension Island (25.0%), Aves Island/Surinam (23.0%), Costa Rica (19.0%), and Florida (18.5%), with a lesser but significant contribution from Mexico (10.3%). Linear regression analysis indicated no significant effects of rookery population size or distance of the rookery from the FG on estimated contributions from the source rookeries to the Barbados FG. Our data suggest that the similar-sized green turtles sampled on the Barbados FG are a mixed stock of more diverse origins than any previously sampled feeding aggregations in the Caribbean region. The relatively large contribution from the Ascension Island rookery to the Barbados FG indicates that hatchlings from distant rookeries outside the Caribbean basin enter the North Atlantic gyre and become a significant part of the pool from which eastern Caribbean foraging populations are derived. These data support a life cycle model that incorporates a tendency of immatures to migrate from their initial foraging grounds at settlement towards suitable foraging grounds closer to their natal rookeries as they mature.Communicated by P.W. Sammarco, Chauvin     

Post-nesting migrations of green turtles (Chelonia mydas) at Wan-An Island, Penghu Archipelago, Taiwan

 During the summers of 1994 to 1997, eight green turtles (Chelonia mydas) nesting at Wan-An Island, PengHu Archipelago, Taiwan, were equipped with satellite-telemetry transmitters. Using the Argos-linked satellite system, the turtles' migration routes were tracked until the transmissions stopped. The turtles migrated widely on the continental shelf to the east of Mainland China. The migration distances ranged from 193 to 1909 km, and the migration speeds from 1.2 to 2.8 km h⁻¹. The turtles apparently utilize several coastal areas as temporal residential foraging sites, and their migrations consist of both trans-oceanic and coastal legs. The wide distribution of the foraging sites of the turtles comprising this rookery reflects the extent to which the green turtle migrates in northeast Asia; regional and international cooperation will therefore be needed to conserve this declining population. Received: 14 December 1998 / Accepted: 8 May 2000     

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

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

Migratory and reproductive movements of male leatherback turtles (<Emphasis Type="Italic">Dermochelys coriacea</Emphasis>)

The biology of the endangered leatherback turtle (Dermochelys coriacea) at sea is poorly understood. As research has been almost exclusively limited to studies of nesting females, the movements of male turtles and the timing and location of mating activity have remained unknown. We report on the first deployments of satellite tags on male leatherbacks. Male migration to and residency in waters adjacent low-latitude nesting beaches in the western Atlantic suggest that this is where mating occurs, and return migration to these areas reveals male fidelity for breeding sites. Rate of travel decreased markedly after arriving in coastal breeding areas, where males remained for up to 96 days before assuming northward migrations. The initiation of these northward migrations coincided with peak nesting activity in adjacent nesting colonies. Data from satellite-linked time-depth recorders attached to two males revealed diel dive patterns in breeding areas and marked differences in diving behaviour between migratory and breeding periods in one turtle. When male turtles were in waters adjacent nesting colonies, their movements differed from those reported for nesting females, with females ranging farther from shore. Our results suggest that male leatherbacks may be vulnerable to entanglement in coastal fishing gear in waters adjacent nesting beaches.Communicated by R.J. Thompson, St. Johns     

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

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

Foraging areas differentially affect reproductive output and interpretation of trends in abundance of loggerhead turtles

Diet items and habitat constitute some of the environmental resources that may be used differently by individuals within a population. Long-term fidelity by individuals to particular resources exemplifies individual specialization, a phenomenon that is becoming increasingly recognized across a wide range of species. Less is understood about the consequences of such specialization. Here, we investigate the effects of differential foraging ground use on reproductive output in 183 loggerhead sea turtles (Caretta caretta) nesting at Wassaw Island, Georgia (31.89°N, 80.97°W), between 2004 and 2011 with resulting possible fitness effects. Stable isotope analysis was used to assign the adult female loggerheads to one of three foraging areas in the Northwest Atlantic Ocean. Our data indicate that foraging area preference influences the size, fecundity, and breeding periodicity of adult female loggerhead turtles. We also found that the proportion of turtles originating from each foraging area varied significantly among the years examined. The change in the number of nesting females across the years of the study was not a result of uniform change from all foraging areas. We develop a novel approach to assess differential contributions of various foraging aggregations to changes in abundance of a sea turtle nesting aggregation using stable isotopes. Our approach can provide an improved understanding of the influences on the causes of increasing or decreasing population trends and allow more effective monitoring for these threatened species and other highly migratory species.     

Interactions among endocrinology,seasonal reproductive cycles and the nesting biology of the female green sea turtle

We collected data on plasma levels of testosterone+5a-dihydrotestosterone (T+DHT) and corticosterone (CORT) from adult female green sea turtles (Chelonia mydas) from southern Queensland during distinct stages of their reproductive cycle. Those females capable of breeding in a given year had elevated plasma steroid levels (T+DHT 0.91ǂ.08; CORT 1.05ǂ.29 ng/ml), associated with follicular development, until courtship began in October. At the beginning of the nesting season in November plasma levels of CORT were related to when the female first nested (r²=0.06; F=10.45; P=0.01). However, they were not correlated with the number of clutches a female laid in that season (F=3.65; P=0.08). We repeatedly sampled 23 turtles over the nesting season and profiled changes in steroids immediately following oviposition of each clutch. Levels of T+DHT (range 0.41-0.58 ng/ml) and CORT (range 2.13-2.81 ng/ml) were similar through the early stages of the nesting season and inter-nesting period, and declined to near basal levels (T+DHT 0.37ǂ.03 and CORT 1.85-ng/ml) following the last clutch for the season. Steroid hormone levels were also low (T+DHT 0.38ǂ.16; CORT 0.46ǂ.21 ng/ml) in four independent post-breeding (atretic) females; samples for these females were taken at a time when body condition was presumably at the lowest for the season. Subtle changes in the nesting environment, such as variation in nesting habitat or the time of night that nesting occurred, were associated with a small and slow CORT increase. We suggest CORT is increased in nesting females to assist in lipid transfer to prepare the ovarian follicles and/or the reproductive organs for ovulation.     

Population structure and genetic diversity in green turtles nesting at Tortuguero,Costa Rica,based on mitochondrial DNA control region sequences

The green turtle (Chelonia mydas) nesting population at Tortuguero, Costa Rica, is the largest nesting aggregation in the Atlantic, by at least an order of magnitude. Previous mitochondrial DNA (mtDNA) surveys based on limited sampling (n = 41) indicated low genetic diversity and low gene flow with other Caribbean nesting colonies. Furthermore, a survey of nuclear DNA diversity invoked the possibility of substructure within the Tortuguero rookery. To evaluate these characteristics, mtDNA control region sequences were determined for green turtles nesting at Tortuguero in 2001 (n = 157) and 2002 (n = 235). The increased sample revealed three additional haplotypes; five haplotypes are now known for Tortuguero female green turtles. Analyses of molecular variance indicated that there was no significant spatial population structure along the 30-km nesting beach. In addition, no temporal population structure was detected either between the two nesting seasons or within the nesting season. As a result of the larger sample size and additional haplotypes, estimates of genetic separation among Caribbean nesting colonies have changed and the concordance of phylogenetic and phylogeographic patterns reported in the past for green turtles in the Greater Caribbean has weakened. The five haplotypes from Tortuguero represent 36% of the haplotypes identified in green turtle nesting aggregations in the Greater Caribbean and 17% of the haplotypes known to occur in nesting or foraging aggregations in the Greater Caribbean. Haplotype diversity (0.16) and nucleotide diversity (0.0034) for the Tortuguero population are substantially lower than those for the combined rookeries in the Greater Caribbean (0.44 and 0.0078, respectively). Although comprehensive evaluation of regional genetic diversity requires nuclear DNA data, our study indicates that conserving genetic diversity in Caribbean green turtles will require careful management of the smaller rookeries in addition to the Tortuguero rookery.     

Tracking hawksbill sea turtles (<Emphasis Type="Italic">Eretmochelys imbricata</Emphasis>) during inter-nesting intervals around Barbados

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados (Needham’s Point, 13° 04′ 41.33′′ N, 59° 36′ 32.69′′W) were outfitted with GPS dataloggers over three breeding seasons (2008–2010) to track movement during inter-nesting intervals. Most females established spatially restricted resident areas up current and within 7 km of the nesting beach where they spent the majority of the inter-nesting interval. Females nesting earlier in the season settled on shallower sites. Only experienced remigrant turtles occupied the most distant resident areas. Females tracked for multiple inter-nesting intervals exhibited site fidelity, but the area contracted and the activity of females decreased with each successive interval. Hawksbills may trade off site characteristics with distance from the nesting beach and reduce activity over the course of the breeding season to optimise energy reserves during inter-nesting intervals.     

Foraging habitats and migration corridors utilized by a recovering subpopulation of adult female loggerhead sea turtles: implications for conservation

From 1998 to 2008, 68 adult female loggerhead sea turtles (Caretta caretta) were instrumented with platform transmitter terminals at nesting beaches in Georgia, North Carolina (NC) and South Carolina (SC) on the East Coast of the United States of America (30°48′N, 81°28′W to 33°51′N, 77°59′W). The majority of post-nesting loggerheads (N = 42, 62 %) migrated to foraging habitats in the Mid-Atlantic Bight during May–October, with a subsequent migration occurring during November–March to foraging habitats south of Cape Hatteras, NC. Nine (13 %) loggerheads initially foraged in the near-shore, coastal areas of the South Atlantic Bight, but moved to offshore habitats—closer to the Gulf Stream—during November–March, while fourteen (21 %) loggerheads remained in foraging areas along the mid-continental shelf off of the eastern coast of Florida and/or continued southward to Florida Bay and the Bahamas. The present study delineates important, post-nesting foraging habitats and migration corridors where loggerheads may interact with commercial fisheries—providing managers opportunities to develop and implement optimally effective conservation actions for the recovery of this threatened species.     

Satellite telemetry reveals behavioural plasticity in a green turtle population nesting in Sri Lanka

Satellite transmitters were deployed on ten green turtles (Chelonia mydas) nesting in Rekawa Sanctuary (RS-80.851°E 6.045°N), Sri Lanka, during 2006 and 2007 to determine inter-nesting and migratory behaviours and foraging habitats. Nine turtles subsequently nested at RS and demonstrated two inter-nesting strategies linked to the location of their residence sites. Three turtles used local shallow coastal sites within 60 km of RS during some or all of their inter-nesting periods and then returned to and settled at these sites on completion of their breeding seasons. In contrast, five individuals spent inter-nesting periods proximate to RS and then migrated to and settled at distant (>350 km) shallow coastal residence sites. Another turtle also spent inter-nesting periods proximate to RS and then migrated to a distant oceanic atoll and made forays into oceanic waters for 42 days before transmissions ceased. This behavioural plasticity informs conservation management beyond protection at the nesting beach.     

Fine-scale distribution of juvenile Atlantic and Mediterranean loggerhead turtles (Caretta caretta) in the Mediterranean Sea

Loggerhead turtles nesting in the Mediterranean Sea exhibit remarkable genetic structuring. This paper tests the hypothesis that young loggerhead turtles from different rookeries do not distribute homogeneously among the major Mediterranean foraging grounds, due to a complex pattern of surface currents. We extracted long fragments of mitochondrial DNA from 275 stranded or bycaught juvenile turtles from six foraging grounds (Catalano-Balearic Sea, Algerian basin, Tyrrhenian Sea, Adriatic Sea, northern Ionian Sea and southern Levantine Sea). We used a Bayesian mixed-stock analysis to estimate the contributions from rookeries in the Mediterranean, the North-west Atlantic and Cape Verde to the studied foraging grounds. Differences were found in the relative contribution of juvenile turtles of Atlantic and Mediterranean origin to each foraging ground. A decreasing proportion of Atlantic juveniles was detected along the main surface current entering the Mediterranean, with a high prevalence of turtles from eastern Florida in the Algerian basin and lower numbers elsewhere. In regard to the turtles of Mediterranean origin, juveniles from Libya prevailed in central and western Mediterranean foraging grounds other than the Algerian basin. Conversely, the Adriatic Sea was characterised by a large presence of individuals from western Greece, while the southern Levantine Sea was inhabited by a heterogeneous mix of turtles from the eastern Mediterranean rookeries (Turkey, Lebanon and Israel). Overall, the distribution of juveniles may be related to surface circulation patterns in the Mediterranean and suggests that fisheries might have differential effects on each population depending on the overlap degree between foraging and fishing grounds.     

Different growth rates between loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) of Mediterranean and Atlantic origin in the Mediterranean Sea

We estimated for the first time the growth rates of loggerhead sea turtles of Mediterranean and of Atlantic origin found in the Mediterranean Sea, combining both skeletochronological and genetic analyses. Our growth models suggested that the growth rate of loggerhead sea turtles of Mediterranean origin was faster than that of their conspecifics with an Atlantic origin exploiting the feeding grounds in the Mediterranean Sea. The age at maturity for Mediterranean origin loggerhead sea turtles, estimated using our best fitting model, was 24 years, which suggests that loggerhead sea turtles nesting in the Mediterranean are not only smaller than those nesting in the western North Atlantic but also younger.     

Bottom-up and climatic forcing on the worldwide population of leatherback turtles

Nesting populations of leatherback turtles (Dermochelys coriacea) in the Atlantic and western Indian Oceans are increasing or stable while those in the Pacific are declining. It has been suggested that leatherbacks in the eastern Pacific may be resource limited due to environmental variability derived from the El Ni?o Southern Oscillation (ENSO), but this has yet to be tested. Here we explored bottom-up forcing and the responding reproductive output of nesting leatherbacks worldwide. We achieved this through an extensive review of leatherback nesting and migration data and by analyzing the spatial, temporal, and quantitative nature of resources as indicated by net primary production at post-nesting female migration and foraging areas. Leatherbacks in the eastern Pacific were the smallest in body size and had the lowest reproductive output due to less productive and inconsistent resources within their migration and foraging areas. This derived from natural interannual and multidecadal climate variability together with an influence of anthropogenic climate warming that is possibly affecting these natural cycles. The reproductive output of leatherbacks in the Atlantic and western Indian Oceans was nearly twice that of turtles in the eastern Pacific. The inconsistent nature of the Pacific Ocean may also render western Pacific leatherbacks susceptible to a more variable reproductive output; however, it appears that egg harvesting on nesting beaches is their major threat. We suggest that the eastern Pacific leatherback population is more sensitive to anthropogenic mortality due to recruitment rates that are lower and more variable, thus accounting for much of the population differences compared to Atlantic and western Indian turtles.     

Diet of the Humboldt penguin (<Emphasis Type="Italic">Spheniscus humboldti</Emphasis>) in northern and southern Chile

The diet of the Humboldt penguin (Spheniscus humboldti) was examined and compared in two colonies in Chile. Field work was conducted on Pan de Azúcar Island in northern Chile in the breeding season 1998/1999 and on the Puñihuil Islands in southern Chile over two successive breeding seasons during 1997/1998 and 1998/1999. Penguin diet was studied by stomach-pumping birds and analysed by species composition, size and mass of prey. Fish were the dominant prey item at both sites, the contribution of cephalopods and crustaceans varying between sites. The fish prey consisted predominantly of school fish, but there were clear latitudinal differences in fish prey taken. Penguins in the northern colony consumed primarily garfish (Scomberesox saurus), while birds at the southern colony of Puñihuil fed primarily on anchovy (Engraulis ringens), Araucanian herring (Strangomera bentincki) and silverside (Odontesthes regia). The results showed significant differences in terms of numbers of fish taken between the two breeding seasons at Puñihuil. In 1997/1998 penguins consumed almost exclusively anchovy, while they fed primarily on silversides in the successive year. Almost all prey, except stomatopods, were characterised as being pelagic species that occur in relatively inshore water, consistent with the foraging behaviour of Humboldt penguins. The dependence of Humboldt penguins on commercially exploited, schooling prey species makes the species particularly susceptible to changes in prey stocks, due to non-sustainable fisheries management.Communicated by O. Kinne, Oldendorf/Luhe     

Flexible foraging movements of leatherback turtles across the North Atlantic Ocean

Some marine species have been shown to target foraging at particular hotspots of high prey abundance. However, we show here that in the year after a nesting season, female leatherback turtles (Dermochelys coriacea) in the Atlantic generally spend relatively little time in fixed hotspots, especially those with a surface signature revealed in satellite imagery, but rather tend to have a pattern of near continuous traveling. Associated with this traveling, distinct changes in dive behavior indicate that turtles constantly fine tune their foraging behavior and diel activity patterns in association with local conditions. Switches between nocturnal vs. diurnal activity are rare in the animal kingdom but may be essential for survival on a diet of gelatinous zooplankton where patches of high prey availability are rare. These results indicate that in their first year after nesting, leatherback turtles do not fit the general model of migration where responses to resources are suppressed during transit. However, their behavior may be different in their sabbatical years away from nesting beaches. Our results highlight the importance of whole-ocean fishing gear regulations to minimize turtle bycatch.     

Breeding biology of the green turtle, Chelonia mydas (Reptilia: Cheloniidae), on Wan-An Island, PengHu archipelago. II. Nest site selection

Nest site selection of the green turtles on Wan-An Island in the summer of 1996 was determined. Turtles (Chelonia mydas) laid on average one clutch for every three emergences. Even though the total track length was 115 m on average, individual lengths varied considerably depending on the nesting beach where the turtles emerged. Limited accessibility, i.e. adequate distance from the nearest village and a well-protected environment, make beaches A and D suitable nesting beaches for green turtles on Wan-An Island. Both total track and nesting track apexes were found clustered in the interface zone, and turtles preferred to reach the vegetation zone once they emerged from the sea. It is suggested that the turtles on Wan-An Island exhibit nest site selection behavior. Based on these results and the high nest site fidelity to their first nesting beach, conservation recommendations are proposed to the county and central governments for the preservation of nesting beaches in their natural state, by prohibiting illegal sand mining and properly controlling turtle watch groups on Wan-An Island. Received: 21 November 1997 / Accepted: 24 December 1998     

Satellite tracking experiments on the navigational ability and migratory behaviour of the loggerhead turtle Caretta caretta

Four loggerhead females (Caretta caretta) were caught when emerging at their nesting beach on the Natal coast, prevented from egg laying and displaced along the coast 38 to 70 km from the capture site. They were then released either on the shore or 37 km offshore. The successful journeys back to the capture area and the successive migrations were tracked by satellite. In compensating for the displacement, loggerheads showed a capability of true navigation. The 545 to 1000 km long migratory journeys of three turtles were followed along the Mozambique coast up to the feeding grounds. Migratory speed was similar at night and during the day. During the trip, submergences were shorter and more frequent than during the stay at the feeding grounds. Received: 17 March 1997 / Accepted: 21 April 1997