Satellite tracking of migrating loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) displaced in the open sea

Loggerhead turtles (Caretta caretta) are known to migrate towards fixed, individually-specific residential feeding grounds. To study their spatial behaviour and their navigational ability, five loggerheads nesting in South Africa were captured when about to start their postnesting migration and tracked by satellite after having been displaced from their usual migratory route. The first turtle, released south of Madagascar about 1,148 km from the capture site, moved west up to mainland Africa and then reached her feeding grounds by following the coast. A second turtle, released farther away (2,140 km) close to La Réunion Island, stopped for some time on the Madagascar east coast, then turned southwards to round the island and regain the African mainland in the northwest, without however allowing us to establish the location of her residential grounds. Three other turtles were released off the Tanzanian coast, 2,193 km north of their nesting area, at the northern edge of the distribution of the feeding grounds along the African coast. All of them headed north, and one turtle found her residential grounds located north of the release site. The other two females started long-distance oceanic wanderings in which they crossed nearly the entire Indian Ocean, apparently being transported by the sea currents of the region. We conclude that adult loggerhead turtles are apparently unable to compensate for the displacement and can return to a pelagic life style characteristic of juvenile turtles. These findings suggest that South African loggerheads rely on simple orientation mechanisms, such as the use of the coastline, as a guide, and compass orientation, possibly integrated by spatiotemporal programmes and/or acquired maps of familiar sites.Communicated by R. Cattaneo-Vietti, Genova     

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     

Satellite tracking reveals a dichotomy in migration strategies among juvenile loggerhead turtles in the Northwest Atlantic

Few data are available on the movements and behavior of immature Atlantic loggerhead sea turtles (Caretta caretta) from their seasonal neritic foraging grounds within the western north Atlantic. These waters provide developmental habitat for loggerheads originating from several western Atlantic nesting stocks. We examined the long-term movements of 23 immature loggerheads (16 wild-caught and seven headstart turtles) characterizing their seasonal distribution, habitat use, site fidelity, and the oceanographic conditions encountered during their migrations. We identified two movement strategies: (1) a seasonal shelf-constrained north–south migratory pattern; and (2) a year-round oceanic dispersal strategy where turtles travel in the Gulf Stream to the North Atlantic and their northern dispersal is limited by the 10–15°C isotherm. When sea surface temperatures dropped below 20°C, neritic turtles began a migration south of Cape Hatteras, North Carolina (USA) where they established fidelity to the waters between North Carolina’s Outer Banks and the western edge of the Gulf Stream along outer continental shelf. Two turtles traveled as far south as Florida. Several turtles returned to their seasonal foraging grounds during subsequent summers. Northern movements were associated with both increased sea surface temperature (>21°C) and increased primary productivity. Our results indicate strong seasonal and interannual philopatry to the waters of Virginia (summer foraging habitat) and North Carolina (winter habitat). We suggest that the waters of Virginia and North Carolina provide important seasonal habitat and serve as a seasonal migratory pathway for immature loggerhead sea turtles. North Carolina’s Cape Hatteras acts as a seasonal “migratory bottleneck” for this species; special management consideration should be given to this region. Six turtles spent time farther from the continental shelf. Three entered the Gulf Stream near Cape Hatteras, traveling in the current to the northwest Atlantic. Two of these turtles remained within an oceanic habitat from 1 to 3 years and were associated with mesoscale features and frontal systems. The ability of large benthic subadults to resume an oceanic lifestyle for extended periods indicates plasticity in habitat use and migratory strategies. Therefore, traditional life history models for loggerhead sea turtles should be reevaluated.     

Movements and site fidelity of grass shrimp (<Emphasis Type="Italic">Palaemonetes pugio</Emphasis> and <Emphasis Type="Italic">P. vulgaris</Emphasis>) in salt marsh intertidal creeks

Grass shrimp are abundant residents of shallow-water habitats in US Atlantic and Gulf coast estuaries. Mark-recapture events determined the extent and direction of their movements in meso-tidal salt marsh creeks at North Inlet, South Carolina. Microwire-tagged Palaemonetes vulgaris demonstrated high fidelity for a dock in a subtidal channel. In the 48 days following release, 11 % of the 422 tagged shrimp were recaptured and 99 % of all recaptures were made there an average of 14 days post-release. Palaemonetes pugio, which favored the use of shallow intertidal areas, exhibited moderate fidelity for pools within creek beds with 53 % of the recaptured shrimp collected at the release site. Higher fidelity was observed for confluences of intertidal creeks and the subtidal channels. Of the 5565 shrimp released with coded microwire tags, 7.5 % were recaptured and 98 % of those recaptures were at release sites up to 53 days later. During another event, P. pugio released 235 m from their origin demonstrated relatively low fidelity for the new site and a lack of homing behavior. Of the 544 tagged shrimp, 3 % were recaptured; only 40 % of those recaptured were from the release site. Site fidelity is a mechanism by which previously discovered large and consistent differences in grass shrimp use of neighboring intertidal creek basins can be sustained over weeks, seasons, and years. Spatial variations and the tendency of these keystone organisms to resist relocation by tidal currents and occupy certain areas for extended periods should be considered in decisions about proposed alterations to creeks and shorelines.     

Comparative skeletochronological analysis of Kemp’s ridley (<Emphasis Type="Italic">Lepidochelys kempii</Emphasis>) and loggerhead (<Emphasis Type="Italic">Caretta caretta</Emphasis>) humeri and scleral ossicles

Skeletochronological analysis of Kemp’s ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtle humeri and scleral ossicles was conducted to (1) describe the characteristics of scleral ossicles in these species, (2) determine whether the scleral ossicles contain annually deposited skeletal growth marks and (3) evaluate the potential for skeletochronological analysis of ossicles to obtain age data for size classes and species of sea turtles whose humeri exhibit prohibitive amounts of growth mark resorption. Humeri, entire eyes, and/or individual scleral ossicles were collected from stranded, dead sea turtles that were found along the coasts of Florida, North Carolina, Virginia, and Texas, USA. Samples were taken from a total of 77 neritic, juvenile Kemp’s ridleys ranging from 21.1 to 56.8 cm straightline carapace length (SCL), as well as two Kemp’s ridley hatchlings. For loggerheads, samples were obtained from 65 neritic juvenile and adult turtles ranging from 44.7 to 103.6 cm SCL and ten hatchlings. Examination of the ossicles revealed the presence of marks similar in appearance to those found in humeri. The number of marks in the ossicles and humeri of individual juvenile Kemp’s ridleys for which both structures were collected (n = 55) was equivalent, strongly indicating that the marks are annual. However, in large juvenile and adult loggerhead turtles (n = 65), some significant resorption of early growth marks was observed, suggesting that although ossicles might be useful for skeletochronological analysis of small juveniles, they may not provide a reasonable alternative to humeri for obtaining age estimates for older loggerhead sea turtles.     

Home range and habitat use of juvenile Atlantic green turtles (Chelonia mydas L.) on shallow reef habitats in Palm Beach, Florida, USA

Many animals, including sea turtles, alter their movements and home range in relation to the particular type and quality of the habitat occupied. When sufficient resources are available, individuals may develop affinities to specific areas for activities, such as foraging and (or) resting. In the case of green sea turtles (Chelonia mydas L.), after a number of years in the open ocean, juveniles recruit to shallow-water developmental habitats where they occupy distinct home ranges as they feed and grow to maturity. Our goal was to study the habitat use and home range movements of juvenile green turtles along a shallow, worm-rock reef tract in Palm Beach, Florida. Six turtles, measuring from 27.9 to 48.1 cm in straight carapace length and from 7.2 to 12.6 kg in mass, were tracked via ultrasonic telemetry from August to November 2003. Upon capture, each turtle’s esophagus was flushed via lavage to determine recently ingested foods. In addition, four turtles were recaptured and fitted with a time-depth recorder to study dive patterns. Home range areas measured with 100% minimum convex polygon and 95% fixed kernel estimators varied from 0.69 to 5.05 km² (mean=2.38±1.78 km²) and 0.73 to 4.89 km² (mean=2.09±1.80 km²), respectively. Home ranges and core areas of turtles were largely restricted to the reef tract itself, and showed considerable overlap between food and shelter sites. The mean number of dives during daylight hours (0600–1800 hours) was 84±5.0 dives, while the mean during night hours (1800–0600 hours) was 39±3.0 dives. Dives during the day were shallower (mean=3.20±1.26 m) than dives at night (mean=5.59±0.09 m). All six turtles were found to have a mixed diet of similar macroalgae and sponge fragments. Our results reveal that juvenile green turtles occupy stable home ranges along the nearshore worm-rock reefs of Southeast Florida, during the summer and fall. Determining which habitats are used by green turtles will assist conservation managers in their global effort to protect this endangered species.     

The spatial ecology of juvenile loggerhead turtles (Caretta caretta) in the Indian Ocean sheds light on the “lost years” mystery

While our understanding of the early oceanic developmental stage of sea turtles has improved markedly over recent decades, the spatial context for this life history stage remains unknown for Indian Ocean loggerhead turtle populations. To address this gap in our knowledge, 18 juvenile loggerheads were satellite tracked from Reunion Island (21.2°S, 55.3°E) between 2007 and 2011. Nine turtles swam north toward Oman (20.5°N, 58.8°E), where one of the world’s largest rookeries of loggerheads is located. Three individuals traveled south toward South Africa and Madagascar, countries that also host loggerhead nesting grounds. Fourteen of the transmitters relayed diving profiles. A dichotomy between diurnal and nocturnal diving behavior was observed with a larger number of shorter dives occurring during the day. Diving behavior also differed according to movement behavior as individuals spent more time in subsurface waters (between 10 and 20 m) during transit phases. The study provides an understanding of the oceanic movement behavior of juvenile loggerheads in the Indian Ocean that suggests the existence of an atypical trans-equatorial developmental cycle for the species at the ocean basin scale in the Indian Ocean. These results address a significant gap in the understanding of loggerhead oceanic movements and may help with the conservation of the species.     

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.     

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.     

Hitchhikers reveal cryptic host behavior: new insights from the association between Planes major and sea turtles in the Pacific Ocean

Studies that incorporate information from habitat-specific ecological interactions (e.g., epibiotic associations) can reveal valuable insights into the cryptic habitat-use patterns and behavior of marine vertebrates. Sea turtles, like other large, highly mobile marine vertebrates, are inherently difficult to study, and such information can inform the implementation of conservation measures. The presence of epipelagic epibionts, such as the flotsam crab Planes major, on sea turtles strongly suggests that neritic turtles have recently occupied epipelagic habitats (upper 200 m in areas with >200 m depth) and that epipelagic turtles spend time at or near the surface. We quantified the effects of turtle species, turtle size, and habitat (neritic or epipelagic) on the frequency of epibiosis (F ₀) by P. major on sea turtles in the Pacific Ocean. In neritic habitats, we found that loggerhead (F ₀ = 27.6 %) and olive ridley turtles (F ₀ = 26.2 %) host crabs frequently across a wide range of body sizes, and green turtles almost never host crabs (F ₀ = 0.7 %). These results suggest that loggerheads and olive ridleys display variable/flexible epipelagic-neritic transitions, while green turtles tend to transition unidirectionally at small body sizes. In epipelagic habitats, we found that loggerheads host crabs (F ₀ = 92.9 %) more frequently than olive ridleys (F ₀ = 50 %) and green turtles (F ₀ = 38.5 %). These results suggest that epipelagic loggerheads tend to spend more time at or near the surface than epipelagic olive ridleys and green turtles. Results of this study reveal new insights into habitat-use patterns and behavior of sea turtles and display how epibiont data can supplement data from more advanced technologies to gain a better understanding of the ecology of marine vertebrates during cryptic life stages.     

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     

A quantitative study of intertidepool movement of the wooly sculpin Clinocottus analis

Movements of the wooly sculpin Clinocottus analis between all pools in a designated area of a southern California (USA) intertidal zone were studied. Fish were captured during low tides, finclipped or bead-tagged, and released in the pool of capture. Percent recaptured in pool of first capture declined from 30 after 2 weeks to about 5 after 20 weeks. Percent recaptured in any pool in the study area declined from 50 after 2 weeks to 20 after 8 weeks, but remained at 20 through 16 weeks. A higher fidelity to an area of the intertidal zone than to a specific pool was suggested. Large fish exhibited higher probability of recapture than smaller individuals, indicating they become more sedentary with age. Changes in pool topography influenced percent recurrence in a pool, most likely as a consequence of changes in quality and quantity of cover available. Such responses to changes in specific pools and fidelity to intertidal areas containing several pools appear to be advantageous behavioral patterns in an environment where topographic change is frequent and often massive.     

A model of area fidelity,nomadism, and distribution patterns of loggerhead sea turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) in the Mediterranean Sea

Sea turtle tagging carried out in Italy in the period 1981–2006 resulted in 125 re-encounters of loggerhead turtles (Caretta caretta) after a mean of 2.5 years, from different marine areas in the Mediterranean. At first finding, turtles ranged 25–83 cm of curved carapace length. Data were analyzed according to size, area, habitat type, season, in order to provide indication of movement patterns. When integrated with other information, results indicate that: (1) a part of turtles in the oceanic stage show a nomad behavior with movements among different oceanic areas; (2) another part show fidelity to an oceanic area; (3) turtles in the neritic stage show fidelity to neritic areas, and once settled to one area, change to other neritic areas is unlikely; (4) nomad oceanic turtles are significantly larger than sedentary ones, and also larger than turtles found in neritic areas; it is hypothesized that these could be Atlantic turtles that eventually leave the Mediterranean; (5) ecological transition from oceanic to neritic habitats occurs at a wide range of sizes, and some turtles may have a very brief oceanic stage; (6) turtles in the oceanic stage are more likely to recruit to neritic areas close to their oceanic areas than to distant ones; (7) part of turtles from some Mediterranean nesting beaches might frequent a relatively limited area range, including both oceanic and neritic areas; (8) in most of the Mediterranean, latitudinal seasonal migrations are unlikely. A general model of movement patterns of loggerhead turtles in the Mediterranean is proposed.     

Ecology of loggerhead marine turtles Caretta caretta in a neritic foraging habitat: movements, sex ratios and growth rates

Much is still to be learned about the spatial ecology of foraging marine turtles, especially for juveniles and adult males which have received comparatively little attention. Additionally, there is a paucity of ecological information on growth rates, size and age at maturity, and sex ratios at different life stages; data vital for successful population modelling. Here, we present results of a long-term (2002–2011) study on the movements, residency, growth and sex ratio of loggerhead turtles (Caretta caretta) in Amvrakikos Gulf (39°0′N 21°0′E), Greece, using satellite telemetry (N = 8) and ongoing capture–mark–recapture (CMR; N = 300 individuals). Individuals encountered at sea ranged from large juvenile to adult (46.2–91.5 cm straight carapace length) and demonstrated growth rates within published norms (<2.7 cm yr^?1) that slowed with increasing body size. We revealed that an unexpectedly high proportion of animals were male (>44 % of captures above 65 cm straight carapace length), compared to region-wide female-biased hatchling production, indicating sex-biased survival or possible behavioural drivers for likelihood of capture in the region. Satellite tracking confirmed that some turtles establish discrete, protracted periods of residency spanning more than 1 year, whilst others migrated away from the site. These findings are underlined by CMR results with individual capture histories spanning up to 7 years, and only 18 % of individuals being recaptured.     

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.     

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     

Detection of coastal mud odors by loggerhead sea turtles: a possible mechanism for sensing nearby land

For sea turtles, an ability to detect land masses from a considerable distance away, and to distinguish coastal areas from the open sea, might be adaptive. The loggerhead turtle, Caretta caretta, can detect airborne odorants associated with food. To investigate whether sea turtles can also detect odors associated with land, we studied the responses of juvenile loggerheads to odors from coastal mud. Turtles were tested in a water-filled arena in which odorants could be introduced to the air above the water surface. Turtles exposed to air that had passed over a cup containing mud spent more time with their noses out of the water than did control turtles exposed to air that had passed over a cup containing distilled water. The results demonstrate for the first time that loggerheads can detect airborne odorants associated with land, an ability that might play a role in foraging, navigation, or both.     

Tracking post-nesting movements of loggerhead turtles (Caretta caretta) with sonic and radio telemetry on the southwest coast of Florida, USA

Nine post-nesting loggerhead turtles (Caretta caretta) were tracked using sonic and radio telemetry. Tracking began immediately after the turtles left the beach and continued until contact was either lost or terminated. As sonic tags transmit continuously underwater, they were much more effective than the radio tags in determining the paths of the turtles. Radio tags transmit only at the surface and were useful in ascertaining submergence durations. For nine of the ten turtles tracked with sonic signals, the gross movement was away from the beach in a westerly direction. The tracking periods ranged from 3.35 to 8.25 h, while the straight-line movements ranged from 3.05 to 12.88 km, respectively. Sixty-seven percent of the submergence durations recorded were <3 min. This respiratory behavior suggests continuous swimming, and the paths of the turtles suggested directed movement offshore immediately after nesting. The gradual littoral slope and lack of nearshore structure in this part of the Gulf of Mexico could be contributing factors to the patterns of dispersal observed, as benthic structures provide resting and foraging habitat for loggerheads.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Habitat use by loggerhead sea turtles <Emphasis Type="Italic">Caretta caretta</Emphasis> off the coast of eastern Spain results in a high vulnerability to neritic fishing gear

Previous studies of loggerhead sea turtles have concluded that drifting longlines were the main threat for immature specimens in the western Mediterranean, because immature loggerhead sea turtles mainly inhabit oceanic waters. However, recent aerial surveys have revealed large numbers of immature loggerhead sea turtles over the continental shelf of eastern mainland Spain, where turtles are exposed to neritic fishing gears but not to drifting longlines. We satellite-tracked seven loggerhead sea turtles (minimum straight carapace length (SCLmin) range: 36.5–55.0 cm) to assess whether the turtles in this region are vagrants from the adjoining oceanic regions or whether these loggerheads mostly inhabit the continental shelf. Satellite-tracking revealed that six of the tagged turtles avoided the oceanic realm and made extended use of the continental shelf, whereas only one individual could be considered a true vagrant as it avoided the continental shelf and primarily used the oceanic habitat. These results are in sharp contrast with those previously reported for immature loggerhead sea turtles of similar size from the south-western Mediterranean and fit well a relaxed ontogenic model that was recently proposed for loggerhead sea turtles in the central Mediterranean. Furthermore, these results demonstrate the vulnerability of loggerhead sea turtles of eastern mainland Spain to neritic fishing gears, as three of the seven turtles died and one was bycaught incidentally while being tracked over the continental shelf.