Juvenile Hawksbill Research Articles

Population structure of marine turtles in coastal waters of Qatar

Knowledge of the interrelationships between habitats and life-stage development in marine turtles requires an understanding of recruitment, size and age at maturity, sex ratios, growth and sexual development rates, survivorship and nesting probabilities. These data may be used to determine the status and survival of turtle populations during earlier life stages and for the development of appropriate conservation strategies. We sampled in-water stocks of marine turtles in coastal waters of Qatar using rodeo-style captures, entrapments in an industrial cooling intake and opportunistic bycatch to determine species, size, gender and age class. Our results revealed that Qatar is home to a resident population of small juvenile green turtles (<40 cm curved cara- pace length, CCL) and a transient population of juvenile hawksbills (<25 cm CCL) at an approxi- mate 7:3 ratio of green to hawksbill turtles. Hawksbills were male-biased (4M:1F) while green tur- tles were slightly female biased (2M:3F). Given the extreme high ambient and water temperatures in the Arabian Gulf, which may be considered a living laboratory for understanding climate change effects on marine species, our results are not conclusive that elevated temperatures have led to feminisation of marine turtle populations. We instead believe that there may be a regional and/or evolutionary shift in the pivotal temperature that regulates ecologically appropriate sex determination, which requires further investigation. Our data provide, for the first time, a descrip- tion of the foraging marine turtle population structure in Qatari waters, and point to a need for protection of seagrass beds, effective mitigation measures for sedimentation from coastal develop- ment and rehabilitation of coral-reef habitats.

Characterization of a subtropical hawksbill sea turtle (Eretmocheyles imbricata) assemblage utilizing shallow water natural and artificial habitats in the Florida Keys.

In order to provide information to better inform management decisions and direct further research, vessel-based visual transects, snorkel transects, and in-water capture techniques were used to characterize hawksbill sea turtles in the shallow marine habitats of a Marine Protected Area (MPA), the Key West National Wildlife Refuge in the Florida Keys. Hawksbills were found in hardbottom and seagrass dominated habitats throughout the Refuge, and on man-made rubble structures in the Northwest Channel near Cottrell Key. Hawksbills captured (N = 82) were exclusively juveniles and subadults with a straight standard carapace length (SSCL) ranging from 21.4 to 69.0cm with a mean of 44.1 cm (SD = 10.8). Somatic growth rates were calculated from 15 recaptured turtles with periods at large ranging from 51 to 1188 days. Mean SSCL growth rate was 7.7 cm/year (SD = 4.6). Juvenile hawksbills (<50 cm SSCL) showed a significantly higher growth rate (9.2 cm/year, SD = 4.5, N = 11) than subadult hawksbills (50–70 cm SSCL, 3.6 cm/year, SD = 0.9, N = 4). Analysis of 740 base pair mitochondrial control region sequences from 50 sampled turtles yielded 12 haplotypes. Haplotype frequencies were significantly different compared to four other Caribbean juvenile foraging aggregations, including one off the Atlantic coast of Florida. Many-to-one mixed stock analysis indicated Mexico as the primary source of juveniles in the region and also suggested that the Refuge may serve as important developmental habitat for the Cuban nesting aggregation. Serum testosterone radioimmunoassay results from 33 individuals indicated a female biased sex ratio of 3.3 females: 1 male for hawksbills in the Refuge. This assemblage of hawksbills is near the northern limit of the species range, and is one of only two such assemblages described in the waters of the continental United States. Since this assemblage resides in an MPA with intensive human use, basic information on the assemblage is vital to resource managers charged with conservation and species protection in the MPA.

Recognition of juvenile hawksbills Eretmochelys imbricata through face scale digitization and automated searching

Advancements in digital photography have facilitated the use of photo-ID to track individual animals, making this technique of great value for conservation biology. However, the time required to manually match new photographs to those stored in a database is proportional to the size of the database. Therefore, there is need for investigating the potential to automate the searching processes through computerized means. We encountered hawksbill turtles Eretmo che - lys imbricata (n = 2) that were members of an ongoing study but had lost flipper tags and shell etchings. To identify individuals, we first manually searched photographs of turtles previously captured and released. Manual visual matching of the 2 turtles encountered was successful for 100% of tested photographs. To investigate automated recognition of turtles in a database, we used the spot recognition program, I 3 S, to digitize scutes on the dorsal and lateral surfaces of the head and to compare spot patterns through the automated system. I 3 S successfully identified the 2 return turtles as the same turtles identified by the manual visual matching method. To assess the ability of I 3 S to identify turtles both present in and absent from the database, we blind-tested a series of photographs of turtle heads and faces using both manual visual methods and I 3 S. With I 3 S, 84.6% of the computerized photos were successfully matched with photos in the database, with scores produced ranging from 0.069 to 0.435. This study showed the potential for using a photo-database for long-term identification of individual turtles, but that the usefulness of a photo- database depends on the quality of the photos and the flexibility of the computer program used.

Ascension Island as a mid-Atlantic developmental habitat for juvenile hawksbill turtles

Ascension Island in the South Atlantic Ocean is renowned for its globally-important nesting population of green turtles (Chelonia mydas) that has been the subject of long-term research. By comparison, very little is known about the apparently small population of hawksbill turtles (Eretmochelys imbricata) that have been recorded in its waters, thousands of kilometres from known nesting beaches. Here, we collate 10 years of in-water tagging data, opportunistic public sighting records and underwater observations to provide a baseline for future research, and present preliminary data on habitat use derived from two individuals fitted with GPS transmitters. Although public sightings were inevitably biased towards popular recreation areas, the resulting distribution suggests that hawksbill turtles occur year round in Ascension Island's waters along the entire 65 km of coastline. Hawksbills were observed feeding on benthic algae and encrusting sponges, and were frequently seen scavenging on fish discards around the Island's pier at night aided by anthropogenic lighting. Between 2003 and 2013, 35 turtles were captured, measured, tagged and then released. Curved carapace lengths ranged from 33.5 to 85 cm (mean = 48.8 cm) indicating that most (if not all) individuals encountered around Ascension are post-pelagic juveniles. Four individuals were recaptured at least once giving a mean minimum residence time of 4.2 yr (range: 2.8–7.3 yr) and a mean growth rate of 2.8 cm yr−1. Turtles fitted with Fastloc™ GPS devices remained at Ascension Island for the duration of the study (&gt;90 days) and occupied restricted home ranges with an average area of 2.5 km2 and an average ‘core use area’ (50% utilization distribution) of 0.05 km2. Together, these results suggest that Ascension Island serves as a mid-Atlantic developmental habitat for benthic-feeding, juvenile hawksbill turtles on extended oceanic migrations before recruiting to their adult foraging grounds, likely to be located in Brazil or tropical West Africa.

Plasma biochemical and PCV ranges for healthy, wild, immature hawksbill (Eretmochelys imbricata) sea turtles

In recent years, the use of blood chemistry as a diagnostic tool for sea turtles has been demonstrated, but much of its effectiveness relies on reference intervals. The first comprehensive...

High rates of growth recorded for hawksbill sea turtles in Anegada, British Virgin Islands.

Management of species of conservation concern requires knowledge of demographic parameters, such as rates of recruitment, survival, and growth. In the Caribbean, hawksbill turtles (Eretmochelys imbricata) have been historically exploited in huge numbers to satisfy trade in their shells and meat. In the present study, we estimated growth rate of juvenile hawksbill turtles around Anegada, British Virgin Islands, using capture–mark–recapture of 59 turtles over periods of up to 649 days. Turtles were recaptured up to six times, having moved up to 5.9 km from the release location. Across all sizes, turtles grew at an average rate of 9.3 cm year−1 (range 2.3–20.3 cm year−1), and gained mass at an average of 3.9 kg year−1 (range 850 g–16.1 kg year−1). Carapace length was a significant predictor of growth rate and mass gain, but there was no relationship between either variable and sea surface temperature. These are among the fastest rates of growth reported for this species, with seven turtles growing at a rate that would increase their body size by more than half per year (51–69% increase in body length). This study also demonstrates the importance of shallow water reef systems for the developmental habitat for juvenile hawksbill turtles. Although growth rates for posthatching turtles in the pelagic, and turtles larger than 61 cm, are not known for this population, the implications of this study are that Caribbean hawksbill turtles in some areas may reach body sizes suggesting sexual maturity in less time than previously considered.

Numerical dispersal simulations and genetics help explain the origin of hawksbill sea turtles in Ascension Island

Long-distance dispersal and ontogenetic shifts in habitat use are characteristic of numerous marine species and have important ecological, evolutionary, and management implications. These processes, however, are often challenging to study due to the vast areas involved. We used genetic markers and simulations of physical transport within an ocean circulation model to gain understanding into the origin of juvenile hawksbill sea turtles (Eretmochelys imbricata) found at Ascension Island, a foraging ground that is thousands of kilometers from known nesting beaches. Regional origin of genetic markers suggests that turtles are from Western Atlantic (86%) and Eastern Atlantic (14%) rookeries. In contrast, numerical simulations of transport by ocean currents suggest that passive dispersal from the western sources would be negligible and instead would primarily be from the East, involving rookeries along Western Africa (i.e., Principe Island) and, potentially, from as far as the Indian Ocean (e.g., Mayotte and the Seychelles). Given that genetic analysis identified the presence of a haplotype endemic to Brazilian hawksbill rookeries at Ascension, we examined the possible role of swimming behavior by juvenile hawksbills from NE Brazil on their current-borne transport to Ascension Island by performing numerical experiments in which swimming behavior was simulated for virtual particles (simulated turtles). We found that oriented swimming substantially influenced the distribution of particles, greatly altering the proportion of particles dispersing into the North Atlantic and South Atlantic. Assigning location-dependent orientation behavior to particles allowed them to reach Ascension Island, remain in favorable temperatures, encounter productive foraging areas, and return to the vicinity of their natal site. The age at first arrival to Ascension (4.5–5.5years) of these particles corresponded well to estimates of hawksbill age based on their size. Our findings suggest that ocean currents and swimming behavior play an important role in the oceanic ecology of sea turtles and other marine animals.

Habitat Use and Diet of Juvenile Eastern Pacific Hawksbill Turtles (Eretmochelys imbricata) in the North Pacific Coast of Costa Rica

The hawksbill turtle (Eretmochelys imbricata) is critically endangered throughout its global range and is particularly threatened in the eastern Pacific, a region where our knowledge of the ecological traits is very limited. Understanding habitat preferences of hawksbills at different life stages is necessary to create effective local and regional conservation strategies. We studied habitat use and the diet of juvenile hawksbill sea turtles at Punta Coyote, a rocky reef located along the Nicoya Peninsula on the north Pacific coast of Costa Rica, along the northern boundary of the Caletas–Arío National Wildlife Refuge. We tracked 12 juvenile hawksbills (36–69-cm curved carapace length) with acoustic transmitters to study their habitat use. Turtles were on the rocky reef more frequently than the sandy bottoms (χ21 = 29.90, p = 0.00). The 95% fixed kernel density home range analysis revealed high-intensity use of the rocky reef, where hawksbills mainly dove in shallow waters (7.6 ± 3.3 m). Less than 5% of the 95% home range area overlapped with the Caletas–Arío National Wildlife Refuge. Hawksbills fed mainly on 2 invertebrate species regardless of season: a sponge (Geodia sp.) (mean volume = 67%) and a tunicate (Rhopalaea birkelandi) (mean volume = 51%). Our surveys along the Nicoya Peninsula suggested that use of rocky reefs by juvenile hawksbill turtles was common. To protect juvenile hawksbills in the study area, we recommend that this site be granted official protection status as part of the Caletas–Arío National Wildlife Refuge. We also suggest studying other discrete rocky reefs along the Nicoya Peninsula to determine critical habitats for the hawksbill turtle to improve conservation and management policy.

Ecology and Conservation of Marine Turtles in a Central Pacific Foraging Ground

Abstract Foraging grounds are critical to the survival of marine turtles, yet studies of these areas lag behind those of nesting sites. Our study represents the first data and discussion on marine turtle distribution, abundance, and health at a marine turtle foraging ground in the central Pacific, Palmyra Atoll National Wildlife Refuge, which constitutes a regionally important mixed-size-class foraging ground for green turtles (Chelonia mydas) and, to a lesser extent, for hawksbill turtles (Eretmochelys imbricata). Surveys and anecdotal reports suggest that nesting activity is rare, and we have confirmed the presence of limited suitable nesting habitat. During in-water activities from 2008 to 2011, we caught 211 green turtles ranging from postpelagic juveniles to adults (weight: mean = 44.6 kg, range = 7.2–146.3 kg; curved carapace length (CCL): mean = 69.7 cm, range = 41.0–113.6 cm) and 2 juvenile hawksbills (weight2009 = 16.3 kg, CCL2009 = 57.0; weight2011 = 11.2 kg, CCL2011 = 50.5 cm). ...

Ecology of juvenile hawksbills (Eretmochelys imbricata) at Buck Island Reef National Monument, US Virgin Islands

Surveys of juvenile hawksbills around Buck Island Reef National Monument, US Virgin Islands from 1994 to 1999 revealed distributional patterns and resulted in a total of 75 individual hawksbill captures from all years; turtles ranged from 23.2 to 77.7 cm curved carapace length (CCL; mean 42.1 ± 12.3 cm SD). Juveniles concentrated where Zoanthid cover was highest. Length of time between recaptures, or presumed minimum site residency, ranged from 59 to 1,396 days (mean 620.8 ± 402.4 days SD). Growth rates for 23 juveniles ranged from 0.0 to 9.5 cm year−1 (mean 4.1 ± 2.4 cm year−1SD). Annual mean growth rates were non-monotonic, with the largest mean growth rate occurring in the 30–39 cm CCL size class. Gastric lavages indicated that Zoanthids were the primary food source for hawksbills. These results contribute to our understanding of juvenile hawksbill ecology and serve as a baseline for future studies or inventories of hawksbills in the Caribbean.

Estimating sex ratios in Caribbean hawksbill turtles: testosterone levels and climate effects

Evolutionary theory predicts that male and female offspring should be produced at a 1:1 ratio, but this may rarely be the case for species in which sex is determined during incubation by temperature, such as marine turtles. Estimates of primary sex ratio suggest that marine turtle sex ratios are highly skewed, with up to 9 females per male. We captured juvenile hawksbill turtles Eretmochelys imbricata in waters around Anegada, British Virgin Islands, a regionally important foraging aggregation, and analysed concentrations of plasma testosterone and oestra- diol-17β from 62 turtles to estimate sex ratio. There were 2.4 to 7.7 times more females than males. Testosterone concentrations correlated with sampling date and sea surface temperature (SST), with higher con centrations in the late summer when SST was highest, suggesting that assigning sex through threshold values of sex hormones must be carried out cautiously. The sex ratio in the juvenile foraging aggregation around Anegada is more male biased than at other locations, sug- gesting that turtles at Anegada have resilience against feminising effects of climate change. Future work should (1) integrate the relative contributions of different genetic stocks to foraging aggregations and (2) investigate the annual and seasonal cycles of sex hormones, and differences among individuals and life history stages.

Home Range and Foraging Ecology of Juvenile Hawksbill Sea Turtles (Eretmochelys imbricata) on Inshore Reefs of Honduras

Despite the recognition of the historical importance of hawksbills in the Caribbean region of Honduras, prior sea turtle research in the area has been extremely limited, and little is known about hawksbill turtle (Eretmochelys imbricata) ecology from this region. We tracked 6 juvenile hawksbills (28.7–35.6 cm, straight carapace length [SCL]) with radiotelemetry off the coast of Roatán in the Bay Islands of Honduras, conducted habitat assessments at 14 sites, and examined the diet of 5 juvenile hawksbills (19.8–49.7 cm, SCL) using gastric (n = 4) and fecal (n = 1) samples. Home ranges of all 6 turtles were small, with 100% minimum convex polygons from 0.15 to 0.55 km2, and a 50% fixed kernel density for all animals pooled of 5.46 km2. The habitat assessment showed that common prey items in hawksbill diets were abundant in areas where juvenile hawksbills were resident and in nonresident areas, with sponges (Chondrilla sp., Geodia sp.) and octocorals (Pseudopterogorgia sp.) being most prevalent. We found sponge to be the primary component in the diet, comprising 59% of total ingesta. The most prevalent sponge species in the diet samples were Melophlus ruber and Chondrilla caribensis. Although C. caribensis is a common constituent of hawksbill diets, the current study provides the first report of M. ruber as a component of hawksbill diets. Home ranges of juvenile hawksbills in the Port Royal region of Roatán are small (< 1 km2), and their primary dietary component is the sponge M. ruber. Conservation efforts on Roatán should be established in the Port Royal region, and should include protection of dietary items and turtles.

Effect of Food Availability on the Abundance of Juvenile Hawksbill Sea Turtles (Eretmochelys imbricata) in Inshore Aggregation Areas of the Culebra Archipelago, Puerto Rico

Habitat features influence the distribution and abundance of marine animals and are used to identify critical areas to protect threatened marine species. In this study, we surveyed juvenile hawksbill turtles in 5 localities of the Culebra Archipelago, Puerto Rico; described the habitats using cover of benthic features; and related relative abundance of turtles among localities with food availability. We tested the hypothesis that variability in turtle abundance among study sites was related to spatial variability in the availability of diet items. Our results point out that spatial variability in turtle abundance is not related to food availability by itself; rather, the structural complexity and types of benthic structure played a more important role in explaining the turtles' local abundance. The importance of structural complexity is most likely related to sheltering.

Foraging Selectivity of the Hawksbill Sea Turtle (Eretmochelys imbricata) in the Culebra Archipelago, Puerto Rico

Recent literature on foraging in Hawksbill Sea Turtles in the Caribbean region concludes that prey selectivity is a combination of preference for certain prey species and their local abundance. In this study, prey selectivity patterns were measured in five juvenile Hawksbill Sea Turtle (Eretmochelys imbricata) aggregations in the Culebra Archipelago, Puerto Rico, and the hypothesis that juvenile Hawksbill Sea Turtles exhibit selectivity for certain prey items independent of their environmental availability was tested. Hawksbill Sea Turtles showed positive selection for the corallimorph Ricordea florida, which was rare in all four study sites, and for the alga Lobophora variegata, that was abundant in one site. Turtles exhibited low preference for the sponge Chondrilla nucula, the most common prey item in both diet samples and the environment at all study sites. Low preference for this sponge corresponds to its high availability in the environment. Turtles also exhibited low preference for the sponge Cinacyrella sp. and the branching anemone Lebrunia danae. That juvenile hawksbills exhibited strong positive selectivity for rare items indicates that diet selection is not necessarily related to the abundance of the items in the environment. In addition, spatial variability in diet composition among Hawksbill Sea Turtles in the Culebra Archipelago indicates plasticity in their foraging habits.

Insights into habitat utilisation of the hawksbill turtle, Eretmochelys imbricata (Linnaeus, 1766), using acoustic telemetry

Patterns of distribution, key biometric parameters and home range extent were determined for hawksbill turtles at Lighthouse Reef Atoll (LRA), Belize over two field seasons (16days, 2009; 30days, 2010). Relative abundance was determined using 49 sightings transects (≈1km) distributed across the atoll and of all turtles encountered (n=68), 91% were immature (CCLmin≤65cm). Habitat type was significantly correlated with abundance, with more turtles encountered on the coral reef than in the lagoon (GzLMM, χ22=6.85, p<0.05; CPUE reef=1.41turtlesh−1, CPUE lagoon=0.62turtlesh−1). Hawksbills were also significantly more abundant within protected areas (GzLMM, χ21=8.69, p<0.05; CPUE Blue Hole Natural Monument (BHNM)=2.96turtlesperson−1h−1; CPUE Half Moon Caye Natural Monument (HMCNM)=2.34turtlesh−1; outside boundaries=0.88 turtlesh−1). Of 26 captures, 19 focal individuals were equipped with ultrasonic transmitters for active acoustic telemetry, and tracked for 6–25days (n=10, 2009; n=9, 2010). Spatial habitat utilisation was found to be highly variable, with large areas of overlap between distinct home ranges. Home range averaged 31.2ha±32.6 (range 5.1–111.3ha) for the juveniles that were successfully tracked (n=15), with maximum displacement in the order of 1.8km±1.0 (range 0.5–4.0km) and net displacement at 1.2km±0.9. This offshore atoll constitutes an important developmental habitat for the regional population and although our tracking durations were limited, home range of juvenile hawksbills at this site is significantly more expansive than that documented elsewhere.

Plasma Biochemistry and Hematology Values in Juvenile Hawksbill Turtles (Eretmochelys imbricata) Undergoing Rehabilitation

The hawksbill turtle (Eretmochelys imbricata) is a regular inhabitant of the Arabian Gulf. Sea turtles are included in the IUCN red list, and the hawksbill is listed as critically endangered. From March 2004 to September 2010, the Dubai Turtle Rehabilitation Project received 150 sick and injured juvenile hawksbill turtles, rescued in the Arabian Gulf. Blood samples taken from the animals during convalescence and prior to release were analyzed, establishing a hematology and biochemistry reference interval for clinically healthy rehabilitated juvenile hawksbill turtles from the Arabian Gulf. Hemoglobin, packed cell volume (PCV), white blood cell count (WBC), aspartate aminotransferase (AST), creatine kinase (CK), uric acid, glucose, calcium, phosphorus, total protein, albumin, globulin, potassium, and sodium were evaluated. When compared to values at first presentation, clinically healthy rehabilitated turtles had significantly higher PCV (P = 0.006) and significantly lower WBC (P = 0.0001), heterophils (P = 0.005), monocytes (P = 0.04), AST (P = 0.03), and CK (P = 0.0001). There was no significant change in hemoglobi n, eosinophils, basophils, uric acid, glucose, calcium, phosphorus, total protein, albumin, globulin, potassiu m, or sodium levels between turtles at first presentation and post-rehabilitation.

Inferring vertical and horizontal movements of juvenile marine turtles from time-depth recorders

Acquiring knowledge of the spatial ecology of many aquatic species, particularly their juvenile life stages, is challenging when they are small in size; this limits the attachment of tracking devices that routinely provide spatially explicit information on larger juveniles and adults. Using depth utilisation data gathered by time-depth recorders, we inferred patterns of habitat utilisation of juvenile hawksbill turtles Eretmochelys imbricata occupying a shallow reef system in the Caribbean. Hawksbill turtles (n = 9, curved carapace length = 42.3 ± 9.7 cm, range = 27.7 to 60.0 cm) demon- strated diel patterns of behaviour, with greater activity and shorter dives during the day (mean dura- tion = 7.5 ± 5.0 min, range = 2.6 to 34.4 min) and longer, less active dives during the night (mean dura- tion = 16.6 ± 12.0 min, range = 2.5 to 61.5 min). A level of fidelity to sites facilitated recaptures (mean minimum straight-line distance from release of TDR-equipped turtles to their subsequent recapture locations = 0.9 ± 0.9 km, range = 0.01 to 2.3 km), but recapture success after 130 h, over a 43 d period, was relatively low: of 19 individuals instrumented, 9 were recaptured. From depth records, i.e. max- imum depths achieved, it was clear that some recaptured individuals moved considerably during the monitoring period; 3 individuals moved to deeper waters, with minimum possible straight-line move- ment distances from their capture sites of 3.7 to 9.2 km. These findings emphasize the likely influence of habitat structure on site fidelity and further highlight that data from traditional capture-mark- recapture studies could lead to an underestimation of home-range size.

Turtle groups or turtle soup: dispersal patterns of hawksbill turtles in the Caribbean

Despite intense interest in conservation of marine turtles, spatial ecology during the oceanic juvenile phase remains relatively unknown. Here, we used mixed stock analysis and examination of oceanic drift to elucidate movements of hawksbill turtles (Eretmochelys imbricata) and address management implications within the Caribbean. Among samples collected from 92 neritic juvenile hawksbills in the Cayman Islands we detected 11 mtDNA control region haplotypes. To estimate contributions to the aggregation, we performed 'many-to-many' mixed stock analysis, incorporating published hawksbill genetic and population data. The Cayman Islands aggregation represents a diverse mixed stock: potentially contributing source rookeries spanned the Caribbean basin, delineating a scale of recruitment of 200-2500 km. As hawksbills undergo an extended phase of oceanic dispersal, ocean currents may drive patterns of genetic diversity observed on foraging aggregations. Therefore, using high-resolution Aviso ocean current data, we modelled movement of particles representing passively drifting oceanic juvenile hawksbills. Putative distribution patterns varied markedly by origin: particles from many rookeries were broadly distributed across the region, while others would appear to become entrained in local gyres. Overall, we detected a significant correlation between genetic profiles of foraging aggregations and patterns of particle distribution produced by a hatchling drift model (Mantel test, r = 0.77, P < 0.001; linear regression, r = 0.83, P < 0.001). Our results indicate that although there is a high degree of mixing across the Caribbean (a 'turtle soup'), current patterns play a substantial role in determining genetic structure of foraging aggregations (forming turtle groups). Thus, for marine turtles and other widely distributed marine species, integration of genetic and oceanographic data may enhance understanding of population connectivity and management requirements.

Ecology of Hawksbill Turtles, Eretmochelys imbricata, on a Western Caribbean Foraging Ground

Abstract We present results of an inwater research program focusing on basic ecology of juvenile hawksbill turtles (Eretmochelys imbricata) in the Cayman Islands. We made 206 captures of 135 hawksbills in Little Cayman and 103 captures of 97 hawksbills in Grand Cayman. The Cayman Islands aggregation demonstrated a broad size distribution (20.5–62.6 cm straight carapace length), slow growth rate (3.0 ± 0.9 cm/y), and multiple recaptures, suggesting long-term residence in some individuals. Demonstrated home range was small (mean distance from capture to recapture 545 ± 514 m, range 2–2080 m); although, an international tag return suggested a long-range developmental migration. Vertical features provided important habitat in Little Cayman, and larger turtles were generally captured in deeper waters. Behavior at sighting varied by habitat: resting, swimming, and feeding were observed in coral reef, reef wall, and hardbottom colonized by sponges and gorgonians, and resting was frequently observed in uncolonize...

Diving behavior and movements of juvenile hawksbill turtles Eretmochelys imbricata on a Caribbean coral reef

As historically abundant spongivores, hawksbill turtles Eretmochelys imbricata likely played a key ecological role on coral reefs. However, coral reefs are now experiencing global declines and many hawksbill populations are critically reduced. For endangered species, tracking movement has been recognized as fundamental to management. Since movements in marine vertebrates encompass three dimensions, evaluation of diving behavior and range is required to characterize marine turtle habitat. In this study, habitat use of hawksbill turtles on a Caribbean coral reef was elucidated by quantifying diel depth utilization and movements in relation to the boundaries of marine protected areas. Time depth recorders (TDRs) and ultrasonic tags were deployed on 21 Cayman Islands hawksbills, ranging in size from 26.4 to 58.4 cm straight carapace length. Study animals displayed pronounced diel patterns of diurnal activity and nocturnal resting, where diurnal dives were significantly shorter, deeper, and more active. Mean diurnal dive depth (±SD) was 8 ± 5 m, range 2–20 m, mean nocturnal dive depth was 5 ± 5 m, range 1–14 m, and maximum diurnal dive depth was 43 ± 27 m, range 7–91 m. Larger individuals performed significantly longer dives. Body mass was significantly correlated with mean dive depth for nocturnal but not diurnal dives. However, maximum diurnal dive depth was significantly correlated with body mass, suggesting partitioning of vertical habitat by size. Thus, variable dive capacity may reduce intraspecific competition and provide resistance to degradation in shallow habitats. Larger hawksbills may also represent important predators on deep reefs, creating a broad ecological footprint over a range of depths.