Global Analysis of Anthropogenic Debris Ingestion by Sea Turtles

Ingestion of marine debris can have lethal and sublethal effects on sea turtles and other wildlife. Although researchers have reported on ingestion of anthropogenic debris by marine turtles and implied incidences of debris ingestion have increased over time, there has not been a global synthesis of the phenomenon since 1985. Thus, we analyzed 37 studies published from 1985 to 2012 that report on data collected from before 1900 through 2011. Specifically, we investigated whether ingestion prevalence has changed over time, what types of debris are most commonly ingested, the geographic distribution of debris ingestion by marine turtles relative to global debris distribution, and which species and life‐history stages are most likely to ingest debris. The probability of green (Chelonia mydas) and leatherback turtles (Dermochelys coriacea) ingesting debris increased significantly over time, and plastic was the most commonly ingested debris. Turtles in nearly all regions studied ingest debris, but the probability of ingestion was not related to modeled debris densities. Furthermore, smaller, oceanic‐stage turtles were more likely to ingest debris than coastal foragers, whereas carnivorous species were less likely to ingest debris than herbivores or gelatinovores. Our results indicate oceanic leatherback turtles and green turtles are at the greatest risk of both lethal and sublethal effects from ingested marine debris. To reduce this risk, anthropogenic debris must be managed at a global level. Análisis Global de la Ingesta de Residuos Antropogénicos por Tortugas Marinas     

Identifying oceanic foraging grounds of sea turtles in the Atlantic using lead isotopes

Many species of marine organisms go through ontogenetic shifts that occur in unknown or inaccessible locations. Finding these areas is crucial to understand connectivity and resilience of populations, both of which have conservation implications. When extrinsic markers are not suitable to track organisms, intrinsic markers can be useful to infer the location of inaccessible areas where these cryptic stages occur. Our study focuses on the location of oceanic foraging areas of the cryptic early juvenile stage of green turtles, Chelonia mydas, in the Atlantic. Due to the small size of hatchlings, the use of telemetry is limited to short periods of time and small spatial ranges, which do not allow determining the location of oceanic foraging areas. We used lead (Pb) stable isotopes to determine the possible location of oceanic foraging areas of small green turtles in the Atlantic Ocean. Pb stable isotope ratios in the scute tissue deposited when turtles were in the oceanic habitat were compared to ratios of major sources of lead in the Atlantic and oceanic areas in the Atlantic to determine the location of oceanic foraging grounds. The Pb isotope ratios in the scute of oceanic-stage green turtles indicated that turtles use different regions in the Atlantic and that they are capable of transatlantic migrations. We compare the oceanic locations identified by this study with those suggested by two previous studies.     

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.     

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.     

Modelling the fate of marine turtle hatchlings

The SLIM oceanographic model was used to examine the fate of hatchling flatback turtles (Natator depressus) in the first two weeks of their dispersal starting at Wild Duck Island, a major turtle-nesting site in the central Great Barrier Reef region of Australia. We ran simulations to investigate the effects of spring versus neap tides, hatchling's swimming behaviour during their first three days at sea, and the location of nesting beaches. The model predicted that up to 50% of the turtle hatchlings entering the sea from the windward, southern beach remained after 14 days in shallow, nearshore waters, irrespective of tides and swimming. These waters are turbid and may be inhospitable to hatchlings. In contrast >80% of hatchlings dispersing from the leeward, northern beach were dispersed to deeper water (10-40 m) in a quasi-stationary dispersion core centred around 10 km north of the nesting beach after 14 days and the offshore spread of the turtle plume was enhanced by the hatchling's seaward swimming during the first three days. This was due to the presence of a coastal boundary layer and a stagnation zone around the northern side of island, but not the southern side. The model confirmed that dispersal from eastern Queensland flatback turtle rookeries is restricted to the lagoons and coastal waters, and that water circulation and hatchling's swimming control dispersion. The model explains why more turtles nest on the northern than the southern side. This study highlights the usefulness of oceanographic models to increase knowledge about a cryptic life stage of marine turtles.     

Biological and environmental influences on the trophic ecology of leatherback turtles in the northwest Atlantic Ocean

Understanding the causes and consequences of variability in trophic status is important for interpreting population dynamics and for identifying important habitats for protected species like marine turtles. In the northwest Atlantic Ocean, many leatherback turtles (Dermochelys coriacea) from distinct breeding stocks throughout the Wider Caribbean region migrate to Canadian waters seasonally to feed, but their trophic status during the migratory and breeding cycle and its implications have not yet been described. In this study, we used stable carbon and nitrogen isotope analyses of bulk skin to characterize the trophic status of leatherbacks in Atlantic Canadian waters by identifying trophic patterns among turtles and the factors influencing those patterns. δ¹⁵N values of adult males and females were significantly higher than those of turtles of unknown gender (i.e., presumed to be subadults), and δ¹⁵N increased significantly with body size. We found no significant differences among average stable isotope values of turtles according to breeding stock origin. Significant inter-annual variation in δ¹⁵N among cohorts probably reflects broad-scale oceanographic variability that drives fluctuations in stable isotope values of nutrient sources transferred through several trophic positions to leatherbacks, variation in baseline isotope values among different overwintering habitats used by leatherbacks, or a combination of both. Our results demonstrate that understanding effects of demographic and physiological factors, as well as oceanographic conditions, on trophic status is key to explaining observed patterns in population dynamics and for identifying important habitats for widely distributed, long-lived species like leatherbacks.     

The stomach contents of post-hatchling green and loggerhead sea turtles in the southwest Pacific: an insight into habitat association

Dietary information obtained from stomach contents can provide a wealth of information on an animal’s ecology. Where animals are cryptic, such as the post-hatchling life history stage of a sea turtle, the ecological insight that dietary analyses can provide, may be otherwise unobtainable. Investigations into post-hatchling turtle stomach contents have found planktonic organisms, dominated by pelagic molluscs and crustaceans, hydrozoans, Sargassum and fish eggs. The nature of these dietary organisms provides evidence for the widely accepted hypothesis that, with the exception of the flatback turtle (Natator depressus), the post-hatchling stage of a sea turtle’s life history is pelagic and oceanic. As the majority of studies that have investigated the stomach contents of post-hatchling sea turtles have been conducted on loggerhead turtles (Caretta caretta) in the northern Atlantic and Pacific Oceans, insight derived from dietary investigations into post-hatchling ecology is biased. This study investigates the diet of post-hatchling green turtles (Chelonia mydas) and loggerhead turtles in the southwest Pacific Ocean. Stomach contents were obtained from 55 green and loggerhead post-hatchling turtles that had stranded or been consumed by Coryphaena hippurus. Our findings demonstrate that loggerhead and green post-hatchlings in the southwest Pacific share similar feeding ecology and feed on a variety of neustonic items that are indicative of an oceanic and pelagic existence. The dietary items consumed by both species investigated belong to similar taxonomic groups as those found in previous studies with species level distinctions occurring owing to the different geographical location.     

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.     

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.     

Magnetic orientation by hatchling loggerhead sea turtles (Caretta caretta) from the Gulf of Mexico

Loggerhead sea turtle hatchlings emerge from nests on either the east or west coast of the South Florida peninsula and then migrate offshore in opposite directions. Under laboratory conditions, magnetic cues induce east coast hatchlings to swim in directions that promote their transport by oceanic surface currents, such as the North Atlantic gyre. However, the surface currents used by west coast hatchlings are unknown. We examined the responses of west (Sarasota) hatchlings to magnetic cues in the Gulf of Mexico, the Florida Straits, and the Gulf Stream to determine their (1) likely migratory routes (2) orientation where currents lead into the Atlantic Ocean, and (3) orientation adjacent to Florida’s east coast. The results suggest that migration inside Gulf waters may be circuitous, that the turtles respond appropriately to enter Atlantic waters, and that orientation along Florida’s east coast probably promotes transport by the Gulf Stream into the North Atlantic gyre.     

Asymmetric genetic exchange in the brown seaweed Sargassum fusiforme (Phaeophyceae) driven by oceanic currents

Geological phenomena (e.g. drastic sea level fluctuations during the Quaternary Ice Age in the Northern Hemisphere) have been demonstrated to intensively affect the biogeographic patterns and tempo-spatial compositions of genetic diversity of marine organisms. However, it is poorly understood whether contemporary factors such as oceanic surface currents have also shaped inter-regional population genetics of specific coastal marine flora, with or without limited dispersal capability. In this study, we determined mtDNA Cox1 gene sequences of the brown seaweed Sargassum fusiforme from nine populations along the Chinese coast and one population from the west coast of South Korea, in an effort to understand what factors are contributing to their current genetic structure and geographic distribution patterns. Genetic analyses indicated a deep genetic break between the Yellow-Bohai Sea (YBS) and the other two marginal seas, the East China Sea (ECS) and the South China Sea (SCS). In particular, the amount of genetic exchange from the SCS to each of the ECS and YBS was significantly higher than that from the opposite directions. Our analyses supports the hypothesis that biogeographic patterns of genetic variation in S. fusiforme are probably an interactive consequence of post-glacial colonization from two scattered refugia driven by the offshore Kuroshio Current and asymmetric gene flow among adjacent sea margins.     

Marine turtle threats in Uruguayan waters: insights from 12 years of stranding data

We present the first study conducted in a wide spatio-temporal scale on marine turtles strandings (N = 1,107) over a 12-year period (1999–2010) in Uruguay. Five species were recorded Chelonia mydas (N = 643; 58.1 %), Caretta caretta (N = 329; 29.7 %), Dermochelys coriacea (N = 131; 11.8 %), Eretmochelys imbricata (N = 3; 0.3 %), and Lepidochelys olivacea (N = 1; 0.1 %). The first three species stranded throughout the Uruguayan coast, but differences in distribution patterns were detected among species. Although occurring year round, stranding records show a clear seasonal pattern with variation in monthly distribution among species, but with a peak of records in austral summer. Strandings provide indirect evidence of threats to marine turtles in Uruguayan and surrounding waters, particularly fisheries and marine debris. Our results demonstrate that Uruguayan coastal waters likely serve as a foraging or development area for at least three endangered marine turtle species in temperate waters.     

Complex genetic patterns and a phylogeographic disjunction among New Zealand mud snails Zeacumantus subcarinatus and Z. lutulentus

The comparative analysis of genetic structure and phylogeography of marine species can reveal the relative importance of common biogeographic barriers and species-specific evolutionary histories. In the present study, mitochondrial COI sequences from a total of 724 individuals collected from 38 localities throughout New Zealand during 2006 and 2007 were used to examine the genetic structure and demographic histories of the intertidal gastropods Zeacumantus subcarinatus and Zeacumantus lutulentus. For both species, results revealed isolation of populations located along the northern South Island and southern and western North Island, and extensive genetic structure throughout the remainder of their ranges. Despite this, long-distance dispersal and secondary admixture of divergent haplotypes was evident, especially for the widespread Z. subcarinatus. These findings reveal the importance of common barriers to gene flow and highlight how the interaction of inherent dispersal limitations of direct-developing marine organisms and periodic long-distance movements can produce complex genetic patterns.     

Western Mediterranean immature loggerhead turtles: habitat use in spring and summer assessed through satellite tracking and aerial surveys

An aerial survey was conducted in early spring 2002 over the continental shelf of the Balearic Archipelago to study the distribution of neritic loggerhead turtles. Furthermore, five juvenile loggerhead turtles [straight carapace length (SCL) range 37.1–48.7 cm], were instrumented with transmitters and monitored during 2003 by satellite tracking to study habitat use over a broader geographical range. The distribution of the turtles over the continental shelf matched habitat availability, as defined by depth. However, those tracked by satellite spent most of the time in the oceanic waters of the Algerian basin and generally avoided continental shelf areas. In these turtles, average speed of travel and mean cosine of turning angle did not significantly differ between habitats, indicating that avoidance of shelf areas is not due to active habitat selection. On average, tracked turtles spent 35.1±19.7% of the time at the surface, although surface time was much greater in the turtle with the shortest carapace length, suggesting that this individual had limited swimming capacity. We conclude that the transition between passive drifting and active habitat selection occurs at an SCL of about 40 cm. The turtles followed tracks that matched prevailing currents, but on some occasions they also swam upstream. Hence, the distribution of late juvenile loggerhead turtles in the southern and central western Mediterranean may reflect a combination of passive drifting and active habitat selection.Communicated by O. Kinne, Oldendorf/Luhe     

Determining factors that influence the dispersal of a pelagic species: A comparison between artificial neural networks and evolutionary algorithms

Because of increasing transport and trade there is a growing threat of marine invasive species being introduced into regions where they do not presently occur. So that the impacts of such species can be mitigated, it is important to predict how individuals, particularly passive dispersers are transported and dispersed in the ocean as well as in coastal regions so that new incursions of potential invasive species are rapidly detected and origins identified. Such predictions also support strategic monitoring, containment and/or eradication programs. To determine factors influencing a passive disperser, around coastal New Zealand, data from the genus Physalia (Cnidaria: Siphonophora) were used. Oceanographic data on wave height and wind direction and records of occurrences of Physalia on swimming beaches throughout the summer season were used to create models using artificial neural networks (ANNs) and Na?ve Bayesian Classifier (NBC). First, however, redundant and irrelevant data were removed using feature selection of a subset of variables. Two methods for feature selection were compared, one based on the multilayer perceptron and another based on an evolutionary algorithm. The models indicated that New Zealand appears to have two independent systems driven by currents and oceanographic variables that are responsible for the redistribution of Physalia from north of New Zealand and from the Tasman Sea to their subsequent presence in coastal waters. One system is centred in the east coast of northern New Zealand and the other involves a dynamic system that encompasses four other regions on both coasts of the country. Interestingly, the models confirm, molecular data obtained from Physalia in a previous study that identified a similar distribution of systems around New Zealand coastal waters. Additionally, this study demonstrates that the modelling methods used could generate valid hypotheses from noisy and complicated data in a system about which there is little previous knowledge.     

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.     

Sustainable fishing gear: the case of modified circle hooks in a Costa Rican longline fishery

Our research aims to identify longline fishing gear modifications that can improve fishing selectivity and reduce incidental capture of non-target species. Catch rates and anatomical hook locations (AHL) were compared when using a 14/0 standard ??control?? circle hook with a 0° offset and an experimental ??appendage?? hook in a Costa Rican longline fishery. With the appendage, the maximum dimension of the appendage hook was increased by 10% and the minimum dimension of the hook by 19%. A total of 1,811 marine animals were captured during five fishing trips. By taxonomic groups, sea turtles represented the largest total catch (27%), followed by sharks (26%), rays (25%), mahimahi (Coryphaena hippurus) (12%), and tunas and billfish (10%). Non-target and discard species, such as rays and sea turtles, accounted for over half of the total catch. Catch per unit effort (CPUE; number of individuals per 1,000 hooks) was higher with control hooks compared to appendage hooks for all species?? categories except rays; appendage hooks caught 52% fewer sea turtles and 23% fewer tunas and billfish than standard hooks, which represents a significant reduction in bycatch of endangered and other species. No differences were found in the AHL for sea turtles, suggesting use of the appendage may not incur additional advantages regarding turtles?? post-release survivorship. Despite lower catch rates for marketable species, such as sharks and mahimahi, use of the appendage resulted in dramatic reductions in catch rates of sea turtles. The results suggest that large scale adoption of hooks with a significantly wider hook dimension could be an effective conservation measure to maintain marine biodiversity while allowing for continued fishing.     

Chemical aspects of mass spawning in corals. II. (-)-Epi-thunbergol,the sperm attractant in the eggs of the soft coral Lobophytum crassum (Cnidaria: Octocorallia)

Sea turtles migrate between feeding and nesting areas that are often geographically separated by hundreds or thousands of kilometers. Observations of their aggregations at sea and at nesting beaches have led to the hypothesis that sea turtles migrate in socially structured groups. While this migratory strategy is common to many marine vertebrates, socially facilitated behavior is not well documented in testudines. In 1990 and 1991, we attached satellite transmitters to olive ridleys (Lepidochelys olivacea Eschscholtz) found ovipositing together during a mass nesting at Nancite Beach, Costa Rica, to determine whether they migrate independently or in groups after they leave the nesting beach. Results showed that the turtles were not spatially associated during the internesting period, were capable of re-establishing themselves as a group during a subsequent nesting emergence, and were not spatially associated during their postnesting migrations to oceanic feeding areas. We suggested that what appear to be socially structured groups of L. olivacea are in fact individual turtles simultaneously using the same habitat.     

Shark-inflicted injury frequencies, escape ability, and habitat use of green and loggerhead turtles

Interactions between large marine predators and their prey are difficult to observe and little is known about the risk of predation faced by sea turtles. The frequency of predator-inflicted injuries, however, has afforded insights into the predation risk faced by many taxa. We measured the frequency of shark-inflicted injuries on green (Chelonia mydas) and loggerhead (Caretta caretta) sea turtles in Shark Bay, Western Australia with a view to determining differences between species and sex-classes in the risk of predation from tiger sharks (Galeocerdo cuvier). Furthermore, we investigated how escape ability and habitat use might influence the probability of turtles being injured by sharks. Shark-inflicted injuries were more frequent on loggerhead than on green turtles, and most frequent on adult male loggerhead turtles. Species effects could not be attributed to differences in habitat use, since green turtles were found in habitats favored by tiger sharks more often than were loggerhead turtles. Green turtles, however, were faster and maneuvered better than loggerhead turtles, suggesting that escape ability is a factor in interspecific differences in injury frequency. The sex-class difference in injury frequency of loggerhead turtles suggests that males face greater predation risk than females and may take more risks. For green turtles, the lack of a sex difference in injury frequency might be due to greater escape ability lowering overall predation risk or to no differences between sexes in the benefits of risk-taking.