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

Exploring the demography and conservation needs of hawksbill sea turtles Eretmochelys imbricata in north-west Mexico

The hawksbill sea turtle Eretmochelys imbricata is categorized as Critically Endangered on the IUCN Red List and its population has declined by over 80% in the last century. The Eastern Pacific population is one of the most threatened hawksbill populations globally. Western Mexico is the northern distribution limit for hawksbill sea turtles in the Eastern Pacific and recent research indicates that the Mexican Pacific portion of the population is a separate management unit because of the restricted movements of these turtles. Here we use the most complete database of sighting records in the north-west Pacific of Mexico to identify sites where hawksbill turtles are present. We also develop a conservation index to determine the conservation status of hawksbill turtle sites. Our results demonstrate the importance of this region for juveniles and the relevance of rocky reefs and mangrove estuaries as habitats for hawksbill turtles. We identified 52 sites with records of hawksbill turtles. Most of these sites (71%) are not protected; however, sites with high conservation value included islands and coastal sites along the Baja California peninsula that are established as marine protected areas. Reefs and mangrove estuaries relevant for hawksbill turtles are probably also significant fish nursery areas that are important for local fishing communities, creating opportunities for conservation strategies that combine science, local engagement and policy to benefit both local fishing communities and hawksbill sea turtle conservation.

Vulnerability of sea turtles and fishes in response to two catastrophic Caribbean hurricanes, Irma and Maria

Extreme weather events (e.g., cyclones, floods, droughts) are capable of changing ecosystems and altering how animals obtain resources. Understanding the behavioural responses of animals being impacted by these natural events can help initiate and ameliorate conservation or management programs. This study investigated short- and long-term space-use of the critically endangered hawksbill sea turtle (Eretmochelys imbricata), as well as five species of fishes and stingrays, in response to two of the most destructive Caribbean hurricanes in known history - Irma and Maria, which were at their peak intensity when they passed the US Virgin Islands in September of 2017. Using passive acoustic telemetry in St. Thomas, US Virgin Islands, we show a variety of short-term behavioural patterns initiated across species to reduce exposure to the strong environmental conditions, such as moving to deeper habitats within the study area. Although short-term expansion of activity space was evident for several sea turtles, long-term impacts on space-use and body condition were limited. In contrast, southern stingrays (Hypanus americanus) left the study area shortly after the hurricanes, suggesting vulnerability stemming from altered habitat, prey availability, or temperature/oxygen profiles. This study shows the strong spatial resilience of several nearshore species despite exposure to two consecutive category 5 hurricanes.

Time in tortoiseshell: a bomb radiocarbon-validated chronology in sea turtle scutes

Some of the most basic questions of sea turtle life history are also the most elusive. Many uncertainties surround lifespan, growth rates, maturity and spatial structure, yet these are critical factors in assessing population status. Here we examine the keratinized hard tissues of the hawksbill (Eretmochelys imbricata) carapace and use bomb radiocarbon dating to estimate growth and maturity. Scutes have an established dietary record, yet the large keratin deposits of hawksbills evoke a reliable chronology. We sectioned, polished and imaged posterior marginal scutes from 36 individual hawksbills representing all life stages, several Pacific populations and spanning eight decades. We counted the apparent growth lines, microsampled along growth contours and calibrated Δ(14)C values to reference coral series. We fit von Bertalanffy growth function (VBGF) models to the results, producing a range of age estimates for each turtle. We find Hawaii hawksbills deposit eight growth lines annually (range 5-14), with model ensembles producing a somatic growth parameter (k) of 0.13 (range 0.1-0.2) and first breeding at 29 years (range 23-36). Recent bomb radiocarbon values also suggest declining trophic status. Together, our results may reflect long-term changes in the benthic community structure of Hawaii reefs, and possibly shed light on the critical population status for Hawaii hawksbills.

Age and body size of captive hawksbill turtles at the onset of follicular development

The aim of this study was to record the age and body size of 23 captive female hawksbill turtles at the onset of follicular development. The age, straight carapace length (SCL), and body mass (BM) of the turtles were recorded between 2006 and 2014 at follicular development (determined via ultrasonography) these parameters were 17.7 ± 1.7 years (range: 13-20 years), 77.7 ± 3.3 cm (73.3-83.5 cm), and 61.1 ± 8.0 kg (48.2-76.1 kg), respectively. When the year of the onset of follicular development was designated year 0, the increase in SCL in years -7-0 and 0-3 averaged 2.2 cm and 1.0 cm, respectively. Correspondingly, the increase in BM in years -7-0 and 0-3 averaged 5.0 kg and 2.2 kg, respectively. This is the first study to report the age and body size of captive female hawksbill turtles at the onset of follicular development, which indicates the beginning of sexual maturation. The reduction in growth after follicular development suggests that at the onset of sexual maturation, female hawksbills may utilize energy for follicular development rather than growth.