In-nest mortality and pathology of hawksbill sea turtle (Eretmochelys imbricata) embryos and hatchlings in St. Kitts and Nevis

Strategies to improve the hatch success and survival of critically endangered hawksbill turtles (Eretmochelys imbricata) require knowledge of threats to them including pathological conditions. The objective of this study was to describe the mortality and pathology of embryos and dead-in-nest hatchlings on St. Kitts and Nevis. Over the 2019/20 and 2020/21 nesting seasons, the combined mean (SD) hatch success for the two islands was 81.9% (13.2%) and deceased individuals within excavated nests were early-stage embryos (70.7%), late-stage embryos (17.7%), pipped-hatchlings (8.2%) or dead-in-nest hatchlings (3.4%). From 2017 to 2021, a post-mortem examination was performed on 183 turtles, including histology for 116. Anatomical malformations affected 77 (42.1%) examined turtles and included abnormal scute shape or number (22.4%), dysmelia (8.7%), schistosomus reflexus (7.7%) and compressed carapace (7.7%). Microscopic lesions were found in 49.1% of turtles and included tissue mineralization (26.7%, including renal, fetal membrane, liver, heart or muscle), chorioallantoitis (16.2%) and skeletal muscle degeneration and necrosis (10%). Inflammatory lesions associated with fungal or bacterial infections were in the skin (n = 3), chorioallantois (n = 4), lung (n = 3) or yolk sac (n = 1). These lesions may reflect non-specific terminal conditions but their presence in-nest helps explain some of the mortality and pathology documented in hatchlings that die during rehabilitative care. All of the gonads adequately represented for histological determination of sex were female (n = 62), supporting concern for feminization of Caribbean hawksbill turtle nests. The study identifies lesions that could affect hatch and emergence success. The high frequency of skeletal malformations indicates the need for investigations addressing regional impact and pathogenesis, especially genetic and environmental aetiologies including nest temperature. Immediate examination of live hatchlings on nest emergence is warranted to better determine the prevalence of non-fatal malformations that could impact fitness and population genetics.

First successful head-start program of leatherback sea turtles (Dermochelys coriacea) in Thailand and proposed dietary strategy

Leatherback sea turtle (Dermochelys coriacea) hatchlings have previously been kept alive for over a year in captive conditions but these were the few survivors of initially larger groups. In this report, newly hatched leatherback sea turtles were randomly harvested from two nests in Thailand and successfully reared before release back to the wild. In captivity, the survival of the turtles decreased sharply during the first 4 or 5 months, and then steadied until the end of the 12-month trial. The survival of yearlings from one nest was 13.3% and from the other nest 46.7%. Their growth was exponential, reaching 1.36-3.35 kg (n = 9) at the end of program. The causes of death of the reared turtles were accidents (25.0-38.5%) and infections from water and live food (61.5-75.0%). The dietary requirements of the turtles were investigated by determining the digestibility of protein and carbohydrate in vitro, using enzymes from the digestive tracts of hatchlings that had died in an accident (70.1-92.9 g body weight). The results indicated that the most suitable source of protein was wheat gluten, followed by soybean meal, nonruminant meat and bone meal, fish meal, nonruminant meat meal, pork meal, and skimmed milk, while suitable carbohydrate sources were mashed cassava, corn, wheat flour, and alpha starch, followed by cereal meal and rice flour. Findings from the current report provide a practical protocol for head-starting leatherback sea turtles, and indicate the possible basis of an effective artificial diet for this species.

Environmental and Nesting Variables Associated with Atlantic Leatherback Sea Turtle (Dermochelys coriacea) Embryonic and Hatching Success Rates in Grenada, West Indies

Annual monitoring of leatherback sea turtle (Dermochelys coriacea) nesting grounds in Grenada, West Indies has identified relatively low hatch rates compared to worldwide trends. This study investigated the impact of selected environmental variables on leatherback sea turtle embryonic development and hatching success rates on Levera Beach in Grenada between 2015-2019. The mean number of nests per year and eggs per nest were 667.6 ± 361.6 and 80.7 ± 23.0 sd, respectively. Within excavated nests, 35.6% ± 22.0 sd of eggs successfully developed embryos and 30.6% ± 22.6 sd of eggs successfully hatched. The number of eggs per nest, along with embryo and hatching success rates, differed by nesting year. Embryo development success rate was associated with nest location, and both embryo development and hatching success rates were positively associated with nest depth and negatively associated with the percentage of eggs exhibiting microbial growth and with the presence of inspissated yolk. There was no embryo development or hatchling success association with month of the nesting season, distance from the high-water mark, distance from vegetation, nor maternal carapace length. The mean nest temperature was 31.7 °C ± 1.64 sd and mean temperatures during the middle third of egg incubation suggest clutches are highly skewed towards a preponderance of female hatchlings. Histopathologic findings in hatchling mortalities included severe, acute, multifocal, heterophilic bronchopneumonia with intralesional bacteria in 4/50 (8%) hatchlings. Data from this study guide conservation strategies by identifying risk factors and further avenues of research needed to support reproductive success of leatherback sea turtles in Grenada and the greater Caribbean region.

NONPIGMENTED VERSUS PIGMENTED: HEALTH VARIABLES AND GENETICS OF ALBINO FLORIDA GREEN TURTLE (CHELONIA MYDAS) HATCHLINGS COMPARED WITH NORMALLY PIGMENTED HATCHLINGS FROM THE SAME CLUTCH

At the time of hatchling emergence from a nest laid on Juno Beach, Florida, USA, by a normally pigmented green turtle (Chelonia mydas), 23 albino hatchlings and 75 normally pigmented hatchlings were observed. This condition is rarely seen in sea turtles, and little is known about blood analytes and genetics of albino wildlife to date. Therefore, the objective of our study was to assess and compare morphometric measurements (mass, minimum straight carapace length, body condition index), carapacial scute anomalies, a suite of hematologic and plasma biochemical analytes, and two glucose analysis methodologies (glucometer and dry chemistry analysis) in albino (n=20) versus normally pigmented (n=24) hatchlings from this nest. Genetic analyses were completed to identify paternal contributions of hatchlings and to test Mendelian inheritance assumptions. Although morphometric measurements, scute anomalies, and leukocyte morphology were similar between albino and normally pigmented hatchlings, several differences were observed in blood analyte data: immature erythrocytes, packed cell volume, heterophil:lymphocyte ratio, and glucose concentrations (by both methodologies) were significantly higher, whereas absolute immature heterophils, absolute lymphocytes, number of erythrocyte micronuclei, sodium, and chloride were significantly lower in albino hatchlings compared with normally pigmented hatchlings. Considerations for these differences include a stress response from sampling (e.g., timing of procedures or possibly from photosensitivity or reduced visual acuity in albinos) and different osmoregulation, which may reflect physiologic variations or stress. There was a small positive bias (0.10 mmol/L) with glucose by glucometer, similar to reports in other sea turtle species and confirming its suitability for use in hatchlings. All albino hatchlings analyzed (n=10) were from the same father, but the normally pigmented hatchlings (n=24) were from two other fathers. These findings provide insight into the physiology and genetics of albinism in sea turtles.

Congenital Malformations in Sea Turtles: Puzzling Interplay between Genes and Environment

Simple Summary

Congenital malformations can lead to embryonic mortality in many species, and sea turtles are no exception. Genetic and/or environmental alterations occur during early development in the embryo, and may produce aberrant phenotypes, many of which are incompatible with life. Causes of malformations are multifactorial; genetic factors may include mutations, chromosomal aberrations, and inbreeding effects, whereas non-genetic factors may include nutrition, hyperthermia, low moisture, radiation, and contamination. It is possible to monitor and control some of these factors (such as temperature and humidity) in nesting beaches, and toxic compounds in feeding areas, which can be transferred to the embryo through their lipophilic properties. In this review, we describe possible causes of different types of malformations observed in sea turtle embryos, as well as some actions that may help reduce embryonic mortality.

Abstract

The completion of embryonic development depends, in part, on the interplay between genetic factors and environmental conditions, and any alteration during development may affect embryonic genetic and epigenetic regulatory pathways leading to congenital malformations, which are mostly incompatible with life. Oviparous reptiles, such as sea turtles, that produce numerous eggs in a clutch that is buried on the beach provide an opportunity to study embryonic mortality associated with malformations that occur at different times during development, or that prevent the hatchling from emerging from the nest. In sea turtles, the presence of congenital malformations frequently leads to mortality. A few years ago, a detailed study was performed on external congenital malformations in three species of sea turtles from the Mexican Pacific and Caribbean coasts, the hawksbill turtle, Eretmochelys imbricata (n = 23,559 eggs), the green turtle, Chelonia mydas (n = 17,690 eggs), and the olive ridley, Lepidochelys olivacea (n = 20,257 eggs), finding 63 types of congenital malformations, of which 38 were new reports. Of the three species, the olive ridley showed a higher incidence of severe anomalies in the craniofacial region (49%), indicating alterations of early developmental pathways; however, several malformations were also observed in the body, including defects in the carapace (45%) and limbs (33%), as well as pigmentation disorders (20%), indicating that deviations occurred during the middle and later stages of development. Although intrinsic factors (i.e., genetic mutations or epigenetic modifications) are difficult to monitor in the field, some environmental factors (such as the incubation temperature, humidity, and probably the status of feeding areas) are, to some extent, less difficult to monitor and/or control. In this review, we describe the aetiology of different malformations observed in sea turtle embryos, and provide some actions that can reduce embryonic mortality.

Leatherback sea turtle (Dermochelys coriacea) hatch success and essential and nonessential metals in eggs and embryos from nests in St. Kitts (2015)

Northwest Atlantic leatherback sea turtles (Dermochelys coriacea) are endangered and low hatch success limits potential for population recovery. We examined essential and nonessential metal concentrations in 43 eggs from nests on St. Kitts to determine if there was a relationship with hatch success. Whole homogenized embryos and undeveloped eggs contained detectable concentrations of arsenic, barium, copper, iron, selenium, vanadium, and zinc, but not beryllium, cadmium, chromium, cobalt, lead, mercury, molybdenum, and thallium. Of detected metals, only vanadium concentrations negatively correlated with hatch success (P = 0.01). Manganese and vanadium were associated with pneumonia occurring in the nest, and arsenic with renal mineralization. This study adds to the knowledge regarding baseline values for environmental contaminants in sea turtles, supporting the trend that leatherback eggs have relatively low concentrations of toxic metals, lacking a strong relationship with hatch success, and normally contain the essential elements copper, iron, selenium, and zinc.