Alan B. Bolten

Origin of Hawksbill Turtles in a Caribbean Feeding Area as Indicated by Genetic Markers

Hawksbill turtles move between nesting colonies and feeding grounds, but in most cases it is not known which reproductive populations occupy a particular feeding habitat. In this study, genetic markers derived from mitochondrial DNA sequences are used to estimate the contribution of Caribbean nesting colonies to a feeding ground at Mona Island, Puerto Rico (n = 41). Maximum likelihood analysis indicates that this feeding population is not composed primarily of turtles from the neighboring nesting colony (also on Mona Island), but is drawn from nesting populations throughout the Caribbean region. A sampled nesting colony in the southern hemisphere (Bahia, Brazil) did not contribute, at detectable levels, to the Mona Island feeding ground. From this evidence, we concluded that hawksbill turtles recruitment to feeding grounds over a scale of hundreds of kilometres, but not over the scale of 7000 km that separate Mona Island from Bahia, Brazil. These data indicate that a hawskbill turtle harvest on feeding grounds will reduce nesting populations throughout the Caribbean region.

Stable isotopic comparison between loggerhead sea turtle tissues

RATIONALEnStable isotope analysis has been used extensively to provide ecological information about diet and foraging location of many species. The difference in isotopic composition between animal tissue and its diet, or the diet-tissue discrimination factor, varies with tissue type. Therefore, direct comparisons between isotopic values of tissues are inaccurate without an appropriate conversion factor. We focus on the loggerhead sea turtle (Caretta caretta), for which a variety of tissues have been used to examine diet, habitat use, and migratory origin through stable isotope analysis. We calculated tissue-to-tissue conversions between two commonly sampled tissues.nnnMETHODSnEpidermis and scute (the keratin covering on the carapace) were sampled from 33 adult loggerheads nesting at two beaches in Florida (Casey Key and Canaveral National Seashore). Carbon and nitrogen stable isotope ratios were measured in the epidermis and the youngest portion of the scute tissue, which reflect the isotopic composition of the diet and habitat over similar time periods of the order of several months.nnnRESULTSnSignificant linear relationships were observed between the δ(13)C and δ(15)N values of these two tissues, indicating they can be converted reliably.nnnCONCLUSIONSnWhereas both epidermis and scute samples are commonly sampled from nesting sea turtles to study trophic ecology and habitat use, the data from these studies have not been comparable without reliable tissue-to-tissue conversions. The equations provided here allow isotopic datasets using the two tissues to be combined in previously published and subsequent studies of sea turtle foraging ecology and migratory movement. In addition, we recommend that future isotopic comparisons between tissues of any organism utilize linear regressions to calculate tissue-to-tissue conversions.

Somatic Growth Rates of Green Turtles (Chelonia mydas) and Hawksbills (Eretmochelys imbricata) in the Galápagos Islands

Abstract Growth rates can be used as an indicator of overall turtle population health and provide a baseline against which to compare the quality of, or changes in, the conditions in foraging habitats. Previous studies of Green Turtles (Chelonia mydas) in the waters of the Galápagos Archipelago in the late 1970s revealed some of the slowest growth rates ever reported for immature Green Turtles. In this study, we evaluate whether growth rates have changed since the earlier study and the effects of color morph, body size, recapture interval, year, and site of capture on growth rates for Green Turtles at four key foraging grounds in the Galápagos Islands between 2003 and 2008. Results of this study confirm that somatic growth in Galápagos Green Turtles is very slow. In addition, somatic growth is significantly affected by morph, body size, and spatial variation. Mean growth rates generate implausibly long estimates of 133–200 yr for Galápagos Green Turtles to grow from 40-cm straight carapace length to sexual maturity. We also present some data for growth in Hawksbills (Eretmochelys imbricata), representing the first information of growth rates for Hawksbills in the Archipelago. Resumen Las tasas de crecimiento pueden ser usadas como un indicador de la salud global de una población de tortugas marinas y así proporcionar una línea base con la cual comparar la calidad o los cambios en la condición de los hábitats de forrajeo. Estudios previos en la tortuga verde (Chelonia mydas), llevados a cabo en las aguas del Archipiélago de Galápagos a fines de 1970, revelaron las tasas de crecimiento más lentas que se han reportado para especímenes inmaduros de tortuga verde. En el presente estudio, evaluamos si las tasas de crecimiento han cambiado desde la realización del estudio anterior, y si el color del morfo, tamaño corporal, intervalo de recaptura, año y sitio de captura, tienen algún efecto sobre las tasas de crecimiento de tortugas verdes en cuatro sitios clave de forrajeo de las islas Galápagos entre los años 2003 y 2008. Los resultados de este estudio confirman que las tortugas verdes de Galápagos tienen un crecimiento somático muy lento. Además, el crecimiento somático es significativamente afectado por el morfo, el tamaño corporal y la variación espacial. Las tasas promedio de crecimiento registradas generan largas e inverosímiles estimaciones de 133 a 200 años de vida para las tortugas verdes de Galápagos que, crecen desde los 40-cm de largo recto caparazón hasta la madurez sexual. También presentamos aquí algunos datos para el crecimiento de tortugas carey (Eretmochelys imbricata), representando éstos la primera información sobre tasas de crecimiento de tortugas carey en el Archipiélago.

Supplement 1. Raster format of loggerhead δ13C and δ15N isoscapes and associated standard deviation.

File Listn loggerhead_d13C_isoscape.txt (md5: 75d5be745e2018c1fbf639224e598736)n loggerhead_d15N_isoscape.txt (md5: d76570667098245e4102e8380b588324)n loggerhead_d13C_error.txt (md5: 7f8bb3cc91d34eb8ad033942bd2f93cf)n loggerhead_d15N_error.txt (md5:995ce245c4e066001d6f8322e33038ef )n Descriptionn loggerhead_d13C_isoscape.txt – krigged surface of δ 13 C values from 41 calibration loggerhead sea turtles in coastal waters < 200m depth of the Gulf of Mexico and Greater Caribbeann loggerhead_d15N_isoscape.txt – krigged surface of δ 15 N values from 41 calibration loggerhead sea turtles in coastal waters < 200m depth of the Gulf of Mexico and Greater Caribbeann loggerhead_d13C_error.txt – standard deviation of the kriging prediction of δ 13 C valuesn loggerhead_d15N_error.txt – standard deviation of the kriging prediction of δ 15 N valuesn These four files are the δ 13 C and δ 15 N isoscapes and standard deviation rasters that are depicted in Fig. 1 of the main text. They are ASCII-formatted text files and contain a header to identify the structure of the file. They can be opened in ArcGIS by using the ASCII to Raster conversion tool or in R with the raster() function using the Raster package and then assigned a spatial reference within the program used. Resolution of each of the files is 0.0572 degrees.