Age and growth determination by skeletochronology in loggerhead sea turtles (<i>Caretta caretta</i>) from the Mediterranean Sea

Abstract

SUMMARY: Skeletochronology was applied to humerus bones to assess the age and growth rates of loggerhead sea turtles (Caretta caretta) in the Mediterranean Sea. Fifty-five dead turtles with curved carapace lengths (CCL) ranging from 24 to 86.5 cm were collected from the central Mediterranean. Sections of humeri were histologically processed to analyze annual growth marks. Two approaches were used to estimate the somatic growth in the form of a von Bertalanffy growth function. The first approach was based on calculating the total number of growth marks, which corresponds to the age of turtles at death. The second approach estimates the carapace length at old growth marks in order to provide the growth rate of each turtle. The observed individual growth rates ranged from 1.4 to 6.2 cm yr -1 , and showed both elevated inter-and intra-individual variability possibly related to the environmental variability experienced by turtles during their lifetime. Both approaches gave similar results and suggest that Mediterranean loggerhead turtles take 14.9 to 28.5 years to reach a CCL of 66.5 to 84.7 cm. This size corresponds to the average size of nesting females found in the most important Mediterranean nesting sites and can be considered the approximate size at maturity.Keywords: loggerhead sea turtle, growth rate, age at size, skeletochronology, Mediterranean. RESUMEN: Determinación de la edad y el crecimiento por esclerocronología en la tortuga boba marina Caretta Caretta del mar Mediterráneo. -La esclerocronología se aplicaba a los huesos de los húmeros para determinar la edad y las tasas de crecimiento de la tortuga boba Caretta caretta del Mediterráneo. Cincuenta y cinco tortugas bobas muertas de 24 a 86.5 cm de longitud de la curvatura del caparazón (CCL) fueron recogidas del Mediterráneo central. Secciones de los húmeros fueron procesados histológicamente para analizar las marcas anuales de crecimiento. Se aplicaron dos aproximaciones para determinar el crecimiento somático utilizando la función de crecimiento de von Bertalanffy. La primera aproximación se basaba en el número total de marcas de crecimiento, correspondiendo a la edad de las tortugas en el momento de la muerte. La segunda aproximación era una estimación de la longitud del caparazón en las marcas de crecimiento más antiguas, con la intención de saber la tasa de crecimiento de cada tortuga. Las tasas de crecimiento individual observadas, oscilaban entre 1.4 y 6.2 cm año -1 , mostrando una elevada diversidad individual intra e interanual, posiblemente ligada a la variabilidad ambiental experimentada por las tortugas bobas durante su vida. Ambas aproximaciones dieron resultados similares y sugieren que la tortuga mediterránea tarda 14.5-28.5 años en alcanzar un tamaño de 66.5-84.7 cm de CCL. Este tamaño corresponde al tamaño medio de las tortugas bobas hembras nidificantes, encontradas en la mayoría de lugares nidificantes del Mediterráneo y puede ser considerado el tamaño aproximado de la madurez.Palabras clave: tortuga boba marina, tasa de crecimiento, ...

The first ‘lost year’ of Mediterranean sea turtles: dispersal patterns indicate subregional management units for conservation

“…For loggerhead turtles, this period is several years in duration: on the basis of available age-size curves for loggerheads in the Mediterranean, turtles > 40 cm CCL are probably older than 7 yr (Casale et al 2009b(Casale et al , 2011a. Age-size curves of Mediterranean green turtles are not available; however, curves from the Atlantic indicate a similar age, i.e.…”

“…However, most observations relate to the western and central Mediterranean, while less information is available for the easternmost part (the Levantine basin). Moreover, the turtles studied by the above methods are often adults or large juveniles above 50 cm curved carapace length (CCL); whereas the distribution of the elusive small turtles < 40 cm CCL, corresponding approximately to the first 7 yr of life (Casale et al 2009b(Casale et al , 2011a, represents the main knowledge gap. This is a common problem worldwide, with the first period of life of sea turtles also known as 'lost years' (Carr & Meylan 1980), because individuals are small, usually live in open waters and are generally difficult to observe.…”

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…The Mediterranean turtles are no exception. The various empirical methods employed to study turtle distribution and movements in Mediterranean waters usually observe adults or large juveniles, thus leaving out loggerheads smaller than 40 cm CCL, roughly corresponding to the first seven years of life (Casale et al 2009(Casale et al , 2011a(Casale et al , 2011b. The only method available to investigate their movement patterns is through simulations of particle dispersals in large-scale oceanographic models (e.g.…”

Age and growth of loggerhead sea turtles in southern Brazil

“…Smedstad & Holm (1996) applied and validated the method for Atlantic cod Gadus morhua. In sea turtles, the back-calculation method has been applied and validated for loggerheads and green sea turtles Chelonia mydas (Snover et al 2007, Goshe et al 2010, Casale et al 2011a.…”

“…In contrast, skeletochronological studies have been validated and applied to Caretta caretta (Zug et al 1986, Klinger & Musick 1992, Parham & Zug 1997, Snover & Hohn 2004, Casale et al 2011a, allowing estimation of age from growth increments formed in the humerus bone (Parham & Zug 1997). This approach allows for understanding some age-based parameters, similar to mark−recapture; however, the skeletochronological method has the potential to yield results more rapidly.…”