Growth rates and age at adult size of loggerhead sea turtles (<em>Caretta caretta</em>) in the Mediterranean Sea, estimated through capture-mark-recapture records

Abstract

sUMMarY: growth rates of the juvenile phase of loggerhead turtles (Caretta caretta) were estimated for the first time in the Mediterranean sea from capture-mark-recapture records. thirty-eight turtles were released from italian coasts and re-encountered after 1.0-10.9 years in the period 1986-2007. their mean CCl (curved carapace length) ranged from 32.5 to 82.0 cm and they showed variable growth rates, ranging from 0 to 5.97 cm/yr (mean: 2.5). the association between annual growth rate and three covariates (mean year, mean size and time interval) was investigated through a non-parametric modelling approach. only mean size showed a clear effect on growth rate, described by a monotonic declining curve. Variability indicates that factors not included in the model, probably individual-related ones, have an important effect on growth rates. based on the monotonic decreasing growth function which indicates no growth spurt, a von bertalanffy growth function was used to estimate the time required by turtles to grow within the observed size range. the results indicate that turtles would take 16-28 years to reach 66.5-84.7 cm CCl, the average nesting female sizes observed at the most important Mediterranean nesting sites, which can be considered an approximation of the size at maturity.Keywords: loggerhead sea turtle, growth rate, capture-mark-recapture, Mediterranean.resUMen: Tasas de crecimiento y talla a la edad adulta de la tortuga boba (Caretta Caretta) en el mar Mediterráneo, estimada a través de registros de captura-marcaje-recaptura. -a partir de registros de capturamarcaje-recaptura, se estimaron por primera vez en el Mediterráneo las tasas de crecimiento de las fases juveniles de la tortuga boba (Caretta caretta). se liberaron treinta y ocho tortugas a partir de la costa italiana y se reencontraron después de 1.0-10.9 años en el periodo 1986-2007. el promedio de lCC (longitud curvada del caparazón) varió de 32.5 a 82.0 cm y se observaron tasas de crecimiento variables, de 0 a 5.97 cm/año (promedio: 2.5). la asociación entre la tasa de crecimiento anual y tres covariables (año promedio, talla promedio e intervalo de tiempo) se investigó a través de un modelo no-paramétrico. solamente la talla media mostró un claro efecto en la tasa de crecimiento, descrito por una curva monotónica descendente. la variabilidad observada indica que factores no incluidos en el modelo, probablemente relacionados con el individuo, tienen un importante efecto en las tasas de crecimiento. en base a la función de crecimiento monotónicamente decreciente que indica que no hay esfuerzo en el crecimiento, se uso una función de crecimiento de von bertalanffy para estimar el tiempo requerido por las tortugas para crecer dentro del rango de tallas observado. los resultados indican que las tortugas necesitarán de 16-28 años para alcanzar 66.5-84.7 cm lCC, la talla promedio de anidación observada en las más importantes áreas de anidación del Mediterráneo, lo que puede ser considerado como una aproximación a la talla de madurez.Palabras clave: to...

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.…”

How much sea turtle bycatch is too much? A stationary age distribution model for simulating population abundance and potential biological removal in the Mediterranean

“…We assumed a constant annual survival probability and stationary adult age classes. A constant survival probability for each adult age class is plausible because, unlike juveniles, sea turtle adults show re duced or even negligible somatic growth (Carr & Goodman 1970, Limpus & Chaloupka 1997, Broderick et al 2003, Casale et al 2009b, 2011a. Therefore, if size affects survival, it is unlikely to vary much among adult age classes.…”

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.…”