Sex ratios of juvenile loggerhead sea turtles Caretta caretta in the Mediterranean Sea

Abstract

Species with environmental sex determination may show sex ratios that differ from 1:1; therefore, sex ratio is an important variable when studying the population dynamics of these species. For instance, when estimating population size and productivity, sex ratio would be a required parameter. For endangered species, such as sea turtles, this is particularly important in order to understand the possible effects of human impacts and conservation measures. Unfortunately, only adult sea turtles show evident external sexual dimorphism; sex ratios are more difficult to obtain for the juvenile class, which represents the largest part of a population. Here we present the first extensive assessment of the sex ratio of juvenile loggerhead turtles Caretta caretta in the Mediterranean Sea. A total of 310 dead turtles from 4 different areas were sexed by direct examination of gonads, the most reliable sexing method. Females comprised 54.2% of the whole sample, and no significant differences were observed among study areas. However, this value cannot be ascribed to a single population, because specimens from different nesting sites - both within and outside the Mediterranean - share the same foraging areas, and each population may potentially contribute a different sex ratio. Although we recorded an unbiased sex ratio, our results were compatible with a hypothetical scenario in which Mediterranean nesting beaches produce a majority of females when other information from the region (distribution, mixed stocks and sex ratios) was considered. © Inter-Research 2006

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

“…The second important area for loggerhead hatchlings appears to be the Ionian-south Adriatic. Accordingly, turtles of the size range (<10 cm), corresponding approximately to the age range considered in this study (< 6 mo; Casale et al 2009a), have been found stranded along the Ionian-south Adriatic coasts of Italy (Casale et Table 3. Results of the simulation of the dispersal of drifting particles from loggerhead and green sea turtle nesting areas to marine zones of the eastern Mediterranean basin.…”

“…4 to 6 mo after release. Loggerheads of about 6 mo in age have a CCL of about 10 cm length (Casale et al 2009a), and it is likely that passive drift is no longer the only form of movement; hence particle tracking may be less useful to infer dispersal at this point. However, other studies carried out passive drifting simulations for 1 yr or more (e.g.…”

“…Furthermore, loggerhead and green turtles feed upon pelagic prey in the first period of their life, and then switch to benthic prey and seagrasses or algae, respectively (Bjorndal 1997). In the Mediterranean, isotopic signatures indicate that the 2 species still have a similar diet at a size of 25 cm CCL (Cardona et al 2010), corresponding to an age > 2 yr (Casale et al 2009a, Goshe et al 2010.In this study, simulations of the dispersal of sea turtle hatchlings in the Mediterranean were performed using a total of 38 and 10 nesting sites of loggerhead and green sea turtles, respectively. These included (Fig.…”

Advances in the Application of Genetics in Marine Turtle Biology and Conservation

“…This was similar to an ATM using capture-mark-recapture (CMR) and skeletochronology in headstarted Kemp's (10-17 years; Snover et al, 2007), but longer than an estimate from captive animals (5-12 years; Bjorndal et al, 2014), suggesting that growth and maturity may differ in the wild. Skeletochronology has also shed light on ATM in green, loggerhead, and leatherback turtles (Avens et al, 2009;Turner Tomaszewicz et al, 2015), as have a small number of direct observational studies from headstarted turtles (e.g., Florida and Caribbean green turtles, Keske et al (2016) and Bell et al (2005), respectively), CMR via carapace punches in South African loggerheads (Tucek et al, 2014) or growth rates (Casale et al, 2009). The general consensus emerging from these studies, is that each species and perhaps each population may have different ATM ranges.…”

A critical review of the Mediterranean sea turtle rescue network: a web looking for a weaver

“…1). Moreover, the southern Adriatic and to a lesser extent the northern Adriatic and Ionian sea are important developmental areas for loggerheads in the first four years of their lives (Casale et al 2009). Preferred loggerhead habitats off the Spanish Mediterranean coast are characterized by a large number of juveniles, especially around the Balearic islands during spring and summer (Camiñas and de la Serna 1995) and around Columbretes Island Marine Reserve throughout the year (Gómez de Segura et al 2003).…”