Age-size relationship at reproduction of South African female loggerhead turtles Caretta caretta

Abstract

Average age and size at first reproduction are important demographic parameters used in the management and conservation of populations. For sea turtles, absolute values for these parameters are still ambiguous, as most species are slow-growing, late-maturing migrants which are rarely encountered during the first 1 to 2 decades of their lives. Additionally, growth is significantly influenced by a variety of intrinsic and extrinsic factors which make it difficult to describe age−size relationships. Extensive notching (mutilation-tagging) of South African loggerhead turtles was used to determine age and size at reproduction (putative first nesting season), and thus to identify the trigger for sexual maturation. To date, 137 clearly identified notched adult females have been encountered at the nesting beach. A Gaussian and log-normal distribution were fitted to the age distribution data but only the Gaussian distribution can be used to safely estimate age at first observation, as the right part ('older ages') of the distribution is still unknown. The estimated age at first observation was corrected for the possibility that a female was not encountered during her first nesting season. Results indicate an average age of 36.2 ± SD 7.71 yr (95% CI 28.2 to 44.3 yr) with a straight carapace length (SCL min ) of 83.7 ± 4.15 cm (95% CI 83.0 to 84.4 cm). It was concluded that size is a more important threshold for the initiation of the maturation process than age and that the onset of sexual maturity is dependent on intrinsic and extrinsic factors. KEY WORDS: Age and size at reproduction · Loggerhead turtle · Mutilation tagging Resale or republication not permitted without written consent of the publisherEndang Species Res 23: [167][168][169][170][171][172][173][174][175] 2014 extrinsic factors. Intrinsic factors that affect the growth rate in sea turtles include species, genotype, health status and sex (Chaloupka & Limpus 1997, Van Dam 1999, Heppell et al. 2003. Extrinsic factors that regulate growth rate are, for example, water temperature, food quality and food availability (Parker 1929, Bjorndal et al. 2003, Balazs & Chaloupka 2004. These factors are easy to regulate in captive studies but are often highly variable and difficult to measure under natural conditions (Mendonca 1981) as sea turtles migrate over thousands of kilometres and experience large habitat variations that additionally affect their growth rate (Musick & Limpus 1997, Casale et al. 2007, Koch et al. 2007). The variability in growth rate has already been documented in different species and several populations. Green turtles from the Hawaiian archipelago (Balazs & Cha loupka 2004) and the southern Great Barrier Reef grow at different rates due to differences in food quality and availability, as well as in sea surface temperatures of their foraging grounds. Furthermore, Hughes (1974) and Bjorndal et al. (2003) found that compensatory growth (accelerated growth) appears in juvenile sea turtles when they move from a suboptimal environment to b...

Growth rates of adult sea turtles

“…The authors are aware of only one study in a wild population of loggerhead turtles Caretta caretta (Tucek et al 2014) which found no evidence for such a trade-off. Variation in juvenile growth rates could be dampened if individuals performed compensa-tory growth -which in some cases they appear to do (e.g.…”

“…Bell et al 2005, Caillouet et al 2011, Tucek et al 2014, Rees et al 2016. To overcome this problem, a number of studies have investigated growth rates using captive individuals of known age (e.g.…”

“…Although empirical evidence (e.g. Choat et al 2006, Armstrong & Brooks 2013, Tucek et al 2014 suggests that sexual maturity is frequently the result of a genetically determined size threshold (Roff 2000), differences in growth curves, SSM and ASM are likely to arise between individuals (Bernardo 1993). Indeed, enormous variation in both ASM and SSM can be observed within and among species (e.g.…”

Managing conflicts between economic activities and threatened migratory marine species toward creating a multiobjective blue economy

“…Most programs employ members of local communities and thus contribute directly to rural economies. Because turtles are slow growing, late maturing (Tuček et al 2014), and have low survival rates (1/1000 [Hughes 1973]), they are strongly conservation dependent. How-ever, rookery protection is insufficient to conserve turtles; ocean-based threats need to be managed as well (Nel et al 2013).…”

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.…”