Life cycle and ecology of the loggerhead turtle (Caretta caretta, Linnaeus, 1758) (original) (raw)
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Somatic growth model of juvenile loggerhead sea turtles Caretta caretta: duration of pelagic stage
Marine Ecology Progress Series, 2000
The pelagic juvenile stage of sea turtles is poorly studied. We present a growth model and estimates for duration of the pelagic juvenile stage for loggerhead sea turtles Caretta caretta in the North Atlantic based on length-frequency analyses and sizes of young-of-the-year stranded in the Azores. The size-specific growth model is a monotonic, nonlinear, declining function. The growth model is consistent with growth rates calculated from recaptures of tagged loggerheads. Loggerheads leave the pelagic habitat and recruit to neritic habitats over a range of sizes from 46 to 64 cm curved carapace length (CCL). From this size range and the growth model, we estimate the duration of the pelagic stage varies from 6.5 to 11.5 yr. Nonparametric smooths of the size frequency distributions of loggerheads in pelagic (n = 1692) and neritic (n = 1803) habitats intersect at 53 cm CCL, which is equivalent to an 8.2 yr duration for the pelagic stage. More growth data from loggerheads < 2 yr old would strengthen the database for our growth model and perhaps lengthen our estimates of the duration of the pelagic stage. Incorporating our estimates for duration of the pelagic juvenile stage into the stage-based population model developed for North Atlantic loggerheads would have a major effect on estimates of population growth.
Determinate or indeterminate growth? Revisiting the growth strategy of sea turtles
Marine Ecology Progress Series, 2018
Traditionally, growth can be either determinate, ceasing during the natural lifespan of individuals, or indeterminate, persisting throughout life. Although indeterminate growth is a widely accepted strategy and believed to be ubiquitous among long-lived species, it may not be as common as previously thought. Sea turtles are believed to be indeterminate growers despite the paucity of long-term studies into post-maturity growth. In this study, we provide the first temporal analysis of post-maturity growth rates in wild living sea turtles, using 26 yr of data on individual measurements of females nesting in Cyprus. We used generalised additive/linear mixed models to incorporate multiple growth measurements for each female and model post-maturity growth over time. We found post-maturity growth to persist in green Chelonia mydas and loggerhead Caretta caretta turtles, with growth decreasing for approximately 14 yr before plateauing around zero for a further decade solely in green turtles. We also found growth to be independent of size at sexual maturity in both species. Additionally, although annual growth and compound annual growth rates were higher in green turtles than in loggerhead turtles, this difference was not statistically significant. While indeterminate growth is believed to be a key life-history trait of ectothermic vertebrates, here, we provide evidence of determinate growth in green and loggerhead turtles and suggest that determinate growth is a life-history trait shared by cheloniid species. Our results highlight the need for long-term studies to refine life-history models and further our understanding of ageing and longevity of wild sea turtles for conservation and management.
Environmental effects on growth, reproduction, and life-history traits of loggerhead turtles
2017
Authors: Nina Marn, Marko Jusup, Tarzan Legovic, S.A.L.M. Kooijman, Tin Klanjscek Understanding the relationship between the environmental conditions and life-history traits (such as growth, reproduction, and size at specific life stages) is important for understanding the population dynamics of a species and for constructing adaptable, relevant, and efficient conservation measures. For the endangered loggerhead turtle, characterizing effects of environmental conditions on the lifehistory traits is complicated by this species’ longevity, global distribution, and migratory way of life. Two significant environmental factors – temperature and available food – often account for most of observed intra-population variability in growth and reproduction rates, suggesting that those two factors determine the biological responses of an individual. Adopting this hypothesis, we simulate a range of the two environmental factors to quantify effects of changes in temperature and food availability on an individual’s physiology (energy investment into processes such as growth, maturation, and reproduction) and the resulting life-history traits. To represent an individual, we use a previously developed mechanistic dynamic energy budget (DEB) model for loggerhead turtles. DEB models rely on one of the empirically best validated general ecological theories, which captures rules of energy acquisition and utilization. We found that the ultimate size (length and mass) is primarily affected by food availability, whereas growth and maturation are primarily affected by temperature whilst also showing positive correlation with available food. Reproduction increases with both food availability and temperature because food availability determines energy investment into egg production, and temperature affects the rate of related processes (such as vitellogenesis). Length at puberty varies between simulated scenarios by only a small proportion, suggesting that inter-individual variability plays a larger role for length at puberty than the environmental factors do.
Marine Biology, 2015
mark associated with maturation were 90.5 for females (range 75.0-101.3) and 95.8 for males (range 80.6-103.8). Ages at maturation estimated from (1) the rapprochement skeletal growth mark; (2) back-calculated SCL-at-age data; and (3) bootstrapping and fitting Fabens modified von Bertalanffy growth curve to back-calculated growth data were very similar between approaches, but demonstrated a wide possible range. Mean age predictions associated with minimum and mean maturation SCLs were 22.5-25 and 36-38 years for females and 26-28 and 37-42 years for males. Post-maturation longevity (i.e., adult-stage duration) was similar for males and females, ranging from 4 to 46 years (mean 19 years).
Compensatory Growth in Oceanic Loggerhead Sea Turtles: Response to a Stochastic Environment
Ecology, 2003
Compensatory growth (CG, accelerated growth that may occur when an organism that has grown at a reduced rate as a result of suboptimal environmental conditions is exposed to better conditions) is considered an adaptation to variable environments. Although documented thoroughly under captive conditions, CG has rarely been studied in wild populations. In their first years of life, oceanic-stage loggerhead sea turtles (Caretta caretta) have relatively little control over their geographic position or movements and thus have an extremely stochastic lifestyle with great variation in food availability and temperature. This environmental variation results in variable growth rates. We evaluate somatic growth functions of oceanic-stage loggerheads from the eastern Atlantic based on skeletochronology that allowed us to assign age and cohort to each individual. We demonstrate CG in these turtles based on three different analytical approaches: changes in coefficients of variation in size-at-age, generalized additive model regression analyses of somatic growth, and linear regression of age-specific growth rates. As a result of CG, variation in size-at-age in these juvenile loggerheads is substantially reduced. Thus, size is a better predictor of age than expected based on variation in growth rates. CG decreases with age, apparently as loggerheads gain greater control over their movements. In addition, we have evaluated for the first time in wild sea turtles the time-dependent nature of somatic growth by distinguishing among age, year, and cohort effects using a mixed longitudinal sampling design with assigned-age individuals. Age and year had significant effects on growth rates, but there was no significant cohort effect. Our results address critical gaps in knowledge of the demography of this endangered species. Ecology, Vol. 84, No. 5 PLATE 1. An oceanic-stage loggerhead with a curved carapace length of 17.3 cm. The sharp projections on the vertebral scutes are characteristic of this life stage. Photograph by Skye White.
2019
Population of loggerhead turtles nesting in the Mediterranean Sea has probably evolved from the North Atlantic (NA) population, but is geographically and genetically distinct. We aggregated previously published and new unpublished data, and took two approaches to comparing these populations: an empirical one based on statistical analyses of morphological data, and a physiological one based on a Dynamic Energy Budget (DEB) model. We then analyzed causes of faster growth and maturation, but smaller size at puberty and ultimate size of the Mediterranean (MED) loggerhead turtles relative to their NA conspecifics. The empirical analysis showed that young juvenile, sexually mature, and fully grown MED individuals were consistently smaller in terms of length and mass. The physiological approach suggested physiological adaptations of the MED population to higher salinity and scarcer food availability. In particular, these adaptations included an increase in somatic maintenance needs, and a decrease in energy investment to reach and maintain sexual maturity. Our study therefore offers a mechanistic underpinning of previously observed but unexplained life-history traits, and showcases an application of DEB theory as a tool for comparative analysis of two distinct populations of the same species.
Scientia Marina, 2009
3 sea turtle rescue Centre WWF italy, CP 92010 lampedusa, italy. 4 a.r.C.H.e', via Mulinetto, 40/a 44100 Ferrara, italy. 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.
Life-History Variation in Marine Turtles
Copeia, 1994
We studied correlations among traits related to body size and reproductive behavior in marine turtles, using data from 96 different populations representing seven species. Our analyses focused on patterns of phenotypic covariation among species and among populations within species. At the species level, body size correlated positively with several reproductive traits, including egg size and overall reproductive effort. A trade-off between clutch size and egg size was confirmed for marine turtles, after factoring out the effects of body size. Patterns of variation within species were different from those among species. For example, in five out of six species there was a positive relationship between adult body size and clutch size, although this correlation was not found at the interspecific level. We also found important differences among species in the way life-history traits correlated with one another. Four species having a sufficient number of samples exhibited congruent worldwide patterns of body size variation. A comparative approach may prove useful for extending demographic models developed for loggerhead turtles to less well-known species, even though many of the model parameters have not been estimated for other species.