Effect of body size on the long-term reproductive output of eastern Atlantic loggerhead turtles Caretta caretta

Abstract

We assessed the relationship between body size and several important life history parameters to understand the demographic significance of interpopulation variability in the body size of loggerhead turtles Caretta caretta nesting on Boa Vista Island (Cabo Verde). The adult growth rate (0.34 ± 0.60 cm yr-1), annual mortality rate (0.13, 95% CI: 0.12-0.15) and remigration interval (3.1 ± 1.2 yr) were independent of curved carapace length (minimum curved carapace length [CCLmin]). Conversely, the body condition index decreased significantly with female CCLmin. The clutch size, mean egg mass, mean hatchling straight carapace length and mean hatchling mass increased significantly with female CCLmin. However, there was no relationship between female size and hatching success. Randomization and bootstrapping were used to incorporate variability when calculating the average individual fecundity over 20 yr, a period that accumulated, on average, 94% of the adult mortality. The overall fecundity during this period increased with carapace length at first maturity (71 cm CCLmin: 815 eggs, 95% CI: 653-863; 80 cm CCLmin: 906 eggs, 95% CI: 822-959; 90 cm CCLmin: 1089 eggs, 95% CI: 926-1415). However, only 8% of the adult females nesting on Boa Vista Island are larger than 90 cm CCLmin, and they produce less than 12% of the total annual egg production. The scarcity of large females might result from a shortage of high-quality foraging grounds where females may reach first sexual maturity at a large carapace length and from the combined effect of a small carapace length at first sexual maturity, low adult somatic growth and high adult mortality.

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population

“…Hatchling (≤16.7 cm, survival [ φ ] = 0.744), small juvenile (16.8–42.9 cm, φ = 0.744), and immature (43–72.9 cm, φ = 0.830) stages were defined. We also defined 3 reproductively mature adult‐stage sizes: small (73–79.9 cm, φ = 0.870), medium (80–88.9 cm, φ = 0.870), and large (≥89 cm, φ = 0.880) (Martins, Cardona, et al., 2022). The 73‐cm size cutoff for adults represents the 97.5th quantile of the breeding adult size distribution, and the 43‐cm cutoff represents the smallest bycaught individuals, likely indicating different juvenile–immature buoyancy and swimming capabilities (Revelles et al., 2007).…”

“…From humeral growth rings, we estimated individuals reached reproductive maturity at ∼28.75 years old and 73 cm, and once mature, adults had a slower constant adult growth rate of 0.34 cm∙year −1 (L.C., unpublished data; Eder et al., 2012; Martins, Cardona, et al., 2022). Necessarily turtles grow incrementally, yet highly variable growth rates in immature developmental environments result in turtles of different sizes at maturation (Dalleau et al., 2014).…”

“…Population capture-recapture (encounter) data were collected over 6 nesting seasons (2013-2018) from João Barrosa beach, Boa Vista (16.014 • N, 22.735 • W) (Martins, Cardona, et al, 2022) and provide the basis for population matrix modeling. Where possible, demographic parameter estimates were derived directly from this data set or from previous Boa Vista subpopulation studies, although hatchling, juvenile, and immature stage survival parameters are from estimates in the literature.…”

“…The loggerhead turtle ( Caretta caretta ) is one of the most abundant sea turtle species in the CCLME, and the Cabo Verde archipelago supports the only regular nesting beaches in the region (Marco et al., 2012; Wallace et al., 2013). The Cabo Verde population is classified as endangered (IUCN; Casale & Marco, 2015) and is subject to very high levels of adult mortality (Martins, Cardona, et al., 2022). However, little has been done to mitigate bycatch, and conservation efforts since 2000 have focused on translocating clutches to hatcheries to improve hatching success (Martins et al., 2021), although the demographic value of this management effort remains unclear.…”

“…However, little has been done to mitigate bycatch, and conservation efforts since 2000 have focused on translocating clutches to hatcheries to improve hatching success (Martins et al., 2021), although the demographic value of this management effort remains unclear. Recently, the nest counts in Cabo Verde have increased dramatically (Laloë et al., 2020; Martins, Cardona, et al., 2022; Patino‐Martinez et al., 2022), but the underlying reasons are unknown.…”