Integrated mixed-effect growth models for species with incomplete ageing histories: a case study for the loggerhead sea turtle Caretta caretta

Abstract

For stochastic growth processes, integrated mixed-effects (IME) models of capture-recapture data and size-at-age data from calcified structures such as otoliths can reduce bias in model parameters. Researchers have not fully explored the performance of IME models for simultaneously estimating the unknown ages, growth model parameters, and derived variables. We simulated capture-recapture observations for tagging experiments and skeletochronology (i.e. humerus growth) observations for stranded loggerhead sea turtles Caretta caretta based on previously published parameter estimates for 3 growth processes (logistic, Gompertz, and von Bertalanffy). We then fit IME models to the integrated and non-integrated data. For the integrated data (both tagging and skeletochronology), we found decreased bias and uncertainty in estimated growth parameters and ages, and decreased misspecification of the growth process based on AIC. Applying the IME model to Western Atlantic loggerheads, the von Bertalanffy growth process provided the best fit to the skeletochronology data for the humeri from 389 stranded turtles and capture-recapture data from 480 tagged turtles. The estimated mean growth coefficient (μk) and mean asymptotic straight carapace length (μ×) were equal to 0.076 yr-1 and 92.1 cm, respectively. The estimated mean ages of the stranded turtles and recaptured tagged turtles were 13.5 and 14.6 yr, respectively. Assuming the size-at-sexual maturity (SSM) is 95% of the asymptotic size, the mean and 95% predictive interval for the age-at-sexual maturity (ASM) was 38 (29, 49) yr. Our results demonstrate that IME models provide reduced bias of the growth parameters, unknown ages, and derived variables such as ASM.

Forty years of monitoring increasing sea turtle relative abundance in the Gulf of Mexico

“…One of the contributing factors of increased growth may be due to the implementation of turtle excluder devices (TEDs) on shrimp trawling vessels in the 1990s. Reducing bycatch invariably expands the number of sea turtles reaching sexual maturity—loggerheads reach sexual maturity between 27 and 38 years 13 , 24 and green sea turtles reach sexual maturity between 19 and 44 years 22 , 88 , 89 . Thus increasing the number of potential nesters for future generations.…”

Forty Years of Monitoring Increasing Sea Turtle Abundance in the Gulf of Mexico

“…One of the contributing factors of increased growth may be due to the implementation of turtle excluder devices (TEDs) on shrimp trawling vessels in the 1990's. Reducing bycatch invariably expands the number of sea turtles reaching sexual maturity -loggerheads: 27-38 years [13,24] ; green turtles: 19-44 years [22,75,76] , and increases the number of potential nesters for future generations. There was an estimated 60% reduction in bycatch of all species of sea turtles in the Atlantic following the TED regulation (mortality: 94% reduction [77] ).…”

Allometry and Individual Growth of the Temperate Pacific Sardine (Sardinops sagax) Stock in the Southern California Current System

“…Lastly, it is important to point out that growth can also be approached using random or mixed effects models (random and fixed), through which the effects that different intrinsic and extrinsic covariates have on the estimation of growth and its variability have been explored [79,[81][82][83][84][85][86]. On the other hand, it has been noted that integrated mixed-effects models could reduce bias in growth model parameters versus non-integrated models [87], but that this line of research has not yet fully explored the performance of integrated mixed-effects models to simultaneously estimate unknown ages, growth model parameters, and derived variables. In this context, for this species, there is an open route in which the growth of the different Pacific sardine stocks that inhabit the California Current and the Gulf of California can be explored.…”