Long‐term trends in marine turtle size at maturity at an important Atlantic rookery

Abstract

For species reaching maturity at a range of ages or sizes, factors that influence juvenile growth and size at maturity may have lasting impacts on overall fitness. Assessing when animals reach maturity is especially challenging for species which are difficult to follow through time as a result of highly migratory behavior, long life spans, or both. We examined nesting female size in a reproductive assemblage of green turtles (Chelonia mydas) and loggerheads (Caretta caretta) on the east coast of Florida, USA. We used a long-term dataset from 1982 to 2019 to estimate a minimum size at maturity interval on the basis of two standard deviations below mean female size for each species. The minimum size intervals for green turtles (81.4-89.3 cm) and loggerheads (68.1-79.1 cm) were lower than most previous estimates in the literature, many of which were simply the smallest individual ever observed. There was a significant decrease in the upper bound of the minimum size interval over the study period for both green turtles (1.6 cm) and loggerheads (4.1 cm). These shifts in size at maturity may be the result of changes in population demographics, habitat quality, and behavioral reactions to these changes. The development and periodic reassessment of robust estimators of maturity are an important part of programs centered around the monitoring and conservation of vulnerable wildlife populations.

Changes in mean body size in an expanding population of a threatened species

“…There are limited sites to test this prediction, since while many marked long-term increases in turtle nesting numbers have been described [ 8 ], the annual mean size of individuals is often not reported. Nevertheless, when both nesting numbers and mean size have been reported, a decrease in mean size accompanied an increase in the number of nests for nesting sites in the Atlantic (green turtles at Ascension Island [ 11 ], loggerhead and green turtles in Florida [ 22 ], the Pacific (green turtles in Hawaii [ 23 ]) and the Indian Ocean (loggerhead turtles in South Africa [ 21 ]).…”

“…In particular, relatively few turtles were tagged in proportion to the number of nests, largely due to the huge volume of nesting turtles and hence the logistic challenge of intercepting a high proportion of turtles while they were ashore. In other regions where populations are expanding and the mean turtle size decreasing [ 11 , 21 , 22 ], it may be possible to tag a greater proportion of nesting turtles and so, for example, more clearly identify the relative numbers of neophytes versus remigrants as well as any possible changes in breeding intervals.…”

Intraspecific spatial segregation on a green turtle foraging ground in the Florida Keys, USA

“…Individuals with estimated SSCLs < 60 cm were classified as Small Juveniles, individuals with SSCLs estimated between 60 and 84 cm were classified as Large Juveniles and individuals with SSCLs ≥ 85 cm were classified as Adults. This life stage classification to determine Adults is also bolstered by the recommendations provided by Phillips et al (2021), who found a minimum size range of 81.4-89.3 cm SSCL. This size range spans between the absolute minimum SSCL measurement to two standard deviations below the mean of 3401 mature female green turtles nesting on the east coast of Florida.…”

“…This size range spans between the absolute minimum SSCL measurement to two standard deviations below the mean of 3401 mature female green turtles nesting on the east coast of Florida. Chabot (2017) determined through stable isotope analysis that a majority of the 117 nesting green turtles sampled on the same nesting beach as Phillips et al (2021) were likely to forage in and around the Eastern Quicksands and the greater Florida Keys prior to nesting. The nesting beach Phillips et al (2021) and Chabot (2017) sampled represents > 30% of all green turtle nesting in Florida (FWCC unpubl.…”

“…Chabot (2017) determined through stable isotope analysis that a majority of the 117 nesting green turtles sampled on the same nesting beach as Phillips et al (2021) were likely to forage in and around the Eastern Quicksands and the greater Florida Keys prior to nesting. The nesting beach Phillips et al (2021) and Chabot (2017) sampled represents > 30% of all green turtle nesting in Florida (FWCC unpubl. Data; K. Mansfield unpubl.…”