# Biomarkers of foraging and reproduction in captive adult female hawksbill sea turtles (Eretmochelys imbricata)

## TL;DR

This study tracks energy and hormone levels in captive hawksbill sea turtles to understand how they prepare for and engage in reproduction.

## Contribution

The study provides the first annual physiological profile of foraging and reproduction in captive hawksbill sea turtles.

## Key findings

- BHB and TRG levels were higher during breeding compared to non-breeding periods.
- Testosterone concentrations peaked during breeding months, particularly in May.
- Elevated TRGs correlate with vitellogenesis in breeding female hawksbills.

## Abstract

Hawksbill sea turtles (Eretmochelys imbricata) are listed as critically endangered by the International Union for the Conservation of Nature (IUCN). To implement best conservation practices for this species, its biology should be well understood. Attempting to characterize the foraging physiology of free-ranging hawksbill sea turtles is complicated by the fact that sampling is typically limited to nesting females during the reproductive season. Without data from non-reproductive periods, it is difficult to determine whether observed physiological values reflect baseline conditions or are specific to the energetically demanding nesting season. Accordingly, in this study, we described the physiology of foraging in a captive-held population of hawksbill sea turtles for an entire year. Across the year, we sampled a total of five captive adult female hawksbills at the Okinawa Churaumi Aquarium in Okinawa, Japan. We measured the concentration of β-hydroxybutyrate (BHB), triglycerides (TRGs) and testosterone. Foraging biomarkers BHB and TRGs were both significantly higher during gonadal recrudescence and breeding than during gonadal quiescence, consistent with mature animals that were not foraging actively during breeding activities. Testosterone concentration also was higher during breeding months than during non-breeding months, especially in May, which marked the onset of mating. Elevated BHB during breeding activities indicated that captive hawksbills accumulated energy reserves during the non-breeding season to invest it in breeding activities. Additionally, elevated TRGs are correlated to vitellogenesis occurring in the breeding female hawksbills.