Precise natal homing and an estimate of age at sexual maturity in hawksbill turtles

The geographic specificity of natal philopatry (how precisely breeding individuals return to their natal origins) influences breeding biology, genetic diversity and habitat range, and therefore has important implications for species resiliency and management. Also, the age at which individuals reach sexual maturity and enter the breeding population is a vital parameter for demographic analyses. Empirical research on philopatry and maturation, however, is challenging for long-lived animals that are difficult to observe, such as marine turtles that have complex oceanic life histories. Regional natal philopatry is well established for marine turtles, but the geographic specificity of philopatry is unclear. Similarly, estimates of age at maturity vary widely, and direct evidence is lacking. Here, we targeted these information gaps by assessing kinship among 256 females from Antigua's Jumby Bay (JB) hawksbill turtle rookery, a population with demonstrated nest-site fidelity and neophyte assimilation. We estimated mother-daughter and full sibling relationships with a maximum-likelihood full-pedigree reconstruction approach, incorporating genotypic (12 microsatellites), maternal genealogy (mitochondrial DNA) and age structure (long-term mark-recapture) data. We validated relationships with parentage assignment and pairwise relatedness estimators. Fourteen veteran nesters were the mothers of 42 younger nesters, and 94 nesters formed 35 full sibships. Time between the first nesting records of mothers and their daughters indicated maximum time to maturity as short as 14 years in Caribbean hawksbills. Thirteen of the 14 mothers showed consistently high fidelity to JB for two decades, providing compelling evidence that 41 of these daughters originated from JB nests and returned to this 1-km-long natal site to breed. Rookeries with strongly philopatric individuals might have limited colonization potential and be at a disadvantage in the event of habitat loss. This study demonstrates the utility of long-term mark-recapture data in kinship analyses for answering questions relevant to endangered species conservation.

Automated summary

The geographic specificity of natal philopatry plays a crucial role in breeding biology, genetic diversity, and habitat range, while the age at maturity is a vital parameter for demographic analyses. This study focused on kinship among female sea turtles to address gaps in knowledge, demonstrating the importance of such information for endangered species conservation.