Finding the lost years of a nearly lost population: Revealing key demographic parameters of eastern Pacific hawksbill sea turtles (Eretmochelys imbricata)

Understanding vital rates of sea turtles and obtaining improved estimates of demographic parameters is a central theme in onging efforts to monitor and recover sea turtle stocks listed on the Endangered Species Act. Specifically, the need to estimate growth rates, life-stage duration, age-at-maturity, and survivorship in different habitats, is critical for accurate population assessments and sea turtle recovery planning. Progress on estimating these demographic parameters, however, has been slow—partially due to the slow somatic growth of sea turtles but also due to the lack of dedicated long-term studies that can follow these long-lived animals throughout their entire life cycle. Here we present the first-ever results for age and growth for the endangered hawksbill sea turtles in the eastern Pacific by applying skeletochronology with sequential stable isotope analysis (“skeleto-iso”).

In the 1700s, hawksbills were a common occurrence along the coast of Mexico and Central America. Yet by the 1960’s, intense commercial harvests had dramatically reduced the population and just 15 years ago, this species was considered on the verge of extirpation in the eastern Pacific. By 2010, collaborative international work had at last identified some key nesting and foraging habitats, especially in El Salvador and Nicaragua, giving hope to the recovery of this nearly lost population, but still very little was known about these rare turtles.

With knowledge of the demographics of this population still scant, we used a rare dataset of nearly 100 hawksbill bones collected opportunistically from two unique ocean ecosystems of coastal El Salvador, the mangrove estuary at Bahía de Jiquilisco, and the open coast at Punta Amapala. Here we describe the rapid growth and movements of young, post-hatchling hawksbills, as well as age-at-maturation for adults. Via skeleto-iso analysis we recreated the multi-year movements of these animals to better inform the recovery efforts of this population.