Secondary nesting beaches for leatherback turtles on the Pacific coast of Costa Rica

Abstract

Leatherback turtles (Dermochelys coriacea) have declined dramatically in the eastern Pacific Ocean (EP) in recent decades. Traditionally, population assessments have relied on the numbers of turtles on the beaches with the highest abundance of turtles (index beaches) and often disregarded the importance of nesting beaches with smaller, but still regular, numbers of nesting turtles (secondary beaches). We characterize leatherback nesting on secondary beaches throughout Pacific Costa Rica. Nesting distribution was significantly reduced since the 1990s and it currently appears to be constricted to the Santa Elena and Nicoya peninsulas. Over the past five years, nesting abundance on secondary beaches was low, ranging between 0.4 ± 0.5 and 5.3 ± 1.5 females and 3.8 ± 5.2 and 22.8 ± 10.8 nests per beach and per year. There was some exchange of turtles between beaches. The exchange rate (percentage of females that nested at least once on a different beach) ranged between 7% and 28%. While Caletas still registers multiple clutches that are laid by 1-2 females in some years, it may no longer qualify as a secondary beach due to the infrequent nature of nesting events registered recently and the total absence of nests in some of those years. Although nesting abundance is relatively low at secondary beaches, they host at least ~25% of total leatherback nesting abundance in Costa Rica. As the EP leatherback turtle declines, not only do the numbers of nesting turtles decrease but local extirpations are occurring on, previously categorized, secondary beaches. The critically low number of turtles at present may prevent recolonization of sites where they have been extirpated.