The island hoppers: how foraging influences green turtle Chelonia mydas abundance over space and time in the Lakshadweep Archipelago, India

Abstract

Adult green turtles are known to display either preference in their foraging habits or fidelity to their foraging sites which, in turn, influences their migrations and the availability of forage. With an abundant supply of seagrass and algae, the lagoons of the Lakshadweep Archipelago off the Indian west coast serve as significant feeding grounds for green turtles. In the last 2 decades, the numbers of foraging green turtles have varied across islands, leading to speculation about their foraging patterns and movements. We collated secondary data and conducted periodic surveys between 2013 and 2019 to record trends in green turtle abundance and seagrass characteristics and investigate relationships between them. Over the last decade, green turtle abundances have fluctuated widely with increases followed by sharp declines within different lagoons. Our results also show that a reduction in seagrass density, particularly Thalassia sp. and Cymodocea sp., coincided with the decline in green turtle abundance. Moreover, turtle presence was observed at sites with higher seagrass density and canopy height. Our findings indicate that green turtles appeared to forage in particular lagoons until their preferred resources declined, before moving to other islands within the Archipelago or other unknown locations. Therefore, to devise effective management strategies, it is crucial to understand how this green turtle population will adapt to the decline in foraging resources. The declining seagrass populations also suggest the need for an ecosystem approach towards green turtle conservation.