Foraging ecology of sea kraits Laticauda spp. in the Neo-Caledonian Lagoon

To understand the magnitude and ecological impact of predation, we need to know not only predator abundance and feeding rates, but also the area from which the prey are taken. Previous work on amphibious sea snakes (sea kraits Laticauda spp.) in New Caledonia has documented the former parameters, and suggested that these marine snakes may be major predators within coral-reef ecosystems. To estimate the area over which these snakes forage, we have developed methods based on detailed assessments of (1) the eel species consumed (and, hence, their habitats of origin), (2) the state of digestion (and, hence, time since capture) of prey items inside snakes returning to their home islands after foraging trips, and (3) the rate of digestion of prey in experimental trials. In combination with data on rates of snake movement, we conclude that one species (Laticauda laticaudata) forages mostly on soft-bottom habitats within 23 km of the home island, whereas the other species (L. saintgironsi) forages on coral substrates within 38 km of the home island. The distribution of estimated foraging ranges was similar between these 2 species (about one-third of prey taken within a few kilometres of the home island; the rest from a wide range of much further sites), despite interspecific divergence in traits such as prey types, prey sizes and rates of digestion. These extensive foraging ranges suggest that sea kraits are significant predators of eels over the entire area of the lagoon; and imply that populations of these top predators can be affected by disturbance to prey resources even many kilometres from the home island.