Light- and flotsam-dependent ‘float-and-wait’ foraging by pelagic sea snakes (Pelamis platurus)
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Efficient detection of food patches in oceanic areas by pelagic predators is often linked to large-scale physical structures (e.g. fronts, upwellings) that are usually rich and predictable. At smaller scales, however, predictability of resource becomes less clear because of the lability of smaller physical structures such as slicks and drift lines. Here, we explore how light levels and quantity of flotsam affect the occurrence of foraging Yellow-bellied sea snakes (Pelamis platurus) on slicks. Although this pelagic species was formerly hypothesised to surface randomly and drift passively to reach slicks, our results show that foraging snakes are far more abundant on slicks if light levels are high and if slicks display flotsam. The combination of both light and flotsam should enhance the contrast between a potentially favourable slick and the adjacent waters as seen from an underwater viewpoint. Although our results do not unambiguously demonstrate the ability of Pelamisplaturus to visually detect surface drift lines, they clearly suggest a role of both light levels and amount of flotsam on surfacing decision. Accordingly, this hypothesis is supported by several complementary traits that are specific to this species. ‘Float-and-wait’ foraging undoubtedly requires efficient detection of, and orientation to, oceanic slicks—processes that are likely less random and passive than formerly believed. Successful pelagic foraging is no doubt important to this species of sea snake that is the world’s most widely distributed snake species.
KeywordsCloud Cover Abundant Prey Food Patch Deep Current Ambient Light Level
We thank Joe Pfaller, Coleman Sheehy and Harold Heatwole for assistance in the field. Adán Barrera provided boat transportation and helped to locate slicks and snakes. We are grateful to Alejandro Solórzano and Mahmood Sasa for managing the permits (018-2009-ACAT, DNOP-002-2010, DGT-013-04-2010), and we thank Sönke Johnsen, as well as anonymous referees for helpful comments on the manuscript. Funding was provided by National Science Foundation grant IOS-0926802 to HBL.
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