Going with the flow?: The relationship between sponge foraging dolphins (Tursiop sp.) and tidal current
Dolphins in Shark Bay use sponge tools to ferret prey from the sea floor (Smolker et al. 1997). This foraging tactic is costly, as sponging females have larger foraging activity budgets, dive for longer periods, and have fewer associates than non-sponging females (Mann et al. 2008). One factor that has not been considered in this discussion though, is the relationship between sponging and tidal current. Sponging occurs primarily in deep-water channels (Sargeant et al. 2007) with strong tidal current (unpublished data), which is likely to have implications for the overall energetic cost of this foraging technique. Our results show that dolphins predominantly travel with the current, and when doing so, move at faster speeds and cover greater distances. These results suggest that sponge foraging may not be as energetically costly as initially believed. Foraging with the strong tidal flow may save energy for spongers relative to those that forage in minimal current (outside of channels). Although spongers forage more than non-spongers, their movement may be more efficient per unit of time. Future work will explore movement of spongers during non-sponging bouts as well as movement of non-sponging dolphins in these channels.
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