Marine turtles in the open ocean often forage in areas of enhanced productivity, but how they locate those sites and what they do once there is poorly understood. One possibility is that odors from prey might be informative. We explored those possibilities in laboratory experiments using juvenile marine turtles. We analyzed responses to an airborne by-product of predation (dimethyl sulfide or DMS) and to airborne and waterborne odors made from extracts of fresh prey (squid, jellyfish, penaeid shrimp, and algae [Sargassum spp.]). Observations were made in a seawater-filled arena containing an enclosed air space. Airborne odors were delivered across the water surface and waterborne odors were introduced as extracts into the water. Tethered loggerheads (Caretta caretta) and leatherbacks (Dermochelys coriacea) failed to swim “upwind” in the presence of any airborne odor, suggesting that these stimuli, alone, do not evoke orientation from a distance. Free-swimming loggerheads and green turtles (Chelonia mydas), presented with either an airborne or waterborne squid odor, directed bites at the tank walls, at one another, and (most frequently) at a stationary visual stimulus (a small plastic sphere) anchored under water. DMS did not evoke a comparable response. We conclude that close to productive hot spots, both air- and waterborne prey odors elicit a similar visual search for underwater prey targets. A review of the literature suggests that at a distance, juvenile turtles might use magnetic maps to locate areas that include sites of greater oceanic productivity.
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Vol. 15 • No. 1