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First published online May 19, 2008
Journal of Experimental Biology 211, 1719-1728 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.015792

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The sensory ecology of ocean navigation

Kenneth J. Lohmann^*, Catherine M. F. Lohmann and Courtney S. Endres

Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA

View larger version (12K): [in this window] [in a new window]   Fig. 1. Diagram illustrating potential problems in attempting to infer mechanisms of navigation from the tracks of animals. (A) Overhead view of the track of a hypothetical sea turtle moving hundreds of kilometers through the ocean and monitored with satellite telemetry; events that occurred along the way are indicated. (B) A plausible but erroneous interpretation of the turtle's path. In this hypothetical example, researchers unaware of what happened in the ocean superimposed the track on several topographical and geophysical maps until correlations were found between changes in the turtle's behavior and specific features of the environment. These environmental cues were then assumed to have elicited the behavioral changes, leading to incorrect inferences about navigational mechanisms.

View larger version (13K): [in this window] [in a new window]   Fig. 2. (A) Diagrammatic representation of the Earth's magnetic field illustrating how field lines (represented by arrows) intersect the Earth's surface, and how inclination angle (the angle formed between the field lines and the Earth) varies with latitude. At the magnetic equator (the curving line across the Earth), field lines are parallel to the Earth's surface. The field lines become progressively steeper as one travels north toward the magnetic pole, where the field lines are directed straight down into the Earth and the inclination angle is 90°. (B) Diagram illustrating four elements of geomagnetic field vectors that might, in principle, provide turtles with positional information. The field present at each location on Earth can be described in terms of a total field intensity and an inclination angle. The total intensity of the field can be resolved into two vector components: the horizontal field intensity and the vertical field intensity. (Whether animals are able to resolve the total field into vector components is not known.)

View larger version (19K): [in this window] [in a new window]   Fig. 3. Orientation of hatchling loggerhead turtles in magnetic fields characteristic of three widely separated locations (marked by black dots on the map) along the migratory route. Generalized main currents of the North Atlantic gyre are represented on the map by arrows. In the orientation diagrams, each dot represents the mean angle of a single hatchling. The arrow in the center of each circle represents the mean angle of the group. Dashed lines represent the 95% confidence interval for the mean angle. Figure modified from Lohmann et al. (Lohmann et al., 2001).

View larger version (14K): [in this window] [in a new window]   Fig. 4. Evidence for a magnetic map in juvenile green turtles. Juvenile turtles were captured in feeding grounds near the test site in Florida, USA. Each turtle was exposed to a magnetic field that exists at one of two distant locations (represented by stars along the coastline). Turtles exposed to the field from the northern site swam approximately south, whereas those exposed to the field from the southern site swam approximately north. In the orientation diagrams, each dot represents the mean angle of a single turtle. The arrow in the center of each circle represents the mean angle of the group. Dashed lines represent the 95% confidence interval for the mean angle. Figure modified from Lohmann et al. (Lohmann et al., 2004).

View larger version (12K): [in this window] [in a new window]   Fig. 5. Ocean distribution of sockeye salmon (Oncorhynchus nerka) that spawn in Iliamna Lake, Alaska. Salmon begin their spawning migrations from widely separated locations that are sometimes more than 1000 km from the final target area. Figure modified from Dittman and Quinn (Dittman and Quinn, 1996).

View larger version (45K): [in this window] [in a new window]   Fig. 6. Perception of ocean wave direction by hatchling sea turtles. (A) The motion of a hatching turtle swimming with and against the direction of wave propagation. For a hatchling oriented into waves (left), the sequence of accelerations during each wave cycle is upwards, backwards, downwards and forwards. A turtle swimming with the waves (right) is accelerated upwards, forwards, downwards and backwards. Modified from Lohmann and Lohmann (Lohmann and Lohmann, 1992). (B) A machine designed to simulate wave motion by reproducing the sequence of accelerations that occur beneath a propagating wave. The responses of hatchling turtles to these simulated waves have been studied by placing turtles into cloth harnesses (see C) and subjecting them to orbital movements while they are suspended in air. Modified from Lohmann et al. (Lohmann et al., 1995b). (C) A hatchling turtle suspended in air on the wave simulator. Hatchlings suspended in this way act out their normal swimming behavior and will attempt to turn until facing into simulated waves.

View larger version (15K): [in this window] [in a new window]   Fig. 7. Diagram of wave refraction patterns around an island in the open ocean. As waves pass around an island, the parts that encounter shallow water are slowed relative to the parts remaining over deeper water. As a result, refraction occurs and a pattern of wave interference often forms on the leeward side of the island.