Effect of ocean current on the dead-reckoning estimation of 3-D dive paths of emperor penguins

Abstract

The dead-reckoning technique is a useful method for obtaining 3-D movement data of aquatic animals. However, such positional data include an accumulative error. Understanding the source of the error is important for proper data interpretation. In order to determine whether ocean currents affect dive paths calculated by dead-reckoning, as has previously been hypothesized, we examined the directions of the estimated positions relative to the known real points (error direction) and the relationship between the error direction and the current direction. 3-D dive paths of emperor penguins Aptenodytes forsteri diving at isolated dive holes in eastern McMurdo Sound were reconstructed by dead-reckoning, and the net error and error direction were calculated. The net error correlated positively with the dive duration. The error directions were not distributed uniformly, and the mean error direction tended to be north of the starting point of dives. Because there was a southwardflowing current in eastern McMurdo Sound, the ocean current was likely to affect the calculated dive paths. Therefore, the method of error correction generally used, in which the net error divided by the dive duration is applied to each estimated position, is realistically appropriate, provided that the current does not change significantly during a dive.

Technological innovation in archival tags used in seabird research

“…Using this together with estimates of speed (e.g. Ropert Coudert et al 2002, Shepard et al 2008a, the movements of seabirds can be determined with very fine (relative; sub-metre [Wilson et al 2002b]) resolution, even when they are underwater (Wilson 2002, Shiomi et al 2008, where the more commonly used GPS systems (which rely on radio-signals from satellites) cannot function. The seamless nature of dead-reckoned tracks together with their high temporal resolution (Wilson et al 2007a) mean that they have particular potential for determining behaviour from the precise form of the track.…”

“…Considered combination of sensors in seabird archival tags can yield more than the simple sum of each of the sensors. An example of this is in deadreckoning, or vectorial calculation of animal movements , Wilson et al 1991b, made possible by geomagnetic sensors that allow derivation of bird heading during travel (Shiomi et al 2008). Using this together with estimates of speed (e.g.…”

“…com) and IGOR-Pro (www.wavemetrics. com) are vastly superior programs for this but, given the relatively complex computations necessary to derive, for example, a dead-reckoned track from geomagnetic, pressure and speed data (Shiomi et al 2008), the seabird community really needs bespoke software. Some tag manufacturers such as Wildlife Computers (www.…”

Linking northern fur seal dive behavior to environmental variables in the eastern Bering Sea

“…The dead-reckoner channels recorded compass bearing, inclination, body orientation, depth, and speed-through-the-water for each female. We used the dead-reckoning channel vectors of compass bearing, speed, and depth to reconstruct the 2-and 3-dimensional swim paths of the fur seals (e.g., Wilson et al 1993, Ropert-Coudert et al 2002, Shiomi et al 2008). We processed the tag's speed channel to correct for cumulative errors due to bias in the speed paddle's position.…”

Underwater and surface behavior of homing juvenile northern elephant seals

“…An ascending pitch angle is represented as a positive value. Headings were computed from 3-D geomagnetism and acceleration, and the 3-D dive paths were reconstructed from headings, pitch, depth and swimming speed data using dead-reckoning methods (Johnson and Tyack, 2003;Mitani et al, 2003;Shiomi et al, 2008). Horizontal migration paths were derived from headings and horizontal swimming speed every second using dead reckoning.…”