Microelectronic detection of activity level and magnetic orientation of yellow European eel, Anguilla anguilla L., in a pond

We studied the circadian and monthly activity, the distribution patterns, and orientation to the earth's magnetic field, of yellow (non-migratory) female eels in a freshwater pond by means of microchips injected into their muscles. Detectors for microchips mounted in tubes were placed in the pond to detect if eels oriented themselves with respect to earth's magnetic field. Based on the frequency of tube visits (search for shelter), the data indicated that the presence of eel in the tubes decreases gradually during the study period. We saw more activity during the night in the first months. There was a seasonal component in the orientation mechanism, with a significantly lower preference component in the summer compared to the fall. A preference for tubes oriented in a south-southwest direction (the direction of the Sargasso Sea) in fall suggests an orientation to the earth's magnetic field.[PUBLICATION ABSTRACT]