Das Wanderverhalten verpflanzter und heimfindender Gelbaale(Anguilla anguilla) in der Nordsee

Abstract

1. Four yellow (stationary) eels (Anguilla anguilla L.) were transplanted from Northern Denmark to the German Bight and to the central North Sea about 300 km SSW of the home area. They were tagged with ultrasonic transmitters and tracked for 7 to 35 hours. 2. The mean direction adopted by the four individuals was SE (140°), away from the direction of the home area (NNE). One eel discontinued activity after 5 h of active swimming. Combined with earlier tracking results on yellow eels a significant directional choise of 126° is calculated; it is concluded that a South-Eastern or perhaps a North-Western compass course is the first swimming performance of yellow eels towards home, regardless of the direction of their home area. 3. Earlier results with conventionally tagged yellow eels transplanted over long distances have also shown a South-Eastern trend and are now explainable. 4. With a mean migratory speed below 1 kn (1.85 km/h), the experimental specimes moved more slowly than individuals tracked one year previously in similar experiments. 5. One yellow eel tagged with a pressure sensing ultrasonic transmitter got lost twice because of an insufficiently adjusted receiver. During the first minutes of tracking it preferred a depth between 4 and 18 m; 24 h later it swam in a depth of 7 to 9 m. The water depth was 41 m. 6. From the discussion it becomes evident that yellow as well as silver eels prefer trenches if water depth decreases. Upon arrival in inshore waters directional behaviour in yellow eels probably might change; at daylight a minimum water depth of about 4 m is preferred.