Schwimmverhalten und Schwimmgeschwindigkeit bei den Larven des HeringsClupea harengus

The present study is based on two year experiments; it analyses swimming behaviour and swimming speed at different developmental stages of the herring. Yolk sac larvae tend to sink rather rapidly during resting phases. At the end of the yolk sac stage the sinking rate is at its minimum; it increases again with increasing larva size. During the phase of yolk sac resorption, vertical movements become gradually transformed into horizontal ones. Generally, three types of swimming can be distinguished: (1) “Abrupt swimming” consisting of very short periods of fast swimming; normally each dart is connected with a change in swimming direction. (2) “Normal swimming” characterized by steady movements for several seconds; it results in a winding path. (3) “Slow meandering” representing search swimming, a slowly winding locomotion with a large amplitude of each winding but with very little net progression of the larva. Swimming speed varies considerably in all size groups. The 8 to 11 mm (total length) larvae reach a mean swimming velocity (undulation) of 1.0 to 1.2 cm per second. Swimming speed, measured as the straight line distance between start and end points of a single swimming phase, attains mean values of 7 to 8 mm/sec in 8 to 11 mm larvae, 10 to 11 mm/sec in 11 to 15 mm larvae, 21 to 25 mm/sec in 19 to 24 mm larvae, and 40 to 50 mm/sec in 32 to 40 mm larvae. Swimming activity changes during larval development and seems to be influenced by food supply. The total distance travelled in 5 minutes by the head of a yolk sac larva is 1 to 3 m. About 8 days after hatching, sinking rate is low and “search swimming” (slow meandering movements) prevails. The path covered by the head within 5 minutes is 0.8 to 1.5 m.