Small scale distribution patterns and vertical migration of North Sea herring larvae (Clupea harengus, Teleostei: Clupeidea) in relation to abiotic and biotic factors
Holger Haslob, Norbert Rohlf and Dietrich Schnack
The distribution of herring larvae in relation to environmental conditions and the occurrence of possible prey and predator organisms was studied during a 4-day period on a permanent station in the northern North Sea in September 1999. The vertical distribution of herring larvae was sampled in 20-m intervals by means of a multiple-closing net. To resolve the small-scale patchiness of herring larvae and planktonic prey and predator organisms, a towed in-situ video system was used, the Ichthyoplankton Recorder. A diel vertical migration of herring larvae was observed with different intensities depending on their body length. Small larvae (<10 mm) were concentrated in the upper water layers during daytime and were distributed more homogenously during night time. Large larvae (>16 mm) showed the highest abundances in the upper water layers during the day and were concentrated in deeper water layers during the night. The presented results appear to be relevant for individual-based modelling of the fate of larval herring populations.