Herring larvae (Clupea harengus) investigations in the Skagerrak area, December 1987 to March 1988. A preliminary report

Abstract

From December 1987 to March 1988 two transects, Torungen - Hirtshals and Oksøy - Hanstholm, were performed once a month for sampling of herring larvae. The gear used was a 9 feet Isaac-Kid Midwater trawl sampling in the upper 60 m of the water column. High numbers of herring larvae were caught in the inflowing waters to the Skagerrak area from January to March 1988 and in the Norwegian Coastal Current moving out of the Skagerrak area, specially in January and February 1988. All the sampled herring larvae were stored in 80 % buffered alcohol, and were examined within 7 days for total and standard length. Later between 38 and 70 larvae from each cruise were examined for daily increments in their otoliths. In addition the wet and dry weights of the same larvae were decided. Estimated hatching date of the examined larvae ranged from 18 August 1987 to 28 November 1987 with a main hatching period in the middle of September, except for the larvae sampled during the March survey. These larvae had an average hatching date in the first part of October. The estimated hatching periods indicate that the larvae entering the Skagerrak area mainly came from the spawning area of the Northern and Central North Sea in December 1987 to February 1988, while the larvae collected in March have their origin in the Central North Sea.