Herring larvae ( Clupea harengus) in the Skagerrak area from December 1987 to April 1988

Abstract

Herring larvae were sampled once a month from December 1987 to April 1988 on two transects, Torungen-Hirtshals and Oksøy-Hanstholm, and in April 1988 on two other transects, Jomfruland-Skagen and Lysekil-Skagen. The gear used was an Isaacs-Kidd midwater trawl (10 m 2 mouth opening) sampling in the upper 60 m of the water column, except for the April cruise, when sampling extended to 95 m depth. The vertical distribution of herring larvae was examined during a 24 h station on 3–4 April. High numbers of herring larvae were caught in the inflowing waters to the Skagerrak area from January to April 1988 and in the Norwegian Coastal Current leaving the Skagerrak area. The 24-h sampling station indicated high abundance of larvae in the whole water column at night, whereas sampling during the days seems to be inadequate for quantitative estimates of larvae longer than 30 mm. Between 38 and 70 larvae from each cruise during December to March were examined for daily increments in their otoliths. Their estimated hatching dates ranged from 18 August to 28 November 1987, with a main hatching period in the middle of September, except for the larvae sampled during March. 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 from December 1987 to March 1988 originated mainly from spawning areas in the central North Sea.