Food and feeding of young herring larvae of Norwegian spring spawners

The gut contents of young herring larvae sampled each hour from 3 to 9 April 1967 at three depth intervals around a floating drogue were examined to study their feeding. Copepod eggs constituted more than 90% of the food items. Feeding started shortly after sunrise within the same hour in the depth intervals 25-5 m, 30-50 m and 75-55 m. Mean length increased with diminishing yolk sac until absorption when mean length decreased. The latter could indicate lack of suitable food. The mean gut content of feeding larvae did not increase until after absorption of the yolk sac. Larvae from the deepest strata had less gut contents than the others, probably because a lower percentage of them had absorbed yolk sacs. A high percentage of larvae feeding during day-time contradicted total defecation due to capture. No correlation was found between numbers of Calanus eggs in the guts and in plankton. Larvae containing Calanus nauplii had more assorted gut contents than larvae containing Calanus eggs. The critical period concept is discussed