Infection of larval herring by helminth parasites in the North Sea and the effect on feeding incidence

Abstract

Specimens of larval herring ( Clupea harengus L.) collected during the Autumn Circulation Experiment in the North Sea were found to be infected with two species of helminth parasites—a trematode Hemiurus sp. and a cestode Scolex pleuronectis. The prevalence of both parasites was significantly dependent on larval length, sampling month and sampling area. Analysis of larval stomach contents indicated that feeding incidence was significantly lower in larvae which were infected with S. pleuronectis. The difference in feeding incidence between parasitized and non-parasitized larvae represented up to 50% reduction in prey uptake rate. Up to 40% of larvae were infected with S. pleuronectis and the consequences of infection for the mean growth rate in the population could therefore be significant. The geographical variation in the distribution of S. pleuronectis infection suggests the possibility of an interaction between larval advection routes and growth rate, which could influence recruitment.