Spatial and temporal variations in parasite prevalence and infracommunity of spawning herring caught west of the British Isles and in the Baltic Sea.

Herring (Clupea harengus L.) viscera were examined for endoparasitic infections as part of a multidisciplinary stock identification project (WESTHER) funded by the European Union. Spawning herring were caught by commercial and research vessels from numerous locations to the west of the UK and Ireland, and a control sample from the eastern Baltic Sea. The metacercariae of two renicolid digeneans (Cercaria pythionike and Cercaria doricha), one nematode (Anisakis simplex s.s) and one cestode (Lacistorhynchus tenuis) were used to compare the parasite infracommunities in spawning herring. A significant variation in infracommunity structure was observed between different spawning grounds. Significant differences in prevalence and abundance of infections and comparisons of parasite infracommunity enabled the separation of putative herring stocks west of the British Isles. Preliminary results suggest that the parasite fauna of herring remains temporally stable.