Diet and fish stock availability as possible factors in the mass death of auks in the North Sea

In February 1983 more than 30 000 birds died on the North Sea coasts of England and Scotland. The birds were unoiled, and there was no immediately obvious cause of death. Stomach contents of auks killed in this incident were examined to ascertain whether they provided any indication of the causal factors. Analysis of food remains showed differences between sample sites and between guillemots, Una aalge (Pont.), and razorbills, Alca tarda L. In all areas gadoid remains comprised a higher, and sandeels a lesser, proportion of the stomach contents in guillemots than in razorbills. The relative importance of clupeid remains varied with area. These differences, combined with current trends in the fisheries biology of major prey species, provided an ecological basis for a hypothesis explaining the incident. It was concluded that starvation was probably a major factor in the death of the auks, and that this may have been related to a combination of adverse weather conditions and changing patterns of abundance in North Sea sprat, Sprattus sprattus (L.), populations.