Size-selective predation by fourhorn sculpin,Myoxocephalus quadricornis (L.) (Pisces) on Mesidotea entomon (L.) (Crustacea,Isopoda)

During three different seasons Mesidotea entomon specimens from fourhorn sculpin stomachs were analyzed, and compared with the M. entomon population in the field. The field samplings were carried out in the northern Bothnian Sea. Feeding experiments revealed fourhorn sculpins to be highly selective when feeding on M. entomon.The fourhorn sculpin most preferably selected large M. entomon in the field as well as in the laboratory experiments. The preference for large M. entomon remained after correction for availability of differently sized M. entomon. In summer the actual sizes of M. entomon eaten by fourhorn sculpin were smaller than in autumn and winter. During all three seasons the oldest M. entomon were the ones most preferred. Ultimate effects of predation by fourhorn sculpin on the life-history of M. entomon are discussed.