Prey size selection by common eiders, Somateria mollissima, preying on common mussels, Mytilus edulis, in northern Norway is described. The mean length (± 1 SD) of mussels preyed upon was 13.9 ± 5.7 mm (range 3.5–38.1 mm). The dry flesh weight as a percentage of the total dry weight ranged from 4.2 to 8.6% in different body-length categories and was greatest in the mussels most frequently fed upon. There was a close negative correlation between the size of mussels fed upon and the estimated total shell weight that birds had to ingest to obtain their daily requirement of food (rs = −0.86). A hypothesis is proposed that common eiders select mussels of certain size classes to minimize the daily shell weight intake.
Predictive framework for codend size selection of brown shrimp (Crangon crangon) in the North Sea beam-trawl fishery