Krill (Family: Euphausiidae) are an important food web component within the U.S. Northeast Shelf ecosystem, but are relatively understudied.  Euphausiids are principal prey of Atlantic herring (Clupea harengus), often accounting for greater than 60% (by weight) of the diet of herring in some years. The importance of this prey appears to vary inter-annually, which may be related to oceanographic processes.  In general, increases in percent diet composition of krill during spring lag behind those of the previous fall.  This may be a response to oceanographic conditions--particularly to the timing of fall blooms