What Are They Eating? Spatio-Temporal Variability of Diet Composition in Atlantic Herring Larvae (Clupea harengus) Off the Coasts of Newfoundland

Atlantic herring play an important role in the North Atlantic ecosystem by transferring energy from secondary producers to higher trophic levels. Newfoundland herring populations are composed of spring and fall spawners, targeted as a mixed fishery. In the past, spring spawners accounted for ~90% of the total catch. Within the last decade, spring spawners substantially decreased, while fall spawners slightly increased, now dominating the catch. Peak production of copepods species such as Pseudocalanus sp. and Calanus finmarchicus has simultaneously shifted from spring to fall. These copepods are known to play an important role in the diet of several species of larval fishes. We test the hypothesis that the shift in herring abundance is related to larval feeding success and survival. Larval samples were collected using bongo tows in Trinity Bay, Newfoundland, between 2002 and 2013. In 2013, simultaneous mesozooplankton collection allowed us to estimate prey selectivity. We also relate the time series of diet composition to a zooplankton time series (1999-2013) to examine if changes in the timing of preferred prey production correspond to those in the dynamics of the herring stock. This study will provide information on how prey availability contributes to the early survival and recruitment of herring.