Size structure and trophic interactions of age-0 river herring and age-0 smallmouth bass in the Mactaquac Reservoir and Oromocto Lake, New Brunswick

Freshwater stages of herring early life histories share similar food and space resources with age-0 smallmouth bass. Given the similar ecologies, there is potential for competition for food resources.{09}Size distributions potentially influence trophic dynamics in fish communities. We examined age-0 river herring size distributions and trophic interactions with smallmouth bass in the Mactaquac Reservoir, where river herring escapement is managed, and in a nearby natural lake, Oromocto Lake. In Mactaquac Reservoir, herring hatched over a relatively short interval and growth was rapid compared to Oromocto Lake. Stable isotopes and gut contents indicate competition for food was higher in the reservoir, and bass were not piscivorous in their first year. In Oromocto Lake, bass were piscivorous at an early age and attained more growth before the winter period. Our results suggest that in reservoirs where passage of river herring spawners is managed, it may be possible to implement management strategies that promote early piscivory, faster growth rates, and increased first-year survival in smallmouth bass.