Recovery of River Herring Alosa Spp. Influences Smallmouth Bass Micropterus Dolomieu Diet and Growth in the Penobscot River, Maine

Restoration efforts on the Penobscot River (Maine, USA) include the removal of the two lower-most dams and improvements to fish passage at remaining barriers.  This restoration effort, accompanied by stocking of river herring Alosa spp., has resulted in a marked increase in this anadromous herring in the Penobscot River.  River herring juveniles are sympatric with introduced smallmouth bass Micropterus dolomieu residing in the river until fall, when they migrate seaward.  The increased availability of river herring as prey may increase the growth of smallmouth bass.  To test this, we collected smallmouth bass, via angling and electrofishing, from May – October 2015 in the Penobscot River watershed to determine the seasonal prevalence of river herrings in stomach contents.  We also measured over 800 otoliths from M. dolomieu collected in different areas of the watershed to examine differences in growth.  Diet and growth analyses will be used to inform a bioenergetics model used to assess sensitivity of growth to increased river herring consumption.  These results will elucidate the impact of alosine population growth on seasonal smallmouth bass diet and illustrate the impact of large dam removal projects on riverine food webs.