Fixed, Side-Aspect Acoustic Sampling of a Diverse Diadromous Fish Community in a Tidal River

Dam removals and passage improvements by the Penobscot River Restoration Project will improve connectivity and access for 12 diadromous fish species in New England’s second largest river by 2013. As part of a larger assessment of changes in fish community dynamics, we are using fixed location, side-aspect acoustics to estimate the number of fish passing our sampling site and apportion these counts to the lowest taxonomic level possible. Our methods are derived from similar, ongoing research of diadromous fishes in rivers of the Northwest (US and Canada) and Southeast, however strong (3 m) tidal flux and tight restrictions on capture sampling pose unique challenges. Since May of 2010 (excluding months of ice cover), two Biosonics DTX, 200 kHz, split beam transducers, have been mounted on opposite sides of the river (rkm 35), sampling perpendicular to flow. Automation software provide continuous collection, noise removal and data export of individual fish trace measures (e.g. target strength, speed, trajectory). Complementary sampling with Dual Frequency Identification Sonar (DIDSON) and additional sources of information (e.g., upstream fish ladder counts, concurrent sampling projects) are used to validate split beam data and provide physical and behavioral characteristics for taxonomic discrimination (to varying levels) of individual fish and subsequent apportionment of counts. These methods will be discussed and fish passage estimates from May through October of 2010 and spring of 2011 will be presented in the context of documented environmental cues and clues to migration.