NEAFWA 2018

AUTHORS: Christopher W.D. Gurshin, Ph.D., Matthew P. Balge – Normandeau Associates, Inc.

ABSTRACT. The timing of the outmigration of juvenile American Shad (Alosa sapidissima) in the Connecticut River was described from a time series of hydroacoustic data collected in support of a downstream passage study at the Vernon Hydroelectric Project. Acoustic backscatter was continuously sampled by an upward-facing, 420-kHz split-beam transducer mounted on the riverbed near the entrance to the downstream fish pipe in the forebay of the Vernon Dam powerhouse from August 15 through November 15, 2015. Echogram patterns of manually classified school echoes indicated small schooling fish first appeared in the Vernon forebay on August 17 and last appeared on October 30 (74 days), however were not consistently present until the beginning of September. Fish density increased to the major peak density during the period from September 25 to October 3 which coincided with a sharp decrease in water temperature (20°C to 16°C). Density declined through October with two isolated moderate peaks on October 23-24 and 30 before declining to zero by November when water temperatures remained below 10°C. Data from visual observations, electrofishing, cast netting, and ARIS imaging sonar verified these echo patterns reflected the timing of emigrating juvenile shad arriving and departing the forebay of the Vernon Dam powerhouse.