Interdam Movements and Passage Attraction of American Shad in the Lower Merrimack River Main Stem

Abstract

In May and June of 2002, 72 adult American shad Alosa sapidissima were internally radio-tagged on four dates and were monitored in the Merrimack River, Massachusetts, between Essex Dam (first main-stem dam above the Atlantic Ocean) and Pawtucket Dam (second main-stem dam), a distance of 22 kilometers. From 1989 to 2001, the number of American shad that passed Pawtucket Dam via the Boott Station fish lift and fish ladder averaged 17% of the number that passed Essex Dam. The objectives of the study were to (1) determine the number of tagged American shad that pass Essex Dam and reach the Boott Station tailrace and (2) monitor American shad movements between Essex and Pawtucket dams. Three stationary receivers and one mobile receiver were used to track fish over a 2-month period. Sixty-five tagged fish were deemed healthy after release from the Essex Dam fish lift. From this group, 43 fish (66%) reached the pool immediately downstream of the Boott Station tailrace and 36 fish (55%) entered the tailrace. The median travel time for tagged fish that reached the tailrace was 41.5 h (range = 14.5–365.0 h). Four radio-tagged American shad (6% of 65 fish) versus an estimated 5,283 untagged American shad (10% of 54,450 fish that passed Essex Dam) passed through the Boott Station fish lift in 2002. These results indicate that American shad passage efficiency at the Boott Station fish lift needs improvement to achieve full American shad restoration upstream of the Pawtucket Dam. The extent of structural or operational measures necessary to improve American shad passage rates should be examined and evaluated.