Passage of American Shad: Paradigms and Realities

Abstract

Despite more than 250 years of development, the passage of American shad Alosa sapidissima at dams and other barriers frequently remains problematic. Few improvements in design based on knowledge of the swimming, schooling, and migratory behaviors of American shad have been incorporated into passage structures. Large-scale technical fishways designed for the passage of adult salmonids on the Columbia River have been presumed to have good performance for American shad but have never been rigorously evaluated for this species. Similar but smaller fishway designs on the East Coast frequently have poor performance. Provision of effective downstream passage for both juvenile and postspawning adult American shad has been given little consideration in most passage projects. Ways to attract and guide American shad to both fishway entrances and downstream bypasses remain marginally understood. The historical development of passage structures for American shad has resulted in assumptions and paradigms about American shad behavior and passage that are frequently unsubstantiated by supporting data or appropriate experimentation. We propose that many of these assumptions and paradigms are either unfounded or invalid and that significant improvements to American shad upstream and downstream passage can be made via a sequential program of behavioral experimentation, application of experimental results to the physical and hydraulic design of new structures, and controlled tests of large-scale prototype structures in the laboratory and field.

Evaluation of Fish Passage at a Nature‐Like Rock Ramp Fishway on a Large Coastal River

“…Detection records showed tagged American Shad (including ones at LD‐1) being suddenly undetected in the array, indicating that they potentially succumbed to starvation, predation, or harvest. Immediately downstream of LD‐1, many acoustic‐tagged American Shad experienced delays (e.g., only 33% passed within a week), and we observed numerous individuals in eddies to the side of the main fishway flow during electrofishing, something also observed by Haro and Castro‐Santos (). Simulation modeling suggested that migratory delays (especially downstream) are more detrimental than reduced passage for American Shad populations along the northeast Atlantic coast, as mortality reduces repeat spawners in iteroparous populations (Castro‐Santos and Letcher ; Stich et al.…”

“…At the spillway along the partially removed dam in the Little River, North Carolina, American Shad passage increased with water depth; depth had no relationship with Flathead Catfish passage (Raabe and Hightower ). American Shad (evening peak) and Striped Bass (morning peak) both appeared to prefer traversing the fishway with light, similar to behavior observed at other fishways (Haro and Castro‐Santos ), possibly due to their being able to see while navigating through the structure. Conversely, Flathead Catfish primarily completed passage during nocturnal hours, when they typically are more active (Vokoun and Rabeni ).…”

“…Passage by Flathead Catfish showed no relationship with flow, but there was some model support for higher passage by American Shad at intermediate flows. American Shad may avoid shallow depths at low flows, while at higher flows the associated velocities and turbulence may be issues (Haro and Castro‐Santos ). At the spillway along the partially removed dam in the Little River, North Carolina, American Shad passage increased with water depth; depth had no relationship with Flathead Catfish passage (Raabe and Hightower ).…”

The effects of horizontally and vertically oriented baffles on flow structure and ascent performance of upstream-migrating fish

“…This behaviour suggested that Alewife seem to avoid strong horizontal vortices, perhaps related to the fact that they are an ocean-dwelling, schooling species that is not particularly adapted to bed-generated turbulent flow. Avoidance and disorientation in highly turbulent flow has also been observed for other clupeids such American shad (Larinier and Travade 2002;Haro and Castro-Santos 2012). In contrast, Brook Trout frequently sought shelter behind both horizontal and vertical baffles and therefore reached higher D max particularly in repeated attempts.…”

Observations of American Shad Alosa sapidissima Approaching and Using a Vertical Slot Fishway at the Head‐of‐Tide Brunswick Dam on the Androscoggin River, Maine

“…The construction of fishways at dams is one approach used to mitigate obstructions to migrating fish. However, many of the fishways in rivers along the east coast of the United States have not been thoroughly evaluated for passage of American Shad and often adopted designs intended to be suitable for Pacific Salmon (Haro and Castro‐Santos ). Quantifying fish behavior under the variability of altered environmental conditions (e.g., flows) imposed by dams may inform managers of the efficacy of fish passage structures and identify areas for modification.…”