Abstract
AbstractDespite 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.Received March 22, 2011; accepted August 24, 2011
Highlights
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
SUMMARY: PARADIGMS AND REALITIES Over the last 250 years, some progress has been made in improving upstream passage for American shad in fishways and other structures, yet the performance of even the most advanced structures is still not as high as it is for adult salmonids
Summary
Overcrowding and high mortality in the upper fishway; modification of these weirs with partial-depth side slots improved passage for both American shad and salmon (Monk et al 1989). American shad tend to be diurnal in their migratory habits and to enter and pass upstream passage structures primarily during the day (Fisher 1997; Haro and Kynard 1997; Sullivan 2004), while falling back to lower-velocity zones at night (Theiss 1997). They are somewhat reluctant to immediately pass under darkened areas of open channels (e.g., under low bridges or strong shadows, or where there is a strong light transition). Juvenile American shad were reluctant to pass accelerating flows of 2 m · s−1 · m−1 at surface bypass entrances; this avoidance behavior was reduced at acceleration rates of 1 m · s−1 · m−1 (Haro et al 1998)
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