Passage of American shad: Paradigms and realities

Despite over 140 years of development, implementation of passage of American shad at dams and other barriers remains problematic. Large scale technical fishways designed for passage of adult salmonids on the Columbia River have been presumed to have good performance for shad, but have never been rigorously evaluated for shad passage.  Similar but smaller fishway designs on the East Coast have poor performance. Few improvements on designs based on knowledge of swimming and migratory behavior of shad have been incorporated into current fishway and other passage structure designs.  Provision of effective downstream passage of both juvenile and postspawning adult shad has been given little consideration in most passage projects.  Components of attraction and guidance of shad to both fishway entrances and downstream bypasses remain poorly understood.  We review the evolution of development of passage structures for shad and resulting assumptions and paradigms about shad behavior and passage that may not be conducive to effective passage performance.  We offer several new insights on shad swimming performance and behavior, as well as results from traditional and novel passage structure evaluations that provide important baseline data for potential improvements of new and existing shad passage structures.