Wall diffuser velocity effects on American Shad (Alosa sapidissima) inside a fishway entrance channel

Attraction water for fishways is typically introduced through a diffuser inside the entrance channel, often through the floor or wall. In the spring of 2019, this laboratory study examined how 151 adult American Shad (Alosa sapidissima) responded to different gross velocities through a wall diffuser inside a full-scale fishway entrance channel. Two velocity conditions were studied, 0.152 m/s and 0.305 m/s, both without turning vanes inside the auxiliary water channel. The fish were tracked using the passive integrated transponder telemetry technique. The results of the experiments showed no difference in American Shad behavior when exhibited to the low and high velocity treatments. Moreover, shad passed the diffuser in roughly 3 out of every 4 attempts, regardless of the treatment. However, the similarity in shad behavior and passage performance is believed to be more of a result of the similarity in flow fields that resulted from the lack of flow guidance devices inside the auxiliary water channel. These findings therefore highlight the importance of properly maintained flow guidance devices, an often-overlooked component of an auxiliary water system.

Automated summary

This laboratory study examined the behavior and passage performance of adult American Shad in a fishway entrance channel under different velocity conditions. The results showed no difference in Shad behavior between low and high velocity treatments, and the majority of Shad were able to pass through the diffuser successfully. However, the similarity in behavior and passage performance is believed to be due to the lack of flow guidance devices in the auxiliary water channel, highlighting the importance of properly maintained flow guidance devices.