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

Considerable effort has been expended to construct culverts and fishways that allow for fish
passage. However, the designs have seldom considered behaviour, energetics, and
biomechanics of fish. In this study, we performed controlled experiments, in which upstreammigrating
Alewife (Alosa pseudoharengus) and Brook Trout (Salvelinus fontinalis) were allowed
to volitionally enter either one of two open channels. These channels were outfitted with
horizontally and vertically oriented baffles. The flow structure was characterized using acoustic
Doppler velocimeter measurements. The added baffles had a marked influence on the flow
field, which was distinct between horizontal and vertical baffles, indicative of horizontally and
vertically orientated vortices, respectively. Passage success was measured, both in terms of
attraction and ascent performance under each flow condition. The results indicated that
Alewife and Brook Trout staged significantly more attempts into the vertical baffled channel
compared to the horizontal baffled channel. However, Alewife traversed greater distances
swimming in the channel with the horizontal baffles at the lower flow condition. Brook Trout
also swam further under low flow but traversed similar dtistances in both channels. This
information furthers our understanding of both ascent performance and behavioural responses
of fish in relation to turbulent flow and roughness orientation.