Smaller Body Size and Warmer Water Improve Two Temperate Fishes’ Upstream Passage over Wetted Ramps

Most artificial fishways allow upstream passage of large-bodied, strong-swimming fish species. Wetted ramps, which are moderate in inclination and have little water flow, could allow passage of smaller-bodied fishes over low-head dams and culverts. We observed creek chubs (Semotilus atromculatus) and white suckers (Catostomus commersonii) on wetted ramps in a laboratory setting. Smaller individuals entered the ramps at lower absolute swim velocities but exhibited superior upstream passage due to positive acceleration in the thin (<1 cm) water layer on the ramps. Larger fish displayed more pronounced, probably less efficient, head and tail amplitudes during passage. We argue that the relatively smaller depth of immersion in water was responsible for hampering the larger-bodied individuals on the ramps. Warmer water temperatures (15 °C vs. 10 °C) roughly doubled the mean distance fish traveled up the ramps. Our findings can inform fishway design for small-bodied fishes. In regions with low-head barriers against invasive sea lamprey (Petromyzon marinus), wetted ramps may help connect habitats for native fish species.