Upstream passage of inanga Galaxias maculatus and redfin bullies Gobiomorphus huttoni over artificial ramps

Abstract

The effects of surface type and slope on fish passage over artificial ramps were evaluated for two small diadromous fish species native to New Zealand: the redfin bully Gobiomorphus huttoni and adult and juvenile inanga Galaxias maculatus. Surfaces tested include smooth plastic, sand, gravel (limestone chips 5–20 mm), nylon brush and two plastic moulded cores of ground drainage products Cordrain® and Miradrain®. Slopes of 15° (1:3·7), 30° (1:1·7) and 45° (1:1) were assessed. Slope was the greatest factor influencing successful passage, with the lowest gradient tested (15°) providing the highest passage for both fish species. Most ramps at 45° only allowed the passage of redfin bullies, these fish being capable of ‘climbing’ the wetted margin of the ramps. Because of this climbing ability, redfin bullies were not as affected by the ramp surface, as inanga. Nevertheless, the smooth plastic surface, which resulted in the highest water velocities over the ramps, was un‐passable by either species at slopes >15°. Gravel, the nylon brush and the two plastic moulds provided high passage rates for inanga at gradients of 15 and 30°. At a slope of 45°, Miradrain® was the only surface inanga could pass. Overall, Miradrain® produced the most successful passage for both inanga and redfin bullies, but to maximize passage, slope should not be >15° and a wetted margin is essential for climbing species.