ASFB Home > 2003 > Biological Invasions: Consequences for Parasites, Pathogens, Emerging Diseases, and Fisheries in the Marine Environment.

Use of ramps for fish passage past small barriers.

Cindy Baker and Jacques Boubée

National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand
Email: c.baker@niwa.co.nz

Close to half of New Zealand’s native freshwater fish are diadromous, with part of their life cycle spent at sea and part in fresh water. During their annual migration into freshwater habitats, migratory fish can encounter many types of barriers. There are natural barriers, such as waterfalls and debris jams, but increasing artificial barriers such as dams, culverts and weirs are also a concern. Some migratory species possess the ability to climb the wetted margins of in-stream obstacles, while other fish species must rely on short “burst” or fast swimming to get past high velocity areas. Ramps may be a simple way of ensuring successful passage for both swimming and climbing fish past in-stream obstacles. This study investigated the effects of ramp slope (vertical) and surface type on fish passage. Two native diadromous fish species were tested, adult and juvenile inanga, a swimming species, and adult and juvenile redfin bullies, a species with both swimming and climbing abilities.

Fish were tested on 2 m long and 0.4 m wide ramps lined with gravel, sand, bristles, and plastic moulds that are similar to egg cartons, and rounded cones on a flat surface (stripdrain). A smooth bare ramp with no substrate attached was also tested. The slope of each ramp was set at 15°, 30° and 45°. As a wetted margin may be important for climbing fish passage, the ramps were tilted at an angle of 10°.

The stripdrain surface provided the most successful passage for both inanga and bullies. At a slope of 45°, stripdrain was the only surface that enabled adult inanga passage. Juvenile inanga could not surpass any ramp at 45° with similar passage success to adult fish on all ramps at 15° and 30°. Because of their climbing ability, redfin bullies could negotiate all ramps at 45°, except the bare ramp, which was only surpassed at 15^o. The presence of a wetted margin was essential, as it provided rest areas for swimming fish and a wetted surface for climbing species.