/ 21 August 2007

Research yields fishy solutions

Have you ever wondered what the possible reasons are for the slow disappearance of fish from our rivers and if we will ever see their numbers restored?

A recent research initiative by the Water Research Commission, undertaken by a doctoral student in the zoology department at the University of Johannesburg (UJ), Mathew Ross, assisted by his lecturer Professor Victor Wepener and various professional ecological and hydrological consultants, has assessed the ability of indigenous fish species to negotiate different fishway designs in an attempt to optimise and develop new models.

Wepener says that fish have always had to bear the brunt of human interference in ecosystems, ranging from pollution to building barriers in our rivers. Various barriers along the river systems in the form of weirs, dam walls and low-level bridge crossings limit the freedom of movement for fish.

“This fragmentation of the riverine habitat means that fish are not able to undergo seasonal breeding migrations that many species — such as yellowfish, mudfish and others — have to undergo to find suitable breeding and spawning areas upstream,” says Ross, adding that upstream spawning areas are being limited to these fish through the need to support increased development and gauge the flows of our rivers. This means that these fish are not able to attain their natural breeding potential.

Fishways (or fish ladders) have been around since the 1800s, when the importance of upstream migrations for trout and salmon became clear. Since then, many designs of fishways have been explored, including pool-and-weir and even a “fish-lift” system that traps fish downstream and transports them to above-barrier riverine habitats to ensure the overall health of an aquatic ecosystem.