Fish don't have legs so how do they use ladders?
Well, fish do, but not the type of ladders you would normally see around the house or construction sites.
Fish ladders, also known as fishways or fish passes, are designed to allow fish to move up or around weirs, barrages and locks.
Today’s 2022 United Nations World Wildlife Day’s theme is Recovering key species for ecosystem restoration. Fish ladders in the Basin are a fantastic example of how we are using infrastructure to assist key species to successfully complete their life cycles.
Fish migrate for many reasons. This includes breeding, also known as spawning, to feed, or to look for better places to live. Fish need to move up and down stream for their health and lifecycle, but weirs, barrages, locks and dams can be barriers.
Without free passage to move along the river, the long-term survival of many fish species is at risk. Fish are a strong indicator of river health, and the health of native fish populations is a key indicator of the overall state of the Murray—Darling Basin’s rivers.
Not all fish ladders are the same. The preferred fish ladder depends on the type and size of fish in the area, how the fish migrate and the construction of the barrier or structure.
There have been many fish ladders built throughout the Murray–Darling Basin. The Sea-to-Hume fish passage project, which built fish ladders along the Murray River from the Southern Ocean in South Australia to Hume Dam, near Albury–Wodonga. That’s 13 sites and more than 2,225 km of river that have been opened up for fish to move up and down.
Fish ladders used on the River Murray
The vertical slot fish ladder
The rock ramp fish ladder
The fish-lock (more like an elevator than a fish ladder!)
At some infrastructure locations, we use fishlocks to help smaller fish (usually between 12 and 100 mm) to navigate through.
Combined vertical slot fishways and fishlocks are in place at the River Murray Locks 2–6 as the steepened vertical slot fishways are designed to pass the medium to larger-sized fish (those larger than 100 mm).
The other major fishlock in the Murray–Darling Basin is the standalone fish lift at Yarrawonga Weir which was constructed in 1996. It was built as a fishlock due to the significant height differential of around 10 m between upstream and downstream.
Fish are attracted through an entrance and accumulate in a holding area at the base of the lock. This holding area is then sealed and filled with water to reach a level equal to the water upstream of the barrier. Fish are then able to swim out of the lock.
Fish ladder success
The first modern fish ladder or fishway was installed on the old Torrumbarry Weir, Victoria in the late 1980s. People fishing in the area soon reported greater numbers of young fish in the River Murray, upstream of the weir. As a result of this success, more fish ladders were built and are being built on major barriers across the Basin. Now, any upgrade to older structures require fish ladders to be added.
Of the many fish species that use fish ladders, one of the most important is the golden perch, also known as yellow belly or callop. Golden perch have a unique lifecycle that, when flow conditions are right, results in large-scale breeding events that contribute to golden perch populations in many parts of the Basin. Fish ladders are critical for older perch to spread across the Basin following these large-scale breeding events, allowing fish to move up the River Murray from the junction of the Murray and Darling (Baaka) Rivers and into tributaries like the Edward–Wakool, Kolety and Goulburn–Broken.
