Cobble clusters create new hideaways for native fish

‘Cobble clusters’ added to the Ōpāwaho Heathcote River are breathing life into the river by creating new habitats for native fish.

More than 6000 stones and boulders have been used to create the cobble clusters at seven sites along the river between Barrington Street and Waltham Road.

They are designed to provide mid-channel cover for small cryptic native fish that like to hide during the day and come out to feed at night and should help to improve the ecology of the river.

Christchurch City Council Stormwater and Waterways Team Leader Keith Davison says the cobble clusters were added as part of the Ōpāwaho Heathcote River bank works improvement programme.

“A lot of work has been done along the Heathcote to reduce the flood risk but we also wanted to take the opportunity to improve the health of the river and to breathe life back into it.

“The cobble clusters are very obvious at the moment but they will soon become less visible as they become colonised by algae. They will provide natural, sheltered habitats for fish and enhance the ecology of the river,’’ Mr Davison says.

“Our urban rivers are typically devoid of mid channel habitat, so it’s important that we find ways to bring that habitat back to our rivers,’’ adds Shelley McMurtrie, EOS Ecology principal scientist and the project ecologist for the river bank works programme.

“Cobble clusters are especially great habitat for some of our more uncommon and ‘at risk’ native fish species such as redfin bully and bluegill bully, which are known to prefer larger substrate,’’ Ms McMurtrie says.

The first record of a redfin bully in the Ōpāwaho Heathcote River was made last year by the Department of Conservation at a trial cobble cluster site near Colombo Street.

“Following a year-long trial at two sites in the river we have been able to realise the project’s vision to create this habitat along a much wider area,’’ says Martin Densham, project manager for the river bank works programme.

* Pictured above, bluegill bully, one of the 'at risk' native fish species that could benefit from the new cobble clusters. Photo courtesy of ©EOS Ecology.