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Helping hand for Waikato River fish

NEW ZEALAND - A fish pass, which allows small fish to access one of the streams running into the Waikato River when water levels are low, has been built at Bankwood Stream.

The sloping concrete channel with inset rocks, allows the fish to swim and climb up to gain access from the river to the stream at Swarbricks Landing.

The fish pass, a joint project between Hamilton City Council and National Institute of Water and Atmospheric Research (NIWA), has been funded by a $34,000 grant from Waikato Catchment Ecological Enhancement Trust.

NIWA studies showed that stream populations of small fish – smelt, common bullies, inanga, and banded kokupu – were absent or limited in numbers because access from the Waikato River was blocked at low water levels. This was a key  issue because many indigenous fish spend part of their life at sea, and the Waikato River is their only route between the streams and the open ocean.

The fish 'find' the pass by using sensory perception  to detect the flowing current in the channel.

The pass has been designed to regulate the depth of water flow down the ramp to allow some fish, such as inanga, to swim up the ramp. It also provides a shallow edge for species such as the banded kokopu, which prefer to travel along the margins. At the top of the ramp is a pool that allows fish to rest before continuing their journey.

This is the first fish pass of its kind to be constructed for the many tributaries flowing into the Waikato through Hamilton. A number of streams have access problems and  if this project proves successful and fish populations increase, similar passes will be installed at other sites.

NIWA also plans improvements to the upstream habitats including bank planting and the  installation of logs as cover.

the Fish Site Editor

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