Migratory native fish will soon find it easier to make their way along rivers and streams in the Ōhiwa area following an extensive survey of the catchment’s culverts and bridges.
Bay of Plenty Regional Council is carrying out the ambitious project to check all the culverts in the Ōhiwa Harbour Catchment to see whether they allow fish to freely swim through or not, on behalf of the seven Ōhiwa Harbour Strategy partner organisations.
Regional Council Land Management Officer Tim Senior said many of our native fish species migrate between fresh and salt water during their lifecycles and it was important culverts, and other man-made structures, allowed fish to access spawning and rearing habitat as well as food sources.
These fish include inanga, koaro, three species of kōkopu (whitebait), and tuna (long and shortfin eels).
“Essentially some man-made structures, like culverts, if not properly constructed or maintained can prevent fish from returning to their spawning sites to breed or to leave their spawning site to mature,” said Mr Senior.
“This leads to a decrease in population numbers. For a healthy ecosystem and increased biodiversity, we need to ensure these fish species can complete their migration pattern.”
Lincoln University student Mikayla Binney has been working as a summer assistant at the Regional Council during the summer holidays.
As part of her work, she has been visiting culverts previously identified on aerial photographs to check whether they allow for migration of fish.
This includes measuring the diameter of the culvert, whether it is perched too far above the stream bed or whether it has become buried in the stream bed.
Miss Binney also notes down any fish species she sees in her inspection.
Observations made during these visits are then uploaded to a map for Regional Council staff to easily see where fish may become stuck and which culverts may need improving.
Mr Senior said the next step over the next year or so will be to retrofit culverts where necessary with devices to allow fish passage. This is usually a fairly simple process and will be done at no cost to landowners.
“We would like to thank landowners for their assistance in this project and welcoming us onto their farms,” he said.
“We’re grateful to see locals supporting this work to improve conditions for our often unnoticed and forgotten but unique migratory fish.”
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Below: Bay of Plenty Regional Council Summer Assistant Mikayla Binney checks culverts on a farm in the Ohiwa area. Both of these pictured provided good fish passage and do not need to be remediated.
Below: An example of a culvert that is perched too high and does not allow for fish passage.