Efforts under way to improve stream access for fish
Kelly Hughes, a contractor from Bay of Plenty, working on the culvert in Wainui Bay.
Work is proceeding to allow fish to find their way up the Bay’s streams again. During the last few decades of land and road development, structures such as culverts, weirs and dams have increasingly obstructed the natural movement of native fish along waterways.
Last week, a crew from TDC, Fulton Hogan and DOC retro-fitted several culverts in Wainui Bay with concrete aprons to assist a range of freshwater fish to move freely once again. Volunteering Wainui farmer, Jim Robertson, was right in there to help improve the aquatic environment.
Eddies and resting pools were important particularly for “burst swimmers” such as inanga, said TDC resource scientist Trevor James, who is overseeing the design of the project.
“Because most of our native fish are migratory, when there is a significant barrier to their passage, the creeks become largely bare of fish. So far, we have concentrated on the coastal areas of the district because these streams usually contain higher biodiversity.”
Since 2004-05, Mr James has been supervising student assessments of culverts, weirs, dams, tide-gates and other structures in waterways throughout the Tasman District each summer. Out of approximately 1000 structures assessed, some 300 structures have been classified as posing a barrier or significant impediment to fish passage.
Even structures that were initially fish-friendly can change over time. One Onekaka Hydro road culvert, fixed about two years ago, became a barrier only a couple of years after its installation.
“It doesn’t take much to erode the bottom end of a culvert in Separation Point granite country,” said Mr James. “We have some great video footage of different species of whitebait trying to make it up this vertical wall downstream of one of the culverts. Inanga burst-swim up to about 300mm and then fall back, while banded kokopu and koaro climb like eels with the aid of little barbs on their pectoral fins. But even the climbers, who are happy scaling up many metres vertically, are foiled by the overhanging lip of the culvert.”
In the Onekaka area, two privately-owned culverts that have become barriers to fish passage are also being retro-fitted with aprons with the assistance of the property owners. Inspired by TDC’s approach, the NZ Transport Agency (NZTA) is also looking at remediating the culverts under their management.
“By starting with some of the highest priority barriers first, we intend to maximise the length of streams opened up to our native fish for the given effort and cost. It’s hoped that this remediation work will occur progressively each year,” Mr James said.
“It’s important that we check out the success of such culvert restoration on at least a few streams to ensure its effectiveness. TDC will be conducting fish surveys in early March next year, and we invite interested people to come along. You would have to be prepared to work late in the evening as a lot of the survey work is at night because most of our freshwater fish are nocturnal. If this is too late for some people, there are also opportunities to do some survey work during the day, using electric fishing methods.”
Anyone interested in fishy work can contact Trevor James at trevor.james@tdc.govt.nz or call TDC on 525 0020.
Ina Holst
