Students continue work on fish passage
To date over 1000 culverts, weirs and other structures (the majority owned by council) have been surveyed by students. Photo: Supplied
This summer TDC student employee Mark Derksen has been working with land owners to identify fish passage barriers that hinder or prevent the migration of fish upstream.
Research has shown that habitat loss and fish passage barriers pose the greatest threat to the survival of our freshwater fish, not whitebaiting, which only plays a minor role in determining the abundance of many species.
New Zealand’s native migratory fish can climb, “but they can’t jump”. This means that overhanging culverts with a drop into the pool below, undercut concrete structures, degraded culvert pipes and tidal floodgates can create impassable obstructions for fish wanting to move upstream.
The five species that make up the traditional whitebait catch, inanga, koaro, banded kokopu, shortjaw kokopu and giant kokopu, and other species such as eels, all require passage from fresh to saltwater. They develop in the marine environment but they return to freshwater to live out the majority of their adult lives.
Water velocity in a culvert or over a structure can also provide a barrier, so culvert diameter and gradient are important considerations. If the flow is greater than 0.3m/sec, inanga, the poorest of the swimmers, will not be able to make it through.
The project started six years ago. To date over 1000 culverts, weirs and other structures (the majority owned by council) have been surveyed by students. The focus now is on structures in streams and on private land.
Managing the project for the council is resource scientist Trevor James.
“Remediating structures by removing barriers to fish passage often provides very high environmental benefit for a relatively low cost,” he said. “It can be as simple as a rope or ramp made out of conveyer belt material exiting the culvert. The cost of building of a small concrete apron or resetting a culvert pipe is considerably lower than the fencing, planting and monitoring that is associated with habitat restoration.”
Golden Bay farmer Sue Brown is co-ordinating expressions of interest in this project.
“So far we’ve only advertised this by word of mouth and the response has been really good. Farmers are as keen as anyone to help ensure good whitebait catches in future years. Taking part and achieving compliance now while the assessments are free and there is some help with remedial work simply makes sense,” said Sue.
Trevor James says this is a legacy issue and council will not be expecting results overnight. “
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