Eels good sign for health of lake

Improved water quality in a Northland lake and its only outlet, the Utakura River, has put tuna (eel) back on the menu at local marae.

The 1200ha Lake Omapere about 5km north of Kaikohe was a valued food source before it was lowered to a depth of about 2m by drainage nearly a century ago to allow farming around it.

However, by the 1980s fertiliser runoff from these farms was promoting the growth of algae in the shallow water, causing pollution affecting fishing and swimming there and in the river.

Carp were introduced to eat the algae and the lake - unique because it is owned by Maori - is recovering, with local community environmental group Te Roopu Taiao o Utakura charting the return to health.

With the support of a Nga Kanohi Kitea community grant from the Health Research Council (HRC), the group has gathered data about current fish stocks through monitoring eight sites from Lake Omapere to the outlet of the Utakura River into the Hokianga Harbour.

A researcher with the group, Wendy Henwood (Te Rarawa), said gathering data about the health of the waterways involved observing environmental factors, testing water clarity, pH levels and temperature, and identifying and classifying invertebrates living in the waterways.

A report summarising the research is being developed.

Ms Henwood said the National Institute of Water and Atmospheric Research (Niwa) had helped the group establish a monitoring programme to record tuna numbers, species, weights, lengths and health.

"We had some bones analysed to see how old the tuna are right down the river, Ms Henwood said.

"We found out through this survey that we have a healthy mix of ages, which is promising for the future."

As part of the project, Te Roopu Taiao o Utakura also received support from Niwa freshwater fishery ecologists Dr Erica Williams and Dr Jacques Boubee and Niwa has produced two reports for the project team, one on metal levels in tuna from the Lake Omapere catchment and the other analysing the lake's nutrient levels.

Archival photographs show kuta (Eleocharis sphacelata), an indigenous freshwater sedge or grass-like plant, was once plentiful in the lake margins and wetlands of the catchment.

It's now scarce, but Ms Henwood said Te Roopu Taiao o Utakura planned to fence small sites to encourage kuta regeneration by keeping carp away.

APN News & Media