Publications: Research reports and publications

Ōhau Loop Phase 2: Enhancing knowledge of inanga habitat

13 May, 2015
Cawthron Report 2695. Manaaki Taha Moana Research Report No. 25. Prepared for Taiao Raukawa and Manaaki Taha Moana.

EXECUTIVE SUMMARY

This latest project in the Ōhau Loop (‘the Loop’), has focused on inanga (whitebait) habitat knowledge and restoration, and was built on an existing research relationship between Taiao Raukawa, Manaaki Taha Moana (MTM) project Horowhenua research team and Cawthron Institute (Cawthron). This relationship was forged through the successes of the Manaaki Taha Moana (MTM): Enhancing Coastal Ecosystems for Iwi/Hapū project. Once a highly valued area for mahinga kai (or food gathering area), the Ōhau Loop was part of a meandering tidal section of the Ōhau River. Flood protection works on the lower ŌhauRiver in 1972–1972 saw this 3.5 km meander cut off from the main flow by the creation of ‘the Cut’; a diversion channel which by-passed the Loop. Today the Loop is surrounded by intensive dairy farming by the Māori shareholder's farm Tahamata Incorporation and has poor water quality, degraded biodiversity, and an abundance of aquatic weeds. In 2011 the Loop was targeted for rehabilitation through the MTM project.

In the Phase 1 project under MTM, the ecological state of the Ōhau Loop was assessed and potential restoration measures identified for the benefit of the Tahamata Incorporation farm and the Ōhau Loop ecosystem. The 2011 Ōhau Loop Phase 1 report (Allen et at. 2011) led to the installation of a fish-friendly flood-gate at the bottom end of the Loop by Horizons Regional Council (Horizons), supported by Tahamata and Māori shareholders in February2013.

Preliminary recommendations from Phase 1 included the removal of accumulated fine sediments from the Loop and the re-connection of adjacent lagoons to form a continuous channel connected by fish-friendly culverts. It was also recommended that some (yet to be determined) flow should be diverted from the Ōhau River into the top of the Loop to alleviate poor water quality. Further study is required to calculate the flow requirements for mahinga kai species, whilst maintaining flood protection. More suitable riparian fencing and planting native species was also recommended to provide shade, habitat and filtering of sediments from farm runoff.

For the current study, Cawthron scientists, Horizons staff, and members of Taiao Raukawa, including local kaitiaki and whitebaiters, undertook community environmental monitoring and enhancement of inanga egg-laying (spawning) habitat within the lower reaches of the Ōhau Loop.

(See pdf for full summary)