154 mitigation and offset planting described above is a separate component but necessarily a key component of the proposed landscape plan. For the most part the same vegetation types are proposed that extends the ecological benefit beyond the calculated offset laid out above. These areas will be fenced for stock exclusion and subject to pest and weed management. 23.9 Tailings lakes enhancement The existing and planned (TSF3) tailings lakes form notable features within the OGNZL land holdings, and across the broader landscape. The tailings lakes are large, shallow and as they are elevated receive little runoff from the surrounding land. This means that the water quality can reach high levels of clarity and quality. Even without extensive ecological management, these lakes are developing as ecological features. Wildfowl are temporary visitors to the lakes, and reed beds are forming naturally along some of the margins. Active management of the lakes will provide further ecological enhancements. We estimate that enhancement of the tailing lakes will provide 7,485 m of littoral margin length (cf. 1.5 ha36), and an open water area of some 88 ha. 23.10 Specific enhancements for tuna (eel) habitat We have given some thought to the potential to further improve habitat conditions for freshwater tuna (shortfin and longfin eels). These enhancements include actions already provided for, but special consideration can be given to the following: • Riparian planting along the margins of the Ohinemuri River and tributaries. Riparian vegetation has well known benefits for freshwater environments providing bank stability (reducing erosion), shade, provision of logs and leaves to watercourses, and additional source of food as terrestrial insects fall into the water. • Potential redoubts or backwater refuge areas along streams. These can be shallow holes in the stream bed or cut outs of banks to create shallow backwaters along the Ohinemuri River and/or tributaries. Erosion control features would need to be applied to ensure further erosion did not take place. These areas can provide refuge for eels during high water flows and additional habitat for feeding. • Extend or create potential open water and channels into and within the littoral wetland and seepage areas along the Ohinemuri River and tributaries. Channels connected to the main watercourses provide access for eels into wetland areas. • Retrofit any perched culverts along tributaries with fish passage solutions such as ramp or mussel spat ropes. No survey of perched culverts or other barriers has been undertaken within the Ohinemuri River catchment. The NPSFM requires that Councils provide for meeting the objectives of fish passage. • Opportunity for a fish ladder (for eels and other climbing fish) over the heritage weir downstream on the Ohinemuri River. Although elvers undoubtedly surmount the weir, the provision of a fish ladder for elvers and other climbing fish (e.g., banded kokopu) will aid that passage. Preferable to make it unfavourable for the upstream passage of trout. 36 Assuming an average of 2 m width of vegetated littoral zone within each lake.
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