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be almost totally eliminated so is a worst case scenario and unlikely to occur to this degree for
the reasons mentioned above.

Cascades: Most invertebrates prefer pool run and riffle habitat than cascade habitat, where
water velocities usually preclude occupation. The splash zones occurring on the edge of
cascades, sometimes provide limited invertebrate habitat. There is very a high percentage of
cascade habitat within the 2.3 km reach, due to the high gradient gorge environment. Cascade
habitat is estimated to occupy 30-40% of the survey reach, and provides virtually no fish
habitat and limited invertebrate habitat. Much of this habitat will disappear with flow
reductions thereby reducing food producing area for invertebrates to a limited degree (most
invertebrates inhabit pools/runs/riffles, rather than cascades).

Fish passage flows below the dam:

Provided some flow remains continuously over the top of the intake structure and is sufficient
to maintain ecosystem health within pools in the upper gorge, as discussed earlier, fish
passage throughout the survey reach will be provided for. Juvenile koaro and longfin eels,
and other galaxiid juveniles such as banded and shortjaw kokopu, often migrate on a fresh,
when the intake structure will be regularly overtopped by small freshes from rainfall events.
Freshes, and larger floods, will provide attractant flows enticing fish into the lower gorge.
Provided pools remain healthy, fish should gradually work their way up the gorge and past the
intake structure. Even if complete cessation of flows occurred in the top of the gorge, the
migratory ability of these two species means intermittent fish passage would still occur during
freshes and floods. Provision of fish passage for these climbing species over the final
dam/intake structure will also need to be provided for, in terms of surface design, angle, and
avoidance of a water ‘drop-structure’, or overhanging lip, that may impede their ability to
climb the structure.

Blue duck

Whilst not the specific focus of this report, the observation of blue duck presence requires
some discussion. The area immediately below the gorge outlet provides low-moderate density
food producing capacity for blue duck, and the individual observed was located here at the
bottom of the survey reach. Around 200-500 metres of this potential feeding area could be
affected by the proposal depending upon where the power-house discharge is located.
Limited low productivity blue duck feeding area exists within the gorge (probably in the order
of 20% of the 2.3 km reach), however the area may be used as a migratory pathway, and/or
resting/nesting area. A lack of suitable feeding area and low number of invertebrates within
the gorge probably preclude continuous occupation. Given that a blue duck breeding pair
need a minimum of 0.8 km of very productive river habitat, but can require up to 4.5 km in
less productive river habitat, little habitat potentially capable of supporting blue duck exists
within the 2.3 km study reach. Favourable blue duck feeding areas would be represented by


Fish & Game New Zealand
Nelson Marlborough Region Sports Fish and Game Bird Management ...p23

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