Pool habitat: Pool habitat is estimated to occupy around 40-50% of the 2.3 km gorge section
subject to proposed flow reductions. Given the type of environment present within the
Parapara Gorge, water temperature increase due to flow reduction below the one in five year
low flow (Q5), is not considered to be an issue. The key consideration for maintenance of
pool habitat is adequate flushing flows to prevent de-oxygenation and other processes such as
algal proliferation. Complete cessation of flows will obviously result in ecosystem collapse at
the head of the gorge above side tributaries, but equally, some reduction below the Q5 in this
type of gorge environment should not result in large scale pool habitat loss provided an
adequate minimum flow remains to adequately sustain ecosystem functioning within pools.
Without adaptive management it is very difficult to ascertain exactly how far below the Q5
flows could be lowered without significantly adversely affecting overall ecosystem
functioning within the Parapara Gorge. All that can be done is to take an educated guess
within the bounds of Q5 (250 l/s) being an optimum at one end of the scale, and complete
cessation of flows resulting in ecosystem collapse at the head of the gorge, at the other end of
the scale.

Run/riffle habitat: Favourable run/riffle habitat for low densities of koaro and juvenile longfin
eel within the gorge likely to be adversely affected by flow reductions below the Q5, is
estimated to occur at between 5-20% of the gorge area surveyed. This habitat is referred to in
the previous fishery survey (Fish & Game 2003). This estimation is based on the assumption
that a minimum flow will remain to keep static water habitat within pools healthy, and
therefore significant pool habitat loss will not also affect these species.

Unlike pool habitat, run/riffle fish habitat loss will occur as soon as flows are lowered below
the Q5, as this type of physical habitat area often reduces directly with flows. As mentioned
earlier, this habitat type is estimated to occur in between 5-20% of the gorge area. The worst
case scenario would be loss of nearly all the run/riffle habitat within the gorge. This scenario
ignores the fact that some run/riffle habitat would remain due to tributary inflows and
whatever minimum flow release is agreed upon as part of the consent process, and that some
habitat areas currently too swift for fish to occupy, may become available under a reduced
flow regime.

If near total loss of run/riffle habitat is applied to the entire 2.3 km reach, then an estimate of
total potential habitat loss for koaro and juvenile longfin eels can be obtained. This would
equate to 2300 m multiplied by 8 metres (average wetted width of river), multiplied by 0.2,
which would give a total of 3680 square metres of habitat. If this is then multiplied by the
average density of koaro and LF eels located in this habitat within the gorge (0.039 fish m2),
then habitat capable of supporting approximately 144 koaro, and 144 juvenile LF eels is at
risk from the proposed development. Given 1 pass electric fishing only was undertaken, it
would be prudent to increase these estimates to habitat capable of supporting say 200 fish for
each species. This estimate assumes the favourable run/riffle habitat within the gorge would

Fish & Game New Zealand Nelson Marlborough Region Sports Fish and Game Bird Management ...p22