DSS for setting turbidity limits at base flows

Instructions

Banded kokopu migrants were the most sensitive fish species tested [see references 1, 2]. The presence of adults upstream therefore requires turbidity limits downstream, but these need only be applied during the migration season (August–December) [3, 4].
At other times (i.e., when migrants are not present), and in waters where banded kokopu do not occur, rainbow trout are likely to be the most sensitive species [5, 6]. In the lower reaches of rivers and coastal streams where rainbow trout are scarce or absent, inanga are expected to be the most sensitive species [4, 5, 6].
Determine the site at which turbidity levels are to be set within the river network (i.e., identify the latitude and longitude, or NZ Topographical map easting and northing).
Determine whether banded kokopu, rainbow trout and/or inanga are present at, or above this site, or in the stream reach immediately below the site but above the first tributary below it (NB: fish species above the site can be expected to move through it. Species below the site, but above the first tributary below it, need to be determined because high turbidity levels will not be diluted greatly until the stream is joined by another tributary).
Fish distributions can be determined directly by examining records in the New Zealand Freshwater Fish Database and plotting fish distributions on a map of the waterway. Where there are no records available, then indirect methods may need to be used.
Work through the DSS from the top down. The graphs referred to in the DSS are shown on the right hand side of this page. If there are no fish present that are known to be sensitive to turbidity, then there is no level that can be used to protect fish life.

More information on the New Zealand Freshwater Fish Database

Indirect methods for assessing fish occurrence

References

1. Boubée, J.A.T.; Dean, T.L.; West, D.W.; Barrier, R.F.G. (1997). Avoidance of suspended sediment by the juvenile migratory stage of six New Zealand native fish species. New Zealand Journal of Marine and Freshwater Research. 31: 61–69.

2. Rowe, D.K.; Dean, T.L. (1998). Effects of turbidity on the feeding ability of the juvenile migrant stage of six New Zealand freshwater fish species. New Zealand Journal of Marine and Freshwater Research. 32: 21–29.

3. Rowe, D.K.; Hicks, M.; Richardson, J. (2000). Reduced abundance of banded kokopu (Galaxias fasciatus) and other native fish in turbid rivers of the North Island of New Zealand. New Zealand Journal of Marine and Freshwater Research 34: 547–558.

4. Richardson, J.; Rowe, D.K.; Smith, J. (2001). Effects of turbidity on the upstream movement of migratory banded kokopu (Galaxias fasciatus) in a small agricultural stream. New Zealand Journal of Marine and Freshwater Research 35: 191–196.

5. Rowe, D.K.; Smith, J.; Williams, E. (2002). Effects of turbidity on the feeding ability of adult, riverine smelt (Retropinna retropinna) and inanga (Galaxias maculatus). New Zealand Journal of Marine and Freshwater Research 36: 143–150.

6. Rowe, D.K.; Dean T.; Williams, E; Smith, J. (2003). Effects of turbidity on the ability of juvenile rainbow trout, Oncorhynchus mykiss, to feed on limnetic and benthic prey in laboratory tanks. New Zealand Journal of Marine and Freshwater Research 37: 45–52.