New Zealand Journal of Marine and Freshwater Research abstracts

---

Effects of a severe flood on instream habitat and trout populations in seven New Zealand rivers

IANG.JOWETT¹

JODY RICHARDSON²

¹Freshwater Fisheries Centre Ministry of Agriculture and Fisheries P. O. Box 8324, Riccarton Christchurch, New Zealand

²fisheries Research Centre Ministry of Agriculture and Fisheries P. O. Box 6016 Rotorua, New Zealand

Abstract The effects of a major flood on instream habitat and trout numbers in 7 rivers in the South Island, New Zealand, were determined by drift diving (snorkeling) sections of each of the rivers before and after the event. A general coarsening of the substrate was noted in runs and pools but not in riffles. In most of the rivers there was significant scouring of pools but little change of run and riffle habitats. In 6 of the 7 rivers, brown trout (Salmo trutta) abundance decreased significantly, with small fish (10-20 cm fork length) being reduced by 90-100%, medium fish (20-40 cm FL) by 62-87%, and large fish (> 40 cm FL) by 26-57 %. Rainbow trout (Salmo gairdneri) occurred in 3 of the rivers but were not present in 2 of these after the flood. In the third river theabundance oflargerainbowtroutincreased substantially whereas thatof small fish decreased by 94%. The percentages of trout remaining in the surveyed reaches after the flood were highly correlated with river gradient and instream cover but not with relative severity of the flood.

Keywords floods; instream habitat; survival; drift diving; snorkeling; rainbow trout; Salmo gairdneri; brown trout; Salmo trutta

New Zealand Journal of Marine and Freshwater Research, 1989, Vol. 23: 11-17 0028-8330/89/2301-0011$2.50/0 © Crown copyright 1989 Received 3 August 1987; accepted 12 May 1988

PDF file of entire paper: medium quality (951K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page