New Zealand Journal of Marine and Freshwater Research abstracts
Comparison of habitat use by fish in normal and flooded
river conditions
IAN G. JOWETT
National Institute of Water and
Atmospheric Research
P. O. Box 11-115
Hamilton, New Zealand
JODY RICHARDSON
National Institute of Water and
Atmospheric Research
P. O. Box 11-115
Hamilton, New Zealand
Abstract Floods are often considered one of the major
regulators of fish populations, but there are few observations of fish
behaviour or habitat use at such times. To investigate habitat use and fish
movement during floods, two locations on the Pohangina River, North Island,
were sampled at the peak of a small flood. Habitat use at normal flows was
determined by repeating the same sampling procedure in runs and riffles on the
Pohangina and two nearby rivers. The sampling procedure was to electrofish runs
and riffles in lanes, stratified by depth (0-0.125 m, 0.125-0.25 m, 0.25-0.5 m,
and 0.5-0.75 m). Water depths and velocities were measured in each sampling
lane. Fish were most abundant along the river margins less than 0.25 m deep,
both during the flood and in normal flows. Two days after the flood, these
shallow areas, that had been occupied by fish during the flood, were dry again.
This suggests that the edge-dwelling fish species in these rivers respond
quickly to flow changes, moving with the river margins to minimise any change
in depth. Response to changes in velocity were less apparent and the water
velocity in the areas occupied by edge-dwelling fish during the flood was
sub-optimal in terms of normal habitat preference. The response of fish to flow
and habitat change and the use of sub-optimal habitat for short periods of time
highlights the difficulty of interpreting a time series of weighted usable
area.
Keywords physical habitat; flood; fish response; habitat time
series
New Zealand Journal of Marine and Freshwater Research, 1994: Vol. 28:
409-416
0028-8330/94/2804-0409 $2.50/0 (c) The Royal Society of New Zealand
1994
PDF file of entire paper: medium quality (572K); (scanned from paper original: notes about this process)
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