New Zealand Journal of Marine and Freshwater Research abstracts
Size-related impacts of introduced brown trout on the distribution of native
common river galaxias
ANGUS R. McINTOSH
TODD A. CROWL1
COLIN R. TOWNSEND
Department of Zoology
University of Otago
P. O. Box 56
Dunedin, New Zealand
1also Department of Fisheries and Wildlife, Utah State University, Logan, UT
84322-5210, USA
Abstract The impact of small (fork length < 100 mm) and
large (>= 100 mm) brown trout (Salmo trutta L.) on the distribution
of the common river galaxias (Galaxias vulgaris Stokell) was
investigated in the Shag River (South Island, New Zealand). Riffle reaches were
sampled by electrofishing and their macrohabitat was described in terms of
substratum, flow, elevation, and vegetation characteristics. Galaxias densities
in reaches containing large trout were lower than reaches with only small trout
or no trout and trout size was the most important variable determining galaxias
density. Densities of galaxias < 80 mm were reduced in the presence of large
trout, but not galaxias > 80 mm. Reaches with large, small, or no trout
varied in terms of water depth, percentage cobble, and elevation. However,
these differences were unlikely to account for variations in galaxias densities
because selection for these particular habitat features accounted for only a
small proportion of the observed variation in galaxias density. A change in
macrohabitat use by galaxias from fast current velocities in sites without
trout to slower velocities in sites with large trout may be explained by
competition for areas of high velocity (potentially the better feeding areas).
However, a combination of interspecific competition and predation by large
brown trout is likely to be responsible for the observed reductions in the
density of smaller galaxias.
Keywords Brown trout; Salmo trutta; common river
galaxias; Galaxias vulgaris; competition; macrohabitat selection; fish
size.
NB: This paper has an erratum here.
PDF file of entire paper: medium quality (738K); (scanned from paper original: notes about this process)
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