Native brook trout, Salvelinus
fontinalis, populations could be at risk as a result of the introduction of
Brown trout, Salmo trutta, according to a new U.S. Geological Survey study. Both species are valuable sport fish
that coexist in many parts of the world due to stocking introductions.
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USGS researchers
found that, in New York State, direct interactions between the two species,
such as competition for food, have minor effects on diminishing brook trout
populations compared to human-caused habitat disturbances. However, repeated,
disproportionate stocking of brown trout in brook trout habitats could drastically
decrease brook trout numbers.
“There is great
potential for brown trout stocking to reduce native brook trout
populations,” said James McKenna, USGS scientist and lead author of the
study. “But brown trout aren’t necessarily causing the current brook trout
declines, and managers may be able to develop sustainable scenarios to support
both fisheries.”
The USGS study found
that human-induced degradation (from dams and roads, among other causes) of the
habitats of both species could affect the populations of either. However,
because brook trout do better in forested watersheds, whereas brown trout can
thrive in more agricultural environments, degraded watersheds and/or the
elimination of forests may affect brook more than brown trout.
McKenna’s team used
artificial neural network models, regression, principal components analysis,
and simulation to evaluate the effects of Brown Trout, environmental
conditions, and stocking on the distribution of Brook Trout in the center of
their native range. They found evidence for the decline of Brook Trout in the
presence of Brown Trout across many watersheds; 22% of sampled reaches where
both species were expected to occur contained only Brown Trout. However, a
model of the direct relationship between Brook Trout and Brown Trout abundance
explained less than 1% of data variation. Ordination showed extensive overlaps
of Brook and Brown Trout habitat conditions, with only small components of the
hypervolume (multidimensional space) being distinctive.
Simulation results
indicated that direct interactions and habitat conditions were relatively minor
factors compared with the effects of repeated stocking of Brown Trout into
Brook Trout habitat. Intensive annual stocking of Brown Trout could eliminate
resident Brook Trout in less than a decade. Ecological differences, harvest
behavior, and other habitat changes can exacerbate Brook Trout losses. Custom
stocking scenarios with Brown Trout introductions at relatively low proportions
of resident Brook Trout populations may be able to sustain healthy populations
of both species within their present range.
Read more at USGS.
Fisherman
image via shutterstock.