Copper Avoidance and Mortality of Juvenile
Brown Trout (Salmo trutta) in Tests with
Copper-Sulfate-Treated Water from West
Branch Reservoir, Putnam County, New York
by Barry P. Baldigo and Thomas P. Baudanza
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 99-4237
ABSTRACT
Copper-avoidance tests and acute-toxicity
(mortality) tests on hatchery-reared, young-of-
the-year brown trout (salmo trutta) were
conducted with water from West Branch
Reservoir to assess the avoidance response to
copper sulfate treatment, which is used
occasionally by New York City Department of
Environmental Protection to decrease
phytoplankton populations in the reservoir.
Avoidance-test results indicate that juvenile
brown trout tend to avoid dissolved copper
concentrations greater than about 55 μg/L
(micrograms per liter), which is the
approximate avoidance-response threshold.
The mean net avoidance response of brown
trout to dissolved copper concentrations of 70
and 100 μg/L, and possibly 80 μg/L, was
significantly different (at α = 0.1) from the
mean net avoidance response of fish to control
(untreated) water and to treated water at most
other tested concentrations. Mortality-test
results indicate that the 96-hr median lethal
concentration (LC50) of dissolved copper was
61.5 μg/L. All (100 percent) of the brown trout
died at a dissolved copper concentration of 85
μg/L, many died at concentrations of 62 μg/L and
70 μg/L, and none died in the control waters
(7 μg/L) or at concentrations of 10, 20,
or 45 μg/L. The estimated concentration of
dissolved copper that caused fish mortality
(threshold) was 53.5 μg/L, virtually equivalent
to the avoidance-response threshold.
Additional factors that could affect the
copper-avoidance and mortality response of
individual brown trout and their populations
in West Branch Reservoir include seasonal
variations in certain water-quality parameters,
copper-treatment regimes, natural fish
distributions during treatment, and increased
tolerance due to acclimation. These warrant
additional study before the findings from this
study can be used to predict the effects that
copper sulfate treatments have on resident fish
populations in New York City reservoirs.
Citation: Baldigo, B.P. and Baudanza, T.P., 2001, Copper Avoidance and
Mortality of Juvenile Brown Trout (Salmo trutta) in Tests with
Copper-Sulfate-Treated Water from West Branch Reservoir, Putnam County, New York:
U.S. Geological Survey Water-Resources Investigations Report 99-4237, 25 p.
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