8180

• UCREFRP Catalog Number: 8180
• Author: Hamilton, S. J.
• Title: Hypothesis of Historical Effects From Selenium on Endangered Fish in the Colorado River Basin.
• USFW Year: 1999.
• USFW - Doc Type: \
• Copyright Material: YES

Hypothesis of Historical Effects from Selenium

River Basin, con tracted in 1981 to have short-term tests conducted to deter-
mine the toxicity of selenium and several other inorganic and organic chemi-
cal constituents to sub-adult Colorado pikeminnow and humpback chub (Beleau
and Bartosz, 1982). Those tests seemed to indicate at the time that selenium
and other inorganic elements and organic chemicals were not contributing to
the decline of the species. However, the release of NIWQP reconnaissance
investigations of federal irrigation projects on the middle Green, upper Colo-
rado, Gunnison, Uncompahgre, and San Juan rivers reported elevated sele-
nium concentrations in water and biota. Consequently, additional toxicity tests
were conducted with several early life stages of Colorado pike minnow, razor-
back sucker, bonytail, and tlannelmouth sucker in water qualities simulating
environmental conditions (Hamilton, 1995; Buhl and Hamilton, 1996; Buhl,
1997; Hamilton and Buhl, 1997a, 1997b). In these short-term tests, the endan-
gered fish had similar sensitivity to selenate, selenite, and other elements as
other fish species. However, tests with environmentally relevant mixtures of
inorganic elements showed a high hazard was present in some areas of the
Green River and San Juan River basins.
Long-term tests with larval razorback sucker and bonytail exposed to an
environmental mixture of inorganic elements including selenium and tested
in a reconstituted Green River water showed adverse effects at concentrations
less than 10-fold of the environmental concentrations, which suggested a high
hazard (Hamilton et al., 2000). In another long-term study, larval razorback
sucker were fed live zooplankton collected from six sites at Ouray National
Wildlife Refuge (NWR), Ouray, UT, adjacent to the Green River, that con-
tained different amounts of selenium. Survival was 0 to 20% in four studies
initiated with larvae aged 5, 10, 24, and 28 days old (Hamilton et al., 1996).
Both of the Ashley Creek and Ouray NWR studies showed adverse effects on
larval razorback sucker at selenium concentrations presently in the upper
Colorado River basin.
Elevated selenium concentrations in muscle plugs, eggs, and lcuvae from
wild razorback sucker have been documented in adults inhabiting areas known
to have elevated selenium concentrations in water and biota such as Ashley
Creek and Stewart Lake outlet on the Green River (Waddell and May, 1995;
Hamilton and Waddell, 1994; Stephens and Waddell, 1998; Hamilton et al.,
1998). A similar pattern of elevated selenium residues in muscle plugs of
Colorado pikeminnow collected from areas with elevated selenium in water
and food organisms was found in the upper Colorado River (Osmundson,
May, and Osmundson, 1999). These selenium residues in razorback sucker
and Colorado pikeminnow show that endangered fish in high selenium areas
were accumulating selenium to concentrations that could harm their repro-
ductive success.

mSTORICAL OCCURRENCE OF ENDANGERED FISH

Colorado pikeminnow and razorback sucker were abundant in the upper
Colorado River basin according to Jordan (1891) during a survey of streams

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