9578

• UCREFRP Catalog Number: 9578
• Author: Hamilton, S. J. and e. al.
• Title: The Evaluation of Contaminant Impacts on Razorback Sucker Held in Flooded Bottomland Sites Near Grand Junction, Colorado - 1997.
• USFW Year: 2001.
• USFW - Doc Type: CAP6-WW,
• Copyright Material: NO

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discharge, which was believed to contain elevated selenium concentrations. The south side of
North Pond had a dike and water overflow structure installed to maintain water levels and
confine fish. Fish were held in North Pond with sample stations WW2 and WW3. Water levels
were supplemented by inflow at WWlO from Independent Ranchman's Ditch. Flooding of the
Colorado River in spring 1996 caused water levels at Adobe Creek and North Pond to raise
substantially for several weeks. However, to the author's knowledge, no fish escaped from these
areas nor were wild adults introduced into these areas.
Hatchery brood stock adults previously collected from various locations (upper Colorado
River, Etter Pond adjacent to the Colorado River, the Colorado River arm of Lake Powell, and
the San Juan River arm of Lake Powell) and held at Horsethief were also used in the study as
additional reference fish that supplied larvae for the larval fish study.
Staff gages were installed at WW9, and near ACl and AC6 to monitor water elevation.
Gage heights were recorded daily at WW9 from April 12 to August 28, 1995, and from March
14 to June 16, 1996, and on an irregular basis for the other two stations from March 14 to June
16, 1996.

fish stocking and sampling

Thirty-six adults were randomly stocked by personnel of the CRFP at each site on July 7,
1995, and maintained at each site until they were collected during the last week of April 1996.
Additional adults not needed in the study were held at Horsethief. Prior to stocking, each fish
was PIT tagged, measured for total length and weight, and a muscle plug sample taken from the
area adjacent to the dorsal fin for selenium analysis. Muscle plugs were collected using a 4- or
. 5':mm biopsy punch, placed in cryotubes, stored on ice in the field, stored in a freezer (-200C)
while awaiting analysis, and shipped on dry ice when transported to the sample preparation
laboratory. After the muscle plug was collected, the wound was treated with full-strength
Betadine solution. Fish held at Horsethief were fed the same commercial standard fish food fed
to other stocks of razorback sucker routinely maintained there. Fish at Adobe Creek and North
Pond were not fed artificial food and foraged for natural food items at the site.
Due to the mortality of 17 fish at North Pond 1 month after stocking because of suspected
low dissolved oxygen concentrations (fish were held overnight at day 30 sampling in a hoop net
and had limited access to areas of the pond with higher dissolved oxygen concentrations), North
Pond was restocked with 17 fish from Horsethief on August 10, 1995.
At 30-60 day intervals after stocking, fish were sampled in cooperation with the CRFP
using trammel nets or boat-mounted electrofishing equipment. Captured fish were identified by
their PIT tag, measured for total length and weight, inspected for general health, and a muscle
plug was taken for selenium analysis. Not all fish stocked at Adobe Creek and North Pond were
recovered at each sampling period because of the difficulty in locating and capturing the fish.
Natural food organisms were collected monthly from as many of the 17 stations as
practical for chemical analysis. Collections were accomplished primarily using modified light
traps (Espinosa and Clark 1972), and infrequently by plankton tow net, sediment grab samplers,
and round Hester-Dendy samplers. Light traps were set overnight and the trapped zooplankton
and other aquatic invertebrates were collected the following morning. At each sampling station,
the contents of all the light traps were combined and concentrated by filtering the samples
through the basket of a 153 fJ,m plankton net. The combined samples were then backwashed into

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