9465

• UCREFRP Catalog Number: 9465
• Author: Burdick, B.
• Title: Monitoring and Evaluating Various Sizes of Domestic-Reared Razorback Sucker Stocked in the Upper Colorado and Gunnison Rivers
• USFW Year: 2003.
• USFW - Doc Type: 1995-2001.
• Copyright Material: NO

EXECUTIVE SUMMARY
This was an experimental stocking study aimed at further evaluating if stocking could be
used as a tool to restore and re-establish razorback sucker in the Upper Colorado River Basin.
The purpose of this 6-year investigation was to evaluate the survival and performance of three
different sizes of domestically-propagated and reared razorback sucker following stocking in the
Upper Colorado and Gunnison rivers. Specific objectives were to:
1. Determine the relationship between the size of razorback sucker stocked at 100 mm,
200 mm, and 300 mm [total length]) and their subsequent survival in the wild.
2. Determine the dispersal of stocked fish of various sizes following release over time.
3. Determine habitat use of juvenile (100 mm) or sub-adult (200-300 mm) fish in the riverine
environment.
4. Identify ways to reduce mortality of stocked fish.
5. Evaluate different gear for sampling juvenile and sub-adult razorback sucker that will be
needed to develop a monitoring program for this species.
6. Recommend the size of razorback sucker the Recovery Program should produce in
hatcheries and grow-out ponds to stock for restoring this species in the Upper Colorado
and Gunnison rivers.
A total of 49,954 juvenile, sub-adult, and adult razorback sucker were stocked in both the
Upper Colorado (31,531) and Gunnison (18,423) rivers in Colorado from April 1994 through
October 2001. The mean total length of razorback sucker stocked during this period was 187
mm. A total of 235 razorback sucker stocked in the Upper Colorado and Gunnison rivers were
either recaptured (226) or found dead (9) from sampling or during other research sampling
efforts. This represented about 0.5% of all razorback sucker stocked. Of the 235 fish collected,
84 of these fish were recaptured 6 months or more following stocking.
Eighty-one family lots of razorback sucker were stocked between 1995 and 2001. Forty
different family lots were represented from the 226 razorback sucker recaptured alive between
1996 and 2001. One single family lot (1992-2A), reared at Wahweap State Fish Hatchery, Utah,
was recaptured more than any other lot stocked. This lot accounted for 13.1 % of the 84
razorback sucker recaptured that had been at large for 6 months or more during this evaluation.
This lot comprised 12.4% of the 282 razorback sucker stocked in October 1996. One of these
stocked razorback sucker was recaptured 4.8 years later in the fish trap at the Redlands Dam
passageway. The same family lot was stocked in the San Juan River and recapture rates from that
stocking were also higher than other family lots stocked in that river system (23.2%). It is
speculated that this family lot performed well following stocking because the average size at
release was over 300 mm (San Juan River: mean=400 mm; Upper Colorado and Gunnison rivers:
mean-343 mm).
Results from razorback sucker recaptured in the Upper Colorado and Gunnison rivers
from 1997-2001 following stocking suggest that survival is related to the size of fish stocked.
Larger size-classes (> 200 mm) have a higher recapture rate than razorback sucker stocked at
smaller sizes. Razorback sucker stocked at sizes greater than 200 mm appear to have better
short-term survival following release in the river than smaller fish stocked (e.g., < 200 mm);
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