7880

• UCREFRP Catalog Number: 7880
• Author: Wydoski, R. S.
• Title: Augmentation Plan For Razorback Sucker In The Middle Green River, 1996-1997.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

I. EXECUTIVE SUMMARY

The primary goal for augmentation stocking in the Middle Green River is to
increase the numbers of adult razorback suckers with the intent of stabilizing
that stock from the present estimate of 500 fish to 1,000 fish. The main
objective is to augment the number of adult razorback suckers in the Middle
Green River by 500 fish through stocking.

In 1995, approximately 200 fish from five family lots of captive-reared
razorback sucker were stocked into the Middle Green River. To prevent genetic
swamping in the wild stock, the numbers of captive-reared razorback suckers
will be equalized by stocking about 200 fish from each of 25 family lots.

In 1996, approximately 1,000 captive-reared razorback suckers from various
family lots will be stocked into the Middle Green River (see Table 2). The
estimated survival rates and mean total lengths at the end of each growing
season is summarized in Table 1. Based on the estimated survival rates in
Table 1, about 203 adult razorbacks should be produced by the fall of the Year
2001 from the 1996 stocking (Table 2).

Beginning in 1997, a combination of wild razorback sucker larvae from the
Middle Green River and razorback sucker larvae from pedigreed family lots will
be reared to a desired size, PIT-tagged, and stocked into the Middle Green
River to augment the wild razorback sucker stock.

The number of wild larvae that can be collected with light traps is estimated
to be about 1,000 annually. Therefore, the 1996 propagation effort will be to
collect 1,000 wild razorback sucker larvae and obtain 3,030 captive-reared
larvae from 5 pedigreed family lots. These razorback suckers will be reared
for two years in ponds at the Ouray Endangered Fish Facility, PIT-tagged, and
released into the Middle Green River in October, 1997. Based on estimated
attrition rates, approximately 128 razorback suckers should survive to the
Year 2000 (Table 3). These fish would be approximately 17 inches in mean
total length when they would be expected to mature in the spring of the Year
2001.

Larvae produced from augmentation stocking would supplement larvae from
natural recruitment and will aid in the evaluation of razorback sucker
survival related to the enhancement/ restoration of flooded bottomlands (i.e.,
levee removal evaluation).

II. INTRODUCTION

The current status and trends of the razorback sucker in the Upper Colorado
River Basin is critical (Bestgen 1990; Burdick 1992, 1995; Lanigan and Tyus
1989; Maddux et al. 1993). Current presumptive stocks are comprised of old
individuals that are low in number. The largest concentration of adult
razorback suckers is in a low gradient reach of the Middle Green River between
the mouth of the Yampa River downstream to the mouth of the Duchesne River
(Tyus and Karp 1990; Tyus and Karp 1991). A Lincoln-Petersen estimate of
adult razorback suckers from this reach between 1980 and 1992 was 524 fish
with 95% confidence intervals between 351 and 696 (Modde et al. 1996).

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