7960

• UCREFRP Catalog Number: 7960
• Author: Modde, T., K. P. Burnham and E. J. Wick
• Title: Population Status of the Razorback Sucker in the Middle Green River ‎(U.S.A.)‎
• USFW Year: 1996
• USFW - Doc Type: Conservation Biology
• Copyright Material: YES

116 Status of Razorback Sucker
4 years
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5 years
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Discharge (m3/sec)
years following higher flow years, suggests some level of
recruitment. The absence of significant decline in esti-
mated population size through time and the estimated
71 % annual survival rate (which represents survival mul-
tiplied by tag retention) give greater support to the con-
tention that the middle Green River population of razor-
back sucker is dynamic rather than static. Even if tag-loss
was 20%, survival of adults would be 89%, which would
result in a dramatic reduction in population size through
time without recruitment.
Lanigan and Tyus (1989) estimated that approximately
1000 razorback sucker adults existed in the Green River
between the mouth of the Yampa and Duchesne rivers.
This point estimate using the model CAI'T'LJRE (White et
al. 1982) was based on 7 years of data and made the as-
sumptions of negligible recruitment, mortality or tag
loss. Our estimated 71 % annual survival estimate and the
absence of a significant population decline appeared to
indicate that some recruitment was occurring. Because
Modde et al.
6 years
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of the paucity of juvenile razorback suckers collected in
the middle Green River, we believe that many of the
new, unmarked individuals in the population resulted
from tag loss.
It was impossible to adjust for tag loss in our estimates
of recruitment. Despite this bias, however, the popula-
tion estimates by Lanigan and Tyus (1989) and by us are
of the same order of magnitude. Both estimates suggest
that the population size of Green River razorback sucker
is precariously low but has not changed significantly
during the last 10 years. Our inability to quantify tag loss
prevents an accurate determination of recruitment and
survival. Tyus and Lanigan (1989) directly observed only
a 5.6% tag foss through their 8-year study, although they
were not able to verify greater losses. Our estimated 29%
annual mortality (which includes tag loss) exceeds most
estimates of annual dangler-like tag loss from other fish
species (Rawstron 1973; Kallemyne 1989), suggesting
some level of recruitment. Thus, the middle Green River
Conservation Biology
Volume 10, No. 1, February 1996