7124 ‎(2)‎

• UCREFRP Catalog Number: 7124
• Author: McAda, C. W. and R. S. Wydoski.
• Title: Technical Papers
• USFW Year: 1980.
• USFW - Doc Type: \
• Copyright Material: YES

13
water for short periods.
The four other fish (B, C, D, and E) were followed for
shorter periods than fish A and were always relocated
in quiet water (Fig. 5-. Although two fish moved up-
stream for a short distance, all fish were moving down-
streamwhen contact with them was lost.
Movement Traced with Anchor Tags
In addition to the use of ultrasonic transmitters, we
noted movement of individual razorback suckers by
the recapture of 11 of 98 fish marked with serially
numbered anchor tags. Three were recaptured after
moving considerable distances from the original
capture sites. One female tagged at station 4 (Fig. 1) in
April 1975 was recaptured 2 weeks later at the mouth
of the Yampa River, 21 km upstream (at station 3). It
was ripe and was probably spawning. Although this
movement could be interpreted as a spawning migra-
tion, the extent and magnitude of such migrations (if
any) in the Colorado River system are not known. The
second fish, tagged at station 8 (Walker Wildlife Area)
in October 1975, was recaptured during the following
spring in a backwater area, 26 km upstream from the
place of release, with 40 other razorback suckers (G.
Kidd, personal communication). This area had been
flooded by irrigation flows at that time, but is dry
during most of the year. The third tagged sucker was
recaptured by P. B. Holden (personal communication),
3.5 years after we had tagged it at station 7 in Decem-
ber 1974. It was recaptured upstream from station 5 in
April 1978, about 130 km upstream from the place of
release.
The recovery of eight razorback suckers in the
flooded gravel pit at the Walker Wildlife Area (sta-
tion 8-, indicated a tendency for the fish to remain in
this area of quiet water for extended periods.
Vanicek (1967) recaptured 4 of 13 tagged razorback
suckers during a study in 1963-66. None were recap-
tured more than 1.6 km from the release point and all
movement was downstream.
Food
No quantitative data are available on the food of
razorback suckers, and no fish were sacrificed for
stomach analyses during the present study. However,
limited information on this subject is available from
other studies. Jonez and Sumner (1954) reported that
razorback sucker stomachs were filled with midge
larvae and algae. Banks (1964) found algae and plant
debris, along with Ephemeroptera, Trichoptera, and
larval Diptera in the stomachs of razorback suckers
collected during the chemical fish-removal treatment
of the Green River below the site of Flaming Gorge
Dam. Vanicek (1967) found the stomachs of razorback
suckers to be packed with mud containing chironomid
larvae and plant material.
In the reservoirs of the lower Colorado River basin,
razorback suckers consumed large amounts of plank-
ton (Dill 1944; Minckley 19731. Hubbs and Miller
(1953) noted that razorback suckers have long gill
rakers and suggested that these fish filter plankton
from the water. This suggestion is consistent with the
preference of the razorback sucker for quiet, back-
water areas, where plankton populations in most large
rivers are densest (Hynes 1970-; however, no infor-
mation is available about plankton in the large rivers
of the Colorado River basin.
Catostomid Hybrids
Three hybrids between catostomid fishes were re-
ported recently from the study area-flannelmouth
sucker x razorback sucker, flannelmouth sucker x
white sucker (C commersoni-, and bluehead sucker x
white sucker (Holden and Stalnaker 1975b-. Another,
bluehead sucker x flannelmouth sucker, was reported
earlier (Hubbs et al. 1943; Hubbs and Hubbs 1947-.
Only the flannelmouth sucker x razorback sucker was
observed during the present study-three were col-
lected from the gravel pit at station 8 on the Colorado
River and five at station 3 on the Yampa River (com-
pared with 66 and 29 razorback suckers, respectively.
Holden (1973) collected 40 specimens of this hybrid be-
tween 1968 and 1972.
Hybrids of flannelmouth sucker x white sucker and
bluehead sucker x white sucker have resulted directly
from alteration of the river system by man. The white
sucker, an introduced species, is not common in many
reaches of the Colorado basin. Only one bluehead
sucker x flannelmouth sucker cross was reported from
the upper basin (Hubbs et al. 1943-, and this hybrid
has not been collected since that time.
The flannelmouth sucker x razorback sucker hybrid
was initially reported as a new species (Jordan 1891-.
However, Hubbs and Miller (1953) described it as a
hybrid and it has been reported occasionally since then
(Banks 1964; Vanicek et al. 1970; Holden and Stal-
naker 19756-. Holden and Stalnaker (1975b) found
75%~as many hybrids as they did razorback suckers.
This high percentage may indicate that the incidence
of hybridization is increasing. This increased incidence
might be expected in an altered system where one fish
is more abundant than a closely related fish, and where
both species have similar reproduction requirements.
Since spawning razorback and flannelmouth suckers
were collected together from the same habitat during
the present study, hybridization could easily occur.
The decreased incidence of flannelmouth sucker x