WSP08901

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/13/1993
• Author: USDOI-USFWS
• Title: Draft Biological Opinion-Operation of Glen Canyon Dam as the Modified Low Fluctuating Flow Alternative of the Draft Envronmental Impact Statement Operation of Glen Canyon Dam
• Water Supply Pro - Doc Type: Biological Opinion

Minckley (1991) described the different adaptations to feeding for the three native Grand Canyon
suckers and stated that the razorback sucker possess a "protrusible mouth and special gill rakers
for sieving plankton or detritus." Marsh (1987) examined stomachs (n=32) of adult razorback
suckers and found planktonic crustaceans, diatoms, filamentous algae, and detritus demonstrating
feeding occurs both on plankton and benthic organisms. Dill (1944) found razorback sucker
stomachs (n=4) in a bay below Headgate Rock Dam, Colorado River to be filled with silt "rich
in microscopic organisms" and filamentous algae.

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By examining otoliths from Lake Mohave specimens, ages of razorback suckers were found to
range from 24 to 44 years (McCarthy and Minckley 1987), longevity typical of big river
endangered fish.

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Unpke the humpback chub that successfully recruits young, but actual spawning has not been
observed, the recruitment of razorback sucker in historic habitats (rivers) is unsuccessful, but
considerable information exists on spawning activities. Reviews of the ample data from Lake
Mohave found spawning usually occurs from January to April or May with water temperatures
varying from 10.5 to 21 .C, but usually above IS .C over wave-washed, gravel and cobble
shorelines (Minckley et aI.I991, Minckley 1991). Larvae were produced but did !lot develop
into young-of-year or juveniles until recent experimental actions of placing breeding adults into
a predator-free backwater was begun (paul Marsh, personal communication).

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Sigler and Miller (1963) reported spawning to occur in water about 12 to 18 .C in tributary
streams and reservoir shorelines over silt, sand, gravel, or rocks. Tyus and Karp (1990)
captured ripe razorback suckers in riffles on substrates of cobble, gravel, and sand during the
ascending and high limbs of the hydrograph of the Green River and Yampa River from mid-
April to early June. Spawning was associated with temperatures of about 14 .C, and migrations
of 30 to 106 kilometers were recorded for some individuals but not all. Some ripe female
razorback suckers were captured in flooded bottomlands with temperatures ranging from 17 to
19 .C, and habitats and temperatures were found to vary with various water years experienced
(Tyus 1987). Marsh (1985) found greater success with experimental hatching of razorback
sucker eggs at 20 and 25 .C then at IS .C and complete loss at S, 10, and 30 .C.

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After the adhesive eggs hatch, the larvae settle in spaces between substrate material until swim- ,
up stage; accordingly, spaces free of silt or other sediment were deemed important to their
survival (Inslee 1981, Bozek et aI. 1984).

Sigler and Miller (1963) reported the behavior of larval razorback suckers, approximately 25
mm total length, as traveling in large schools along river and reservoir margins. They note that
two seine hauls on June 15, 1950, collected over 6,000 larval razorback suckers (10 to 35 mm
standard length) from the margin of the Colorado River in Nevada in temperatures ranging from
21.7 to 24.4.C while the river temperature was 14.4 "C. Tyus (1987) collected larvae (10.6

13 October 1993 Omit biological opinion 2-21-93-F-167

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