9713

• UCREFRP Catalog Number: 9713
• Author: VanHaverbeke, D.R.
• Title: Stock assessment and fisheries monitoring activities in the Little Colorado River within Grand Canyon during 2004.
• USFW Year: 2005.
• USFW - Doc Type: U.S. Fish and Wildlife Service
• Copyright Material: NO

EXECUTIVE SUMMARY

The Grand Canyon Monitoring and Research Center (GCMRC) determined
that a rigorous stock assessment program for fishes in the Little Colorado River
(LCR) was a priority in 2000. As a result, since 2000, the U.S. Fish and Wildlife
Service (USFWS) has been contracted by the GCMRC to conduct stock
assessment and monitoring activities in the LCR. A total of four monitoring trips
were conducted during 2004: (1) 29 March to 9 April, (2) 26 April to 7 May, (3) 15
to 26 September, and (4) 20 October to 31 October. The primary goal of these
trips was to obtain stock assessment information of the humpback chub (Gila
cypha; [HBC]). Also presented are summary data gathered during these trips
relating to physical parameters, fish captures, species composition, length
frequency, catch per unit effort (CPUE), sexual condition, predation, and external
parasite occurrence.

The four trips were primarily used to conduct two mark-recapture efforts to
estimate the abundance of HBC 2: 150 mm total length (TL) in fhe lower 13.6 Z3 31.(
kilometers of the LCR. The results of the spring mark-recapture efforts indicate I ~ (Il?
that there were 2,334 (SE = 411) HBC 2: 150 mm in~t during the spring of - ~ I g ~..ho.J4\i<;
2004. Of these fish, it was estimated that there weli 1,816 E = 397) HBC 2:
200 mm (4+ year old adults). The results ofthe fall -recapture effort indicate "L 5""'<;""
that there were 2,565 (SE = 519) HBC 2: 1~O m~e LCR during the fall of 7et'"
2004. Of these fish, it is estimated that there w~E = 184) HBC 2: 200 11;;cr ?t'ht:tL,.}
mm (4+ year old adults). .. ,,7
. JillV>' IPc1..S &eifett':.'''"'t I
During the first spring trip, the LCR was declining from spring runoff. Turbidity
declined from 1,936 nephelometric turbiditY units (NTUs) to 55 NTUs, and daily
afternoon water temperature remained a steady 19 DC. During the second spring
trip, the LCR ran at base flows and was blue in color. Turbidities ranged
between 9.1 and 12 NTUs and daily afternoon water temperatures averaged 20.8
DC. '

Combining both spring trips, a total of 1,085 hoop net sets were deployed,
yielding 25,218 hours of fishing effort. A total of 6,840 fish were captured, of
which 3,871 were HBC. Catch per unit effort (CPUE) for HBC was 0.154
fish/net-hour. Nonnative fishes comprised 10% of the catch. One hundred and
twenty-nine ripe HBC were captured of which six were female. Eleven ripe
flannelmouth sucker (Catostomus /atipinnis) and 120 ripe bluehead sucker (G.
discobo/us) were captured. Two HBC (one TL = 104 mm, the other prey length
unrecorded) were found in the stomachs of 34 black bullhead (Ameiurus me/as)
examined. Percent occurrence of the external anchorworm (Lemaea cyprinacea)
on HBC was only 0.05%.

During the first fall trip, the LCR was undergoing flooding. Turbidities ranged
from 16,280 to 124,416 NTUs, and daily afternoon water temperatures averaged
17.4 DC. During the second fall trip, the LCR ran at base flow and was blue in
color. Turbidities ranged from 23.8 to 61.4 NTUs and daily afternoon water
temperatures averaged 17.9 DC.

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