9489

• UCREFRP Catalog Number: 9489
• Author: Mueller, G.
• Title: The Role of Stocking in the Reestablishment and Augmentation of Native Fish in the Lower Colorado river Mainstream ‎(1998-2002)‎.
• USFW Year: 1998-2
• USFW - Doc Type: 03-288,
• Copyright Material: NO

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Population estimates. Population size was estimated using two methods: (1) mark/recapture data, and (2)
visual surveys conducted by boat. Six hundred ninety-four flannelmouth suckers were marked (PIT) by
January 2002. Fish were collected during eight field trips in 2002 (Table 1.7). Based on the Schumarcher-
Eschmeyer mark-recapture method, it is estimated the flanne1mouth sucker population numbered 2,286 (95%
CL = 1,847-2,998).
Due to known sampling biases, population estimates are presented with caution. Our flanne1mouth sucker
sample is heavily biased toward females and habitats where females convalesce between spawning events.
Channel habitats where flannelmouth suckers are typically found are impractical to sample because of depth
(>2 m) and current (>50 cmlsec).
Schools of flanne1mouth suckers were commonly observed in the main channel between Harrah's Casino
and the old Fort Mohave ruins. Fish were typically observed near or on the bottom at 2 to 4 m depths over
small cobble. The two largest groups, which often numbered over 100 fish, were found year-round just
upstream from the entrance to Laughlin Lagoon and along the Arizona shoreline near the Fort Mohave ruins.
Unfortunately, depth made electrofishing ineffective and swift currents and suspended debris made trammel
nets impractical. We set hoop nets without any success and snags made drift nets impractical.
Fish are most susceptible to capture during their spawning season, which runs from February through May.
Sexual dichotomy is prevalent in dispersal and behavior patterns. Males were primarily found in channels
near spawning areas while females concentrated at the entrance of Laughlin Lagoon and smaller slack waters.
Females are multiple spawners and we suspect they convalesced or rested in these slack water areas between
spawning events.

Table 1.7. Population estimates for the flannelmouth sucker based on multiple censuses usmg
mark/recaptured data from the 2002 sampling season.

Date Captured Marked Recaptured N = MCIR8
January 15-16 23 715 2
February 12-14 18 736 6 2,208
February 26-28 3 747 2 1,121
March 12-14 56 747 22 1,901
March 26-28 47 779 12 3,051
April 9-11 76 812 36 1,714
April 23-25 64 844 18 3,001
May 7-8 42 888 17 2,194
CL 95% n= 2,286
Lower 1,847b
Upper 2.99Sb

* Adjusted for replicate recaptures and mortalities.

aBased on Schumacher-Eschmeyer method (Ricker, 1975).
b
Pearsons 95% CL.

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