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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substrate.
Since flannelmouth suckers were stocked in the Bullhead City area in 1976, the population has expanded.
We encountered one angler that was specifically fishing for them. By all accounts, tlannelmouth suckers were
historically rare in the lower Colorado River and were not reported by Dill (1944) or Moyle (1976). Minckley
(1973) reported only five collections taken downstream of Lake Mead. There are no reports oftlannelmouth
sucker being found in the vicinity of Lake Havasu and Mohave Valley prior to 1976.
Size distribution. Annual size distribution trends were similar for 1999,2000, and 2001. While immature
fish were taken (<5%), the majority were spawning adults that averaged 529 (n = 60),528 (n = 466), and 542
mm (n = 463), respectively. Size distribution in 2002 (N = 349) was bimodal and unique, in that it represented
an old cohort and a strong year class of young adults. Average size of the larger (>425 mm) cohort increased
(568 mm) 27 mm from 2001 while a smaller cohort (30-40 em) constituted 31 % ofthe sample (Figure 1.4).
Aging. The majority of growth occurs by age 6 and the majority (76%) examined (n = 119) were 8 to 13
years old (Figure 1.5). The oldest sucker encountered was 24 years, which was substantially younger than a
39-year-old fish reported by Minckley (Scoppetlone and Vinyard, 1991). All three aging structures suffered
from weak or fuzzy annuli that hindered accurate aging, especially after age 10. Aging was difficult due to the
study area's mild climate and cool waters released from Lake Mohave. These factors prevented development
of sharp annuli on aging structures.
Growth data. Recaptures of 5 7 PIT-tagged flannel mouth suckers provided us growth data. As expected,
smaller fish growth rates were much greater than larger fish. Fish between 450 and 475 mm grew at a rate of
4.51 mrnImonth (Figure 1.6). This declined to 2.25 mrnImonth for 50-cm fish and 1.34 mrnImonth for fish up
to 525 cm. Growth rates leveled offfor fish between 525 and 600 at 1.02 and 1.04 mrnImonth. Growthfurther
declined to 0.52 and 0.35 mrn/month for the largest fish. Based on these growth averages, we estimated a 60-
cm flannelmouth would be close to 14+ years old.
Fish movements. More than 160 tlannelmouth suckers were recaptured at least one month after being PIT-
tagged and released (Table 1.6). The majority were mature females (68%) had returned to their point of
capture at least 12 months later. This was normally at or near suspected spawning areas. Ten (8%) females
returned two consecutive years.

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Percent (%)
30 -
25 1-1999 +2000 ..2001 -2002

20

15

10

5

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Total Length (mm)

Figure 1.4. Length distribution offlannelmouth suckers taken from spawning areas from 1999 to 2002.

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