9721

• UCREFRP Catalog Number: 9721
• Author: Brouder, M.J.
• Title: Age and growth of roundtail chub in the upper Verde River, Arizona.
• USFW Year: 2005.
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

lD in the upper

95) and

'6).

undtail chub
'1as greatest
md declined
2 to 32 mm
tail chub in
ed by

l).

translucent
.nd marginal
ogle opaque
re 2). Mean
ly lower (P
mth, further

+1

Oct Nov Dee

distances by
) collected in

suggesting that opaque bands are formed once per
year.
Otoliths were taken from 110 round tail chub,
ranging from 58 to 236 mm TL, from Bubbling
Ponds Hatchery over a 3-year period to further
validate annulus formation. From the examination
of 99 otoliths (11 were inadvertently destroyed in
preparation) from hatchery-reared, known-age
fish, the number of opaque bands (annuli) agreed
100% of the time with the actual age of the fish.
Daily rings were also observed on the sagittal oto-
liths of age-O hatchery-reared fish (Figure 1), and
ages based on daily ring counts of age-O fish agreed
70% of the time with true age, and 80% and 90%
of the time within 1 and 2 d of the true age, re-
spectively.

Discussion

The age structure of the upper Verde River
roundtail chub population was dominated by two
distinct cohorts. Fish from both the 1993 and 1995
year-classes comprised the majority of the catch
in both 1998 and 1999. In the late winter through
early spring of both 1993 and 1995 floods had
occurred, and Brouder (2001) found a significant
relationship between flooding and the recruitment
of roundtail chub. The presence of two strong year-
classes in years when flooding occurred further
supports this hypothesis.
The maximum observed age (age 7) of roundtail
chub from the upper Verde River population was
similar to that reported for round tail chub in the
Gila and Green rivers (Bestgen 1985; Vanicek and
Kramer 1969). However, mean lengths at age of
roundtail chub in this study were larger than those
reported for roundtail chub in two streams in the
Gila River basin, New Mexico (Bestgen 1985),
Fossil Creek, Arizona (Neve 1976), and the Green
River, Utah (Vanicek and Kramer 1969). In ad-
dition, growth rates were more rapid than those
reported by other researchers but agreed with the
observation that growth is greatest during the first
year. Fast growth rates of roundtail chub from the
upper Verde River during this study may be ex-
plained by the various impacts of the 1993 and
1995 floods. In the Southwest, flooding benefits
native fishes by disproportionately displacing non-
native fishes (Meffe 1984; Minckley and Meffe
1987; Rinne and Stefferud 1997) that prey upon
and compete for resources with native fishes. Dis-
placement of nonnative fishes likely alters re-
source utilization patterns of native fishes, which
may ultimately affect or, as in this case, accelerate
individual growth rates (Werner and Hall 1977).

,

NOTE

869

The apparent discrepancies in the length at age
and growth of round tail chub in this study and
those reported elsewhere may also be attributed to
the use of scales in previous studies and otoliths
in this study. Both Bestgen (1985) and Neve
(1976) concluded that due to the difficulty in dis-
cerning distinct annuli and therefore ages, the use
of scales may not be an accurate method for aging
roundtail chub and, therefore, their length-at-age
data should be viewed as tentative. Furthermore,
the difficulty in discerning distinct annuli in round-
tail chub scales that both Bestgen (1985) and Neve
(1976) experienced may have introduced a bias
toward overestimating the ages of roundtail chub,
which would result in, and explain, the smaller
lengths at age of roundtail chub in their studies
than that of the fish in this study.
Frontally sectioned sagittal otoliths of roundtail
chub contain easily discernible annual marks. The
high degree of precision among three independent
readers of wild roundtail chub confirms the relati ve
ease in counting annuli in sectioned otoliths. Mar-
ginal increment analysis suggests that a single an-
nul mark is deposited in a period extending from
January to May. This period of opaque band for-
mation seems reasonable because factors affecting
the deposition of opaque bands (i.e., reduced win-
ter growth and spawning) occur during this same
time frame. In addition, the number of opaque
bands on known-age, hatchery-raised roundtail
chub was in exact agreement (100%) with the ac-
tual age of fish, further validating the use of sag-
ittal otoliths to age roundtail chub. Because the
roundtail chub used to validate the use of otoliths
in this study were, at most, 3-years-old, it is pos-
sible that true annuli may not be deposited on the
otoliths of older fish, thus possibly making the
aging of older roundtail chub more difficult (Cam-
pana 2001). However, because the relative age of
roundtail chub in this study was age 7 or younger,
this potential problem is likely minimal. Of special
note was the observation of daily increments on
the sagittal otoliths of age-O roundtail chub. Daily
rings on otoliths can be used to gather important
information on hatching times, growth, and mor-
tality of fishes (Miller and Storck 1982; Essig and
Cole 1986; Isley and Noble 1987).
Otolith cross sections are a viable technique for
determining ages of roundtail chub in the upper
Verde River, Arizona, and should be throughout
the species' range. The use of otoliths gives bi-
ologists a reliable means of determining the age
of roundtail chub, which allows for a better un-
derstanding of age structure, growth rates, recruit-