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<br />
<br />Transactions of the American Fishel
<br />@ Copyright by the American Fishe
<br />DOl: JO.I577ff04-096,]
<br />
<br />866-871, 2005
<br />~, 15
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<br />q121
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<br />[Note]
<br />
<br />Age and Growth of Roundtail Chub in the
<br />Upper Verde River, Arizona
<br />
<br />MARK J. BROUDER*I
<br />
<br />Arizona Game and Fish Department, Research Branch, 2221 West Greenway Road,
<br />Phoenix, Arizona 85023. USA
<br />
<br />Abstract.-Estimates of the age and growth of round-
<br />tail chub Gila robusta were made by analyzing thin cross
<br />sections of sagittal otoliths from 280 specimens col-
<br />lected in the upper Verde River, Arizona, from January
<br />1997 to December 1999. Marginal increment analysis
<br />indicated that a single annulus completed formation be-
<br />tween January and May, The use of otoliths to age round-
<br />tail chub was further validated using otoliths of known-
<br />age, hatchery-reared fish for which (upon examination)
<br />the number of annuli agreed 100% of the time with the
<br />true age of the fish, In addition, daily increments were
<br />observed on sagittal otoliths of age-O roundtail chub and,
<br />when counted, agreed with the true age of fish 70% of
<br />the time; daily ring counts were within I and 2 d of the
<br />true age 80% and 90% of the time, respectively. Ages
<br />assigned to wild-caught fish by three independent read-
<br />ers resulted in a coefficient of variation (100 x SOl
<br />mean) of 8.2, Ages of roundtail chub varied from I to
<br />7, the largest fish being a 427-mm total length (TL),
<br />836-g total weight (TW). age-7 female, The largest male
<br />was 413 mm TL, 629 g TW, and age 6, The growth of
<br />age-I-7 round tail chub (both sexes combined) was
<br />greatest during the first year and was best described by
<br />the equation L, = 499.30 [I - e-O.23(,-O.147)], where L, is
<br />length at time t.
<br />
<br />The roundtail chub Gila robusta is one of a di-
<br />verse group of relatively large-bodied cyprinids
<br />that was once widely distributed throughout the
<br />Colorado River basin of the western United States
<br />and northwestern Mexico. Although still locally
<br />common in places throughout its historic range,
<br />the roundtail chub, like many native fishes in the
<br />arid western United States, has been reduced in
<br />numbers and distribution due to altered flow re-
<br />gimes (Miller 1961; Minckley and Deacon 1968;
<br />Minckley and Douglas 1991), predation and com-
<br />petition by introduced exotic species (Meffe 1985;
<br />Miller et al. 1989; Douglas et al. 1994), and in-
<br />advertent introductions of parasites (Hoffman and
<br />Shubert 1984; Brouder and Hoffnagle 1997). Con-
<br />
<br />* E-mail: mark..brouder@fws,gov
<br />I Present address: U,S, Fish and Wildlife Service, Ar-
<br />izona Fishery Resources Office, Post Office Box 39,
<br />Pinetop, Arizona 85935, USA.
<br />
<br />Received June 7, 2004; accepted December 27, 2004
<br />Published online June 13, 2005
<br />
<br />sequently, roundtail chub is on slate-sensitive spe-
<br />cies lists in Colorado, Utah, Arizona, and New
<br />Mexico, and is currently being reviewed for listing
<br />as a federally threatened or endangered species.
<br />The majority of published(literature on this spe-
<br />cies pertains to status, distribution, and abundance
<br />(Vanicek et al. 1970; Minckley 1973; Holden and
<br />Stalnaker 1975; Tyus et al. 1982; Bestgen and
<br />Propst 1989), taxonomy (Holden and Stalnaker
<br />1970; Douglas et al. 1989; McElroy and Douglas
<br />1995; Douglas et al. 1998), recruitment (Brouder
<br />2001), culture (Muth et al. 1985), parasites and
<br />their effects (Mpoame and Rinne 1983; Brouder
<br />1999), and other life history aspects (Vanicek and
<br />Kramer 1969; Schreiber and Minckley 1981; Be-
<br />stgen et al. 1987; Kaeding et al. 1990, Karp and
<br />Tyus 1990; Barrett and Maughan 1995). However,
<br />very little detailed information exists on the age
<br />and growth of roundtail chub, especially in the
<br />lower Colorado River basin. The primary objec-
<br />tives of this study were to describe the age, growth,
<br />and size structure of the roundtail chub population
<br />in the upper Verde River and to validate annulus
<br />formation in the otoliths of roundtail chub.
<br />
<br />Methods
<br />
<br />Fish collections.-To determine age structure
<br />and growth of roundtail chub, fish were collected
<br />quarterly from February 1998 through December
<br />1999 at five sites located within the upper 72 km
<br />of Verde River, Arizona, primarily by using a
<br />Smith-Root backpack shocker but with other tech-
<br />niques (including seining, hoop nets, trammel nets,
<br />and angling) as well. After capture, total length
<br />(TL, mm) and total weight (TW, g) were recorded,
<br />and fish were sacrificed for the removal of otoliths
<br />and determination of sex (based on presence of
<br />testes or ovaries) in the laboratory.
<br />Otolith preparation.-Cross sections of round-
<br />tail chub otoliths were prepared by mounting
<br />whole otoliths on microscope slides using
<br />CrystalBond thermoplastic cement and grinding
<br />frontally through the nucleus using a combination
<br />of 600-2,OOO-grit wet-dry sandpaper. Sectioned
<br />otoliths were then viewed using an image analysis
<br />
<br />866
<br />
<br />
<br />system (EPIX,
<br />a personal cor
<br />equipment con
<br />Otoliths were'
<br />magnification
<br />ments were ta
<br />edge of each (
<br />to the margin
<br />Age and gr
<br />counted the nu
<br />and assigned :
<br />cies occurred,
<br />the readings s
<br />carded. Precis
<br />was determine
<br />iation (CV =
<br />Length of r
<br />back -calculate
<br />the modified F
<br />relevant inter,
<br />size of fish an
<br />from hatcher)
<br />component of
<br />method is bas
<br />linear relation
<br />within an ine
<br />sumption usi!
<br />uses a biologi
<br />less problem
<br />growth than
<br />which uses a ~
<br />(Campana, al
<br />length at age
<br />equation:
<br />
<br />La=Lc-
<br />
<br />where La is tI
<br />a, Lc is the ler
<br />of fish at swin
<br />at annulus a,
<br />and 00 is the
<br />mm). Becaus
<br />differences b
<br />age, data for
<br />calculate gro
<br />Growth rat,
<br />fitting the vo
<br />calculated leI
<br />
<br />where L, is tI
<br />the maximuI
<br />(mm) , K is I
<br />
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