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132
<br />MWCKLEY ET AL.
<br />trend toward extinction of the bonytail is evident,
<br />and the decision was made by the USFWS in the
<br />1970s to establish a brood stock and to develop
<br />holding, culture, and reintroduction capabilities to
<br />preclude extinction and to promote eventual re-
<br />covery.
<br />This paper documents the capture and artificial
<br />propagation of bonytails from Lake Mohave to
<br />found a brood stock at Dexter National Fish
<br />Hatchery, New Mexico. We evaluated allozyme
<br />variation in hatchery-produced bonytails in com-
<br />parison with that of other species. Our purpose
<br />was to provide a baseline for allozyme variability
<br />and to identify polymorphic loci useful for mon-
<br />itoringpopulation structure when recovery through
<br />reintroduction succeeds. The effectiveness of
<br />hatchery practices for maintaining genetic diver-
<br />sity was also assessed.
<br />Methods
<br />Capture of brood fish involved extensive field
<br />operations and the development of holding and
<br />culture protocols for propagation. As a result, about
<br />1,700 F, adult bonytails (1981 year class) now
<br />exist at Dexter National Fish Hatchery, New Mex-
<br />ico (B. L. Jensen, USFWS, personal communi-
<br />cation). Progeny of these fish were produced in
<br />ponds without human intervention and were made
<br />available for electrophoretic analysis. Preserved
<br />specimens from Lake Mohave in the Arizona State
<br />University collections include adults that died at
<br />of after capture; adults used in hatchery produc-
<br />tion of young; larval, juvenile, and adult F, indi-
<br />viduals; and larval and juvenile F~ progeny.
<br />Soluble products of 45 gene loci from 24 FZ
<br />juveniles (1985 year class; 65-95 mm standard
<br />Length) were resolved electrophoretically by the
<br />methods of Crabtree and Buth (1981), Buth (1982,
<br />1984), and Frick (1983) from separate extracts of
<br />skeletal muscle, liver, and brain tissues. Gene
<br />products examined, tissue sources, and electro-
<br />phoretic conditions are listed in Table 1. Enzyme
<br />nomenclature follows IUBNC (1984) recommen-
<br />dationsexcept the names for di- and tripeptidases
<br />follow Frick (1983). Locus nomenclature follows
<br />Buth (1983) with some modifications. Allelic
<br />products are designated by lowercase letters in se-
<br />quence of increasing anodal electrophoretic mo-
<br />bility of electromorphs. Measures of genetic vari-
<br />ation were calculated by the BIOSYS-i program
<br />of Swofford and Selander (1981). Levene's (1949)
<br />correction for small sample size was used for cal-
<br />culating Hardy-Weinberg equilibrium expecta-
<br />tions.
<br />Results and Discussion
<br />An original stock of 18 bonytails was caught in
<br />trammel nets from Lake Mohave during February
<br />1976 (three fish), April 1979 (twu), April 1980
<br />(five), and March 1981 (eight; Ntinckley 1983).
<br />The first 10 fish (1976-1980) were large, old fe-
<br />males (>45 cm total length, TL) which raised con-
<br />cern that males might have disappeared because
<br />of differential mortality. Bonytails proved not only
<br />difficult to capture but were difficult to handle as
<br />well, and only 5 of the first 10 were successfully
<br />transported and maintained at Willow Beach Na-
<br />tional Fish Hatchery, Arizona. Examination of
<br />otoliths from four dead fish indicated apparent
<br />ages of 34, 40, 42, and 49 years (Rinne et al. 1986;
<br />Minckley, unpublished). Because the probability
<br />of capturing males seemed low, ova from the re-
<br />mainingfive females were used in 1980 for studies
<br />of hybridization with male roundtail and hump-
<br />back chubs (Hamman 1981); one female died of
<br />stress from artificial stripping.
<br />The first three fish caught in 1981 were also
<br />females; one died shortly after capture. Five males
<br />were then secured in two net sets at the same site
<br />during a single night, and ail seven fish were trans-
<br />ported successfully to Willow Beach and main-
<br />tained in good condition. In May 1981, after ar-
<br />tificial induction of gonadal development, five
<br />individuals of each sex were spawned (Hamman
<br />1982); one female failed to respond to hormone
<br />treatment and remained barren. Females varied
<br />from 46.9 to 56.4 cm TL, and males varied from
<br />45.4 to 48.0 cm TL.
<br />Hatching rate for the estimated total of 125,450
<br />ova from the five females averaged 95% (range,
<br />91-9996); 80,000 larvae were immediately trans-
<br />ferred to grow-out ponds at Dexter (Hamman
<br />1982) where about 1,700 F, adults remained in
<br />1988. All I 1 fish used for artificial stripping in
<br />1981 survived in good condition, but they died
<br />over the next 1-3 years. About 130,000 fish, in-
<br />cluding original F, fish (54,941), manually cul-
<br />tured FZ individuals (28,710), and naturally pro-
<br />duced FZ fish (46,629) were stocked in Lake
<br />Mohave between 1981 and 1987 to augment that
<br />population (R. L. Hamman, USFWS, persona]
<br />communication).
<br />Field efforts since 1981 resulted in the capture
<br />of 16 additional bonytails: 1 each in 1983 and
<br />1985, 3 in 1986, and 11 in 1988. Of these, two
<br />were taken by fishermen and not retained, eight
<br />fish died in transit to hatcheries or shortly there-
<br />after from injuries, secondary infections, or un-
<br />
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