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176 The Soulhu~eslrrn A'am+alisl vol. 28, no.2
<br />rive identification of two juvenile razorback suckers. Apparently poor repro-
<br />ductive success by razorback suckers in that area was attributed in part by
<br />McAda and ~ti'ydoski (1980) to possible confusion o[ young-obthe-year with
<br />young of [lannelmouth sucker. This is not the case in the lower river, since
<br />no similar sucker species now are present.
<br />Factors directly contributing to failure of successful reproduction. by
<br />razorback sucker include occasional stranding o[ eggs by reservoir ^uctua-
<br />tions in Lake Mohave (Gustafson, 1975b), but more importantly, predation
<br />by introduced piscivores. Jonez and Sumner (1959) similarly believed that
<br />predation by carp and other fishes on freshly spawned eggs limited repro-
<br />ductive success in Lake Mohave, and McAda and Wydoski (1980) attributed
<br />failure of reproduction in Walker Wildlife Area to the presence of "sizable
<br />numbers o[ introduced predaceous fishes..." Ulmer and Loudermilk (pers.
<br />comm.) have documented direct predation by recording razorback sucker ova
<br />in stomachs of channel catfish and carp in Senator Wash Reservoir, observed
<br />bluegill feeding on the substrate in spawning areas, and found smallmouth
<br />and largemouth bass and redear sunfish in substantial numbers near spawn-
<br />ing razorback suckers. William Rinne and Gordon Mueller (U.S. Buteau of
<br />Reclamation, pers. comm.) also confirmed carp predation on razorback eggs
<br />in Lake Mohave in ]982.
<br />Sex Ratios.-Sex ratios are biased toward females in offshore netting sam-
<br />ples o[ razorback suckers (mates/females, n in parentheses): 1975 - 0.29-0.86
<br />(3 samples, X = 0.58 f 0.28, 189 fish); 1976 - 0.93 (57); 1477 - 0.21 (23); 1979
<br />- 0.20 (6); 1980 - 0.21-0.29 (2 samples, 69 fish), and 1981 - 0.46 (73 fish). In
<br />1968, AGFD personnel sexed 30 fish collected by electrofishing, of which
<br />only 9 were females (ratio 2.33). Males are regularly mute abundant than
<br />females on spawning areas (Douglas, 1952). Sex ratio For 97 fish collected
<br />while spawning in ]981 was 3.57, and for 258 fish seined from pre-spawning
<br />aggregation in 1982 the ratio was I.B. The 1968 electrofishing collection pre-
<br />sumably reflected similar circpms[ances.
<br />Sexual Dimorphism.-Six sexually dimorphic characters are obvious in
<br />razorback suckers. Dimorphic coloration and tuberculation are apparent
<br />only- during the spawning period, January through March, although some
<br />expression has been noted as early as November. Four sexing criteria are
<br />independent o[ season: 1) size (both length and weight); 2) pelvic and 3) anal
<br />[in lengths; and 4) length and morphology of the urogeni[ai papillae. An
<br />additional character reported by McAda and Wydoski (1980), curvature of
<br />the last anal [in-ray in male razorback suckers while the ray remains straigh[
<br />in females, was not studied by me.
<br />Male and female razorback suckers exhibit strongly dimorphic pigmenta-
<br />tion and wberculation during the breeding season {Douglas, 1952; Hinckley,
<br />]973). Males are dark-olivaceous to black dorsally, with abright-orange belly
<br />and adark-pink to reddish lateral band. Females remain olivaceous dorsally,
<br />lightening to off-white, yelloti•ish, or mottled ventrally. In males, large coni-
<br />cal tubercles are produced on the anal fin and lower lobe of the caudal fin,
<br />and smaller, conical tubercles are on the pectoral and pelvic fins, and both
<br />above and below the lateral line along sides, and on the ventrum, of the
<br />caudal peduncle. Branson (1961) en'oneously reported wbercles only on the
<br />May 1983 Minckleq-Status of Razorback Sucker 177
<br />TABLE 9.-Sexual dimorphism in adult mzo+bark surke+s f+om Lake Alohave, Rrizona-Ntoada,
<br />1975; means followed by t une standard error.
<br />cearaa~r,~„~~ -Hairs
<br />In> rra,rir~
<br />ml
<br />Standard Lengths 93.1 t 5.5 cm 50.6 t 6.5 cm
<br /> (Z9) (59)
<br />Total Weights 2.07 t 0.92 kg 3.01 t 0.70 kg
<br /> (19) (49)
<br />Pelvic Fin Length _19.5 f 7.3% 11.5 t l.b%
<br />(~, SL) (29) (59)
<br />Anal Fin Length 20.2 t 9.2% 16.1 t L6%
<br />(~ SL) (29) (59)
<br />UrogeniulPapillusLength 5.6t 1.8~ B.Of 1.3'%
<br />(~ SL) (23) (98)
<br />anal fins of males. Small, lower-profile wbercles are often, although not
<br />invariably, present on the anal fin and lower lobe o[ the caudal fin of breed-
<br />ing females, and below the lateral line on their caudal peduncles. Tubercles
<br />on anal fin-rays of females may be tiny and sub-cutaneous. Tubercles were
<br />not found on the pelvic and pectoral fins of females.
<br />Female razorback suckers are larger than males in terms of both length
<br />and total weight (Fig. 2, Table 4). Males, on the other hand, have relatively
<br />longer pelvic and anal [ins. Females have a distinctly longer, more Fleshy
<br />and distally rounded urogenital papillus; in males the papillus is thinner
<br />and accuminate. Differences between sexes for all [our morphological fea-
<br />tures are significant at the 0.05% level (two-tailed t-test percentage data were
<br />subjected to an aresine transformation to normalize distributions; Zar, 1974).
<br />Fecundity.-Results of fecundity investigations are often expressed in
<br />terms of "relative" fecundity, or number of eggs per unit weight of fish.
<br />However, statistical difficulties often arise when gonad weights are either
<br />included or excluded from total weights, and false statistical relations may
<br />result when changes in condition of the fish occur with the approach of
<br />spawning, or when physiological and environmental changes occur through
<br />successive years or in different localities (Bagenal and Braum, 1978). For
<br />these reasons, relative fecundity of razorback suckers are considered most
<br />reliably expressed in terms of number a( ova per unit SL. _
<br />Total numbers of ova in Live ripe females between 39.1 and 57.0 cm 5L X
<br />= 50.4 f 6.8) ranged from 74,600 to 144,000 (X = 100,800 t 26,170), and the
<br />correlation coefficient between total ova and length was r = 0.55. Ovary
<br />weight w_as relatively uniform, ranging from 9.2 to 11.5% of body weight less
<br />gonads (X = 10.1 t 0.95%). Correlation between body weight less gonad and
<br />total ova was r = 0.68. Relative fecundi~~ also was uniform among females,
<br />ranging from 1,680 to 1,908 ova/cm SL (X = 1,812 f 90.5 ova/cm).
<br />McAda and W}'doski (1980) presented data for 10 female razorback suckers
<br />from various localities in the upper Colorado River and taken at various
<br />times o[ year. Their fish varied from ca. 41 to 46 cm SL (calculated from
<br />total lengths) and contained an estimated 27,614 to 76,576 ova (X = 96,791
<br />t 19,076). They likewise found a low correlation between length and fecun-
<br />dity (I calculated r = 0.31). Gonad weights were not given, but I calculated
<br />
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