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61P?.
<br />COPEIA, 1985, NO. 3
<br />TABLE 2. ESTIMATED PERCENTAGE OF EACH YEAR
<br />CLASS OF EACH SEX OF WHITE SUCKERS PRESENT IN
<br />SUMMER-FALL 1979 THAT PARTICIPATED IN 1980
<br />-SPAWNING RUN.
<br />Sea Age Percent Participation
<br />Female 3 14
<br />4 15
<br />5 20
<br />6 26
<br />7 32
<br />7+ 24*
<br />Male 3 92**
<br />4 73
<br />5 74
<br />6 67
<br />7 55
<br />7+ 25*
<br />• Percentage potentially negatively biased due to low recapture
<br />probability of largest six classes in spawning run.
<br />• • Percentage potentially positi-ely biased due to low recapture prob,
<br />ability of small fishes in 76 and 102 mm mesh gillnets.
<br />lection ranges. There was a significant differ-
<br />ence in recapture percentage between the two
<br />mesh-sizes in the 260-280 mm size-class due to
<br />the lower recapture rate of small suckers in the
<br />102 mm mesh. Large suckers (460-480 mm)
<br />were recaptured at a significantly higher rate
<br />in that mesh. White suckers of all size-classes
<br />were captured with similar probability in 76 mm
<br />mesh. Gillnet mortality was observed during
<br />summer months when water temperature ex-
<br />ceeded 20 C. There was no significant corre-
<br />lation between recapture percentage and water
<br />temperature as determined by a Chi-square
<br />contingency table. While such evidence does
<br />not eliminate the possibility of tagging mortal-
<br />ity, it reduces the likelihood of positive bias in
<br />the population estimates due to the delayed
<br />mortality of tagged fish.
<br />The percentage of females in each age class
<br />that participated in the spawning run of 1980
<br />increased from age 3-7, but males did not show
<br />the same trend (Table 2). The percentage of
<br />age 3 males estimated to have participated was
<br />probably too high due to underestimation of
<br />the number in the population, caused by the
<br />low capture-recapture probability of these fish-
<br />es in 76 and 102 mm gillnets. Likewise, the low
<br />percentage participation of both sexes for fishes
<br />older than age 7 may be an artifact caused by
<br />the rather low selectivity of the backpack elec-
<br />troshocker for the largest size-classes. Regard-
<br />less of the potential biases of the youngest and
<br />oldest age classes, the percentage of 6-and 7-year
<br />old females that spawned was approximately
<br />twice as great as the percentage of 3- and
<br />4-year old females that did so. The percentage
<br />of males that spawned was similar for ages 4-6,
<br />with an apparent reduction at older ages. At
<br />no age did the percentage of female participa-
<br />tion approximate that of males.
<br />Sixty-one of the 662 suckers tagged during
<br />the 1979 spawning run were recaptured in the
<br />1980 run. Male consecutive-year spawners rep-
<br />resented 11.1% of the total number of males
<br />captured in the 1980 run while consecutive-
<br />year females represented 3.6% of the female
<br />catch. Three of these female, consecutive-year
<br />spawners were seven years old in 1980; the oth-
<br />er three were four, five and six. Eighty-five per-
<br />cent of the male, consecutive-year spawners were
<br />at least six years old in 1980.
<br />DISCUSSION
<br />Sexually mature white suckers in the Mill Riv-
<br />er watershed spawned less frequently than on
<br />an annual basis. Biased sex ratios in the spawn-
<br />ing run of this population were due largely to
<br />different reproductive schedules of the sexes
<br />since the sex ratio of adults in the watershed
<br />approximated 1:1. Males, in general, were ap-
<br />proximately three times as likely to reproduce
<br />in a given year as were females. Several authors
<br />feel that markedly greater energy is expended
<br />in reproduction by female fishes than males
<br />(Williams, 1966; Loiselle, 1978), but see Baylis
<br />(1981) for a different view. The greater growth
<br />rate exhibited by female suckers than by males
<br />in this watershed (Quinn, 1982) and in other
<br />watersheds (Dente, 1948; Priegel, 1976; Ver-
<br />don and Magnin, 1977; Barton, 1980) may, in
<br />part, be due to the less frequent expenditure of
<br />energy in reproduction by this sex. Regardless
<br />of the potential difference in relative energy
<br />expended between the sexes, it is apparent that
<br />the cost:benefit relationship for any particular
<br />reproductive season is potentially different for
<br />females than for males.
<br />Lake Warner white suckers participated in an
<br />"accessory reproductive activity" as defined by
<br />Bull and Shine (1979). However, the energy
<br />requirements of this 3.75 km spawning run are
<br />probably slight compared to migrations of oth-
<br />er non-annual spawning fish populations. Non-
<br />spawning mortality rates for adults are quite low
<br />for this population (Quinn, 1982) and spawning
<br />mortality may be a major component of total
<br />?s
<br />n
<br />QUINN AND ROSS-WHITE SUCKER SPAWNING 617
<br />adult mortality. Adult white suckers in Lake
<br />Warner have no fish predators and suffer no
<br />fishing mortality. Barton (1980) observed that
<br />spawning white suckers were vulnerable to bird
<br />and mammal predation in the clear, shallow
<br />water of the spawning area. The physiological
<br />rigors of spawning (Reighard, 1920) may also
<br />result in post-spawning mortality. Further as-
<br />sessment of the energy demands of a spawning
<br />run, and the mortality associated with migra-
<br />tion, would be necessary to determine whether
<br />Lake Warner white suckers fit the "low fre-
<br />quency reproduction" model of Bull and Shine
<br />(1979).
<br />Data concerning spawning frequencies by age
<br />class and percentage of consecutive-year spawn-
<br />ing by age class showed that spawning frequency
<br />of females increased with age. The greater fre-
<br />quency of spawning among older females agrees
<br />well with hypotheses of increased reproductive
<br />effort, as it is unlikely that the non-annual
<br />spawning cycle exhibited in our study was due
<br />to nutritional or physiological status of the pop-
<br />ulation. The growth rate of white suckers in the
<br />Lake Warner watershed (Quinn, 1982) was av-
<br />erage or better when compared to the range of
<br />growth rates described in the literature (Car-
<br />lander, 1969). Lake Warner fishes reached a
<br />greater maximum size than many other popu-
<br />lations and both sexes were heavier than aver-
<br />age for their length (Quinn, 1982). Our data,
<br />combined with previously published informa-
<br />tion on the dynamics of white sucker spawning
<br />runs, indicate that a standard reproductive
<br />schedule for adult white suckers is potentially
<br />non-annual, particularly for females. In addi-
<br />tion, it would appear that the net benefit of
<br />reproduction for females may increase with age,
<br />since a higher frequency of reproduction is ex-
<br />hibited by older rather than by young mature
<br />female white suckers.
<br />ACKNOWLEDGMENTS
<br />This study was part of a thesis submitted by
<br />the senior author in partial fulfillment of the
<br />requirements of the MS degree at the Univer-
<br />sity of Massachusetts-Amherst. This work was
<br />supported by the Massachusetts Cooperative
<br />Fishery Research Unit (MCFRU), jointly spon-
<br />sored by the US Fish and Wildlife Service, the
<br />Massachusetts Division of Fisheries and Wild-
<br />life, the Massachusetts Division of Marine Fish-
<br />eries and the University of Massachusetts. This
<br />paper is contribution No. 90 of the MCFRU.
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