Complete Estimates of Repreductive Success in a Closed Population of Smallmouth Bass (Micropterus Dolomieui)
1990
Raffetto, Nancy S. | Baylis, Jeffrey R. | Serns, Steven L.
We conducted a 4—yr study of 154 parental male smallmouth bass (Micropterus dolemieui) and 982 nests in a closed natural population (a temperate seepage lake in Wisconsin). Our goal was to test common assumptions and hypothesis about reproduction in natural populations. Mark—recapture techniques were used to measure changes in the demography, age—specific sex ratios, and mortality rates of the whole population. An area—density method was used to estimate the number of eggs spawned in each sampled males's nest, and we volumetrically estimated the number of larvae produced by sampled males. The lake is closed to migration, allowing us to accurately estimate total population size and individual variance in reproductive success (RS) for each year without having to assume a demographically stable population. We found that a large proportion of non—breeding adults of both sexes were present in each year. We compared estimates of variance in RS among subsets of males and females in the population to examine the effect on variance when mature non—breeding individuals are included in the analysis. Excluding non—breeders resulted in the true variation in RS being underestimated and the mean RS overestimated, both by a factor of °3 for males and 2 for females. Most male bass spawned only once in their lifetimes, and size at age 3 yr appeared to determine whether a male spawned or postponed reproduction. Males that bred at age 3 yr were among the largest of their cohorts, and males that bred at age 5 yr were among the slowest growing. There may be greater selection on adults for opportunity to breed than there is selection in RS among breeding adults in this population.
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