Population Biology of the Brown Bullhead (Ictalurus nebulosusLesueur)

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Abstract
A population of brown bullheads (Ictalurus nebulosus Leuseur) in Muskellunge Lake, New York was investigated to determine population density, age structure, sex ratio, fecundity, survivorship, growth, and the intrinsic rate of population increase. The population density estimate was 887 (664 ≤ N ≤ 1424) per ha. The instantaneous rate of survivorship for females (0.26) was significantly lower than the rate for males (0.33). Fecundity averaged 2169 (1841 ≤ N ≤ 2497) per female. Differences in fecundities among individuals were not correlated with differences in weight or length. The number of eggs produced per gram of weight decreased with fish size. We hypothesize that lower female survivorship is related to higher reproductive effort, and examine a natural selection mechanism to explain variations in fecundity. Population characteristics were summarized in a life table, although this analysis may have been influenced by fluctuations in year class strength.

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