Fish community structure in relation to acidity in three Nova Scotia rivers

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Abstract
The occurrence, density, and age-class structure of endemic fish species were compared over a period of 24 months in three Nova Scotia streams of differing pH. The absence of acid-sensitive species and very low densities of fish characterized the stream with a pH range of 4.5–5.0. Fish densities were lower in the stream with a pH range of 4.7–5.4 than in the stream with a pH range of 5.6–6.3. Juvenile salmon and cyprinids were the most abundant species in the least acidic stream. Their densities were considerably lower in the stream with pH levels of 4.7–5.4, and the young age-classes of the cyprinid species were rare or absent. Both salmon and cyprinids were absent in the most acidic stream. In contrast, American eels were most abundant in the two streams with pH levels less than 5.5, and they accounted for an increasingly large proportion of the fish biomass at the lowest pH levels. White sucker was the most abundant species at the lowest pH levels, but its contribution to biomass was unimportant because of the absence of most age-classes older than 0+. Several other species found in the most acidic stream were not very abundant, and old age-classes were usually absent for most of these. The observed distributional patterns were considered to be mostly pH related.

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