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

Abstract

LACROIX, G. L. 1987. Fish community structure in relation to acidity in three Nova Scotia rivers. Can. J. Zool. 65: 2908-2915.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 apH range of 4.7-5.4 than in the stream with apH 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 O+ . 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.LACROIX, G. L. 1987. Fish community structure in relation to acidity in three Nova Scotia rivers. Can. J. Zool. 65 : 2908-2915.La prksence, I'abondance et la structure des classes d'iges des especes de poissons indigenes ont Ct C comparCes en trois rivieres de la Nouvelle-Ecosse a pH diffkrents au cours d'une pCriode de 24 rnois. La riviere a pH 4,5-5,O Ctait caractCrisCe par I'absence d'especes sensibles a I'aciditC et par la densit6 rCduite des poissons. L'abondance des poissons Ctait plus faible dans la riviere a pH 4,7-5,4 que dans la riviere a pH 5,6-6,3. Les jeunes saurnons et les cyprinidCs Ctaient les especes les plus abondantes dans la riviere la rnoins acide. Leurs densitCs Ctaient considCrablement moindres dans la riviere a pH 4,7-5,4 et les jeunes classes d'ige de cyprins Ctaient rares ou absentes. Les saumons et les jeunes cyprins Ctaient absents de la riviere la plus acide. En revanche, les anguilles Ctaient plus abondantes dans les deux rivieres acides a pH infkrieurs a 5,5 et elles reprksentaient une proportion de la biomasse des poissons de plus en plus importante aux pH les moins ClevCs. Le Meunier noir Ctait l'espece la plus abondante aux pH les plus bas, mais sa biomasse Ctait faible car la plupart des classes d'ige supCrieures a 0 + manquaient. Quelques autres especes Ctaient prksentes dans la riviere la plus acide, mais elles Ctaient peu abondantes et comptaient peu de poissons d'ige avancC. La repartition des poissons observCe dans ces trois rivikres est attribuable aux pH diffkrents.

ACIDIFICATION AND FISH OCCURRENCE IN THE UPPER CHEAT RWER DRAINAGE, WEST VIRGINIA1

“…Other researchers have studied streams with different bedrock types than those of the Cheat River basin, and also found fewer fish species in streams draining bedrock of low buffering capacity (e.g., Lacroix, 1987;Turnpenny et al, 1987;Webb et al, 1989;Pinder and Morgan, 1995). In addition, tributaries associated with the Mauch Chunk group typically had fewer fish species than streams associated with Chemung and Hampshire bedrock.…”

Stability of Microhabitat Use by Brook Trout and Juvenile Atlantic Salmon after Stream Acidification

“…This pH-related mortality was not preceded by a shift in microhabitat use by Atlantic salmon. Numbers of brook trout did not decrease markedly after acidification episodes, and all age-classes were prevalent in the brook, reflecting the greater tolerance of brook trout than of Atlantic salmon to low pH (Lacroix 1987).…”

“…In our study, brook trout apparently did not gain a competitive advantage over juvenile Atlantic salmon during acidification episodes, and they did not displace the latter to less favorable habitat. Juvenile Atlantic salmon are usually dominant over brook trout (Gibson 1973(Gibson , 1978, whereas the latter are more resistant at low pH (Lacroix 1987). We had expected Atlantic salmon to have difficulty retaining preferred microhabitat because of the greater degree of physiological stress in Atlantic salmon than in brook trout at similar low pH (Lacroix and Townsend 1987;Lacroix et al 1990).…”

Timing of episodic acidification in Atlantic salmon rivers influences evaluation of mitigative measures and recovery forecasts

“…1). Physical characteristics of the Westfield River and the hydrology of the drainage basin were described by DeGraeve and Peterson (1982) and Lacroix (1987bLacroix ( , 1989. A flow gauging station was established on the lower Westfield River in 1981, and daily data covering the period 1981-1990 were obtained for discharge (m 3 /s) in the annual surface water data summaries for the Atlantic provinces (site 01EE004) from the Water Resources Branch of Environment Canada (e.g., Water Survey of Canada 1989).…”

“…This represents a potential production area of 25.43 ha of which four reaches (totaling 6.53 ha), with suitable spawning and rearing habitat for juvenile salmon, were intensively sampled. The reaches above Tupper Lake represent 12.15 ha of potential production area that no longer support juvenile salmon because of chronic acidification (Lacroix 1987b). The lower Westfield River was modeled as a single reach between Tupper Lake to its confluence with the Medway River because physical (substrate size and surface gradient), hydrochemical (flow and pH), and biological (measured juvenile abundance) characteristics were very consistent among productive reaches.…”