The fish populations of some streams in Wales and northern England in relation to acidity and associated factors

• Published in: Journal of Fish Biology
• Main Authors: Turnpenny, A. W. H., Sadler, K., Aston, R. J., Milner, A. G. P., Lynam, S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1987
• Subjects: Anguilla anguilla
• Online Access: http://dx.doi.org/10.1111/j.1095-8649.1987.tb05246.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1095-8649.1987.tb05246.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1095-8649.1987.tb05246.x

Electrofishing and water quality surveys were carried out on 60 upland moorland streams in central and north Wales and the Peak District of England (south Pennines). A number of biological characteristics of the fish populations were recorded, including species representation, population density and biomass and, for brown trout, Salmo trutta L., only, growth, condition factor and diet. The stream waters were also analysed over a 2‐year period for pH, calcium, aluminium and the heavy metals copper, zinc and lead. Mean pH levels in the streams ranged from 5.0 to 7.6, with calcium concentrations in the range 0.80–27 mg 1 −1 . Trace metal concentrations (Al, Cu, Zn, Pb) tended to be elevated in the more acid streams. The latter had fewer fish species, and a higher proportion was fishless, 73% at pH < 5.5 compared with 6% at pH >6.5. Trout and eels, Anguilla anguilla L., predominated at lower pH values, but at reduced population levels. Dietary composition and stomach fullness of trout were similar throughout the stream pH range. More than 40% of the diet was derived from surface and terrestrial sources, supplementing autochthonous items. Growth (as back‐calculated length to end of first year of life) and condition factor did not vary significantly with respect to stream acidity. It is thus concluded that the impoverishment of trout populations in the more acid streams was not a second‐order effect acting through the lower trophic levels. Water quality acting directly on fish would appear to account for the poor status of salmonid fisheries in acid streams. Absence or paucity of salmonids was related to high levels of labile monomeric aluminium (>40 μgl −1 ) or Cu‐Zn‐Pb toxicity (>0.4 t‐LC50 to rainbow trout, Salmo gairdneri Richardson). Limiting values in this study correspond well with published laboratory and field data.