Brook trout production dynamics in the streams of a low fertility Newfoundland watershed

Production of brook trout Salvelinus fontinalis ranged from 99 to 651 g . 1 00 m(-2) . year(-1) among headwater streams of the Copper Lake watershed in insular Newfoundland. Ratios of annual production to mean annual biomass ( P/(B) over bar) ranged from 0.9 to 1.5 among the same streams. Empirical mo dels developed from stream salmonid populations in the United States succes sfully predicted modal production based on water alkalinity and P/(B) over bar ratios based on age-class structure of the populations. Differences in production among streams were consistent with previous work in low-fertilit y headwater systems, which suggests habitat attributes of the stream define salmonid production within the range dictated by the water fertility. The most important of these attributes in this study was food abundance. Substr ate composition and habitat complexity may have played secondary roles in d etermining production in the most productive stream.