Physiologic, toxicologic, and population responses of brook trout to acidification: Interim report of the lake acidification and fisheries project: Final report

This report overviews investigations of the ''Lake Acidification and Fisheries'' (LAF) project into the effects of surface water acidification on brook trout (Salvelinus fontinalis) populations. Of the six life stages examined, freshly-fertilized eggs were the most sensitive to reduced pH. In contrast, aluminum was most toxic to fry, juvenile, and adult fish. Increased calcium concentrations reduced the toxic effects of acid/aluminum exposure at all life stages. Little evidence was found to indicate that exposure to acidic waters affects oocyte development or production, suggesting that direct mortality plays a larger role in losses of brook trout populations from acidic waters. For fry and adult fish, the major toxic mechanism of acid/aluminum exposure seems to be disturbance of normal ion regulation at the gill, but aluminum exposure can cause respiratory impairment as well. Using results from LAF toxicity studies and available field data, a modeling framework was developed that predicts the probability of presence or absence of brook trout populations, based ion surface water chemistry. In addition, this framework can be used to evaluate changes in this probability caused by changes in water chemistry (e.g., liming), stocking rates, or fishing pressure. 129 refs., 37 figs., 8 tabs.