An Evaluation of the Effects of Atmospheric Acidic Deposition on Fish and the Fishery Resource of Canada

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Abstract
In Canada, 7.6% of our nation's surface area is water, and approximately 38% of this is found in regions susceptible to acidic atmospheric deposition. We estimate that 390 000 lakes in eastern Canada are sensitive to acidification, and provide significant revenue through the sport fishery to the economy. Evidence indicates that Sudbury lakes and Nova Scotian rivers acidified in the 1950's, '60's, and probably early '70's. Well documented cases of loss of fish species or production due to acidification are restricted to these two regions. However, the documentation of low pH lakes in areas of high acid loading suggest that acidification is more widespread. Recent increases in pH in some Sudbury and Algoma lakes, concomitant with reestablishment of fish populations, indicates that chemical and biological recovery is possible. Evidence from diverse experimental approaches–surveys, bioassays, and whole lake manipulation – are supportive in identifying fish responses to acidification. Fish community response is dependent upon several factors: complexity of the community, stage of acidification, species sensitivity, and availability of tolerant species to invade. If replacement of extirpated species by tolerant ones occurs, total fish biomass may remain stable until critical depauperation. It is unlikely we will be able to directly document further losses due to acidification.

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