From the 1940s on, the Bay of Quinte was subjected to increased point-source phosphorus loading. This and other stresses (exploitation, fish species invasion, and perhaps climate fluctuation) altered the productivity of the ecosystem and community structure. In the late 1970s, point-source loading was greatly reduced. At the same time, walleye (Stizostedion vitreum vitreurn) produced the largest year class ever recorded and surged to abundance greater than those seen in the 1950s before its collapse. Also, the dominant invader white perch (Morone americana), which had flourished in the 1960s and 1970s, was almost eliminated by a low-temperature kill. Studies of the bay ecosystem before and after these events indicated that while nutrients and algae responded to changes in nutrient loadings, changes in secondary producers hinged on the changes in the fish community. Use of Borgmann's biomass size spectrum model provides a focus for the interpretation of nutrient- and predator-related changes in biomass distribution. Deviations of the biomass spectrum are interpreted. The biomass and production spectra are linked to both phosphorus concentrations, observed and predicted, and to fishery exploitation rates. The results suggest that while nutrients control the overall biomass of the ecosystem and the slope of the biomass spectrum, trophic interactions and perturbations (e.g. exploitation) determine the degree to which a smooth biomass spectrum is achieved.

Lakes, streams, and their watersheds in large parts of the world have little ability to neutralize acidity associated with precipitation. Resource management agencies are concerned with the extent of these impacts including the loss/hazard to key fish species, and the likely status of these aquatic systems given alternate emission control scenarios. Two models designed to provide such a large-scale risk assessment are presented herein. The strengths and weaknesses are identified. Since models draw together the best of our theories, experimental, and survey data, these are compared with existing knowledge, theories, and data.

We propose that the optimum habitat of the percid fishes Perca flavescens, P. fluviatilis, Stizostedton vitreum vitreum, and S. lucioperca in lakes may be defined by the littoral and sublittoral environmental conditions equivalent to those in large, temperate rivers. Analogous habitat conditions include sand or gravel substrate, low current velocity, reduced light penetration (Stizostedion spp. only), temperatures optimal for growth and reproduction, and well-oxygenated spawning substrates. The species' evolutionary origins and reproductive patterns also reflect their riverine ancestral habitat. Evidence in support of the hypothesis is derived from the diversity of papers contributed to the PERCIS Symposium. Key words: Percidae, habitat, theory, Perca, Stizostedion

The history of Great Lakes benthic research from 1870 to the present is briefly reviewed. An examination of the status of taxonomic work on benthic components, and a consideration of the zoogeographical history of the benthos leads to a discussion of bottom communities and macroinvertebrate production in the five major lakes.Profundal communities throughout the lakes are dominated by the glaciomarine relict amphipod Pontoporeia affinis and various species of Oligochaeta, Sphaeriidae, and Chironomidae. The specific composition of these components, and natural and recently imposed changes in their proportions within communities are examined. Population densities and standing stocks, and the proportion of oligochaetes in communities, all tend to increase in response to a natural gradient in productivity inferred from increasing concentrations of parameters such as organic matter and water hardness. Man's influence on water quality anywhere along this gradient compounds the effects of natural factors towards tubificid communities of predictable species composition: Limnodrilus hoffmeisteri, L. claparedeianus, L. cervix, L. maumeensis, Peloscolex multisetosus, and often Tubifex tubifex. The ameliorating influence of water depth is shown in Lake Erie where the change in community composition reflects improving profundal water quality from west to east — a reversed model of the Great Lakes system as a whole.