972. Effects of eutrophication on salmonid communities in oligotrophic lakes. J' Fish' Res. Bd. Canada 29:975-983.Oligotrophic lakes respond to progressive eutrophication by a sequence of predictable events. Increased nutrient loads and subsequent increased plant production result in alterations in the abiotic environment, including changes in the color and transparency of the water, increased turbidity, oxygen depletion in the hypolimnion, and increased chemical stratification. The physico-chemical changes precipitate biotic changes among the phytoplankton, littoral algae, zooplankton, and benthos. The salmonid community may respond initially with an increased body growth rate in various taxa and a higher incidence of parasitism, but later inhibition of natural reproduction occurs, and finally, the taxa are replaced by others that can survive in the changed environment.A relation between natural nutrient loading (expressed in terms of a morphoedaphic index) and yield (both quantitative and qualitative) is proposed as an aid to determining the natural successional status of a lake. Knowing the natural baseline of a particular lake the fisheries managers can judge the nature and size of responses due to cultural nutrient loading and then alter the rate of cultural nutrient loading to modify the ecological effects, or they can use biological engineering to capitalize on the present conditions'Among the most important effects of eutrophication is the increased vulnerability of sedentary discrete stocks to changes in other stresses such as fishing. Corsv, P. J., G. R. SraNcr,nn, D. A. Hunuv, .qNo A. M. McCoMers. 1972. Effects of eutrophication on salmonid communities in oligotrophic lakes. J. Fish. Res. Bd. Canada 29:975-983.

Historical and contemporary data on lake whitefish (Coregonus clupeaformis) from the Ontario waters of Lake Huron were examined for evidence of stocks with the objective of defining population boundaries. We delineated the spatial distribution of five stocks from tag–recapture data and the general location of six additional stocks on the basis of population parameters such as growth rate, age structure, and abundance trends.Samples of fish collected (summer and fall) from 5 of the 11 potential stocks were evaluated on the basis of 11 morphometric and 7 meristic characters. We also examined osseometric features such as shape of scales and otoliths, and electrophoretic characteristics at 32 loci associated with 12 enzyme systems.The summer and fall samples for each group were generally not significantly different. For the phenotypes examined electrophoretically, each stock was in Hardy–Weinberg equilibrium; 12 of the 32 loci considered were polymorphic and 4 of the 10 possible genetic distances differed significantly from zero.The Inner Basin stock was distinctly different from all other stocks. The Blind River stock was also found to be different by osseometrics, but not by morphometrics or electrophoresis. Osseometrics separated the stocks by basin of origin. Two stocks, Outer Basin and Burnt Island, appeared to be the most similar and could be separated from each other only on the basis of growth rate and tagging data. These two stocks are adjacent to each other in the main basin of Lake Huron, along the south shore of Manitoulin Island.Whitefish stocks of Lake Huron represent groups of fish that differ phenotypically and genotypically in varying degrees, are spatially separated, and behave as cohesive units. We conclude that they should be regarded as functional units for management purposes.Key words: lake whitefish, Coregonus clupeaformis, Lake Huron, stocks, tag–recapture data, population structure, morphometrics, meristics, osseometrics, scale and otolith shape, starch gel electrophoresis, biochemical genetic variation

Lake Huron is a large, deep, oligotrophic lake, centrally located in the St. Lawrence Great Lakes system. Manitoulin Island and the Bruce Peninsula divide the lake into the relatively discrete water masses of the North Channel, Georgian Bay, and Lake Huron proper. Water quality in Lake Huron has deteriorated only slightly since the early 1800s. The only significant changes are confined to areas adjacent to centers of human activity, chiefly Saginaw Bay and various harbours and estuaries in Georgian Bay and the North Channel. The lake has supported a commercial fishery which has produced annual catches as high as 13000 metric tons. A dramatic decline in landings of commercially valuable species and an instability in fisheries resources has occurred in all areas of the lake since the 1940s. This depression of populations of valued species was associated with the accidental introduction of the sea lamprey, instances of overfishing and deterioration of water quality in Saginaw Bay. The present depressed state of the fisheries will undoubtedly persist until sea lamprey control is achieved and climax predators are reestablished. Governments are proceeding toward the establishment of water quality criteria and fishery management practices which, hopefully, will stabilize the fisheries and prevent further deterioration of the aquatic environment.

Conventional exploitation is described as an opportunistic process directed initially toward the largest members of the fish community and preferentially selecting those species for as long as the fishery persists. Some responses of percid communities to exploitation stress are similar to those previously described for marine stocks and salmonid communities. The most conspicuous responses of percids are changes in variability of recruitment, increases in growth rate, and reductions in the ages of first spawning. The least tractable and potentially most malefic responses are changes in genetic stocks and in interspecific relationships within the aquatic community. Three models are proposed for early detection of exploitation stress in fish stocks or communities. Key words: Percidae, exploitation, community ecology

Anglers on Lake Miltona, Minnesota, who were given fishing information (catch rate and average weight of available species) generally did not show significant differences in satisfaction or expectations from a control group of anglers who were not provided with this information. Exceptions were the successful anglers for walleye Stizostedion vitreum and largemouth bass Micropterus salmoides. Anglers were more satisfied with nonconsumptive aspects of the fishing experience (natural beauty of the lake, water quality, weather, quality of the access to the lake by boats) than with consumptive aspects (size and number of fish caught). Expectations of fish size were more realistic than expectations of catch rate: 67% of the anglers evaluated the average walleye (determined by creel surveys to be 2.1 lb) as “about what I expected,” whereas 47% evaluated the average walleye catch rate (0.2 fish/h) as “less than I expected.” Walleye anglers showed higher expectations of walleye catch rate than other anglers, and fishing experience was positively related to expectations of catch rate. Angler expectations of walleye size were significantly related to both fishing and trip satisfaction.