||Synthesis of Ecological and Fish-Community Changes in Lake Ontario, 1970-2000.
E. L., Mills ;
J. M., Casselman ;
R., Dermott ;
J. D., Fitzsimons ;
||Great Lakes Commission, Ann Arbor, MI.; Environmental Protection Agency, Chicago, IL. Great Lakes National Program Office.
Fish habitats ;
Fish management ;
Ecological changes ;
Natural resources management ;
Fish communities ;
Water quality ;
Fish stocks ;
Exotic species ;
Salmonid Communities in Oligotrophic Lakes (SCOL) ;
Great Lakes Fishery Commission ;
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We assessed stressors associated with ecological and fish community changes in Lake Ontario since 1970, when the first symposium on Salmonid Communities in Oligotrophic Lakes (SCOL I) was held (J. Fish. Res. Board Can. 29: 613-616). Phosphorus controls implemented in the early 1970s were undeniably successful; lower food-web studies showed declines in algal abundance and epilimnetic zooplankton production and a shift in pelagic primary productivity toward smaller organisms. Stressors on the fish community prior to 1970 such as exploitation, sea lamprey (Petromyzon marinus) predation, and effects of nuisance populations of alewife (Alosa pseudoharengus) were largely ameliorated by the 1990s. The alewife became a pivotal species supporting a multi-million-dollar salmonid sport fishery, but alewife-induced thiamine deficiency continued to hamper restoration and sustainability of native lake trout (Salvelinus namaycush). Expanding salmonine populations dependent on alewife raised concerns about predator demand and prey supply, leading to reductions in salmonine stocking in the early 1990s. Relaxation of the predation impact by alewives and their shift to deeper water allowed recovery of native fishes such as threespine stickleback (Gasterosteus aculeatus) and emerald shiner (Notropis atherinoides). The return of the Lake Ontario ecosystem to historical conditions has been impeded by unplanned introductions.