Oligotrophic Species Research Articles

The Future of Salmonid Communities in the Laurentian Great Lakes

The effects of human population growth, industrialization, and the introduction of marine fishes have reduced the suitability of each of the Great Lakes for oligotrophic fish communities. The ultimate consequence has been a reduction of fishery productivity that has ranged from extreme in Lake Ontario to moderate in Lake Superior. If measures are not taken to alleviate the adverse effects of marine invaders and trends in environmental quality, a major reduction in fishery productivity can eventually be expected throughout the Great Lakes.Prospects for the next century will be improved if the lakes can be intensively managed. More stringent control of the sea lamprey (Petromyzon marinus), and subsequent reduction of the alewife (Alosa pseudoharengus), by the reestablishment of populations of large piscivores, should permit the recovery of some of the previous predator and prey species, or the development of populations of new species that are more compatible with a reduced number of lampreys. Even if marine species can be reduced greatly, the full restoration of the former fishery productivity remains uncertain and will require a high degree of coordination among all management and research agencies that have responsibilities on the Great Lakes.Unfavorable trends toward progressive degradation of water quality pose the greatest threat to restoration of the fishery resources of the Great Lakes. Where changes in water quality have been the greatest, oligotrophic species have become scarce or absent, and in the deepwater regions no other species have reoccupied the vacated niches.

Chemical Composition and Phytoplankton of Lakes in Southern Ontario

Water chemistry in southern Ontario lakes is determined primarily by surface and bedrock geology and the impact of cultivation. In areas of uniform bedrock, elevation and lake size are shown to be important. Total dissolved solids give a poor indication of the electrolyte content of lakes, because of the varied geology. Four main lake types are recognised: (1) base-poor lakes, frequently dystrophic, found on the Precambrian shield; (2) moderately base-rich lakes, in the Bancroft–Rideau lakes region, related to the frequent occurrence of more easily weathered rocks; (3) base-rich lakes found in the limestone region south of the shield, and receiving abundant drainage from cultivated land; and (4) base-rich lakes with high levels of magnesium draining from Silurian dolomitic limestone bedrock and dolomite-rich glacial tills.Phytoplankton populations were found to be related in part to the chemical composition of lake waters. Certain species such as Tabellaria flocculosa and to a lesser extent Asterionella formosa and Dinobryon divergens were associated mainly with base-poor lakes; a far larger number of species, including Synedra acus, Pediastrum duplex, Scenedesmus quadricauda, Cyclotella meneghiniana, Synedra ulna, and Cyclotella kutzingiana, were significantly associated with base-rich conditions.An association diagram for all the species found in the lakes showed several groupings, mostly of species that prefer base-rich conditions. Few species confined to base-poor lakes were found to form associations. Apparent associations between oligotrophic species and species known to prefer eutrophic lakes can be explained by the fact that nutrients were depleted at the time of the survey.