1987. Recent changes i n the aquatic food web of eastern bake Ontario. Can. j. Fish. Aquat. Sci. 44(Suppl. 2): 37-52.During the past 18 yr there have been dramatic increases in piscivorous populations of walleye (Stizostedion vitreum) i n the Bay of Quinte and of planted lake trout (Salvelinus namaycush) and double-crested cormorants (Phalacrocorax auritus) i n the Kingston basin of Lake Ontario. This paper documents changes i n the prey stocks shared by these piscivores, including reduction i n size and abundance of the slimy sculpin (Cottus cognatus) with subsequent stock equilibration and unabated reduction i n the sine and abundance of rainbow smelt (Osmerus mordax), both owing to predation pressure from the lake trout. The third primary prey species, alewife (Alosa pseudoharengus), has not yet suffered severely from the depredations of the piscivores. Symptoms of the effects are discernible, however, and the implications of a possible collapse are discussed. Lake trout survivai and growth have not yet been affected by the changes i n prey availability, but their diet has shifted both i n response t o their own expanded size composition and relative abundance of the three prey species. Increased utilization of alewife makes the hunting of the trout more pelagic. Problems of obtaining representative samples of the prey are discussed.Au cours des dix derni$res annees, on a observe un accroissement phenomknal des populations piscivores de dore jaune (Stizostedion vitreum) dans la baie de Quinte et de touladi (Salvelinus namaycush) ensemence et de cormoran 2 aigrettes (Phalacrocorax auritus) dans le bassin de Kingston (lac Ontario). La prksente etude documente les changements dans les stocks de proies partagks par ces deux poissons piscovores, y compris la diminution de la taille et de I'abondance d u chabot visqueux (Cottus cognatus); cette diminution a ete suivie d'un equilibre d u stock et d'une baisse constante de la taille et de l'abondance de l'6perlan arc-en-ciel (Osmerus rnordax). Ces deux evenements sont le resultat de la pression par prkdation exercee par le touladi. Le gaspareau (Alosa pseudoharengus), la troisi&me principale proie, n'a pas encore beaucoup kt4 touche par la prkdation exercke par les piscovores. O n observe toutefois certaines incidences de cette pr6dation et on examine les cons6quences d'un effondrement possible. Chez le touladi, la croissance et O a survie n'ont pas encore etk touchkes par les variations d e disponibilite de proies mais son regime alimentaire a change e n reaction 2 I'expansion de sa composition par taille et % I'abondance relative des trois especes de proie. Etant donne que le touladi consomme plus de gaspareau, la recherche de cette proie s'effectue de plus en plus en milieu pelagique. O n traite des probl$rnes d e collecte d'echantillons representatifs.
Western Lake Ontario sediments record a till–mud–till sequence over bedrock and a thick layer of partly distorted glaciolacustrine clay unconformably overlying this. Another unconformity separates this clay from younger fine (lacustrine?) deposits, which are also distorted. Modern foreset and bottomset beds of the Niagara River overlap the lacustrine and glaciolacustrine deposits.In eastern Lake Ontario, thick glaciolacustrine clays overlie bedrock and the infilling ice-marginal deposits. These glaciolacustrine clays are severely distorted, and in the deepest parts of the area patches of overlying lacustrine (?) clay are preserved. A distorted terracelike deposit is preserved at higher elevation in the St. Lawrence trough. Bedrock, lag gravels, and sandy deposits characterize shallow-water areas.We suggest that after the fall of lake levels in the Lake Ontario basin, during the post-Iroquois lake phases, glaciolacustrine clays were subject to distortion by ice action at the time of the Greatlakean stadial. This deformation was more severe at the east end of the basin. At its lowest level, the surface of early Lake Ontario following the post-Iroquois phases was below the present lakebed in much of western Lake Ontario. Ice-wedge casts formed in sediments at both ends of the basin, soon after the initiation of early Lake Ontario, and are correlated with the Algonquin (St. Narcisse) glacial phase. Whereas there are significant accumulations of modern mud in the western basin of Lake Ontario, in the Kingston basin there is little except in the St. Lawrence trough.
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