This paper is an interpretive review of the "case histories" which documented the changes in each of the Laurentian Great Lakes for the 1971 symposium on Salmonid Communities in Oligotrophic Lakes (SCOL). It suggests that lakes Huron, Michigan, and Superior passed through a parallel series of stock changes after the invasions of those lakes by the sea lamprey. First, the lake trout and burbot stocks collapsed, and then with the relaxation of predation pressure rainbow smelt, deepwater cisco, and alewife stocks increased. Lake herring stocks collapsed in apparent response to the smelt increase. Whitefish were affected by sea lamprey but recovery after the control of the lamprey in lakes Michigan and Superior suggested that the exotic species had little influence. Lake Ontario differed from the other lakes in that it was inhabited by both sea lamprey and alewife before the turn of the century, and provided the reservoir from which these species expanded to colonize the upper lakes. Alewife apparently equilibrated early, but the evidence was that more recent perturbations allowed the sea lamprey to become a significant factor in the loss of the piscivores of Lake Ontario. Subsequent proliferation of ciscoes and smelt, and collapse of the herring, followed a sequence similar to that of the upper lakes. Lake Erie seemed to be similarly affected by loss of predator stocks, but its predominantly eutrophic character made the situation more complex. Overfishing was indicted in many early stock collapses, in the early invasion of the smelt in lakes Huron and Michigan and in the recent cisco declines of lakes Ontario and Huron. Eutrophication and more direct pollution stresses had mainly inshore impacts, but the similarity in the species sequencing in the oligotrophic Great Lakes suggested that although these factors may have supplemented the other effects, their influence before about 1950 was less than that of overfishing and the invasion of exotic species. Control of sea lamprey, overfishing, and eutrophication seemed attainable in the Great Lakes, but the only defense against further invasions by pest species appeared to be maintenance of sufficiently dense piscivore stocks to assure their suppression. Determining the levels of harvest appropriate to this provision will require intensified research.

Ecological, morphological, and electrophoretic variation among five allopatric Ontario lake whitefish (Coregonus clupeaformis) stocks was studied. The stocks differ in terms of diet, growth rate, movement patterns, fecundity, and egg and larval size. Morphologically, the five stocks were also different for characters such as number of gill rakers, number of pyloric ceca, and in size, adjusted for fork length, of the tail, dorsal fin, and the eye. Discriminant functions, derived from body measurements and meristic counts, classified specimens accurately into their lakes of origin. Highly significant allele frequency differences were found at 6 of the 32 electrophoretic loci examined. Standard genetic distances, derived from electrophoretic allele frequency differences, corresponded roughly to the order in which these stocks became isolated following retreat of the last continental glaciation. The genetic distance of the Opeongo stock from the other stocks is about one order of magnitude larger than the genetic distances among the other stocks. The Opeongo stock is also somewhat unusual ecologically, having different egg size and fecundity characteristics compared with the other stocks and being a member of a sympatric dwarf/normal pair. Dendrograms, derived from the Mahanalobis distances for the meristic variation and the Nei genetic distances for the electrophoretic variation, showed similar branching patterns, but the branching patterns for the morphometric versus the biochemical variation were different. A significant part of the morphometric variation among the stocks was related to differences in growth rates of the stocks, most body measurements being negatively correlated with growth rate. The Mahanalobis distances for the meristic variation (including pyloric ceca counts) were correlated with the standard genetic distances from the electrophoretic data. The ecological, morphological, and biochemical variation among the stocks, in relation to local adaptation, is discussed.Key words: lake whitefish, stock concept, genotype, phenotype, ecology, morphology, meristics, multivariate analysis, electrophoresis, growth, diet, fecundity

No abstract

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.

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