Recent Changes in the Aquatic Food Web of Eastern Lake Ontario

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.

Status and Trends of the Lake Ontario Macrobenthos

“…Enfornation on the size structure of the population is not available, but such a shift would most likely be caused by an increase in fish predation (McDonald et al 1990). In the profundal, as noted earlier, fish predation was minimal when the biomass decline occuned (late %96Os/ealy 1978s), while major changes in fish populations in the Kingston Basin during this period were not apparent (Christie et al 1987). On the other hand, a comphson between length-weight relationships for Pontoporee'a in 1967-68 and 1981-82 shows a major decline in the weight per unit length, dong with a corresponding increase in the metabolic rate (Fig.…”

Evaluation of Lake Ontario salmonid niche space overlap using stable isotopes

“…Stable isotope values for Lake Ontario round goby caught deeper than (N15 m) are significantly higher in δ 15 N and more depleted in δ 13 C relative to nearshore (b15 m) round goby (OMNR unpublished data) suggesting that the possibility of round goby inhabiting deeper depths could be contributing a significant portion to lake trout diets. In addition, slimy sculpin (Cottus cognatus) and deepwater sculpin (Myoxocephalus thompsonii) had contributed to lake trout diets historically (Christie et al, 1987;Rand and Stewart, 1998), but with the establishment of alewife and smelt in the lake, densities of sculpin decreased (Christie et al, 1987;Mills et al, 2003). Recently, deepwater sculpin abundances have increased (Ontario Ministry of Natural Resources, 2013) and may once again be diversifying the diet of lake trout.…”

Lake Ontario: food web dynamics in a changing ecosystem (1970–2000)

“…Most notable were sea lamprey control (Pearce et al 1980), quotas to regulate commercial fishing effort, and stocking of salmonid predators to control exotic prey fish like alewife (Christie et al 1987a). Further control measures included efforts to minimize loadings of mercury, chlorinated hydrocarbons of DDT (dichlorodiphenyltrichloroethane) and PCBs (polychlorinated biphenyls), and municipally produced phosphorus (Minns et al 1986).…”