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Quantifying the multi‐dimensional nature of resource partitioning in‐situ represents a fundamental challenge for understanding how environmental conditions contribute to the co‐existence of sympatric species. For aquatic poikilotherms, the availability of temperatures at or near optima generally define the ranges and limitations of species biology and ecology. Specifically, how poikilotherms partition this abiotic resource remains a broader unknown in aquatic ecology.Alewife (Alosa pseudoharengus), deepwater sculpin (Myoxocephalus thompsonii), rainbow smelt (Osmerus mordax), and round goby (Neogobius melanostomus) co‐occur throughout Lake Ontario and are known to share common prey resources. Here, we used a combination of trophic tracers (stable isotopes), pollutants (polychlorinated biphenyls, PCBs), and bioenergetic modelling to illustrate resource partitioning of diet items and thermal habitat among Lake Ontario prey fish species. We predicted that the combined use of δ13C, δ15N, and PCBs will capture the multi‐dimensional nature of resource partitioning among coexisting species inhabiting similar compartments within this ecosystem.The δ13C and δ15N values confirmed our understanding of trophic relationships among these species. A bioenergetic model predicted temperature occupancies for each species and for individuals during the open water growing season when prey consumption rates are likely to be maximised and the PCB congener profiles were highly correlated with these predictions. Three‐dimensional niche modelling demonstrated that ecological tracer assimilation is probably a direct result of species behavioural thermoregulation during the open water growing season when temperatures are at or near physiological optima.These results demonstrate that the ability of aquatic poikilotherms to track optimal temperatures and exploit habitat and food resources is captured by their PCB congener profiles. Consumer PCB congener profiles integrate not only the specific prey resources consumed, but also the predominant thermal conditions under which those resources were acquired and assimilated and that subsequently regulate individual and species growth. Given their global ubiquity and capacity for interpretation under the assumptions applied to ecological tracers, consumer PCB profiles could greatly advance our understanding of the mechanisms regulating resource partitioning, especially among aquatic poikilotherms. [ABSTRACT FROM AUTHOR]

This study investigated polychlorinated biphenyl (PCB) bioaccumulation patterns across age classes of bluegill (Lepomis macrochirus) and cisco (Coregonus artedi) collected from Sharbot Lake, Ontario. For bluegill, lipid normalized concentrations of PCB congeners of log [K.sub.ow] < 6.8 did not demonstrate any significant increases across individuals 2-5 years of age. In similarly aged cisco, however, significant age-related increases in lipid normalized PCB concentrations were observed for the majority of these congeners. For PCBs of log [K.sub.ow] > 6.8, these congeners demonstrated significant and similar age-related fugacity increases in both species. These patterns indicated that the bioaccumulation of less hydrophobic PCB congeners in bluegill suggest quicker growth kinetics and demonstrate the potential of this species to achieve steady state within their lifetime. In contrast, PCB bioaccumulation patterns in cisco demonstrated that biomagnification and non-steady state kinetics better reflect the capacity of this species to bioaccumulate PCBs. These results demonstrated that for pollutants of log [K.sub.ow] < 6.8, growth dilution and age-specific metabolic rates are critical for understanding their bioaccumulation by freshwater fish. However, for increasingly hydrophobic pollutants, their bioaccumulation reflects the biology and ecology of these species in their respective warm-and cold-water habitats. Resume: Nous etudions les patrons de bioconcentration des biphenyles polychlores (BPC) au sein des differentes classes d'age chez des crapets arlequins (Lepomis macrochirus) et des ciscos de lac (Coregonus artedi) recoltes au lac Sharbot en Ontario. Chez le crapet arlequin, les concentrations normalisees par rapport aux lipides des congeneres des BPC de log [K.sub.ow] < 6,8 n'affichent aucune augmentation significative parmi les individus d'ages 2-5. Chez les ciscos de lac de meme age, on observe des augmentations significatives en fonction de l'age des concentrations normalisees de BPC par rapport aux lipides pour la majorite de ces memes congeneres. Pour les BPC de log [K.sub.ow] > 6,8, ces congeneres affichent des augmentations significatives de la fugacite reliees a l'age et semblables chez les deux especes. Ces patrons indiquent que la bioconcentration des congeneres des BPC moins hydrophobes chez les crapets laissent croire a une cinetique de croissance plus rapide et demontrent le potentiel qu'a cette espece d'atteindre l'etat d'equilibre au cours de sa vie. En revanche, les patrons de bioconcentration chez les ciscos de lac demontrent que la bioamplification et une cinetique sans etat d'equilibre representent mieux la capacite de cette espece a accumuler biologiquement les BPC. Nos resultats demontrent que, pour les polluants de log [K.sub.ow] < 6,8, la dilution de la croissance et les taux metaboliques specifiques a l'age sont essentiels pour comprendre leur bioconcentration chez les poissons d'eau douce. Cependant, dans le cas des polluants de plus en plus hydrophobes, leur bioconcentration reflete la biologie et l'ecologie des especes dans leurs habitats respectifs d'eau chaude et froide. [Traduit par la Redaction], Introduction The bioaccumulation of polychlorinated biphenyls (PCBs) by fish species is predicted to proceed through bioconcentration and biomagnification mechanisms during an animal's lifetime (Sijm et al. 1992; Russell et al. [...]

This study used long-term biomonitoring data on lake trout (Salvelinus namaycush) collected from Lakes Erie, Ontario, Huron, and Superior between 1995 and 2004 to investigate latitudinal and temporal trends in body mass and energy density of this top predator in the Great Lakes. Lake trout average body mass and energy density were observed to have negative relationships with latitude that primarily reflected patterns in lake productivities. Temporal declines in energy density occurred for >80% of all lake trout age classes collected from each of the four lakes between 1995 and 2004. von Bertalanffy (VBL) growth models describing the relationships between fish energy density and age demonstrated decreased growth of lake trout energy density during 2000-2004 relative to 1995-1999. VBL growth coefficients (k) and the slopes describing the rates of change in lake trout energy density were negatively correlated with the total number of lake trout and salmonid individuals released into these lakes during this study. We hypothesize that the temporal declines in lake trout body mass and energy density are a manifestation of a bioenergetic bottleneck for this species due to their inability to efficiently compete with non-native salmonids for depleted prey populations. Notre etude se base sur des donnees de surveillance biologique a long terme des touladis (Salvelinus namaycush) recoltees aux lacs Erie, Ontario, Huron et Superieur entre 1995 et 2004 et vise a determiner les tendances latitudinales et temporelles de la masse corporelle et de la densite energetique de ce predateur superieur dans les Grands-Lacs. La masse corporelle et la densite energetique moyennes du touladi sont en relation negative avec la latitude, ce qui est le reflet principalement de patrons de productivite lacustre. Il s'est produit un declin de densite energetique chez >80 % de toutes les classes d'age de touladis recoltees dans chacun des quatre lacs entre 1995 et 2004. Des modles de croissance de von Bertalanffy (VBL) decrivant la relation entre la densite energetique et l'age des poissons demontrent une croissance reduite de la densite energetique des touladis en 2000-2004, par rapport a 1995-1999. Les coefficients de croissance VBL (k) et les pentes decrivant les taux de changements de la densite energetique chez les touladis sont en correlation negative avec le nombre total de touladis et de salmonides individuels liberes dans ces lacs durant la periode d'etude. Nous posons l'hypothse selon laquelle les declins temporels de la masse corporelle et de la densite energetique des touladis sont une manifestation du goulot d'etranglement que connait cette espce a cause de son inaptitude a faire une competition efficace avec les salmonides non indignes pour l'obtention des populations reduites de proies. [Traduit par la Redaction], Introduction As part of its Contaminants Surveillance Program, Fisheries and Oceans Canada (DFO) has collected lake trout (Salvelinus namaycush) annually from the Great Lakes since 1977. The objective of this [...]