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Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish are sympatric benthivores in Lake Huron that are thought to coexist via niche partitioning. However, little is known about long-term resource use and niche overlap across different temporal scales. We used a multiyear (2010-2012) and multi-tissue (liver, muscle, and bone layers) isotopic niche analysis to characterize and compare resource use by lake and round whitefish across several time scales. Lake whitefish consistently used more diverse, [sup.13]C-depleted (mean [delta][sup.13]C = - 21.9[per thousand]) and [sup.15]N-enriched (mean [delta][sup.15]N = +9.3[per thousand]) resources than round whitefish (mean [delta][sup.13]C = -18.2[per thousand]; mean [delta][sup.15]N = +8.3[per thousand]). Niche overlap occurred only in liver, representing the spawning period, while niche segregation was highest in juvenile life stages. Individuals of both species made variable resource shifts among time periods, suggesting that spawning aggregations are composed of individuals representing a variety of feeding strategies and locations. Our study confirms that differential resource use is an important strategy for these fish as adults and demonstrates life-long niche partitioning beginning before age-2. Le grand coregone (Coregonus clupeaformis) et le menomini rond (Prosopium cylindraceum) sont des benthophages sympatriques dans le lac Huron qui coexisteraient grace a la separation des niches. L'utilisation des ressources a long terme et le chevauchement des niches a differentes echelles temporelles demeurent toutefois meconnus. Nous avons utilise l'analyse des niches isotopiques sur plusieurs annees (2010-2012) et dans plusieurs tissus (foie, muscles et couches des os) pour caracteriser et comparer l'utilisation des ressources par le grand coregone et le menomini rond a plusieurs echelles temporelles. Les grands coregones utilisaient uniformement des ressources plus variees, appauvries en [sup.13]C ([delta][sup.13]C moyen = -21,9 [per thousand]) et enrichies en [sup.15]N ([delta][sup.15]N moyen = +9,3 [per thousand]) par rapport aux menominis ronds ([delta][sup.13]C moyen = -18,2 [per thousand]; [delta][sup.15]N moyen = +8,3 [per thousand]). Un chevauchement des niches n'a ete observe que dans le foie, qui represente la periode de frai, alors que la segregation de niches etait maximum chez les individus aux stades juveniles. Les individus des deux especes changeaient de ressources de maniere variable selon la periode, ce qui donne a penser que les regroupements au moment du frai comprennent des individus representant un eventail de strategies et de lieux d'alimentation. L'etude confirme que l'utilisation differentielle des ressources est une importante strategie pour ces poissons a l'age adulte et demontre une separation des niches qui dure toute la vie et commence avant l'age de 2 ans. [Traduit par la Redaction], Introduction Lake (Coregonus clupeaformis) and round (Prosopium cylindraceum) whitefish are important members of a mixed coregonid community in Lake Huron. As benthivores, both species are ecologically valuable for facilitating energy [...]

Anthropogenic activities may facilitate undesirable hybridization and genomic introgression between fish species. Walleye (Sander vitreus) and sauger (Sander canadensis) are economically valuable freshwater species that can spontaneously hybridize in areas of sympatry. Levels of genomic introgression between walleye and sauger may be increased by modifications to waterbodies (e.g., reservoir development) and inadvertent propagation of hybrids in stocking programs. We used genotyping by sequencing (GBS) to examine 217 fish from two large reservoirs with mixed populations of walleye and sauger in Saskatchewan, Canada (Lake Diefenbaker, Tobin Lake). Analyses with 20,038 (r90) and 478 (r100) single nucleotide polymorphisms clearly resolved walleye and sauger, and classified hybrids with high confidence. F1, F2, and multigeneration hybrids were detected in Lake Diefenbaker, indicating potentially high levels of genomic introgression. In contrast, only F1 hybrids were detected in Tobin Lake. Field classification of fish was unreliable; 7% of fish were misidentified based on broad species categories. Important for activities such as brood stock selection, 12 of 173 (7%) fish field identified as pure walleye, and one of 24 (4%) identified as pure sauger were actually hybrids. In addition, two of 15 (13%) field‐identified hybrids were actually pure walleye or sauger. We conclude that hybridization and introgression are occurring in Saskatchewan reservoirs and that caution is warranted when using these populations in stocking programs. GBS offers a powerful and flexible tool for examining hybridization without preidentification of informative loci, eliminating some of the key challenges associated with other marker types. [ABSTRACT FROM AUTHOR]