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Strain performance evaluations are vital for developing successful fishery management and restoration strategies. Here, we utilized genotypes from 36 microsatellites to investigate hatchery strain contribution to collections of naturally produced lake trout (Salvelinus namaycush) sampled across Lake Michigan. Strain composition varied by area, with recoveries of Seneca Lake strain exceeding expectations based on stocking records in northern Lake Michigan but performing similarly to other strains in southern Lake Michigan. Interstrain hybrids were present at moderate frequencies similar to expectations based on simulations, suggesting that strains are interbreeding randomly. We hypothesize that the superior performance of the Seneca Lake strain in northern Lake Michigan is partially due to adaptive advantages that facilitate increased survival in areas with high mortality from sea lamprey (Petromyzon marinus) predation, such as northern Lake Michigan. However, when this selective pressure is lessened, the Seneca Lake strain performs similarly to other strains. Our study demonstrates that strain performance can vary across small spatial scales and illustrates the importance of conducting thorough strain evaluations to inform management and conservation. Les evaluations de la performance de lignees sont d'importance vitale pour l'elaboration de strategies efficaces de gestion et de retablissement des ressources halieutiques. Nous utilisons les genotypes etablis a partir de 36 microsatellites pour examiner la contribution de lignees issues d'ecloseries a des collections de truites de lac (Salvelinus namaycush) produites naturellement prelevees a la grandeur du lac Michigan. La composition des lignees varie selon la region, les taux de recuperation de truites de la lignee du lac Seneca depassant les predictions basees sur les registres d'empoissonnement dans le nord du lac Michigan, alors que ces taux sont semblables a ceux d'autres lignees dans le sud du lac Michigan. Des hybrides issus du croisement de lignees sont presents a des frequences moderees semblables aux frequences predites sur la base de simulations, ce qui indiquerait que le croisement de lignees est aleatoire. Nous postulons que la meilleure performance de la lignee du lac Seneca dans le nord du lac Michigan decoule en partie d'avantages adaptatifs facilitant une survie accrue dans des secteurs de forte mortalite associee a la predation par les lamproies (Petromyzon marinus), tels que le nord du lac Michigan. Quand ces pressions de selection sont reduites, la performance de la lignee du lac Seneca est toutefois semblable a celles d'autres lignees. L'etude demontre que la performance de lignees peut varier sur de courtes distances et souligne l'importance de realiser des evaluations exhaustives des lignees pour appuyer les decisions concernant la gestion et la conservation. [Traduit par la Redaction], Introduction Attempting to rebuild collapsed or extirpated fish populations through stocking of hatchery-reared individuals is a common practice, but the short- and long-term success of this approach is highly variable [...]

Lipid concentration and fatty acid composition of common prey species or taxonomic groups from four distinct regions of Lake Michigan were quantified (n = 894). We used a combination of parametric and nonparametric statistics to assess the differences in fatty acid signatures (FAS) among species and to evaluate intraspecies variation relative to interspecies variation in FAS. Discriminant function analysis performed on 13 species or taxa groups using the 18 most abundant fatty acids revealed clear separation among taxa, with overall classification success reaching 89%. Species were readily distinguished based on their overall fatty acid profile in spite of intraspecies variation (temporal, regional, and size-related). Among species sampled, pelagic and benthic clusters were formed based on the degree of fatty acid profile similarity. In alewife (Alosa pseudoharengus) and round goby (Neogobius melanostomus), fatty acid compositions differed with fish size, sampling location, and temporal variation; however, the magnitude of these differences was small relative to differences between species. Our results demonstrate the utility of fatty acid signatures in studies of food webs in large freshwater ecosystems. This study is also a necessary first step toward development of mechanistic research that investigates the effects of variation in fatty acids within the prey base on top predators. Nous avons mesure les concentrations de lipides et la composition en acides gras des especes ou groupes taxonomiques communs de proies (n = 894) dans quatre regions distinctes du lac Michigan. Une combinaison de methodes statistiques parametriques et non parametriques nous ont servi a determiner les differences dans les signatures d'acides gras (FAS) entre les especes et d'evaluer la variation des FAS au sein des especes relativement a la variation entre les especes. Une analyse discriminante faite sur 13 especes ou groupes taxonomiques avec les 18 acides gras les plus abondants presente une nette separation entre les taxons avec un succes global de la classification de 89 %. Les especes peuvent etre clairement separees d'apres leur profil global d' acides gras malgre la variation intraspecifique (temporelle, regionale et reliee a la taille). Parmi les especes echantillonnees, il se forme des regroupements pelagique et benthique d'apres le degre de similarite de leurs profils d'acides gras. Chez le gaspareau (Alosa pseudoharengus) et le gobie a taches noires (Neogobius melanostomus), la composition en acides gras varie en fonction de la taille du poisson, du site d' echantillonnage et de la variation temporelle, mais l' importance de ces differences est faible par rapport aux differences entre les especes. Notre etude demontre l'utilite des signatures d' acides gras dans les etudes de reseaux alimentaires dans les grands ecosystemes d' eau douce. Notre travail est aussi un premier pas essentiel dans la mise au point d'une recherche mecaniste qui etudie les effets de la variation des acides gras dans le contingent de proies sur les predateurs superieurs. [Traduit par la Redaction], Introduction Lake Michigan's food web has been, and is, undergoing major changes because of various anthropogenic stressors. Successful establishment of invasive species can exert both top-down and bottom-up effects with [...]

Lake Trout Salvelinus namaycush were extirpated from Lake Michigan by the early 1950s, and as part of an effort to restore naturally reproducing populations, hatchery-reared fish have been stocked since the early 1960s. Stocked fish are marked with a fin clip to differentiate them from wild, lake-produced Lake Trout; marking error for the 2007-2010 year-classes of Lake Trout stocked by federal hatcheries averaged 3.0%. Egg deposition, emergent fry, and wild juvenile Lake Trout have previously been observed, but no sustained wild recruitment has been measured in assessment surveys or in sport and commercial fishery catches. In 2011 and 2012, we caught juvenile Lake Trout in gill-net and bottom trawl catches that were targeting Bloater Coregonus hoyi in water depths greater than 80 m. Unclipped, wild Lake Trout represented 20% of all Lake Trout caught in a southern offshore region of Lake Michigan. In northwestern Lake Michigan wild recruits represented from 10% to 27% of the 2007-2009 year-classes, and we recovered a small number of wild Lake Trout from the 2010 year-class. This is the first evidence for consecutive year-classes of naturally produced Lake Trout surviving beyond the fry stage in Lake Michigan. [ABSTRACT FROM AUTHOR]