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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 [...]

Polychlorinated biphenyls (PCB) body accumulation rates of Lake Michigan coho salmon have been found to be robust, with the fish retaining an estimated 50% of the PCB in their food. Sampling techniques determined PCB values in both coho salmon and their prey by using bioenergetics modelling. The estimates are the most reliable because sampling was done in spring, summer and fall at various locations and because sampling was done over a wide range of fish sizes, prey sizes and locations.

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]

Beginning in 1995, the size of yearling lake trout (Salvelinus namaycush) stocked into the upper Great Lakes was increased based on the assumption that these fish would be healthier and survive better since natural mortality is thought to be inversely proportional to body size. We compared the post-release, relative survival of paired stockings of lake trout reared to 44 fish/kg (standard size) with larger fish reared to 22-26 fish/kg (enhanced size) in Lake Michigan. About 60,000 lake trout each of the standard and enhanced sizes for the 1994-1997 year classes were released as yearlings in spring near Clay Banks Reef Wisconsin, and identified with coded-wire tags and an adipose fin-clip. Recaptures were made from 1997 to 2003 in four gill net surveys conducted in spring and fall near the release location. Comparisons of catch-per-unit of effort corrected for numbers stocked generally indicated no significant differences in relative survival of standard and enhanced lake trout. An autopsy-based assessment of overall fish health and condition indicated few measures where significantly different between standard and enhanced lake trout prior to stocking. Size differences between standard and enhanced fish remained statistically significant at all observed ages at recapture; however growth rates were the same for the two groups. Stocking numbers at certain sites on Lake Michigan were reduced concurrent with the change to larger yearlings with the expectation of increased survival, which did not occur; hence recruitment was essentially reduced in these areas for the restoration program. [ABSTRACT FROM AUTHOR]

Estimates of relative egg deposition and larval abundance suggest that events occurring between spawning and the first 1-2 months after hatching play a major role in determining recruitment success of bloater Coregonus hoyi in Lake Michigan. Although relative egg deposition in 1983 was only 57% of that in 1982, larval recruitment was 2.4 times greater in 1983. We investigated mechanisms governing survival of larval bloaters by comparing characteristics of individual 'survivors' through the first 1-2 months of life with those of larvae at earlier life history stages. Otolith analysis was used to identify stress periods and to determine ages, first-feeding dates (close correlates of birthdate), and average growth rates of individual bloater larvae from hatching to nearly 2 months of age in 1982 and 1983. Differences between the observed distribution of first-feeding dates for newly hatched larvae and the expected distribution predicted from egg deposition showed that eggs spawned early experienced higher mortality during the incubation period than did eggs spawned later. Eggs spawned early took about 2.5 weeks longer to develop than eggs spawned later because they incubated at cooler temperatures; this prolonged exposure to mortality sources may account for the observed difference in survival. Differences between the distributions of first-feeding dates for newly hatched larvae and larvae about 1 month old also suggested that early hatching larvae experienced higher initial mortality than late-hatching larvae. Starvation was not an important cause of mortality; growth rates of all larvae collected in the field were as high as or higher than those of larvae reared in the laboratory and fed ad libitum. Larvae hatching early in the season, however, grew only about half as fast during their first 3 weeks as larvae hatched later. These early hatching, slower growing larvae were also more likely to exhibit stress marks in the otolith ring pattern during their first 2 weeks, marks that were similar to those caused in the laboratory by short periods of starvation or low ration. Lower growth rates and higher frequency of stress marks for larvae during the period of higher relative mortality suggest that size or growth-rate-dependent mortality (e.g., predation) during the first few weeks of life may be an important mechanism affecting bloater recruitment. [ABSTRACT FROM AUTHOR]