Advancing broodstock selection to optimize brook trout stocking in Wisconsin

Abstract

Abstract - Brook trout Salvelinus fontinalis is the only native stream-dwelling salmonid to many parts of central and eastern North America and has been intensively stocked across its native range. As wild brook trout stocking programs gain momentum, information is needed detailing patterns of spatial genetic structure, diversity, and stocking influence to aid in the conservation of endemic wild strains. The Wisconsin Department of Natural Resources utilizes a wild trout stocking program, stocking first-filial generation fish (F1; wild parents) or second-filial generation fish (F2; wild grandparents) rather than domestic strain brook trout in many waterbodies. Accurate expectations of post-stocking fitness are needed to help fisheries managers make cost-effective brook trout stocking decisions. The objectives of Chapter I were to determine how measures of genetic diversity, inbreeding, and effective population size vary for wild brook trout populations across Wisconsin. Moreover, I aimed to identify and characterize patterns in genetic structure on the landscape and quantify the influence of domestic strain stocking for each survey population. Brook trout were genotyped from 63 wild populations across Wisconsin and one domesticated hatchery strain at 68 microsatellite loci. Genetic diversity and effective population size showed positive relationships with latitude, and overall levels of domestic strain introgression were low. Six major groups were resolved on a neighbor-joining tree. Distinct groups of genetically similar populations were identified in central and northeastern Wisconsin, but spatial clustering was weak elsewhere. In summary, Chapter I demonstrated higher levels of genetic diversity and effective population size in northern Wisconsin, low overall levels of domestic strain introgression that generally coincide with available stocking records, and some evidence of spatial genetic structure, particularly in central and northeastern Wisconsin. In Chapter II, genetic analyses were used following three years of experimental stocking to estimate relative measures of post-stocking fitness among F1, F2, and domestic strain brook trout. Wild-born brook trout collected in electrofishing surveys were assigned as offspring of F1, F2, or domestic stocked fish using parentage analyses. F1 fish were superior to F2 fish and domestic strain fish, as they were more likely to survive, naturally reproduce, and produce multiple offspring. An overall decline in natural reproduction was observed in each consecutive year of sampling. Collectively, this thesis provides information on genetic diversity, spatial genetic structure, and hatchery influence for wild populations across Wisconsin, in addition to measures of relative fitness of stocked brook trout that were of varying degrees of wildness. These findings may help inform future conservation, management, and stocking practices of brook trout in Wisconsin and beyond.