ABSTRACTSPATIAL, TEMPORAL, AND COHORT-RELATED PATTERNS IN THE CONTRIBUTION OF WILD CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA) TO TOTAL CHINOOK HARVEST IN LAKE MICHIGANByMart Christopher WilliamsDuring 2006-2010, the majority of hatchery-produced Chinook salmon (Oncorhynchus tshawytscha) stocked into Lake Michigan were marked with a combination of oxytetracycline (OTC), coded-wire-tags (CWT), and fin-clips to distinguish between hatchery and wild origin. The goals of this research were to: (1) evaluate the accuracy and reproducibility of the OTC mark, (2) examine spatial, temporal, and cohort-related patterns in the contribution of wild Chinook salmon, and (3) explore how differences in size-at-age and maturity-at-age may affect the proportion of wild Chinook salmon. OTC mark accuracy and reproducibility was determined to be adequate based on the error matrix fish, OTC mark quality distribution, and OTC mark presence/absence reader agreement was excellent. The lakewide proportion of wild age-1 Chinook salmon for four year-classes ranged from 53.52 to 56.92% with little interannual variation. The proportion of wild Chinook salmon increased as the fish became older (i.e., age-effect), suggesting differential survival between hatchery and wild fish. The proportion of wild age-1 Chinook salmon was greater in Michigan than Wisconsin, but was similar for older ages. The proportions of wild Chinook salmon for northern and southern Lake Michigan were similar for all four age-classes. The proportion of wild Chinook salmon in the northeast, northwest, and southwest regions all had an age-effect, however, the southeast region did not have an age-effect. The southeast region had the highest proportion of wild age-1 Chinook salmon.
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