Chinook salmon (Oncorhynchus tshawytscha) population dynamics in Lake Michigan, 1985 to 1996

Chinook salmon remains a popular sport fish in Lake Michigan despite the collapse of the chinook fishery beginning in 1987. This collapse is widely believed to have been caused by a combination of nutritional stress and mortality from bacterial kidney disease (BKD). This study involved a spatial analysis of trends in the chinook fishery, and a lake-wide stock assessment model for chinook salmon. Fishery trend analysis shows that declines in the fishery were more severe in the western regions of the lake than in the eastern regions. Evidence suggests that these spatial differences in fishery trends were due to changes in chinook spatial distribution rather than differences in mortality.; I built a stock assessment model for chinook salmon in Lake Michigan using 1985-1996 recreational fishery data in order to estimate population abundance, fishing mortality, and time-varying natural mortality. This statistical catch-at-age analysis model is fit to observed recreational fishery and weir return data. Results indicate that the natural mortality rate increased from 1986 to 1993, and declined from 1994 to 1996. These results are inconsistent with estimates of BKD incidence from harvest weirs, suggesting that causes of changing natural mortality are not entirely due to BKD, and may be more complex than previously considered.