Long‐term fish community surveys were carried out in the Michigan waters of Lake Huron using bottom trawls from 1976 to 2006. Trends in abundance indices for common species (those caught in 10% or more of trawl tows) were estimated for two periods: Early (1976‐1991) and late (1994‐2006). All common species significantly decreased in abundance during the late period with the exception of the johnny darter Etheostoma nigrum and spottail shiner Notropis hudsonius, which showed no significant trends, and the round goby Neogobius melanostomus, which increased in abundance. Percentage decreases in abundance indices between 1994‐1995 and 2005‐2006 ranged from 66.4% to 99.9%, and seven species decreased in abundance by more than 90%. The mean biomass of all common species in 2006 was the lowest observed in the time series and was less than 5% of that observed in the mid‐1990s. The mean number of common species captured per trawl has also decreased since the mid‐1990s. Several factors, including recent invasion of the lake by multiple exotic species, may have contributed to these declines, but insufficient published data are currently available to determine which factors are most important. Our observations suggest that significant changes have occurred in the ecology of Lake Huron since the mid‐1990s. The extent of these changes indicates that the deepwater demersal fish community in Lake Huron is undergoing collapse.

We used growth and diet data from a fishery‐independent survey of Chinook salmon Oncorhynchus tshawytscha, acoustic estimates of prey density and biomass, and statistical catch‐at‐age modeling to study the influence of the year‐class strength of alewife Alosa pseudoharengus on the prey selection and abundance of age‐1 Chinook salmon in Lake Michigan during the years 1992‐1996 and 2001‐2005. Alewives age 2 or younger were a large part of age‐1 Chinook salmon diets but were not selectively fed upon by age‐1 Chinook salmon in most years. Feeding by age‐1 Chinook salmon on alewives age 2 or younger became selective as the biomass of alewives in that young age bracket increased, and age‐1 Chinook salmon also fed selectively on young bloaters Coregonus hoyi when bloater density was high. Selection of older alewives decreased at high densities of alewives age 2 or younger and, in some cases, high densities of bloater. The weight and condition of age‐1 Chinook salmon were not related to age‐1 Chinook salmon abundance or prey abundance, but the abundance of age‐1 Chinook salmon in year t was positively related to the density of age‐0 alewives in year t − 1. Our results suggest that alewife year‐class strength exerts a positive bottom‐up influence on age‐1 Chinook salmon abundance, prey switching behavior by young Chinook salmon contributing to the stability of the predator‐prey relationship between Chinook salmon and alewives.

No abstract