Changes in the Saginaw Bay, Lake Huron, fish community from 1970-2011

Many aquatic ecosystems experience concurrent anthropogenic stressors that can have complex impacts on fish communities. Limited data and temporal associations among environmental stressors may confound the ability to attribute community-level impacts to single or multiple stressors. Instead, quantitative description of temporal changes in fish communities may shed light on the cumulative and individual impacts of diverse stressors. Saginaw Bay, Lake Huron, has experienced diverse anthropogenic stressors that have been inconsistently quantified over time. We used resampling and multivariate approaches to analyze long-term trawl data to describe how fish community patterns changed in Saginaw Bay from 1970-2011. Total, native, and moderately tolerant fish species richness generally increased from 1970-2011. Dynamic factor analysis and nonmetric multidimensional scaling revealed that fish community structure changed from 1970-2011 and that relative abundances of many fish species increased. In general, increases in richness and CPUE were correlated with decreases in total phosphorus, chl a, and water levels. In addition, breakpoint analyses revealed shifts in species richness in the mid-1980s and 1999. Temporal patterns are consistent with the hypothesis that the Saginaw Bay fish community has changed from one dominated by species tolerant of eutrophy to one with more sensitive species, likely a response to decreased phosphorous loading and resulting changes in water quality. More recently (1999-2011), richness and relative abundance of many fish species in Saginaw Bay declined, a pattern potentially reflective of larger food-web transitions in both Saginaw Bay and open Lake Huron.