Exploring potential drivers of spatiotemporal variation in length-at-age and condition of two common nearshore fishes in southwestern Lake Michigan

Understanding factors like fish size and condition can be crucial to fisheries management. In the Great Lakes, long-term observations of these factors are used to describe the effects of ecosystem dynamics on fish ecology. Considering the diversity of available benthic habitat and dynamic environmental conditions in the nearshore zone of Lake Michigan, we sought to understand the variability in length-at-age and condition of yellow perch and round goby, two important members of the nearshore fish community. We measured these metrics from both species captured in gillnets across three locations in Illinois waters of southwest Lake Michigan from June through October 2008–2012 and related the spatiotemporal differences seen to observed variation in temperature, prey abundance, and competitor abundance. Yellow perch length-at-age varied annually for all three age-classes, with differences relating to thermal regime (age-0 and age-2) and alewife abundance (age-1). Yellow perch condition, measured as residual weight, varied spatially and annually, showing a negative relationship with round goby abundance. Round goby length-at-age was greater at the southern location, likely due to warmer temperatures, while condition was greater at the rockier location. In general, model selection analysis revealed several potential relationships between the relative abundances of competitor species and length and condition of yellow perch and round goby, while prey abundance may be related to round goby condition. These results demonstrate the importance of understanding the diversity in nearshore habitats and the influence of this diversity on factors affecting fish production, including size and condition, in southwest Lake Michigan.