Changes in Habitat Conditions, Fish Populations, and the Fishery in Northern Green Bay, Lake Michigan, 1989–2019. (6th December 2021) - Zorn, Troy G.
Abstract: Aquatic environments and biological communities in nearshore waters of the Laurentian Great Lakes have undergone extensive change in recent decades. The nearshore waters of northern Green Bay, Lake Michigan, have been subject to environmental change but are relatively unstudied, despite hosting important fisheries for Walleye Sander vitreus, Yellow Perch Perca flavescens, Northern Pike Esox lucius, and Smallmouth Bass Micropterus dolomieu . Our objectives were to (1) test for changes in water clarity and fish populations in northern Green Bay, Lake Michigan, during 1989–2019, (2) depict recent spatial patterns in abundance for species of management interest, and (3) test for effects of recent Great Lakes water level changes on Northern Pike recruitment. Fishes were sampled annually in August and September 1989–2019 via trawl and gill‐net surveys at index sites. Mean water clarity increased 30% over this period. Aside from Round Goby Neogobius melanostomus, total catch rate of species in trawls decreased by over 90% between the 1990s and 2010s, with significant declines for Yellow Perch and pelagic forage fishes (coincident with dreissenid mussel invasion). Fish species richness in trawl and gill‐net surveys and total gill‐net catch rates declined significantly over time. Trends in gill‐net catch rates of game fishes during 1989–2019 were species‐specific, with spatial patterns often related to availability of preferred habitat conditions. Similar fish community changes to those we observed in northern Green Bay, Lake Michigan, have been noted in other Great Lakes, many being associated with invasion of dreissenid mussels and Round Goby. Increased water levels in Lake Michigan during the 2010s had a significant positive effect on Northern Pike recruitment, which highlights the importance of varying water levels, shoreline habitat conditions, and early life processes on population dynamics of fishes reproducing in inshore habitats.