High growth rate of young-of-the-year smallmouth bass in Lake Erie: a result of the round goby invasion?

The round goby (Neogobius melanostomus) first appeared in Lake Erie in 1993, quickly reaching extremely high densities (> 100/m(2)) in nearshore habitats frequented by juvenile smallmouth bass (Micropterus dolomieu). As round gobies are both potential competitors and prey for smallmouth bass, we investigated changes in young-of-the-year (YOY) smallmouth bass diet and growth between pre and post-round goby invasion in the Bass Islands, Lake Erie. During 1999-2001, YOY smallmouth bass fed more frequently on fish than in either 1919 or 1975. Fish comprised 21% of YOY smallmouth bass (21-100 mm total length) diets by weight in 1975 and 51% of the diet during 1999-2001, but increased to 90% for YOY > 100 mm during 1999-2001. Of fish consumed by first-year smallmouth bass during 1999-2001, 75% were round gobies. Abundant round gobies may facilitate the transition to piscivory for YOY smallmouth bass, resulting in higher YOY growth rates during 1999-2001 (1.2 mm/d) than in the 1940s, 1950s, or 1970s (0.58-0.85 mm/d). By consuming round gobies, juvenile smallmouth bass growth rate has increased, which has possible consequences for survival, reproduction, and age at maturity. Although the round goby invasion may have increased smallmouth bass growth rate, there are negative effects: round gobies are also predators, changing energy and contaminant transfer through the Lake Erie food web.