Trends in body condition of smallmouth bass and northern pike (1982–2013) following multiple ecological perturbations in the St. Lawrence River

Abstract

Body condition indices can be used to investigate fish response to biological or environmental change. We used quantile regression to analyze a 32-year weight–length data set (1982–2013) for smallmouth bass (Micropterus dolomieu) and northern pike (Esox lucius) from the St. Lawrence River to examine changes in condition (weight-at-length) during three ecologically distinct time periods. Condition of both species varied among time periods, with smallmouth bass experiencing greater proportional changes than northern pike. Smallmouth bass weight-at-length was greatest during 2005–2013 and lowest during 1982–1992. Northern pike weight-at-length was greatest during 2005–2013 for quantiles ≥0.5, similar between the 1982–1992 and 2005–2013 time periods for lower quantiles, and lowest during 1993–2004. The most likely weight–length model for smallmouth bass included terms for length, presence of round goby (Neogobius melanostomus), presence of dreissenid mussels, and an interaction between length and dreissenid mussels (wi = 0.93). The most likely model for northern pike included terms for length, presence of round goby, presence of dreissenid mussels, water temperature, conspecific abundance, and sex (wi = 0.56). Invasive species and environmental change related to invasive species have altered the condition of smallmouth bass and northern pike in the St. Lawrence River.