Chain pickerel Esox niger Lesueur, 1818, is an invasive freshwater fish found in Nova Scotia, Canada. Chain pickerel was illegally introduced to Nova Scotia in the 1940s in Digby County, because of its popularity as a sport fish. Through natural movement and subsequent illegal introductions, Chain pickerel has spread across Nova Scotia, being recorded in 166 waterbodies as of 2020. In 2018, Chain pickerel was first discovered in Kejimkujik National Park and National Historic Site (hereafter “Kejimkujik”). Since the initial invasion, Chain pickerel has successfully spread throughout Kejimkujik. With each passing year, prior to and over this study period, the abundance, body lengths and weights of Chain pickerel continue to increase and demonstrate a successful establishment in Kejimkujik.
Over the course of a four-year monitoring period for this present study, a decrease in the catch per unit effort (CPUE) of native fishes has been observed. When comparing early-invaded with late-invaded lakes, early-invaded lakes were found to have significantly lower CPUE compared to late-invaded lakes. As the abundance of native fishes began to decrease, Chain pickerel shifted diets from primarily piscivorous to an increased importance in invertebrates.
A primary spawning period of Chain pickerel has been identified using trends in GSI, oocyte development and observed spawning behaviour. Spawning occurs from late March to mid-April in Kejimkujik. Evidence of a second, less intensive, fall spawning period was also found.