Production And Outmigration Of Young-Of-Year Northern Pike Esox Lucius From Natural And Modified Waterways Connected To Lower Green Bay, Wisconsin

Production and outmigration of young-of-year (YOY) northern pike from natal sites in Lower Green Bay, WI, USA, were documented over three consecutive years (2013-2015). We tested the hypothesis that spawning success and outmigration characteristics of YOY northern pike would vary among natural and anthropogenically modified habitats. Sixteen focal study locations were surveyed, including a restored natural wetland, agricultural drainage ditches, a flooded forested wetland and several unimpounded tributaries. We collected 1469 YOY northern pike with most individuals (N = 1163) originating from a flooded forested wetland on the east shore. Most sites produced YOY in all years (range N = 2-1145 individuals among study years). Outmigration ranged between 1 and 40 days during 2013-2015. Greater production and extended outmigration times occurred at most sites in 2014 (range 17-40 days) when the region experienced a late spring with heavy precipitation. In contrast, the lowest production and shortest outmigration period occurred at most sites in 2015 (range 14-23 days) when environmental conditions reflected regional averages. Outmigration began nearly 3 weeks earlier in 2015 (5/8) than in other study years (8 June 2013 and 25 May 2014). Total length (TL) of outmigrating northern pike ranged between 17 and 138 mm. Total length of YOY was significantly different among sites in 2013 and 2014, with the smallest fish (17 mm TL) outmigrating from agricultural ditches in both years. There were no significant variations in size among sites in 2015 (range 21-95 mm TL). Our results indicate significant variation in YOY northern pike outmigration characteristics within Lower Green Bay that may reflect the interplay between adult spawning site selection and annual weather patterns. Our findings highlight the importance of quantifying overlooked habitats in regions of mixed development.