Looking for a bottleneck: Assessment of factors influencing post-stocking survival of advanced fingerling Walleye Sander vitreus

Walleye Sander vitreus is a highly valued sportfish in North America. In 2001, 3.8 million anglers spent approximately 51.9 million days angling for Walleye (USFWS-USCB 2002). The popularity of Walleye has resulted in situations where demand exceeds supply, which has led to the development and implementation of stocking programs across the United States and Canada to enhance fishing opportunities (Lathrop et al. 2002), rebuild depleted stocks (Johnson et al. 1996; Li et al. 1996), and mitigate poor year classes from variable natural recruitment (Mitzner 1992; Johnson et al. 1996; Jennings et al. 2005; Logsdon et al. 2016; Reed and Staples 2017). However, mortality rates of stocked fishes can vary widely (27-95%; Stein et al. 1981; Buckmeier et al. 2005; Freedman et al. 2012; Weber et al. 2020) and small changes in survival can result in large differences in year-class strength and success of stocking initiatives. Numerous biotic and abiotic factors can influence survival during early life stages of fish, such as transportation and stocking practices (Forsberg et al. 2001; Barton et al. 2003), predation (Santucci and Wahl 1993; Buckmeier et al. 2005; Thompson et al. 2016), available forage (Johnson et al. 1996; Hoxmeier et al. 2006), competition (Le Pape and Bonhommeau 2015; Chase et al. 2016), fish origin (Kellison et al. 2000; Jonsson and Jonsson 2003; Pollock et al. 2007), body size (Litvak and Leggett 1992; Meekan et al. 2006; Grausgruber and Weber in press), and water temperatures (Akimova et al. 2016; Wagner et al. 2017). Furthermore, the aforementioned factors do not act independently of each other, making it challenging to determine their importance. The growth-predation hypothesis predicts that selective mortality should decline as individuals grow and increase in size (Anderson 1988). Increases in size are also associated with decreased predation risk (Post and Evans 1989; Miranda and Hubbard 1994), where larger body size can reduce the chances of predation due to improved maneuverability and swimming speed (Videler 1993). The argument of "bigger-is-better" (Butler 1988; Miller et al. 1988; Litvak and Leggett 1992) has led hatcheries to raise progressively larger fingerling Walleye (Halverson 2008). However, hatchery production is an expensive and labor-intensive process, where production costs are generally positively related to rearing duration and fish size (Wedemeyer 2001). Therefore, it is advantageous to evaluate factors hypothesized to limit post-stocking Walleye survival (e.g., effects of transport duration and handling practices as well as post-stocking predation and starvation) to assess whether rearing

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