An Evaluation of the Relative Size, Body Condition, and Survival of Triploid Walleye in the Wild

Natural dispersal or unauthorized introductions of nonnative predatory sport fish can undermine native species conservation and other fisheries management objectives. The use of reproductively sterile triploid fish may provide a lower-risk stocking option (i.e., genetic and reproductive containment) for diversifying angling opportunities while possibly reducing angler motivation to illegally transplant fish. Management interest in triploid Walleye Stizostedion vitreum is growing, and these fish are currently stocked by several fisheries agencies. Yet, little is known about the post-stocking growth, body condition, and survival of triploid Walleye, information that is important for calibrating expectations and guiding policy regarding their use. We compared the age-specific size, body condition, and survival of subadult (i.e., ages 0–3) triploid Walleyes to normal diploid conspecifics into two eastern Colorado reservoirs. Paired stockings of triploid and diploid Walleyes occurred over 3 years. Both fry and fingerlings were stocked each year. Triploids were generally smaller in length (6.6% on average) and weight (20.6%) compared to diploids across all age-classes. Despite being smaller, triploids had similar body condition relative to diploids. On average, the survival of triploids from spring-stocking to their first fall was 6.3x lower than that of diploids, but no differences in survival were observed beyond this early life stage. This pattern was consistent across cohorts and reservoirs. This work provides a foundation for future studies designed to clarify patterns of survival from spring to first fall by accounting for size-at-stocking and natural-origin fish, and those planned to assess the post-stocking performance of triploid Walleyes independent of diploids.