Data from: Evaluation of potential overwinter mortality of age-0 walleye and appropriate age-1 sampling gear

Potential recruitment of age-0 Walleye Sander vitreus to adults is often indexed by the relative abundance of age-0 individuals during their first summer or fall. However, relationships between age-0 and adult Walleye abundance are often weak or non-significant in many waters. Overwinter mortality during the first year of life has been hypothesized as an important limitation to Walleye recruitment in lakes, but limited evidence of such mortality exists, likely due to difficulties in sampling age-1 Walleye during spring. The objectives of this study were to: 1) compare results from nighttime electrofishing to index relative abundance of age-1 Walleyes with relative abundance indices of mini-fyke nets in four eastern South Dakota lakes; 2) determine whether size-selective mortality was occurring in those four lakes; and 3) if size-selective mortality was occurring in these lakes, determine whether that mortality was attributed to body condition. Four natural lakes in eastern South Dakota were sampled over 2 weeks after ice-off in 2013 and 2014. Precision of nighttime electrofishing [Coefficient of Variation (CV) = 216.6] was greater than that estimated for mini-fyke nets (CV = 338.5) across both years. No differences in length-frequency distributions of collected spring age-1 Walleye were detected between the two gears. Age-0 fall relative abundance indices from electrofishing were significantly greater (P < 0.01) than spring age-1 nighttime electrofishing indices of relative abundance at three of the four study lakes, indicating that overwinter mortality may occur at a substantial rate during the first year of life for Walleye in these systems. Quantile-quantile regression plots showed evidence of size-selective mortality in three of four lakes sampled. However, body condition of age-0 Walleye appeared to have little to no influence on overwinter mortality. Instead, we suggest that smaller-sized walleye may be more vulnerable to overwinter predation. Collectively, these results provide evidence of previously hypothesized overwinter mortality within the first year for Walleye and indicate possibilities for indexing potential adult recruitment of Walleye just after this critical period.

0龄玻璃梭鲈（Walleye Sander vitreus）向成体的种群补充潜力，通常以其首个夏季或秋季的0龄个体相对丰度作为评估指标。然而，在诸多水域中，0龄与成体玻璃梭鲈的丰度关联往往较弱，甚至无统计学显著性。已有假说指出，生命首年的越冬死亡率是限制湖泊内玻璃梭鲈种群补充的关键因素，但相关实证证据较为匮乏，这大概率是因为春季采样1龄玻璃梭鲈存在较大难度。本研究旨在达成以下目标：1）对比夜间电捕鱼法与小型fyke网（mini-fyke nets）的相对丰度指数，以评估南达科他州东部4个湖泊中1龄玻璃梭鲈的相对丰度；2）明确上述4个湖泊中是否存在体型选择性死亡现象；3）若存在体型选择性死亡，探究其是否与个体身体状况相关联。研究于2013年和2014年冰融后的两周内，对南达科他州东部的4个天然湖泊开展了系统性采样。综合两年的采样数据，夜间电捕鱼法的采样精度[变异系数（Coefficient of Variation, CV）=216.6]高于小型fyke网（CV=338.5）。两种采样渔具所获春季1龄玻璃梭鲈的体长频率分布未检测到显著差异。在4个研究湖泊中的3个，夜间电捕鱼法得到的秋季0龄个体相对丰度指数显著高于春季1龄个体夜间电捕鱼丰度指数（P<0.01），这表明该类系统中玻璃梭鲈在生命首年的越冬死亡率可能处于较高水平。分位数-分位数回归图显示，4个采样湖泊中的3个存在体型选择性死亡的实证证据。不过，0龄玻璃梭鲈的身体状况对其越冬死亡率几乎无影响。据此我们推测，体型较小的玻璃梭鲈可能更易遭受越冬捕食压力。综上，本研究结果为此前提出的“玻璃梭鲈生命首年存在越冬死亡”假说提供了关键实证支持，并表明可在这一关键时期结束后，对玻璃梭鲈潜在的成体种群补充能力进行有效评估。