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，通常可通过其首个夏季或秋季的0龄个体相对丰度进行表征。然而，在多数水域中，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。有假说指出，生命第一年的越冬死亡是湖泊中玻璃梭鲈种群补充的重要限制因素，但相关实证证据较为匮乏，这大概率源于春季采样1龄玻璃梭鲈存在较大难度。本研究的核心目标包括：1）在南达科他州东部的四座天然湖泊中，对比夜间电渔法（nighttime electrofishing）与小型fyke网（mini-fyke nets）的相对丰度指数，以表征1龄玻璃梭鲈的种群丰度；2）明确上述四座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。2013年与2014年冰消后的两周内，研究团队对南达科他州东部的四座天然湖泊开展了系统采样。两年的采样数据显示，夜间电渔法的采样精度[变异系数（Coefficient of Variation, CV）=216.6]高于小型fyke网（CV=338.5）。两种渔具采集的春季1龄玻璃梭鲈的体长频率分布未检测到显著差异。在四座研究湖泊中的三座，夜间电渔法获取的秋季0龄个体相对丰度指数显著高于春季1龄个体的夜间电渔法丰度指数（P<0.01），这表明在该类淡水系统中，玻璃梭鲈生命第一年的越冬死亡率可能处于较高水平。分位数-分位数回归图（quantile-quantile regression plots）显示，四座采样湖泊中的三座存在体型选择性死亡现象。但0龄玻璃梭鲈的身体状况似乎对越冬死亡几乎无影响。据此我们推测，体型更小的玻璃梭鲈可能更易在越冬期遭遇捕食。综合来看，本研究结果为此前提出的玻璃梭鲈生命第一年越冬死亡假说提供了实证支持，并表明可在该关键越冬时期后，对玻璃梭鲈潜在的成体种群补充潜力进行有效表征。