Sample Size Estimation for On-Site Creel Surveys

Conducting sample size analysis is important to ensure that sample sizes are adequate to meet objectives for precision but not so large that valuable resources are wasted. When simple survey designs are used, sample size analysis is straightforward. However, creel surveys often follow complex designs that can make sample size estimation difficult. The objectives of this study were to provide sample size estimators for commonly used creel survey designs and investigate sample size requirements to achieve varying levels of precision. For estimates of angling effort, the average sample size among fisheries required to achieve relative 95% confidence intervals of 40% (i.e., coefficient of variation of approximately 0.2) was 16 d (range = 7–40 d). To estimate mean catch rate with the same level of precision, 43 survey days (range = 8–95 d) were required when the daily catch rate estimator was used, and 11 d (range = 3–30 d) were required when the multi-day estimator was used. Fifty-five days (range = 14–89 d) and 57 d (range = 19–140 d) were required to estimate total catch with relative 95% confidence intervals of 40% when the daily and multi-day estimators were used, respectively. Although absolute precision will vary among fisheries, our results suggest that approximately 30 d of surveying may serve as a reasonable starting point for planning creel surveys when no prior information is available on expected sample variance, as relatively large increases in sample size beyond 30 d were needed to achieve relatively small increases in precision. Received February 14, 2017; accepted June 9, 2017 Published online August 4, 2017

开展样本量分析至关重要，其核心目标是确保样本量足以满足精度要求，同时避免因样本规模过大造成宝贵资源的浪费。当采用简单调查设计时，样本量分析过程较为直观；但钓捕调查（creel survey）通常采用复杂设计，这会使样本量估算工作颇具难度。本研究旨在为常用的钓捕调查设计提供样本量估算公式，并探究实现不同精度水平所需的样本量要求。针对垂钓努力量的估算，当要求相对95%置信区间达到40%（即变异系数约为0.2）时，各渔业研究所需的平均样本量为16天（范围为7~40天）。若以相同精度水平估算平均渔获率，采用单日渔获率估算方法时需43个调查日（范围为8~95天），采用多日估算方法时则仅需11个调查日（范围为3~30天）。当采用单日与多日估算方法分别估算总渔获量、且要求相对95%置信区间为40%时，所需的调查天数分别为55天（范围为14~89天）与57天（范围为19~140天）。尽管不同渔业的绝对精度会存在差异，但本研究结果表明，若缺乏预期样本方差的先验信息，在规划钓捕调查时，以约30个调查日作为合理的起始样本量是可行的——因为当样本量超过30天后，仅需小幅提升精度就需要大幅增加样本量。收稿日期：2017年2月14日；录用日期：2017年6月9日；在线发表日期：2017年8月4日