Seines are a common sampling gear for monitoring small‐bodied fishes in wadeable, sand‐bed rivers. However, sampling effort within a site can vary among time and space, even within the same monitoring program. Determining and standardizing an adequate or optimal amount of effort within a site is an important step for designing fisheries monitoring programs. If budgets are limited, sampling intensity at a site is often a trade‐off between less intense sampling at a greater number of locations or more intense sampling at fewer locations. Inadequate sampling at survey sites could introduce variability into estimates of density, species richness, or relative abundance because of within‐site variability. We evaluated how variability of mean catch‐rates of five species of small‐bodied fishes changed with increasing effort at a fixed number of sites, and how variability changed as more sites were sampled. Focal species were Rio Grande silvery minnow, flathead chub, red shiner, fathead minnow, and western mosquitofish. We sampled 20 sites with 20 hauls in 200 m, 40 hauls in 200 m, and 40 hauls in 400 m. We observed little decrease in variability around expected catch‐per‐unit‐effort [] when 40 seine hauls were performed per site compared to 20 hauls per site, regardless of site length or species, though a 25% increase in labour was required. However, we observed considerable variability around when ≤5 seine hauls were performed at each site. We recommend a minimum of 10 seine hauls per 200 m site. Our results provide guidance and starting point for monitoring programs that use seining to collect information on small fishes.

中文翻译：

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围网力度和站点长度对沙床河流中小鱼捕获率变异性的影响

塞纳河是一种常见的采样工具，用于监测可漫游的沙床河流中的小鱼。但是，即使在同一监视程序中，站点内的采样工作也会随时间和空间而变化。确定场址内适当或最佳工作量并使其标准化是设计渔业监测计划的重要步骤。如果预算有限，则在一个地点的采样强度通常是在多个位置的强度较低的采样或在较少的位置强度较高的采样之间进行权衡。由于现场内部的可变性，在调查地点采样不足可能会将可变性引入密度，物种丰富度或相对丰度的估计中。我们评估了在固定数量的地点上增加的努力，五种小体鱼的平均捕捞率的变化如何变化，以及随着采样点的增加，变异性如何变化。重点物种是里奥格兰德（Rio Grande）银色min鱼，扁头，红色光泽，fat头min鱼和西部蚊子。我们对200个m的20个站点，200 m的40个站点​​和400 m的40个站点​​进行了20个站点采样。我们观察到预期单位捕捞量附近的变异性几乎没有减少[），尽管需要增加25％的劳动力，但每个站点执行40个围网拖网，而每个站点进行20个拖网拖网，无论站点长度或种类如何。但是，我们观察到在每个站点执行≤5次围网拖网时的可变性。我们建议每200 m站点至少有10条围网拖网。我们的结果为使用围网收集小鱼信息的监测程序提供了指导和起点。