Traditional methods to measure body lengths of aquatic vertebrates rely on anesthetics, and extended handling times. These procedures can increase stress, potentially affecting the animal's welfare after its release. We developed a simple procedure using digital images to estimate body lengths of coastal cutthroat trout (Oncorhynchus clarkii clarkii) and larval coastal giant salamander (Dicamptodon tenebrosus). Images were postprocessed using ImageJ2. We measured more than 900 individuals of these two species from 200 pool habitats along 9.6 river kilometers. The percent error (mean ± SE) of our approach compared to the use of a traditional graded measuring board was relatively small for all length metrics of the two species. Total length of trout was −2.2% ± 1.0. Snout–vent length and total length of larval salamanders was 3.5% ± 3.3 and −0.6% ± 1.7, respectively. We cross-validated our results by two independent observers that followed our protocol to measure the same animals and found no significant differences (p > .7) in body size distributions for all length metrics of the two species. Our procedure provides reliable information of body size reducing stress and handling time in the field. The method is transferable across taxa and the inclusion of multiple animals per image increases sampling efficiency with stored images that can be reviewed multiple times. This practical tool can improve data collection of animal size over large sampling efforts and broad spatiotemporal contexts.

中文翻译：

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一种使用数字图像评估活水生脊椎动物的体长的方法

测量水生脊椎动物体长的传统方法依靠麻醉药，并延长了处理时间。这些程序会增加压力，可能会在动物释放后影响其福利。我们开发了一个简单的程序，利用数字图像来估计沿海cut鳟（Oncorhynchus clarkii clarkii）和幼虫沿海sal（Dicamptodon tenebrosus）的体长。）。使用ImageJ2对图像进行后处理。我们在9.6公里的河流中，从200个泳池栖息地中测量了这900个物种的900多个个体。对于这两种物种的所有长度指标，与使用传统的分级测量板相比，我们的方法所占的百分比误差（平均值±SE）相对较小。鳟鱼的总长度为-2.2％±1.0。幼鱼sal的鼻孔长度和总长度分别为3.5％±3.3和-0.6％±1.7。我们由两名独立的观察员对我们的结果进行交叉验证，这些观察员遵循我们的方案测量相同的动物，但未发现显着差异（p > .7），这两个物种的所有长度指标的体型分布。我们的程序可为您提供可靠的体重信息，以减少压力并在现场处理时间。该方法可在整个分类单元间转移，每个图像包含多个动物，可提高存储效率，可多次查看，从而提高了采样效率。该实用工具可以通过大量的采样工作和宽广的时空环境来改善动物体型的数据收集。