The Critically Endangered Smalltooth Sawfish, Pristis pectinata, was once widespread in the tropical and subtropical waters of the Atlantic Ocean, but following substantial declines over the past century, the remaining population(s) are currently confined to Florida in the U.S., and the Bahamas. Recent research and verified public encounter reports suggest that the core population in south and southwest Florida may be stabilizing and potentially expanding into formerly occupied areas of their historic range in the western Atlantic; however, the status of this species outside of core waters is not well understood. Environmental DNA (eDNA) methods provide a relatively cost effective and rapid assessment tool for monitoring species occurrence in aquatic habitats. Here, we have developed an eDNA tool: a species-specific Droplet Digital™ PCR assay targeting a 100-base pair portion of the mitochondrial NADH dehydrogenase subunit 2 gene in P. pectinata, with the ability to reliably detect as little as 0.25 pg of target DNA. The assay was validated by analyzing a water sample from an occupied nursery in southwest Florida, which was found to contain an average of 11.54 copies of target DNA/µL (SE = 0.72) in the reaction. The assay was then further tested by placing a juvenile sawfish in an ex situ tank and analyzing water samples collected at time intervals. The implementation of this eDNA tool into field surveys will provide additional, reliable data to assess species recovery and aid in prioritizing localities in which to focus new research, conservation, and education initiatives.

极度濒临灭绝的小齿锯鱼，Pristis pectinata曾一度广泛分布于大西洋的热带和亚热带水域，但在过去一个世纪出现大幅下降之后，其余人口目前仅限于美国的佛罗里达州和巴哈马。最近的研究和经过验证的公开遭遇报告表明，佛罗里达州南部和西南部的核心人口可能正在稳定，并有可能扩展到其在西大西洋历史范围内的先前占领区；但是，人们对该核心水域以外的物种的状况还不甚了解。环境DNA（eDNA）方法为监视水生生境中物种的出现提供了一种相对经济有效的快速评估工具。在这里，我们开发了一种eDNA工具：P。果胶，能够可靠地检测低至0.25 pg的目标DNA。该分析通过分析佛罗里达西南部一个被占领的苗圃中的水样而得到验证，该水样在反应中平均含有11.54拷贝的目标DNA / µL（SE = 0.72）。然后通过将幼体锯鱼放在异位水箱中并分析在一定时间间隔收集的水样来进一步测试该检测方法。该eDNA工具在现场调查中的实施将提供更多可靠的数据，以评估物种的恢复，并帮助确定地方的优先顺序，从而集中精力进行新的研究，保护和教育计划。