The detection of threatened species, specially where they have been depleted, is key to their conservation but poses severe logistical challenges precisely because of their very low abundances. Sawfishes (family Pristidae) are among the most threatened marine taxa with globally-reported severe reductions in population size and disappearance from large parts of their former distribution range. This study presents the first report on the use of environmental DNA (eDNA) to evaluate the presence of Critically Endangered sawfishes in parts of their former range, where no recent information about their presence exists. During 2016 and 2017 gillnet and eDNA surveys were carried out at Tecolutla Estuary, Veracruz, and Laguna de Términos and Los Petenes Biological Reserve, Campeche, in Mexico, where Pristis pectinata and Pristis pristis were abundant 40–50 years ago. Our study aimed at determining: (a) if eDNA was a suitable tool for assessing the presence of sawfishes at suspected very low abundances, and (b) if sawfishes still occur in Mexico. We found evidence of sawfish presence through eDNA samples in all three sites, at very low frequencies, but no evidence through gillnetting. Species resolution was difficulted by DNA degradation, but 2/12 samples were identified as Pristis pectinata. Our findings confirm that eDNA is a suitable tool to rapidly assess the presence of critically endangered sawfishes in the wild, stress the urgent need for eDNA surveys throughout the former range of sawfishes globally and highlight the need for swift measures to protect the remaining individuals still living in Mexico.

对受威胁物种，特别是已被耗尽的物种的发现，是其保护的关键，但正因为它们的丰度很低，所以在后勤方面面临着严峻的挑战。锯齿鱼类（Pristidae家族）是受威胁最大的海洋生物群之一，全球报告的种群数量急剧减少，并且从其先前分布范围的大部分地区消失。这项研究提出了有关使用环境DNA（eDNA）评估其濒临灭绝的锯鱼在其先前范围的一部分中的存在的第一份报告，而有关它们的存在的最新信息不存在。在2016和2017年刺网和Edna调查是在河口特科卢特拉，韦拉克鲁斯和特尔米诺斯泻湖和洛杉矶Petenes生物保护区，坎佩切，墨西哥，在那里进行锯鳐属珧和Pristis pristis在40到50年前就已丰富。我们的研究旨在确定：（a）eDNA是否是用于评估疑似极低丰度的锯鱼的存在的合适工具，以及（b）锯鱼是否仍然存在于墨西哥。我们通过eDNA样本在所有三个站点中以极低的频率发现了锯鱼的存在证据，但没有通过刺网的证据。DNA降解难以解决物种分离问题，但2/12个样品被鉴定为果胶Pristis pectinata。我们的发现证实，eDNA是用于快速评估野外极度濒危锯鱼存在的合适工具，强调迫切需要对全球前一系列锯鱼进行eDNA调查，并强调需要采取迅速措施来保护仍在世的其余个体在墨西哥。