Endangered species lists (or red lists) are important tools for species conservation, but if they are not supported by data and they are inappropriately applied, they can be sources of conflict. Here, we present and discuss the dilemma of the trigonal clam Tivela mactroides, a beach bivalve used as a subsistence, economic and recreational resource by residents and tourists on the northern coast of the State of São Paulo, Brazil. This species was included in the state list of endangered species, which prohibits the harvesting of the clam according to Brazilian law. The lack of data on the IUCN concepts and criteria supporting its inclusion in the state red list and the potential negative consequences for clam harvesters have raised concerns about the application of this conservation tool to this species. To obtain additional evidence to support the categorization of this clam on the list of endangered species and to shed light on this dilemma, we employed a rapid, diversified and incremental strategy to qualify the information on some IUCN concepts and criteria by considering the geographic distribution and trends in population size and potential threats in the region. We combined incremental steps, considering a review of the literature and data repositories, a simplified habitat suitability model, interviews with experts and the local community, a citizen science approach and beach validation visits. The combination of these methods revealed a wider spatial distribution of T. mactroides (59 out of 191 beaches) than could have been previously identified by the available information (literature review, data repositories and experts; 41 beaches). The literature was also insufficient for informing trends in the population density and possible threats. The perceptions of the experts and local communities suggested an overall decrease in the sizes of the populations and an increase in the threats facing clam populations such as wastewater, oil spills, marine litter, and beach erosion. Since clam capture occurs only at specific locations and was not cited as often as a threat, the São Paulo Red List might not be the most appropriate conservation tool for addressing the multiple threats facing this species, including the risk of habitat loss. An ecosystem-based approach targeting both direct and indirect pressures on clam populations would be the most appropriate course of action to support the conservation and sustainable use of organisms such as T. mactroides while also protecting the habitat and other coexisting species.

濒危物种名录（或红色名录）是物种保护的重要工具，但如果没有数据支持且应用不当，则可能成为冲突的根源。在这里，我们介绍和讨论三角蛤Tivela mactroides的困境，一种海滩双壳类动物，被巴西圣保罗州北部海岸的居民和游客用作生计、经济和娱乐资源。该物种被列入国家濒危物种名录，根据巴西法律禁止收获蛤蜊。缺乏关于 IUCN 概念和标准的数据支持将其列入国家红色名录以及对蛤蜊采伐者的潜在负面影响，引发了对该物种应用该保护工具的担忧。为了获得更多证据来支持将这种蛤蜊归入濒危物种名单并阐明这一困境，我们采用了快速、通过考虑该地区人口规模和潜在威胁的地理分布和趋势，对一些 IUCN 概念和标准的信息进行验证的多样化和增量策略。我们结合了渐进的步骤，考虑了对文献和数据存储库的审查、简化的栖息地适宜性模型、与专家和当地社区的访谈、公民科学方法和海滩验证访问。这些方法的结合揭示了更广泛的空间分布T. mactroides（191 个海滩中的 59 个）比之前可用信息（文献评论、数据存储库和专家；41 个海滩）所能识别的数量多。文献也不足以告知人口密度的趋势和可能的威胁。专家和当地社区的看法表明，蛤种群数量总体减少，而蛤种群面临的威胁增加，如废水、漏油、海洋垃圾和海滩侵蚀。由于捕获蛤蜊只发生在特定地点，并且没有被列为威胁，因此圣保罗红色名录可能不是解决该物种面临的多种威胁（包括栖息地丧失风险）的最合适的保护工具。T. mactroides同时也保护栖息地和其他共存物种。