Time travelling through local ecological knowledge regarding an endangered species Ronaldo Sousa a, ⁎, Joana Garrido Nogueira b , Fernando Miranda c , Amílcar Teixeira c a CBMA - Centre of Molecular and Environmental Biology, Department of Biology, University of Minho, Campus Gualtar, 4710-057 Braga, Portugal b CIBIO/InBIO - Research Center in Biodiversity and Genetic Resources, University of Porto, Campus Agrário de Vairão, Vairão, Portugal c Centro de Investigação de Montanha (CIMO), Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal HIGHLIGHTS • We combine LEK and field sampling to assess the conservation status of M. margaritifera. • In Cávado River the species is possibly extinct but respondents confirm its presence in the past. • In Neiva River the species is still present but few respondents remembered its presence in the past. • LEK is a low cost tool to get information about historical ecological conditions. • Results reinforce concern about the fu- ture conservation of M. margaritifera in Portugal. GRAPHICAL ABSTRACT abstract article info Article history: Received 29 March 2020 Received in revised form 13 May 2020 Accepted 5 June 2020 Available online 6 June 2020 Editor: Sergi Sabater European freshwater pearl mussel (Margaritifera margaritifera) populations are declining despite a growing ef- fort to conserve them. Here we used a combination of local ecological knowledge (LEK) and field sampling to as- sess past and current distribution and conservation status of this endangered species in Cávado and Neiva Rivers (Portugal). We performed face-to-face interviews in both rivers and sampled the entire area where the respon- dents confirmed the historical presence of this species. Abiotic characterization, water quality and fish diversity were also assessed in both rivers. We found that freshwater pearl mussels are now possibly extinct in Cávado River but almost 50% of the respondents confirm its presence in the past, especially elders that lived in villages near its historical distribution. To the contrary, and although the species is still present in Neiva River, only 3.8% of the respondents remembered its presence in the past. In both rivers, respondents suggested pollution as the most important explanation for the freshwater pearl mussels decline. However, nowadays both rivers present excellent water quality and trout Salmo trutta (the freshwater pearl mussel fish host) is still abundant. Since we identified the areas where the species was present in a recent past, this information is vital for possible management actions with the aim of re-introduce or increase the abundance of M. margaritifera populations and/ or for the rehabilitation of habitats in both rivers. We also highlight the vital importance of getting LEK, mainly from elders, in order to avoid shifting baseline syndromes and to get qualitative accurate information of past ref- erences and/or experience with historical conditions. Results reported here reinforce concern about the conser- vation status of freshwater pearl mussel populations in Portugal and can be used to guide future research and management initiatives to better conserve this species. © 2020 Elsevier B.V. All rights reserved. Keywords: Conservation Freshwater ecosystems Freshwater mussels Questionnaires Cávado and Neiva Rivers Science of the Total Environment 739 (2020) 140047 ⁎ Corresponding author. E-mail address: rg.eco.sousa@gmail.com (R. Sousa). https://doi.org/10.1016/j.scitotenv.2020.140047 0048-9697/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv