Management Measures for the Conservation of Freshwater Pearl Mussel (Margaritifera margaritifera) and Brown Trout (Salmo trutta) in Portugal ^†

Abstract

The project “Recovery and Protection of Margaritifera margaritifera” (POSEUR-03-2215-FC-000096) was developed to protect and restore freshwater pearl mussel M. margaritifera and brown trout S. trutta populations in Portugal. To conduct this, in the last 3 years, several in situ and ex situ conservation measures were applied, and several tasks were defined, namely the following: (1) assessment of the spatial distribution and conservation status of the target species; (2) evaluation of the biological and ecological quality of salmonid rivers; (3) analysis of vulnerability to human disturbances; (4) an increase in habitat suitability; (5) definition of management plans for salmonid watercourses; 6) captive reproduction of M. margaritifera and S. trutta; (7) monitoring of M. margaritifera and S. trutta stocking programs; (8) genetic characterization of wild populations of S. trutta. Results showed that M. margaritifera is currently distributed in seven rivers (mainly in Rabaçal and Tuela rivers, and residually in Mente, Paiva, Neiva, Tâmega and Beça rivers). In Portugal, only S. trutta functions as a suitable host for M. margaritifera. Both species are highly vulnerable to human disturbances and the main threats include habitat fragmentation and degradation (e.g., dams and alder tree disease), invasive alien species (e.g., American crayfishes, Pacifastacus leniusculus and Procambarus clarkii) and climate change (e.g., droughts and heatwaves). A riparian area of 2.91 ha was restored, and several management plans were specifically developed in different rivers to contribute to the recovery of both native populations. Moreover, the ex situ reproduction of M. margaritifera produced more than 100,000 juveniles, allowing the implementation of reintroduction actions. Complementarily, eight wild brown trout stocks were selected, based on the genetic diversity, and acclimated to captivity in ICNF fishfarms (Castrelos, Bragança and Torno, Amarante) for future stocking programs according to national legislation. Overall, this project is a first step to improve the conservation status of pearl mussel M. margaritifera and its fish host, brown trout S. trutta.