Management of brown trout populations (Salmo trutta L.) in northeastern Portugal (Douro basin): analysis of habitat use and feeding strategies

• Autor(a) principal: Halkhoums, Wafae
• Data de Publicação: 2017
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10198/14434
• topic: Bioecology; Conservation; Ecological integrity; River; Trout; Domínio/Área Científica::Ciências Agrárias::Agricultura, Silvicultura e Pescas

During the spring/summer of 2017, the ecological integrity of salmonid headwater streams and salmonid/cyprinid Transition Rivers of the Upper Tua basin was evaluated. Abiotic parameters (water quality and aquatic and riparian habitats) and biotic (macroinvertebrate community) parameters were evaluated in 14 selected sampling sites, distributed across six different rivers and streams of Upper Tua. Sampling of the fish and invertebrate communities was done according to the protocol defined by the Portuguese Environment Agency. In relation to the target species of the study, the Brown trout (Salmo trutta L.) were determined: 1) Population parameters 2) Ecological guilds 3) F-IBIP index and 4) Use of resources, namely the strategy developed for food and habitat. The obtained results showed that, in general, aquatic ecosystems have a good ecological integrity, based on the physical and chemical quality of the water (e.g., and low temperature T <20oC, conductivity EC25 <80 μS.cm-1 and content of dissolved salts TDS< 100 mg.L-1, high oxygenation (D.O.> 8 mg.L-1) hydromorphological conditions (e.g. pronounced riffle/pool sequence, diversity of microhabitats and well structured riparian galleries) and biological (e.g. macroinvertebrate communities dominated by stenobiont insects, mostly belonging to Ephemeroptera, Plecoptera, Trichoptera and Diptera orders) . All metrics (e.g. Shannon-Wienner's H'Diversity, taxonomic richness) and biotic indexes (e.g. IBMWP, IPTIN) corroborated the good ecological quality found. However, some signs of anthropogenic influence were detected, especially in small hydroelectric dams (eg T4, Rio Tuela, below the Hydroelectric PowerPlants), with a slight decrease in the quality of habitats and the density and structure of fish stocks, in particular Brown trout. The fish fauna of the sites sampled in the Upper Tua basin is composed of native species, considering populations of: 1) Brown trout (Salmo trutta), dominant or exclusive populations present in the small sampled streams; 2) Cyprinids: Northern chub (Squalius carolitertii), Northern straight-mouth nase (Pseudochondrostoma duriense), common barbel (Luciobarbus bocagei) and Calandino roach (Squalius alburnoides) and (3) Cobitids: in the case of Northern Iberian Spiny Loach (Cobitis calderoni). The biotic Management of S. trutta populations in NE Portugal (Douro basin): Analysis of habitat use and feeding strategies v integrity based on the F-IBIP showed that all the sampled sites had a GOOD or EXCELLENT classification. Regarding to the Salmo trutta populations, significant differences were detected in the physical condition of the fishes, taking into account the different watercourses. In fact, in the Mente river, the Brown trout indivuiduals have a low physical condition, when compared to the other rivers. Differences were also observed in the diet of the trout in the sampling sites, both intra and interpopulational, although the feeding strategies presented by this species, similarly to other studies, is typically microcarnivore with an opportunitic behavior. The obtained results for habitat use allowed to confirm the social hierarchy of these animals, since the best refuges (boulders, undercut banks) are colonized by adult trout, while juveniles were found in microhabitats of lower quality in riffle zones, and with lower degree cover. For the correct management of Brown trout populations in the Upper Tua, it is necessary the preservation of the actual ecological integrity status, in particular the priority habitats that should benefit of specific fishery management measures. Finally, it should be stressed that the management of any target species can only be successful if it is integrated into an ecosystem-wide strategy involving all groups of potential users and, in particular, find the right solutions to the sustinable combination of the exploitation and conservation of resources.