Revision of the Management Plan of the Recreational Fishing Zone of the Rabaçal River (Northern Portugal) ^†

Abstract

This study presents the revision of the Rabaçal River Recreational Fishing Area Management Plan (ZPL), implemented in 2020, aiming to evaluate its effectiveness and identify the need for adjustments after five years. The study area includes part of Montesinho Natural Park, covering water bodies upstream of the Vale de Armeiro Reservoir (RH3—Douro Basin), excluding the Assureira River sub-basin. The methodology followed the initial study design, with electrofishing conducted at ten stations (30 surveys). Hydromorphological and riparian conditions were assessed using the River Habitat Survey (RHS), enabling the calculation of the Riparian Quality Index (RQI), Habitat Modification Score (HMS), and Habitat Quality Assessemt (HQA). Results indicate high habitat diversity and overall good-to-excellent hydromorphological quality, although they are locally affected by human pressures and global change. Brown trout (Salmo trutta) was recorded at all sites, showing wide spatial distribution. Population structure was dominated by young individuals (≤2 years; 70%), indicating high recruitment rates. However, growth patterns and reduced body condition suggest that habitat features, particularly flow regime and riparian quality, are influencing population dynamics, highlighting the need to explicitly integrate habitat–population relationships into management measures. A notable expansion of the invasive signal crayfish (Pacifastacus leniusculus) was also observed (now present at stations T₃, T₄, and T₅), reinforcing the need for targeted monitoring and control actions. Overall, the results support the continuation of the current management model, aligned with the conservation objectives defined in the initial plan and in project POSEUR-03-2215-FC-000096, while emphasizing the importance of habitat conservation to ensure the long-term sustainability of trout populations and aquatic ecosystems.