Effect of river restoration on spawning activity of Iberian barbel (Luciobarbus bocagei)

Abstract

In fluvial systems, where aquatic organisms are limited to living within river networks, anthropogenic barriers can interrupt connectivity and contribute to habitat fragmentation. Habitat connectivity is particularly important for migratory fish that need to move considerable distances for spawning, rearing, and refuge areas. In order to support crucial stages in the native fish species’ life cycles, compensatory measures were established in the Vilariça River due to the construction of the Baixo Sabor Hydroelectric Scheme (BSHS). Thus, the purpose of this work is to evaluate if the implemented measures, such as habitat-enhancing weirs and a flow bypass system releasing water from the BSHS, improved the survival and reproduction of a native species, the Iberian barbel (Luciobarbus bocagei). The assessment included the calculation of the number of spawning individuals and the Weighted Usable Area (WUA) of spawning habitat. In addition, to assess spawning activity, a spawn-per-unit-effort (SPUE) methodology was developed. The results showed that migration and spawning of L. bocagei were improved by increased flow velocity from the bypass system. The installed weirs also contributed to spawning success because they allowed the establishment of resting and spawning areas that were essential during reproductive period. It was possible to estimate the maximum SPUE of 5.4 spawns per minute at the spawning grounds with a 20 m reach and the number of fish observed, which ranged between 251 and 800 per fieldwork at the spawning grounds and resting areas. Furthermore, the maximum WUA was estimated to be 1580 m2 for a discharge of 1 m3/s (between median and maximum flow for spawning season) at a 2 km reach of the Vilariça River. This work showed that the rehabilitation of a tributary of a fragmented river due to the construction of dams was a valid compensatory procedure because it allowed the migration and spawning of the fish.