Recruitment Dynamics Of A Migratory Fish In A Semi-Arid River System

Recruitment dynamics of Neotropical migratory fishes are widely studied in river-floodplain systems, where the flood pulse and wetlands play a central role. In semiarid systems, where the flow regime is less predictable and waterbodies are intermittent, migratory fishes may employ different recruitment strategies. We investigated factors affecting the recruitment dynamics of a migratory fish (Prochilodus hartii) in a semiarid river basin (Jequitinhonha River, Brazil) subjected to river regulation. We sampled eggs, larvae, young-of-the-year (YOY), and subadults over multiple years and at several sites distributed along 300 km of the Jequitinhonha River. Biotic variables were investigated against 13 predictors through different modeling approaches to examine (1) spawning dynamics and its relationship to the flow regime, (2) habitat features related to the presence of YOY, and (3) the relationship between recruitment and floods. Higher densities of eggs and larvae occurred at sites with no influence of river regulation, affected mainly by weekly and daily variations in water level. YOY detection increased by 40% when a lateral stream was present, and occupancy was affected by the length of the lotic stretch. Subadult abundance was not correlated with any predictor related to the flooding regime. Our results show that spawning took place at multiple sites, affected mainly by flow variations, while development and recruitment occurred mostly within river channels and in the confluence of small intermittent tributaries, with little dependence on floods. Therefore, fish recruitment in this semiarid system showed different relationships with floods when compared with river-floodplain systems, highlighting the singularity of drylands.