ABSTRACT

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.

摘要

在河—洪泛区系统中，对新热带迁徙鱼类的招聘动态进行了广泛研究，在该系统中，洪水脉动和湿地起着核心作用。在半干旱系统中，流动状况难以预测，水体是断断续续的，mi游鱼类可能采用不同的招募策略。我们调查了影响迁移鱼类（Prochilodus hartii）处于受河流管制的半干旱流域（巴西杰基廷洪河）。我们采样了鸡蛋，幼虫，年幼（YOY）和亚成虫，历时数年，分布在Jequitinhonha河300公里处的多个地点。通过不同的建模方法针对13个预测因子对生物变量进行了调查，以研究（1）产卵动力学及其与水流状况的关系；（2）与YOY存在有关的栖息地特征；（3）募集与洪水之间的关系。卵和幼虫的高密度发生在不受河流调节影响的地方，主要受水位每周和每天变化的影响。当出现侧向流时，YOY检测增加了40％，并且占用率受乳液拉伸长度的影响。亚成人的丰度与与洪水相关的任何预测因素均不相关。我们的结果表明，产卵发生在多个地点，主要受流量变化的影响，而开发和募集主要发生在河道内以及小型间歇性支流汇合处，对洪水的依赖性很小。因此，与河流-洪泛区系统相比，该半干旱系统中的鱼类募集与洪水的关系不同，从而突出了旱地的奇异性。