Fish conservation must go beyond the concrete: a comment on Celestino et al. (2019)

Abstract

In a recently published paper, Celestino et al. (2019) investigated the effects of a fish ladder located near the Porto Primavera Dam (Paraná River, Brazil) in order to evaluate if it provided free passage for the migratory fish Prochilodus lineatus. Fish were marked with PIT-tags and movements were monitored within the ladder over a 3.5-year period. The main finding was “Our study identified bidirectional movements by P. lineatus through the Porto Primavera fish ladder, including multiple passes by the same fish” (p. 241). It led authors to conclude: “Our results suggest that by providing bidirectional connectivity between upstream and downstream habitats, fishways can be an effective tool for preserving populations of P. lineatus and probably for other species of Prochilodus” (p. 242). Both conclusions, however, may not be correct, because they go beyond the data directly presented in the manuscript. The study overlooked issues related to the spatial scale and experimental design, since it was limited to investigate patterns of movement within the fish ladder alone. In this sense, they encourage the reader to accept patterns and conclusions that were not specifically investigated (e.g., migratory dynamics and conservation success), or that cannot be fully supported by the data (e.g., bidirectional movements and efficient passage). As the conclusions presented in the study have direct implications for the licensing process of hydropower dams and the management/conservation of Neotropical migratory fishes, we provide suggestions to highlight additional important factors and issues that should be considered or addressed in future research.