Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Dazed and confused: why behavioral constraints can impose enormous challenges to fish passage in the Neotropics (#104)

Paulo Santos Pompeu 1 , João Magalhães Lopes 1 , Carlos Bernardo Mascarenhas Alves 2 , Alexandre Peressin 1
  1. Federal University of Lavras, Lavras, MINAS GERAIS, Brazil
  2. Bio Ambiental, Belo Horizonte

Fish passages in South American have presented several problems, related to low attractiveness, presence of hydraulic bottlenecks, high selectiveness, lack of downstream movements of fingerlings and adults, lack of critical habitats (free flowing rivers) upstream, among others. Since the great majority of studies performed in the Neotropics have focused on the passes themselves, it seems to exist a premise that fish would behave as expected and complete their reproductive cycle if they overcome the dam and the reservoir. The behavior of “local populations” and transposed fish so far has not been evaluated. In this study, we compared the migration and behavioral patterns of Prochilodus costatus individuals that inhabit a lotic remnant of the São Francisco River (local population) upstream of the Três Marias reservoir, with transposed individuals captured below the dam, over two reproductive seasons. Local individuals showed a highly synchronic reproductive cycle, relying on environmental cues (changes in water temperature, photoperiod and the arrival of the rains) to perform upstream migration, spawn and return to feeding grounds. This group also showed a high degree of temporal and spatial fidelity in its migratory displacements. However, transposed individuals presented different behavior patterns, including erratic movements, and up- and downstream movements, many times in short intervals. They seem incapable of recognizing geographical and environmental cues to perform spawning migrations, and could not find the spawning grounds used by local individuals to mate. These results indicate that even if individuals were able to efficiently overcome dams and reservoirs, the may not be able to recognize environmental and geographical cues in their new location, and not complete their reproductive cycle as expected. In such cases, the conservation value of a fish pass would be impaired.