The Tocantins-Araguaia River Basin encompasses six Brazilian states and holds a rich
ichthyofaunal diversity with high endemism. A project is planned to improve navigability of
the waterway and enable year-round vessel traffic within the Tocantins-Araguaia drainage
system. An environmental impact analysis was conducted to assess the socio-environmental
feasibility of the process. However, concerning the ichthyofauna, many of the listed species
do not effectively represent the diversity of fishes inhabiting the area, as numerous resident
species have not been accurately cataloged. Therefore, effective and complementary
methodologies are necessary to evaluate and diagnose the impacted rheophilic fish
community, with the risk of neglect depending on the sampling method employed. This study
aims to use visual census through diving as a complementary tool for inventorying rheophilic
ichthyofauna in the Tocantins River in the Marabá region, near the well-known Pedral do
Lourenço. In 2019, a 10-day expedition was conducted, averaging two dives per day during
daylight hours, resulting in 105 minutes of footage. The results obtained were 5583 specimens
from the 2017/2018 campaign by the Environmental Impact Study, 636 specimens collected
during diving, and 143 individual fish records using visual census in 2019. The traditional
methods captured a significant diversity of species (59.3%), but diving and visual census
complemented this information by capturing exclusive and shared species. Characiformes
were predominantly sampled through traditional methods (97.31%), while diving accounted
for 13.52% and visual census for 9.79%. Siluriformes also exhibited differences in specimen
capture, with diving and visual census playing important roles. The combination of these
methods enhances efficiency in detecting fish diversity in rapids. The similarity between
diving and visual census highlights their complementarity, as evidenced by the cluster
analysis.
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