José Fernandes Bezerra-Neto

Hydroacoustic assessment of fish and Chaoborus (Diptera-Chaoboridae) distribution in three Neotropical lakes

AIM: This study aims to demonstrate the potential of hydroacoustics in the study of behavior of the invertebrate Chaoborus and fish in neotropical water environments; METHODS: Synoptic campaigns were conducted in May and June-2008 in Dom Helvecio and Carioca lakes, at the Parque Estadual do Rio Doce (MG), and Nado reservoir, Belo Horizonte (MG). The acoustic scattering of targets was studied using a downward-oriented split-beam 200 kHz echosounder; RESULTS: We detected clear echo signals from fish and Chaoborus larvae, which can be viewed in high density in all environments studied. The normal migratory behavior of the larvae of Chaoborus could be easily monitored in the Dom Helvecio Lake and the Nado reservoir. However, this behavior was not seen in Carioca Lake; CONCLUSIONS: This study revealed the potential application of acoustic approaches to study the behavior of fish and zooplankton organisms in freshwater aquatic systems.

Implementation of hydroacoustic for a rapid assessment of fish spatial distribution at a Brazilian Lake - Lagoa Santa, MG

AIM: To study the distribution, structure, size and density of fish in the karst lake: Lagoa Central (Lagoa Santa, MG - surface area: 1.7 km2; mean depth: 4.0 m; and maximum depth: 7.3 m). METHODS: The hydroacoustic method with vertical beaming was applied, using the echosounder Biosonics DT-X with a split-beam transducer of 200 kHz. The analysis of the acoustic data was performed with the software Visual Analyzer (Biosonics Inc.). Thematic maps of density echoes associated with fish, estimated by the technique of echo-integration, were made using the kriging interpolation. The density and vertical distribution of insonified fish were estimated using the technique of echo-counting. RESULTS: The lake had a mean density of 0.89 echoes associated with fish per m2, showing large spatial variations in the density of fish. The size estimated for the echoes associated with fish range from 2.7 to 15.9 cm (mean = 5.3 cm). CONCLUSIONS: The use of hydroacoustic to obtain rapid and realistic estimates of fish abundance and vertical distribution of the fish stock was successful

Partitioning of the diffuse attenuation coefficient for photosynthetically available irradiance in a deep dendritic tropical lake

We studied the effects of particulate and dissolved optically active components on the attenuation of photosynthetic active radiation (PAR) in a tropical lake. The temporal and spatial distribution of tripton, Chl-a and aCDOM(440) and their relative contribution to the diffuse PAR attenuation coefficient (Kd) was investigated at 21 sites (dry and wet seasons and two intermediate periods) and at monthly interval at 1 pelagic site. Higher values of ​​ Kd were observed during the mixing period, characterized by a higher concentration of tripton and Chl-a compared to the stratified rainy season. In the spatial sampling PAR attenuation was dominated by tripton absorption/scattering (average relative contribution of 79%), followed by Chl-a (average 11.6%). In the monthly sampling tripton and Chl-a accounted for most of the Kd with relative contributions of 47.8% and 35.6%, respectively. Multiple linear regression analysis showed that Chl-a and tripton in combination explained 97% of the monthly variation in Kd (p<0.001), but Chl-a had more influence (higher regression coefficient). Thus, although most of light attenuation was due to tripton, seasonal variations in phytoplankton abundance were responsible for most of the temporal fluctuations in Kd.