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

Abstract

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 Helvécio 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 Helvécio 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.Keywords: echo-sounding, Chaoborus, vertical distribution, fish, zooplankton.Resumo: Objetivos: O presente estudo tem como objetivo demonstrar as potencialidades da hidroacústica no estudo do comportamento do predador invertebrado Chaoborus e de peixes em ambientes aquáticos tropicais; Métodos: Foram realizadas campanhas diurnas e noturnas em maio e junho/2008 nas lagoas Dom Helvécio e Carioca, no Parque Estadual do Rio Doce e no reservatório do Nado em Belo Horizonte (MG). O espalhamento acústico dos alvos foi estudado utilizando-se uma ecossonda com transdutor digital "split-beam" de 200 kHz direcionado verticalmente para o fundo do lago; Resultados: A ecossondagem nos permitiu detectar eco-sinais claros provenientes de peixes e das larvas de Chaoborus, que estavam presentes grande densidade em todos os ambientes estudados. O comportamento migratório normal das larvas de Chaoborus pôde ser acompanhado facilmente na Lagoa Dom Helvécio e no reservatório do Nado. Entretanto, tal comportamento não foi visualizado na Lagoa Carioca. Conclusões: Os resultados mostrados neste estudo revelaram o potencial de aplicação da abordagem acústica no estudo do comportamento de peixes e organismos zooplanctônicos em sistemas aquáticos de água doce.Palavras-chave: hidroacústica, Chaoborus, migração vertical, peixe, zooplâncton.

Porewater methane transport within the gas vesicles of diurnally migrating Chaoborus spp.: An energetic advantage

“…larvae at the surface sediment leads to increased gas bubble release from the sediment6. We therefore speculate that Chaoborus spp.…”

“…Additionally, hydroacoustic surveys show that bioturbation by migrating Chaoborus spp. larvae at the surface sediment leads to increased gas bubble release from the sediment 6 . We therefore speculate that Chaoborus spp.…”

“…Though generally unaccounted for in lake studies and models, Chaoborus spp. are often the most important invertebrate predators 4 and food source for fish 5 , bioturbate sediments 3 (including methane bubble release 6 ), are a significant oxygen sink through respiration 7 , and represent a carbon loss upon emergence and thus an important link to the terrestrial ecosystem 8 . Chaoborus spp.…”

“…This bioturbation has been shown to result in the release of a large amount of gas bubbles from the sediment during emergence of Chaoborus spp. larvae from the sediments of a Brazilian reservoir 6 . In the sediment, Chaoborus spp.…”

Quantification of Chaoborus and small fish by mobile upward-looking echosounding

“…However, our TS range is larger here probably because the mentioned study was conducted in tropical Thailand in February and only small individuals could occur or different species of Chaoborus may have been present. Several observations with an echosounder using a higher frequency of 200 kHz suggest slightly higher range of modal TS -64 to -60 dB (Jones and Xie, 1994;Knudsen et al, 2006;Bezerra-Neto et al, 2012). A higher frequency is likely to be more sensitive for recording small targets, so the TS of Chaoborus may be higher with a 200 kHz echosounder compared to a 120 kHz one.…”