Spatial fish distribution in autumn in a shallow mesotrophic lake, assessed by hydroacoustic surveys, trawling, and beach seining.

Day and nighttime autumn fish abundance and biomass were studied in the pelagic and littoral zones of Lake Sauka in Latvia. Both pelagic methods (hydroacoustics and trawling) revealed significantly higher fish abundance and biomass during the day than at night, especially in deeper zones (below 3 m). Roach (Rutilus rutilus) and Eurasian perch (Perca fluviatilis) dominated the trawl catches during the day, while roach and ruffe dominated at night. Fish smaller than 14 cm strongly dominated in both the trawl catches and hydroacoustic observations. Our hydroacoustic sampling found inhomogeneous pelagic distributions of fish aggregated in big shoals during the day. In the littoral zone, which was sampled by beach seining, both the abundance and biomass were significantly higher at night than during the day. Roach, bleak, and European perch usually dominated in beach seine catches during the day and at night. The daytime pelagic biomass found by hydroacoustics was 62 kg/ha and it decreased to approximately 11 kg/ha at night. The littoral biomass found by beach seining was diurnally opposite, 4 kg/ha during the day and 37 kg/ha at night. It is obvious that diurnal horizontal migrations between pelagic and littoral zones, and shoaling behavior during the daytime are common patterns in the shallow Lake Sauka during the autumn. The study of the spatial distribution of fish is extremely important for the establishment of an appropriate monitoring plan for the purposes of the Water Framework Directive with regard to the morphometry of the lake, the geographical location, and the sampling period of the year. This study also shows that the combination of completely non-invasive hydroacoustic and other methods that are invasive (trawls, beach seines) but not as destructive as gillnets, which are normally used for scientific fish monitoring in Europe, could be a future way forward for fish monitoring.

Chave de identificação dos Ctenophora da costa brasileira / Identification key for the ctenophores from Brazilian coast

Embora abundantes e importantes ecologicamente no meio marinho, os ctenóforos do litoral brasileiro têm sido pouco estudados. O presente estudo tem por objetivo prover informações para auxiliar na identificação desses organismos. Para tal, são descritos métodos de fixação e documentação fotográfica dos ctenóforos. A terminologia referente ao grupo, em língua portuguesa, é apresentada na forma de um glossário. Além disso, as características que distinguem as treze espécies registradas para águas brasileiras são organizadas em uma chave de identificação. A complementação da identificação pode ser feita pela literatura indicada para cada espécie.

Although ctenophores are abundant and ecologically important in the marine environment, they are poorly known in the Brazilian coast. The present study is a taxonomic key for the ctenophores from the Brazilian coast. It aims to help students and non-specialist researchers with the identification of those organisms. Collecting, preserving and photographing methods are described. Characters that distinguish the thirteen species registered in Brazilian marine territories are presented.