Acoustic fish biomass assessment in a deep Tunisian reservoir: effects of season and diel rhythm on survey results.

To determine the best acoustic sampling period for obtaining fish biomass estimates of a Mediterranean deep reservoir in Tunisia, we carried out day and night surveys in each of four seasons [spring (April), summer (September), autumn (December) and winter (March)]. A Simrad EK60 echosounder, equipped with two 120 kHz split-beam transducers for simultaneous horizontal and vertical beaming, was used to sample the entire water column. Data collected in December were not usable because fish merged with methane gas bubbles. However, fish abundance varied across the other seasons with a peak in acoustic biomass observed during summer nighttime hours that was associated with high water temperatures. Across seasons, the fish occupied the entire water column, and fish schools were rarely observed. The preferential timeframe (i.e. maximum fish detectability and low gas flux) for acoustic sampling was nighttime hours in summer and daytime hours during spring and winter. Our findings highlight the importance of collecting data across seasons and photoperiods when determining an acoustic sampling strategy.

Bibliographic Details

Main Authors:	Djemali, Imed, Laouar, Houcine
Format:	Journal Contribution biblioteca
Language:	English
Published:	2017
Subjects:	Target strength., Fisheries., Photoperiod., Gas bubbles, Artificial lake, Acoustics,
Online Access:	https://doi.org/10.2989/16085914.2016.1277181 http://hdl.handle.net/1834/12926
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