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标题：Quantification of Chaoborus and small fish by mobile upward-looking echosounding
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作者：Roman Baran ; Michal Tušer ; Helge Balk 等
期刊名称：Journal of limnology
印刷版ISSN：1129-5767
电子版ISSN：1723-8633
出版年度：2019
卷号：78
期号：1
页码：60-70
DOI：10.4081/jlimnol.2018.1837
出版社：Istituto italiano di idrobiologia
摘要：Chaoborus larvae inhabit frequently the water column of lakes, when they can be mistaken for small fish. Because larvae ascend up to the blind zone of downward-looking echo sounding at night, quantitative acoustic estimation of them is possible only with upward-looking approach. For this reason, the mobile hydroacoustic upward-looking system (120 and 38 kHz split-beam echosounder) in combination with a direct catch method (trawling) was tested to investigate the night community of invertebrates and juvenile fish in the surface layer of the Římov reservoir (Czech Republic). In the target strength range of invertebrates (smaller than -59 dB), the 38 kHz echosounder recorded only a small proportion of targets while the 120 kHz echosounder recorded distinct peaks corresponding to high densities of Chaoborus (target strength, TS range -70 to -60 dB, average TS -66 to -64 dB). At 120 kHz frequency, the TS distribution of smaller cohort of juvenile fish ( 1.5 ind.m-3.
关键词：Římov reservoir;juvenile fish;invertebrate;trawling;hydroacoustics;target strength