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A simple method to correct the results of acoustic surveys for fish hidden in the dead zone
Author(s) -
Tušer M.,
Prchalová M.,
Mrkvička T.,
Frouzová J.,
Čech M.,
Peterka J.,
Jůza T.,
Vašek M.,
Kratochvíl M.,
Draštík V.,
Kubečka J.
Publication year - 2013
Publication title -
journal of applied ichthyology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.392
H-Index - 62
eISSN - 1439-0426
pISSN - 0175-8659
DOI - 10.1111/jai.12091
Subject(s) - perch , benthic zone , fishery , biology , smelt , biomass (ecology) , fish <actinopterygii> , water column , sampling (signal processing) , dead zone , ecology , filter (signal processing) , computer science , computer vision
Summary In lentic freshwater systems, vertical acoustics may underestimate fish abundance in the acoustic dead zone where fish detection capability is limited. To estimate this bias, the height of fish above the lead‐line of a benthic multi‐mesh gillnet (1.5 m high) was used to quantify both the vertical distribution of fish near the bottom and the proportion residing within the acoustic dead zone. The study was carried out at the percid‐dominated B iesbosch R eservoirs in the N etherlands. Acoustic dead zones were estimated at 7 cm above flat bottoms, and 12–34 cm above 8° sloped bottoms at depths of 5–27 m, respectively. Depending on the habitat, 36 to 75% of the gillnet catch by number was present in the acoustic dead zone, representing 5–51% of the biomass. Near‐bottom depths were highly preferred by ruffe G ymnocephalus cernua , often used by perch P erca fluviatilis and pikeperch S ander lucioperca , plus seemingly devoid of smelt O smerus eperlanus . The total amount of fish hidden in the acoustic dead zone was estimated to be 13–39% of the whole water column. The proportion of biomass obscured in the dead zone was lower (1–12%). The conclusion is that undetected fish in the acoustic dead zone can seriously bias density assessment, which can be corrected by concurrent sampling with benthic gillnets.