Fish and methane bubbles in aquatic ecosystems: hydroacoustic separation and quantification

Hydroacoustics technology offers the advantage of scanning large volurnes of water and is therefore used for accurate assessment o f abundance o f highly heterogeneous fish populations (SIMMONDS & MACLENNAN 2005) and methane bubbles rising from the bottom (ÜSTROVSKY 2003). One important limitation of the acoustical approach is the inability to classify individual targets. Gas bubbles are strong backscatterers and thus may be mistakenly identified as fish. The rate of production o f gas bubbles in sediments o f lakes and reservoirs can be high, an d therefore the density o f bubbles in the water column potentially competes with the density of fish (RunsTAM & JoHNSON 1992, ÜSTROVSKY 2003). In such cases, obtaining sound qualitative and quantitative informatian on fish and bubbles represents a challenging task. The main purpose of this work was to elaborate an approach for quantification o f the abundance of pelagic fish and bubbles when both types of acoustic targets are mixed in aquatic system. The spatial heterogeneity in distribution ofvarious types of acoustic targets was also studied.