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

摘要

Hydroacoustics technology offers the advantage of scanning large volumes of water and is therefore used for accurate assessment of abundance of highly heterogeneous fish populations (SIMMONDS & MACLENNAN 2005) and methane bubbles rising from the bottom (OSTROVSKY 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 of gas bubbles in sediments of lakes and reservoirs can be high, and therefore the density of bubbles in the water column potentially competes with the density of fish ( RUDSTAM & JOIINSON 1992, OSTROVSKY 2003). In such cases, obtaining sound qualitative and quantitative information on fish and bubbles represents a challenging task. The main purpose of this work was to elaborate an approach for quantification of the abundance of pelagic fish and bubbles when both types of acoustic targets are mixed in aquatic system. The spatial heterogeneity in distribution of various types of acoustic targets was also studied.