Acoustic Reconnaissance of fish and environmental background in demersal zone in southern Baltic

The paper describes results of studies based on measurements of the Sv distribution in 3m layer over the bottom in the southern Baltic area for the period 1995-2004. These are correlated with values of coincident bottom features, estimated on the basis of all available survey data. It is considered that values of Sv are proportional to demersal fish (herring, cod, flatfish) density. Seabed classification was based on analysis of duration of bottom echo recordings collected during the same series of surveys. Normalized (against the depth) bottom echo duration - Č’/2 was applied as 1D parameter characterizing seabed properties. Geographical distribution of this parameter and its dependence on other determined factors were analyzed. Studies of irregularities in fish distribution and its correlation to Č’/2 values were made. The paper gives a new method of acoustic classification of seabed and shows also some conclusions on coincidence of bottom features and environmental background.