Investigation of the target strength-to-length relationship of Baltic herring (Clupea harengus) for use in biomass estimation

Abstract

EU environmental protection policy, based on a sustainable development approach, requires fast and non-expensive methods of marine ecosystem monitoring. Acoustic techniques, which satisfy these requirements, are widely used as a reliable method of fish stock assessment. Systematic acoustic surveys are conducted in the Baltic Sea in order to estimate the abundance of ecologically and commercially important fish populations such as herring (Clupea harengus) and sprat (Sprattus sprattus). An important requirement for acoustic abundance estimation is the species specific target strength (TS)-to-fish length relationship to convert acoustic energy into numbers of fish. TS is a measure of a fish’s potential to reflect sound and one of the major challenges in the Baltic Sea is the development of a reliable TS-length relationship for Baltic herring. Currently, a TS relationship originally determined for North Sea herring is used for the assessment of Baltic herring.