Methodical aspects of acoustic survey for Antarctic krill in the CCAMLR Convention area
The acoustic survey of krill is the only survey in the international practice of resource research that implements the multifrequency acoustic method of species identification. The purpose of this communication is to describe the main methodical aspects of the CCAMLR acoustic survey for krill, with particular emphasis on the multifrequency identification of krill being specific to these surveys. Identification of krill echoes is achieved through the collection and processing of acoustic data performed at three frequencies of 38, 120 and 200 kHz. Up-to date algorithms and templates for this three frequency identification method allow for identification of krill in 10 mm length groups. A multi frequency method for krill identification is implemented using the Echoview software package (Myriaх). A randomized parallel transects scheme is the basis for conducting acoustic krill surveys. This design allows the use of the most commonly used classical and geostatistical methods for post-survey density field averaging, and above all, the use of the classic Jolly and Hampton method. The survey scheme includes a system of mesoscale and small-scale strata with parallel transects. Traditionally, small-scale strata are formed in the near island zones, which are associated with areas of increased krill densities and areas of its commercial fishing. The estimation of the density and biomass of krill is carried out taking into account the spatial structure of the size composition of krill at the survey area using the data of cluster analysis, implemented on the basis of constructing a similarity matrix using Euclidean distances and the classical Ward's method. The main algorithms for estimating krill biomass from acoustic survey data using the classical Jolly and Hampton method are shown.