Assessment of krill biomass in fishing grounds using the data on fishing intensity and hydroacoustic method

The paper contains a description of the statistical method used for assessment of the fishing intensity based on actual fishing effort and estimating the initial krill biomass prior to beginning of the fishery. Application of the statistical method for assessment of the initial krill biomass may be realistic provided that the conditions exist, which permit to determine the catchability of the midwater trawl. Two methods were used for this purpose: modelil1ing the probabilistic-statistical theory of fishing traw1s and hydroacoustic method. The latter method is based on comparison of the catch and the krill biomass estimate produced by the echo integrating apparatus used in the layer fished with the trawl. As applied to the estimate of trawl catchability in the krill fishery, this method is reliable enough as multiple echo location of one and the same shoal is actually out of the question because of poor swimming ability of the krill. The paper suggests the comparison of estimates of krill catchability obtained by the hydroacoustic method and from the models of probabilistic-statistical theory of fishing trawls in order to illustrate the closeness of the two methods. The estimates of the krill biomass resulting from the catch statistics and from the hydroacoustic survey carried out with the use of the echo integrating apparatus are also compared.
Theoretical bases of the calculation methods used are stated in a concised form with references to corresponding literary sources. Basic principles of the statistical method of assessment of the fishing intensity and of the probabilistic-statistical theory of the fishing trawls were developed by Dr. Yu.V.Kadilnikov, Head of the AtlantNIRO Laboratory, with the exception of the methods of standardizing the fishing effort which were worked out by Ivanova V.F. She also made all calculations of the fishing intensity. Characteristics of the krill distribution, computations of trawl catchability, trawl catchability by the hydroacoustic method and krill biomass from the results of the hydroacoustic surveys were estimated by Kasatkina S.M. Trawl parameters were calculated by the senior scientist Myskov A.S.