Multidisciplinary acoustic surveys with focus on fishes and plankton: how understanding species interaction can support fish stock assessment and management activity

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It was shown that uncertainty in semipelagic species assessments is to the great extent determined by existing biomass distributed in the pelagic zone and becomes unavailable to the bottom survey being traditional method for estimating such species. The authors provided multidisciplinary acoustic survey (in the pelagic layer above the near-bottom layer covered by the bottom trawl) and supplemented bottom surveys with acoustic observations to investigate drivers of spatial distribution of semipelagic mackerel icefish (Ch.gunnary) and increase reliability of survey estimates for this commercial fish in Antarctic water. It was revealed that the significant amounts of icefish (in some years nearly 50-60%) may distribute in the pelagic zone being unavailable to bottom survey. Variability of icefish spatial distribution in the near-bottom layers revealed that bottom survey indices are often of random nature and depend on the location of trawl stations as well as on the trawl efficiency. Simulation model for estimating statistical characteristics of semipelagic abundance indices by age groups with combining their pelagic and bottom components were developed. The authors show that new abundance indices result not only in new stock assessment and population parameters of icefish, but also may significantly change the TAC value