Linking acoustic scattering coefficient to krill fishery data: feasibility of estimating krill abundance using fishing survey

Antarctic krill (Euphausia superba Dana) is a key species in the Southern Ocean ecosystems and supports different levels of predators. It is also an important economic species for Antarctic fisheries. In this paper, using the multi-frequency acoustic data and the fishery data, the relationship between the acoustic scattering coefficient of krill swarms and catch, catch per unit effort (CPUE), catch per unit fishing area (CPUA) were studied for better understanding the feasibility of assessing krill abundance based on fishery data. The results showed that average catch of daytime trawls was significantly higher than average catch of night trawls. The average thickness of krill swarm in the daytime was thinner than that at night. At the depth of over 100 m, the average NASC during the daytime is higher than that at night, with the maximum NASC between 160 and 180 m in depth. Both CPUA and CPUE at the different depth interval are higher during the daytime than that at night. The average NASC value reaches the maximum in 12:00 - 15:00. CPUA and CPUE values reach the maximum in 12:00 - 15:00. The pairwise two-sample t-test analysis shows that a significant correlation existed between NASC and CPUA, the equation is y=1.6768x+5.8976 (R²=0.5818). NASC and catch also had a significant correlation, the equation is y=2.0324x+6.3795 (R²=0.785). More acoustic data and fishery data are needed to verify the relations between NASC and catch and further to explore the feasibility of estimating abundance of krill using acoustic and fishery data.