Abstract:In order to make the best use of the information on fishery resources derived from fishing vessels, a series of processing methods were probed to numericalize the pictorial image of the acoustic echogram taken from a commercial echo-sounder. The resulting methods were then applied to analyze the swarming characteristics of Antarctic krill Euphausia superba utilizing echogram image photos taken from a Chinese Antarctic krill fishing vessel. The thickness, gravity center and relative density were analyzed after a series of preprocessing including adjustment of shooting angle and luminance of the photos, and standardization of the RGB Triplets and binarization of each pixel. Results from 30 images showed that the mean thickness of these krill swarms ranged from 5.6 m to 55.8 m,and the median thickness and mean thickness were 25.7 m and 27.1 m, respectively. The gravity center of these swarms was found between depths of 40.0 m and 156.5 m, and the median depth and mean depth were 68.8 m and 77.3 m, respectively. There was an apparent diel variation in the swarming characteristics of Antarctic krill. the swarms were relatively thinner but krill densities were relatively high in day hours; and the opposite were true at night. This exercise provided an effective tool for the study of fishery resources using fishing vessels where only commercial echo-sounder is available.
