SPATIAL DISTRIBUTION OF ANTARCTIC KRILL (Euphausiasuperba) AND ICE KRILL (E.crystallorophias) IN THE WESTERN ROSS SEA DURING SUMMER 2018

Abstract

Antarctic krill(Euphausia superba) and ice krill(E.crystallorophias) are key links between primary products and the community of predators in the shelf waters of the Ross Sea. In spite of their abundance and important role in Antarctic food webs, relatively few studies have concerned their horizontal and vertical distribution. A combined acoustic and net survey of krill was conducted around Cape Hallett during IBRV Araon Antarctic Cruise(ANA08C) in February - March 2018. Multi-frequency acoustic data (38 and 120 kHz) allowed discrimination of krill from other species. A rectangular net(mesh size 330㎛, mouth area 1 m2) hauls towed obliquely between surface to 200 m used to validate the acoustic identification of krill. Length distribution of Antarctic krill and ice krill were used to parameterize a scattering model to classify echoes and estimate spatial distribution from collected acoustic data. The mean length of Antarctic krill was 36.5 mm(SD = 5.7 mm) and varied from 12.3 to 43.7 mm. Ice krill were ranged from 7.5 to 20.1 mm with a mean of 11.7 mm(SD = 2.2 mm). The catch data of Antarctic krill were composed primarily of adults and sub-adults, while ice krill were mostly composed juveniles. Acoustic backscattering strength from both krill species increased with increasing frequency, which is characteristic of species without an air-filled swim-bladder. Analyses of acoustic observations revealed that Antarctic krill were distributed in the region of the continental slope at depths shallower than approximately 100 m. Ice krill were widely observed in the neritic waters on the continental shelf at 100 - 200 m. This research demonstrated that in the Western Ross Sea the two species of euphausiid inhabited different areas and vertical distribution during the summer period.