Spatial distribution of Antarctic krill(Euphausia superba) and crystal krill(Euphausia crystallorophias)in the Western Ross Sea during summer 2018

Abstract

Antarctic krill(Euphausia superba) and crystal 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 trawl and acoustic survey of krill was conducted around Cape Hallett during IBRV Araon Antarctic Cruise in Febrauary - March 2018. Multi-frequency acoustic data (38 and 120 kHz) was used to discriminate krill marks from other species and estimate the spatial distribution of both krill species. A Rectangular Net(mesh size 330㎛, mouth area 1 m2) was used to obtain length-frequency distribution of Antarctic krill and crystal krill. The mean length of Antarctic krill was 36.5 mm(SD = 5.7 mm) and varied from 12.3 to 43.7 mm. Crystal krill was ranged from 7.5 to 20.1 mm with a mean of 11.7 mm(SD = 2.2 mm). 94% of the Antarctic krill caught were adults and sub-adults, whereas 87% of the crystal krill caught were juvenile, with sub-adults comprising 12% and adults less than 1%. From the results, Antarctic krill were mostly distributed in the region of the continental slope at depths shallower than approximately 100 m. Crystal krill were mainly concentrated in the neritic waters on the continental shelf at depths between 100 and 200 m. This research showed that in the Western Ross Sea the two species of krill inhabited different areas and vertical distribution during the summer period