Spatiotemporal characteristics of population structure for Antarctic krill (Euphausia superba) during austral summer in Amundsen Sea

Abstract

This paper was based on data collected during the 38th and 39th Chinese National Antarctic Research Expeditions in the Amundsen Sea. The spatiotemporal distribution patterns of length (total length, AT) and sexual maturity stages of Antarctic krill (Euphausia superba) were examined. The age structure and geographic distribution of cluster groups also were studied. The results reveal significant diurnal variations in the length and maturity stages of Antarctic krill during the morning (MRN) to morning twilight (MTW) period, with mean lengths ranging from 28.92 to 45.87 mm. Two cyclical patterns were observed. Regarding maturity stages, the krill were composed of juveniles, adult males, and adult females in increasing order of proportion, with a notably higher proportion of non-gravid females compared to gravid females, and mainly distributed in evening twilight (ETW) to dawn (DWN), MTW to day (DAY), MRN to MTW, MRN to MTW and night (NIT) to DAY periods, respectively. Significant spatial variations in krill length and maturity stages occur, with a marked regional boundary around 130°W. K-means clustering analysis of krill length identified Group I, Group II, and Group III, with dominant age classes of 3+, 0 and 3+, and 3+ to 4+, respectively. Group II was widely distributed in the surveyed waters, whereas Group I and Group III were distributed only in waters west of 130°W. The study area features a significant continental slope, where adults and gravid females were primarily distributed on its slopes and to the south. This spatial pattern also profoundly influenced the distribution of different cluster groups