Analysis of acoustic data to examine spatial and temporal variability of krill distribution from repeated transects

Authors present the acoustic data obtained on the R/V Atlantida cruise in 2020 to examine spatial and temporal variability of krill distribution. These data were collected in Subareas 48.1 and 48.2 using the repeated  transect system, including: local survey in Bransfield Strait and two mesoscale reference transects  (one is in the Elephant Island stratum and one is in the  Scotia Sea stratum  along longitude 50⁰ w ). Acoustic observations at the local survey and on each of the reference mesoscale transect were undertaken twice with an interval of about a month (34-36 days). Acoustic data collection and processing were completed in full compliance with CCAMLR recommendations (with references within WG-EMM-16/38; WG-EMM-11/20, ASAM-16/01) and accompanied by trawl sampling and environmental observations. There were no commercial vessels in the study area, excluding the effect of krill fishing on the observed distribution of krill. Significant temporal variability in the krill distribution were identified, both at the local survey area and at each repeated mesoscale transect. Such changes are demonstrated in estimates of the density, horizontal and vertical distribution of krill. The change in the krill biomass in the local area under consideration in Bransfield Strait was 792.6 thousand tons being accompanied by a change in the krill length composition. According to the authors, the observed temporal variability of krill distribution at different spatial scales is a consequence of the influence of the krill flux by the current.