Antarctic Krill Biomass and Flux Measured Using Wideband Echosounders and Acoustic Doppler Current Profilers on Submerged Moorings

Abstract

During austral summer 2018/2019, we deployed an array of six submerged moorings equipped with Nortek Signature100 integrated wideband echosounder and acoustic Doppler current profilers (ADCPs) on the continental shelf of the northern Antarctic Peninsula. Acoustic data from these instruments were used to classify targets, estimate water flow and the biomass of Antarctic krill (Euphausia superba), and quantify krill flux (biomass transport). We differentiated krill from other target aggregations using a supervised classification of data from the echosounder representing five wideband frequency bins spanning 68–113 kHz and two narrowband frequencies at 70 and 120 kHz. We estimated krill biomass using echosounder data collected at 120 kHz and water flow using the ADCP data. We estimated the biomass flux from the product of mean volumetric krill density and flow speed over a depth-integration range of 150 m. The overall mean krill areal biomass density based on hourly averages was 174 g⋅m–2 during the austral summer (December–March). Mean daily biomass decreased by an order of magnitude, from 300 to 31 g⋅m–2, over the sampling period, and fluctuated by nearly a factor of 4 above and below the local trend within weekly intervals. Mean current direction was along-shelf toward the west, and mean flow speed increased from ∼0.10 to 0.14 m⋅s–1 during the season. Krill flux was correlated with biomass variation, and the grand mean flux was 0.13 g⋅m–2⋅s–1. During the study period and in our approximately 1,300 km2 study area, average total biomass of krill was 116265 metric tons, and total cumulative krill biomass was 2.5 million tons. Our results demonstrate the utility of integrated echosounder-ADCP systems for quantifying krill flux in an important foraging area used by krill-dependent predators (seabirds and marine mammals) that breed nearby and highlight the scales of variability in a key prey resource required by these predators.

Contrasting environmental conditions precluded lower availability of Antarctic krill affecting breeding chinstrap penguins in the Antarctic Peninsula

“…The mechanism explained here for the chinstrap decline was based on local conditions observed around Nelson Island colonies. The South Shetland Islands have particular geographic and bathymetric features that shape water flow, krill flux, retention and availability to penguins 64 and may be distinct from other areas. However, many of the environmental variables included in our study are experiencing similar trends at local and wider scales, making this mechanism plausible as an ecological process propagated among multiple colonies across the AP.…”

Analysis and Prospects of an Antarctic Krill Detection Experiment Using Drifting Sonar Buoy

“…PAM (Passive Acoustic Monitoring) is used to detect marine mammals [14,15], enhancing our understanding and protection of marine cetaceans. Active sonar technology is often used in resource assessment [12,13,[16][17][18][19] and marine mapping [20], playing a significant role in these areas. At the same time, sonar technology has been increasingly refined and integrated with emerging technologies like artificial intelligence, allowing it to better serve current production and research work.…”

Research on movement law of the deployment process for submerged mooring system

“…In oceanographic research, oceanographic survey and ocean engineering construction, it is often necessary to monitor the seawater parameters in a specific area for a long time. Submerged mooring system is a kind of platform widely used in Marine environmental monitoring network, which plays an important role in Marine science research [1][2][3].…”