A finer look into the twilight zone : comparing acoustic records from an animal-borne miniature sonar and a multifrequency echosounder [résumé]

Abstract

ICES. Working Group of Fisheries Acoustics, Science and Technology (WGFAST), Somone, SEN, 25-/04/2022 - 28/04/2022An animal-borne miniature active echo-sounder has been recently deployed on southern ele-phant seals (Mirounga leonina) from the Kerguelen and Argentinian colonies. This high frequency sonar (1.5 MHz) has shown a strong potential in detecting small mid-trophic level targets (zoo-plankton and micronekton). Relative abundance and distribution can be assessed, allowing to observe temporal (diel migration) and spatial patterns of plankton. However, the interpretation of the collected data remains uncertain. To address this lack of information, we conducted in situ experiments onboard the Marion Dufresne vessel in the Southern Ocean (10th February to 6th March 2022). The microsonar was fixed on the rosette sampler at 13 locations and attached 16 times to a trawling net (4 mm mesh). Records will be analyzed applying a recent method devel-oped on elephant seals data to detect targets in the beam and estimate organisms abundance. The result will be compared with biological samples and backscattering layers detected by a multifrequency EK80 echosounder (18, 38, 70, 120 and 200 kHz), offering an acoustic landscape of the seals foraging area. This study will benefit to ongoing research regarding biological fields visited by the elephant seals, bringing precision on microsonar target detection capacities