Mission to assess jellyfish abundances

5. 10. 2021

Last week, NTNU completed its mission to assess jellyfish abundances in the Trondheimsfjord using a combination of acoustic and optic approaches. The aim was to adjust current methods to assess in situ jellyfish abundances using semi-invasive methods. The use of acoustic and optic tools could advance current methods for abundance estimates (e.g. trawling techniques) thus allowing more sustainable methods for jellyfish stock assessments in the future. NTNUs ROV Minerva completed fours dives during the mission from 28.-29. September 2021, equipped with a Zoom camera (18 x optical 4 x digital zoom) and an Acoustic Zooplankton Fish Profiler (AZFP). Vertical and horizontal transects with ROV Minerva were performed to assess abundances of the helmet jellyfish (Periphylla periphylla) in Verrasundet/Verrabotten (Trondheimsfjord, Norway). For ground-truthing purposes, a bottom trawl was deployed in addition to relate the abundance data gained from traditional methods to abundance estimates obtained from the acoustic/optic surveys.