2014 Volume 61 Issue 1 Pages 82-86
Although problematic jellyfish blooms have frequently been reported in recent decades in many parts of the world ocean, studies of long-term monitoring based on accurate measurements of abundance and biomass of jellyfish populations are few. Pronounced patchy distributions shown by medusae, such as Aurelia aurita s.l., have precluded researchers from accurate determinations, and some visual and acoustic instruments have been used to replace the traditional sampling gear, i.e. plankton net or trawl. We introduce use of a Dual frequency IDentification SONar (DIDSON, Sound Metrics Co.), a high-definition imaging sonar that provides near-video-quality images of underwater objects, to jellyfish ecological studies. We deployed the DIDSON in a shallow, enclosed water mass where A. aurita medusae dominated, and determined their spatiotemporal distributions, numerical abundances and biomass much more accurately than with conventional net sampling. Therefore, we conclude that the DIDSON can be a powerful tool to monitor the population density and spatial distribution of relatively large jellyfish (bell diameter: >ca. 5 cm) in shallow (<10 m) coastal waters, where problematic jellyfish often bloom.
