Results of the cetacean prey survey using a quantitative echo sounder in JARPA from 1998/99 to 2004/2005

• Main Authors: Hiroto Murase, Hiroshi Kiwada, Koji Matsuoka, Shigetoshi Nishiwaki
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Antarctic; Ross Sea; The Antarctic; Antarc*; baleen whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.452.6094; http://www.icrwhale.org/pdf/SC-D06-J21.pdf

Krill biomass estimation surveys using a quantitative echo sounder have been conducted in JARPA since 1998/99 season to achieve one of the main objectives of JARPA which is elucidation of the role of whales in the Antarctic marine ecosystem. The survey was conducted concurrently with cetacean survey. Similar biomass estimates were obtained in Area IV in the 1999/2000 (34.2 million t) and 2001/2002 (34.1 million t) seasons. In Area V, biomass in the 2000/2001 (20.7 million t) and in the 2002/2003 (22.6 million t) seasons were similar but biomass in 1998/1999 (29.7 million t) was higher than the other two years. Higher biomass in 1998/99 could be explained by seasonal effect and area coverage differences. Biomass density in each stratum as well as overall biomass (7.0 million t) in Area V were low in 2004/2005 even if no krill biomass estimate in North-West stratum because of prevailing poor weather conditions for acoustic survey was taken account. Biomass in Area IV was higher than Area V. There was a unique opportunity to compare the biomass estimate from two independent vessels in the Ross Sea region in 2004/2005. One vessel, Kaiyo Maru, conducted standardized krill biomass estimation survey adopted by CCAMLR using both RMT net sampling and acoustic survey while the other vessel, Kyoshin Maru #2, only conducted acoustic survey as in previous JARPA cruises. The results of biomass estimates from two vessels were comparable. The result suggested that biomass estimations in previous JARPA cruises which thoroughly relied on acoustic were reliable. Because krill biomass surveys in the whole of Area IV and Area V were rarely conducted in the past, krill data collected by JARPA were quite important to understand krill-baleen whale relationships in the Antarctic.