琵琶湖における水中ロボットを用いたアナンデールヨコエビ（Jesogammarus annandalei）のモニタリング

抄録

Monitoring technology for Lake Biwa using imaging methods has been developed since the 1980’s. The autonomous underwater robot “Tantan”, designed for monitoring the lake environment with a high resolution digital camera, was first built in 2000, and applied for monitoring of the lake floor from 2002 to 2010. Recently, dissolved oxygen (DO) depletion has become a serious problem in the deep areas of Lake Biwa because of eutrophication and global warming, and has led to critical issues in the conservation of endemic species. In this study, the population and the rate of pre-copulation of Jesogammarus annandalei (Crustacea, Amphipoda, Anisogammaridae) were investigated using the underwater vehicle to assess the effect of low oxygen. The minimum population of J. annandalei was 1.7 inds. m^-2 in December 2004 when DO at 90 m depth was 1.6 mg L^-1, and the maximum population was 1322 inds. m^-2 in December 2003 when DO was 6.1 mg L^-1. The rate of pre-copulation varied between 0.4% in December 2002 and 50.5% in December 2005. High pre-copulation rates were observed when the water temperature was around 7.7–7.8°C and DO was around 2.4–2.5 mg L^-1. These results suggest that small windows of water temperature and DO might have a profound effect on the pre-copulating behavior. Such monitoring methods, utilizing an underwater robot like “Tantan” provide many advantages such as knowing the behavior of the benthos as well as observing and monitoring the wider lake floor.