This study focused on euphausiid distribution and biomass estimation over the coastal shelf of the Pacific coast of Hokkaido Japan in early summer 2008. Acoustic data were obtained in both day (6:00-18:00) and night (18:00-6:00) using a quantitative echosounder (EK60, Simrad) with two frequencies (120 and 38 kHz). Echoes of euphausiids were specified based on the ΔMVBS, calculated with seasonal theoretical target strength of Euphausia pacifica. The best-fit kriging models were used to quantitatively interpolate euphausiid distribution. The detected euphausiid biomass reached 38,278 t (> 15 gWWm-2), suggesting abundant prey for large fishes over study area. On the other hand, the distribution was spatially heterogeneous in produced GIS map, suggesting the spatially limited available prey. Observed day-night difference of estimated biomass was caused by spatial variability of diel movement of euphausiids. Acoustic dead zones and behavioral change in euphausiids may strongly influence biomass estimation in night in coastal shelf environment.
Tojo, Naoki; Minami, Kenji; Matsukura, Ryuichi; Kawauchi, Yohei; Funamoto, Tetsuichiro; Chimura, Masayuki; Nishimura, Akira; and Miyashita, Kazushi
"SPATIAL ESTIMATION OF EUPHAUSIID BIOMASS ALONG THE PACIFIC COAST OF EASTERN HOKKAIDO, JAPAN IN EARLY SUMMER OF 2008,"
Journal of Marine Science and Technology: Vol. 19
, Article 9.
Available at: https://jmstt.ntou.edu.tw/journal/vol19/iss3/9