Characteristics of Acoustic Backscattering of a Dominant Brown Alga, Ecklonia kurome, by Ex-situ Suspended Measurement

Abstract

Kurome (Ecklonia kurome), a dominant brown alga species found around Honshu, Japan, is an important species as the main component of the costal marine forest. The target strength of 22 algal bodies (22.2–42.4 cm in length) of Kurome was measured in an ex-situ suspended experiment as a scale factor for estimating the abundance of the marine forest by acoustic surveys using quantitative echosounders. A positive linear relationship was found between the logarithmic scale of the dry weight and the target strength of the algal body (TS_weight[dB]=18.2 log W_ind [g] -89.4). The reduced target strength per 1 gram ranged from -86.0 to -74.3 dB (Ave ± S.D. = -79.3 ± 3.2 dB), indicating that the strength of acoustic backscatter was quite low compared to that of other dominant brown algae, such as Sargassum and Kelp.