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.

In recent years, there has been concern about the effects of radiated noise from ship navigation on marine mammals, and options for reducing radiated noise from ships have been discussed worldwide. We have demonstrated that it is possible to estimate the source level of ship noise by measuring the radiated noise level of a navigating ship using a hydrophone system in the sea and calculating the attenuation due to propagation distance based on the location information recorded by the ship’s automatic identification system (AIS) in Normal Mode. The source level of a typical roll-on/roll-off (RORO) vessel, for example, was estimated to be 180 dB. Furthermore, to investigate the effect of this radiated noise on marine mammals, a parabolic equation approximation simulation was used to determine the propagation distance of the noise. It was found that the noise level falls below the environmental noise level (measured value) at approximately 80 km in winter and at approximately 50 km in summer.