Fig 1.
Recording sites and acoustic array system.
(a) Distribution of finless porpoise in Japanese coastal areas (blue) [45]. This map was modified using data set (https://cyberjapandata.gsi.go.jp/xyz/pale/{z}/{x}/{y}.png) under CC BY 4.0 and QGIS 3.30 (https://qgis.org/it/site/). Shoreline data was derived from: United States. National Imagery and Mapping Agency. "Vector Map Level 0 (VMAP0)." Bethesda, MD: Denver, CO: The Agency; USGS Information Services, 1997. (b, c) Maps of the recording points in Seto Inland Sea (St. S) and Mikawa Bay (St. M), Japan. These maps were modified using data set (https://nlftp.mlit.go.jp/ksj/gml/datalist/KsjTmplt-C23.html) under CC BY 4.0 and QGIS software. The locations of the arrays are depicted by circles, and the dotted lines denote the ferry routes. (d) Configuration of the arrays. From the top, the instruments (black in the figure) were placed with their sensors at 2 m (INFINITY-EM), 3 m (A-tag), 3.5 m (SoundTrap), and 4 m (A-tag) from the water surface (blue line).
Table 1.
Location and device information for acoustic recording of finless porpoise at Seto Inland Sea (St. S) and Mikawa Bay (St. M), Japan, in 2021 and 2022.
Fig 2.
Typical echolocation click of finless porpoise.
(a) Waveforms and (b) signal frequency. Both (a) and (b) are sounds obtained from the Seto Inland Sea (St. S) data.
Table 2.
Number of echolocation click trains at Seto Inland Sea (St. S) and Mikawa Bay (St. M) during day/night in the absence/presence of vessel noise.
Table 3.
Summary of environmental parameters, finless porpoise echolocation click and click train parameters at Seto Inland Sea (St. S) and Mikawa Bay (St. M).
The summary shows environmental parameters (temperature, synthetic flow velocity, and noise level), echolocation click parameters (ASL, peak frequency, center frequency, -3 dB BW, and click duration), and click train parameters (ICI, number of clicks per train, and range from array). ASL was compared using Student’s t-test, while the other parameters were compared using Mann–Whitney U-test to determine significant differences between the sites. 0.01 ≤ p < 0.05 is denoted as > or < and p < 0.01 is denoted as >> or <<; > and >> indicate that the parameter in St. S were larger than that at St. M, while < and << indicate that the parameters in St. M were larger than those in St. S.
Fig 3.
Box plots for the relationship between the explanatory variables and respective response variables.
The box plots represent (a) ASL, (b) -3 dB BW, (c) click duration, (d) ICI. The lower box limit represents the 1st quartile and the top box limit represents the 3rd quartile. The middle line in the box represents the median. Refer to Table 3 for sample size. In the (a), “a” means absence of vessel noise, and “p” means presence of vessel noise.
Table 4.
Selection of the best model generalized linear models (GLM) for echolocation click and click train parameters.
The first column shows the ranks, numbered from the smallest Akaike’s Information Criterion (AIC). This table shows models with AICs < 2. The second column shows the explanatory variables for GLMs (vessel = absence/presence of vessel noise, DN = day/night, vessel: DN = interaction between day/night and absence/presence of vessel noise, temp = temperature, flow = synthetic flow velocity, noise level = noise level, site = recording site). Bold text indicates the respective response variable. df: degrees of freedom.