Relationship between the index of relative current direction to the AR (Dir) and eDNA copies (A) and predicted eDNA copies (B) of Engraulis japonicus. Dir values range from -1.0 to 1.0. Negative values (Dir < 0) indicate upstream currents and positive values (Dir > 0) indicate downstream currents. Open triangles, black circles, and gray squares of (A) show the number of eDNA copies at Dist 0.1, 0.2, and 0.4, respectively. The dotted, solid, and gray lines of (B) show the predicted number of eDNA copies at Dist 0.1, 0.2, and 0.4, respectively.