The results of the spatial survey.

<p>(a) The estimated abundance of <i>C</i>. <i>pacifica</i> at the day of survey based on the visual survey. (b) The concentration of <i>C</i>. <i>pacifica</i> eDNA at the surface and (c) on the sea floor.</p

The correlation coefficients among six eDNA sequential samples of the temporal survey.

<p>The correlation coefficients among six eDNA sequential samples of the temporal survey.</p

The schematic drawing of the sampling point for temporal survey and the results.

<p>(a) The schematic drawing of the sampling point for temporal survey conducted at the pier of Maizuru Fisheries Station, Kyoto University. The surface and sea floor water samples were collected at three (A, B, and C) points where the water depth is 4, 6, and 8 m, respectively. (b) The temporal change of observed numbers of <i>C</i>. <i>pacifica</i> in the visual survey and the eDNA concentration in each surface sample. (c) Temporal change in observed numbers of <i>C</i>. <i>pacifica</i> in the visual survey and eDNA concentration in each sea floor sample. Note that the observed numbers of individuals were presented as the average of 10 days and that the same observation data were presented in (b) and (c) for better visibility.</p

The results of the tank experiments.

<p>(a) Time dependent change of eDNA concentration (copies L^-1) in the tank experiment. (b) Relative eDNA concentration, i.e., the concentration at time <i>t</i> divided by the initial concentration in the tank, represents the combined exponential degradation in all three tanks. The exponential regression curve for the eDNA degradation was y = 0.998e^-0.0335x (where x and y mean time in hour and relative DNA concentration at time x, respectively).</p

The comparison between eDNA concentrations of surface and sea floor samples.

<p>The eDNA concentrations in the sea floor were significantly higher than that of surface samples (Wilcoxon signed rank test, <i>P</i> = 0.00051).</p

Observed fish biomass using echo sounder.

<p>Vertical bar on the cruise track (gray line) indicates local s_a values (i.e., fish biomass observed using quantitative echo sounder), which is the integrated s_v of a water column with a cross-sectional area of 1 m². This figure is depicted according to s_a extracted every 80-m intervals. Note that this figure shows a summary of field observation using echo sounder. We used s_v values rather than s_a values as index of fish biomass in regression analyses (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0149786#pone.0149786.s001" target="_blank">S1 Fig</a>).</p

Selected explanatory variables, selected size of water column, and estimated partial regression coefficient of ‘echo’ for each filter series.

<p>Selected explanatory variables, selected size of water column, and estimated partial regression coefficient of ‘echo’ for each filter series.</p

Vertical distributions of echo intensity and the sea bottom.

<p>a, data from all research areas; b, data within 150 m of St. 2; c, data within 150 m of St. 27. Bars indicate the mean echo intensity (the average of s_v) of each depth interval. Dashed lines indicate frequency distribution of water depth. Number below station names indicates the mean water depth.</p

Correlation coefficient between eDNA concentration in surface and bottom waters.

<p>Y-axis indicates vertical distance between surface- and bottom-sampling positions, i.e., the coefficient value of the class of 3.5–8.5 m was calculated using samples obtained at stations where water depth is 3.5–8.5 m. Correlation coefficient was relatively high when using samples from shallower stations, while it was low when using samples from deeper stations. This figure was depicted based on eDNA concentrations of filter series 1.</p

Spatial approximation of jack mackerel eDNA concentration.

<p>Based on CytB gene copy number in a 2 μL template DNA solution at the 47 sampling station, spatial variation of jack mackerel eDNA in west Maizuru Bay was estimated by approximation. The level of the approximate eDNA concentration is indicated by colors between red (relatively high concentration) and blue (low concentration). White areas suggest that the concentration approximated using a regularized spline is ≤ 0. Spatial approximation was performed using a regularized spline with a tension parameter of 40.</p