Abundance estimation depending on target marker length
The zebrafish aquarium experiment showed that target marker length negatively influenced the abundance estimation accuracy (R 2 value), regardless of filter pore size. Although eDNA detectability declined with longer DNA fragment length, the detection of longer eDNA fragments may help identify the exact location of target species because of its shorter persistence in water (Hänfling et al., 2016). However, this advantage of longer eDNA fragments was not fully utilized in a closed and small-scale environment like our experiment. According to the studies by Jo et al. (2017; 2021b), who used longer eDNA fragments in the field, the more satisfactory relationship between longer eDNA fragments and fish abundance could be accounted for by (i) the narrower spatiotemporal range of longer eDNA fragments and (ii) the removal of highly degraded and “non-fresh” eDNA signals probably derived from fish carcasses, resuspension from bottom sediment, and contamination from boat and fishing gear. Further empirical studies are required in natural environments to clarify the situation where abundance estimation via longer eDNA fragments is adequate and to investigate the detailed mechanism of eDNA degradation depending on DNA fragment length.