Study area

The surveys were conducted in summer (August, 2020) and winter (February, 2021), during cruises of Ushio-Maru, the training ship of Hokkaido University (summer: crs-471-2020, winter: crs-484-2021).

Sampling point is about 45 km apart from land (Cape Esan), over the deep continental slope (water depth: ca. 800 m).

Sampling site is affected by the Tsugaru Warm Current and the Coastal Oyashio Current.

In summer, the surface layer is covered by the Tsugaru Warm Current (characterized as higher than 6°C, 33.7–34.3 psu) and the thermocline is present at 20–140 m.

In winter, the Coastal Oyashio Current (characterized as lower than 3°C, 33.0–33.3 psu) is present in the surface layer, while middle layer around 50–200

m is affected by the Tsugaru Warm Current.

For experiment of environmental DNA, 6 experimental treatments were designed (10 L of surface water each treatment for 5 replicates of 2 L). 

Exp１：0.45 um pore size filter (Control)

Exp２：0.22 um pore size フィルター

Exp３：0.45 um pore size filter (Sediments added)

Exp４：0.45 um pore size filter (Diatomite added)

Exp５：0.45 um pore size filter (Zirconia beads added)

Exp６：0.45 um pore size filter (Molecular sieves added)