Understanding the current distribution and biomass of an endangered salmonid species, Sakhalin taimen, by using environmental DNA

• Main Author: 水本, 寛基
• Other Authors: 荒木, 仁志, 秋元, 信一, 冨士田, 裕子, Fausch, Kurt Fausch
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Hokkaido University
• Subjects: 610; Sakhalin
• Online Access: http://hdl.handle.net/2115/87728; https://doi.org/10.14943/doctoral.k13157

Sakhalin taimen (Parahucho perryi) is the largest freshwater fish in Japan and considered critically endangered by the IUCN. Historically distributed in the Russian Far East and Northern Japan, this species has declined drastically due to human activities such as river modification and deforestation. In addition, there were few studies and updates on their distribution or population status, and most of their contemporary distribution is unclear. The rarity and migratory nature of Sakhalin taimen make direct detection and observation difficult, which has been a major limitation of field survey of the endangered species. As the breakthrough for those issues, environmental DNA (eDNA) technique has drawn attentions recently. This technique was first reported in 2008 for detecting aquatic vertebrate species in the wild from environmental water samples. The strong advantages of this technique are that there is no need to observe target species directly and that it is easy to collect samples for monitoring across large spatial and temporal scales. In the present study, I aimed to estimate the current distributions and biomass of Sakhalin taimen in Hokkaido, and to reveal their seasonal migrations and associations to their prey fish by using eDNA. I have four chapters in my thesis targeting (1) the association between the eDNA concentration and biomass in aquarium experiments, (2) evaluation of the eDNA application to natural environments, (3) the current distribution and biomass of Sakhalin taimen, and (4) the association between the presence/absence of Sakhalin taimen and their prey fish across seasons. In Chapter 1, I first developed Sakhalin taimen species-specific primers and probe for quantitative PCR. Strong correlations were found between eDNA 4 concentrations and age, fork length and body weight of Sakhalin taimen in aquarium experiments. Furthermore, I demonstrated that eDNA concentration is a good indicator of total fish body weight contained in the aquarium. In Chapter 2, I found a significantly positive ...