Long‐term observation of fish community in streams inside and outside road construction of Teshio River system, northern Hokkaido, Japan

Abstract

Nakagawa experimental forest of Hokkaido University is located in the middle Teshio River and some tributaries flow through the forest. The construction of Otoineppu bypass route started in 2007. This bypass route will pass through the forest. In order to evaluate the impacts of the road construction on stream ecosystem, a long-term monitoring of fish community and stream environmental characteristics have been conducted including before, during and after the road construction. The survey has been implemented on five streams in Teshio River (three streams inside the bypass construction zone and two streams outside the zone). Here, we report the data of species, body size and weight of fish sampled using an electrofishing unit and the data of stream environmental characteristics such as water temperature, water surface area, pH and EC. The three-pass removal method for fish sampling and measurement of stream environmental characteristics was conducted three times a year (mainly June, August and October) from 1999 to 2018. A total of 57,203 individuals were observed, belonging to 11 species in seven families. After bypass road construction started (2007), the number of fishes gradually increased at both bypass road construction and control sites. Occasionally, the number of fishes at the bypass construction site tended to be lower than at the control site, but there was not always noticeable difference between them.

Driving forces behind the fluctuating growth of the number of successful nests in an inland population of white‐tailed eagles in Hokkaido, Japan

“…Fish abundance gradually increased in one of the branches of the Teshio River (Umatani et al, 2020). However, white‐tailed eagles usually take their prey in the mainstream and riverbed ponds of the Teshio River but not in branches.…”

“…These species prefer slow‐flowing basins and still waters and constituted the main prey of white‐tailed eagles (see Section 3). Umatani et al (2020) reported a gradual increase in fish abundance from 1999 to 2017 in one of the branches of the Teshio River.…”

“…However, white-tailed eagles usually take their prey in the mainstream and riverbed ponds of the Teshio River but not in branches. The species sampled by Umatani et al (2020) do not include the main prey species (the northern snakehead, the Carassius carp, and the common carp). The colony size of the great cormorant and the great blue heron greatly varied in the study area (Oodate & Watanabe, 2020; the authors' observation), but no reliable data are available for the overall abundance of water birds.…”