Ups and downs of non‐native and native stream‐dwelling salmonids: Lessons from two contrasting rivers

Abstract

Freshwater rivers and lakes are particularly vulnerable to anthropogenic disturbance because of their proximity to human occupation. Anthropogenic impacts in fresh water include those caused by dams, water pollution, channelization, and invasive species. One common action to conserve freshwater biodiversity involves supplementing or reintroducing extirpated species, though the benefits of these efforts are controversial. Installation of fishways to dams and removal of invasive alien species has also resulted in recovery of native species. Herein results of long‐term monitoring of salmonids in two rivers in Japan are presented. The first case involves a river above a dam where native white‐spotted charr Salvelinus leucomaenis and masu salmon Oncorhynchus masou declined rapidly in number following dam construction, where non‐native rainbow trout Oncorhynchus mykiss and brown trout Salmo trutta increased in number, and where stocking of native masu salmon was unsuccessful. The second case involves a river formerly dominated by non‐native rainbow trout, in which native Dolly Varden charr Salvelinus curilus and masu salmon increased in numbers following removal of non‐native species and fishway installation. Results reveal natural recovery of masu salmon in a river within which they were once completely extirpated, without stocking. Because salmonids are migratory fish and return to natal rivers, when locally extinct, human intervention to stock or reintroduce them has often been deemed necessary. However, restoration of wildlife would not require stocking or reintroduction if factors that impede the self‐recovery capability of species are removed.

Environmental DNA Characterization of the Fish Species Composition in the Mukawa River and Adjacent Habitats

“…The eDNA of rainbow trout was found at all 16 of their sites, along with some other introduced species. Brown trout, Salmo trutta, has also been introduced into Hokkaido and Honshu [65,66], but was not detected in the Mukawa River or by Iwamura et al [39].…”

Path for recovery: an ecological overview of the Jambato Harlequin Toad (Bufonidae: Atelopus ignescens) in its last known locality, Angamarca Valley, Ecuador

“…With the information at hand, we suggest that the extirpation initiatives should be concentrated in the Guambaine River, neary Quilaló. Although there is not much information on this type of extirpation, examples from small watersheds, like the Guambaine, the extirpation of the Rainbow Trout has been successful to recover native aquatic populations in Japan ( Morita, 2022 ). Other important measures include riparian area protection, to prevent the pollution with fecal coliforms, pesticides and fertilizers used in the agro-cattle mosaic ( Dunn et al, 2022 ; Graziano, Deguire & Surasinghe, 2022 ).…”

Preferential behavior of Tribolodon hakonensis for fishways according to biological characteristics

“…Fishway types are selected to suit the environmental conditions (Mulligan et al, 2019; Tonkin et al, 2022; White et al, 2011), upstream and downstream topography and intake locations, characteristics of resident fish, commercially important fish species, and discharge from dams and weirs (Bunt, 2001; Halleraker et al, 2023; Lindberg et al, 2016; Nyqvist et al, 2017; Wilkes et al, 2018). Approaching the process considering all perspectives is important (García‐Vega et al, 2023; Huuki et al, 2022; Morita, 2022; Ovidio et al, 2017; Prunier et al, 2023).…”