The relationship between the snowmelt flood and the establishment of non‐native brown trout (Salmo trutta) in streams of theChitoseRiver,Hokkaido, northernJapan

Abstract

Flow regime is one of the major determinants of establishment success for non‐native aquatic organisms. Here, we examine the influence of flow variability associated with snowmelt flood on the establishment success of non‐native brown trout in 10 streams in northern Japan. We regarded the presence of Age‐0 brown trout as the index of the successful establishment. The emergence of Age‐0 brown trout in our study region begins in May, a time that overlaps with the occurrence of snowmelt flood. The presence of Age‐0 brown trout was negatively associated with flow variability, and it was also negatively associated with summer water temperature. Our results indicate that the non‐native brown trout tends to establish in the streams with smaller snowmelt floods and lower summer water temperatures. Brown trout is an invasive, non‐native species that is problematic all over the world, and effective management strategies for preventing their further expansion are urgently needed. This study suggests that river managers should recognise that stable streams such as spring‐fed streams (i.e., low flow and summer water temperature) and flow‐regulated streams, have a higher potential risk of brown trout invasion.

Effects of hatchery chum salmon fry on density-dependent intra- and interspecific competition between wild chum and masu salmon fry

“…The stream is springfed and its flow is very stable (Kawai et al 2013). Around the experimental area (200 m long), the stream was 3-12 m wide, and maximum depth and current velocity were about 30 cm and 50 cm·s -1 , respectively.…”

Brown trout in Japan − introduction history, distribution and genetic structure

“…Sampling sites in the Mamachi and Monbetsu streams are described in detail, in Kitano et al (2009) and Kawai et al (2013) respectively (Tab. 1).…”

“…Although both streams are tributaries to the Chitose river, they are physically isolated and are assumed to represent independent populations. Brown trout appeared in and invaded these streams from the 1980s onwards (Kawai et al, 2013). As the Jigoku stream is the inlet of Lake Chuzenji, there is no migration barrier between them, so the Jigoku sample should represent the lake population.…”

“…Therefore, when introduced worldwide, brown trout frequently constitute naturalized (self-sustaining) populations (MacCrimmon and Marshall, 1968;MacCrimmon et al, 1970). It has been reported that for self-sustainability, non-native brown trout require hydrologically stable streams with small snowmelt floods, low summer water temperatures and spawning ground availability (MacCrimmon and Marsall, 1968;Kawai et al, 2013). The capacity of non-native brown trout to settle self-sustainable populations has been largely exploited to provide sport fishing for this species outside its native range.…”

Density‐dependent effects of non‐native brown trout Salmo trutta on the species–area relationship in stream fish assemblages

“…Salmo trutta have spread rapidly since 2000 and their effect on native fishes has become a serious conservation concern (Kitano, ). The effects of S. trutta on native white‐spotted charr Salvelinus leucomaenis (Pallas 1814) and masu salmon Oncorhynchus masou (Brevoort 1856) differ considerably; S. leucomaenis have been largely replaced, whereas O. masou appear able to coexist with S. trutta (Takami et al ., ; Morita et al ., ; Hasegawa & Maekawa, ; Hasegawa et al ., ; Kawai et al ., ). As in other regions, however, little is known about the effects of S. trutta on the wider fish assemblage.…”