Extreme winter aggregation of invasive rainbow trout in small tributaries: implications for effective control

• Published in: Ichthyological research Vol. 64; no. 2; pp. 197 - 203
• Main Authors: Koizumi, Itsuro, Kanazawa, Yukiyo, Yamazaki, Chitose, Tanaka, Yuuki, Takaya, Kousuke
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Japan 01.04.2017; Springer Nature B.V
• Subjects: Animal migration; Animal Systematics/Taxonomy/Biogeography; Biomedical and Life Sciences; Ecology; Ecosystems; Freshwater; Freshwater & Marine Ecology; Indigenous species; Invasive fish; Life Sciences; Oncorhynchus mykiss; Population control; River basins; River systems; Rivers; Salmon; Seasons; Summer; Tributaries; Trout; Winter; Zoology; Alien species; Seasonal migration; Thermal refuge; Introduced species; Non-native species
• ISSN: 1341-8998; 1616-3915
• DOI: 10.1007/s10228-016-0558-z

Because of their high economic and recreational value, salmonids have been extensively introduced worldwide and are responsible for significant impacts on native ecosystems. However, effective methods for controlling or eradicating introduced populations of salmonids are still limited, particularly in large river systems. Here, we demonstrated that invasive rainbow trout Oncorhynchus mykiss immigrated to and extremely aggregated in small tributaries during the winter, which can be utilized for effective population control. Seasonal census was conducted in 10 small tributaries of the Otofuke River in the Tokachi River basin, central Hokkaido, Japan. Winter abundance was 8–125 times higher than summer abundance in four of the tributaries where water velocities were low. Relatively large individuals (200–350 mm) aggregated in several pools at an unusually high density (>2–3 individuals/m 2 or 170–440 individuals per pool). Females were common in the small tributaries in the winter, but not in the summer. Therefore, removal of invasive rainbow trout may be best practised in such small tributaries during early winter. Because many stream fishes overwinter in specific, often limited, habitats, more attention should be paid to such winter habits in the effective management of non-native fish species.