Details

Autor(en) / Beteiligte

• Azuma, Kensaku
• Horioka, Kikuo
• Ohgi, Masayuki
• Iyota, Tsuyoshi
• Matsuoka, Isao
• Iyota, Kuniaki

Titel

Counting the numbers of ascending juvenile ayu based on visual observations and underwater videos in the Shimanto River, western Japan

Ist Teil von

• Aquaculture Science, 2020, Vol.68(4), pp.375-382

Ort / Verlag

Japanese Society for Aquaculture Science

Erscheinungsjahr

2020

Link zum Volltext

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• In the Shimanto River, the native ayu, Plecoglossus altivelis altivelis is generally superiority in number against the released artificial one; therefore, ascending numbers of juvenile ayu in the river have an influence upon the population dynamics. Juvenile ayu swimming upstream was counted through visual observations (9-10 times during March-May) and underwater videos (25-30 times during Februay-May) in the lower reaches of the Shimanto River from 2015 to 2019. Fishes began migrating upsteam during early February to mid-March when water temperatures had increased to approximately 10°C; the number of fishes peaked between early March and mid-April when the temperatures had gradually increased from approximately 12°C to 18°C. The number of fishes and their anuual differences were larger when counted by visual observation than by using a video camera. However, the mean numbers of fish were high in 2015, 2017, and 2018, whereas they were low in 2016 and 2019, irrespective of the counting methods. Furthermore, a significant correlation between the annual catches of ayu and the mean number of fish observed during the study period was evident. The simple methods used in this study shoud effectively and conveniently predict the relative ascending numbers of wild ayu.