Zoological Studies

Vol. 51 No. 5, 2012

Size-dependent Foraging on Aquatic and Terrestrial Prey by the Endangered Taiwan Salmon Oncorhynchus masou formosanus

Lin-Yan Liao1, Ming-Chih Chiu2, Yii-Shing Huang1, and Mei-Hwa Kuo2,*

1Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan
2Department of Entomology, National Chung Hsing University, Taichung 402, Taiwan

Lin-Yan Liao, Ming-Chih Chiu, Yii-Shing Huang, and Mei-Hwa Kuo (2012) Terrestrial subsidies are important resources for drift-feeding fishes.  The contribution of these subsidies to fish diets increases with predator size or age because larger fish can feed on a wider range of prey.  We assessed how the relative abundance of aquatic and terrestrial insects in the diet of the endangered Taiwan salmon Oncorhynchus masou formosanus (Jordan and Oshima) changed with salmon body size.  We found that aquatic invertebrates were the most important prey in the diet of Taiwan salmon.  However, the diet of small (8.0-14.8 cm) Taiwan salmon significantly differed from that of large salmon (19.1-25.2 cm).  The proportion of the diet comprised of terrestrial prey and its trophic diversity increased with salmon body size.  We did not identify the specific reasons, such as foraging limitations, for the size-dependent dietary shift.  However, it is clear that the endangered, drift-feeding, Taiwan salmon relies on terrestrial resources for an important part of its diet.  For conservation and management purposes, we urge that the restoration of forest vegetation, especially in riparian zones, be one of top priorities.

Key words: Drift, Invertebrates, Oncorhynchus masou formosanus, Stream, Taiwan salmon.

*Correspondence: Tel: 886-4-22840361.  Fax: 886-4-22875024.  E-mail:mhkuo@dragon.nchu.edu.tw