| A 1.5 year environmental and faunal analysis was conducted in headwater streams of the upper Ta-chia River in mountainous central Taiwan. The area had distinct wet and dry seasons owing to monsoonal-typhoonal rainfall patterns. Compared to natural stream areas, agriculturally impacted reaches had greater discharge fluctuation, warmer temperatures, higher turbidity, increased nutrient loads, and reduced bedform diversity.; Stream biotic communities varied according to local habitat characteristics. Coldwater algae existed mainly within natural stream reaches while eutrophication indicators occurred abundantly at agriculturally impacted sites. Large-bodies shredder-collector and predatory insects inhabited natural stream areas while smaller scraper-collectors were dominant in an agriculturally modified stream.; Four fish species occur in the system: the endangered Taiwanese landlocked masu salmon (Oncorhynchus masou formosanus), kooye minnow (Varicorhinus barbatulus), Taiwanese tasseled-mouth loach (Crossostoma lacustre) and stream goby (Rhinogobius brunneus). Originally, this stream system was uniquely hospitable to the salmon owing to suitable cold water, a gentle gradient, moderate climate, and rich invertebrate food resources. In the last half-century, the salmon has become restricted because of overexploitation, population fragmentation by dams, and habitat deterioration caused by landslides and agricultural impacts.; Multivariate analyses indicated that the minnow is a habitat generalist primarily associated with boulder cover while the loach is a specialist associated with boulder plus fast current. Both minnow and loach fed extensively upon attached algae and algal detritus, and small insect larvae; the latter ate significantly more insects than the former. Cyclical fluctuations of these food resources are chiefly determined by discharge events.; There is no evidence that the salmon is detrimentally affected by any of its three ichthyofaunal associates because of their spatial and trophic segregation; however, its future could be imperiled by landslides, dams, and any expansion of row-crop agriculture. A comprehensive recovery plan for the salmon is proposed. |
