Formosan landlocked salmon have made a dramatic comeback in the upper reaches of the Dajia River, their only remaining habitat, following the removal of a check dam in 2011, according to National Chung Hsing University professor Lin Hsing-juh March 12.
“After typhoon season each year the salmon population falls by one-third,” Lin said. “Floodwaters wash them downstream, check dams prevent their return and they end up dying in the warmer waters at lower elevations.”
In 2001 there were fewer than 500 of the endangered fish (Oncorhynchus masou formosanus), but population censuses over the last three years show their numbers reaching 5,400, nearly reaching the 5,800-fish carrying capacity of the Qijiawan River, Lin said. This stream, part of the Dajia River system, is located at high altitude in the Wuling area of Taichung City’s Heping District.
Lin has led an interuniversity team studying the fish’s habitat since 2004, working in conjunction with Shei-Pa National Park Headquarters. After the researchers observed that check dams interfere greatly with the ecological system, the park decided to remove one of the sediment dams on the Qijiawan River that blocked the salmon from swimming back upstream.
Initial results indicate that the ecological corridor created for the fish by the elimination of the dam is very effective, without causing serious siltation in reservoirs further down river, he noted. Moreover, since the dam was dismantled, floods bring larger rocks into the fish’s habitat, creating places for the salmon to take shelter during typhoons, so that fewer of the fish are washed downstream.
The salmon, endemic to Taiwan, are believed to have been trapped in the cold waters of the central mountains during the last ice age. (THN)