Author: Laurie Battle 仈羅利

           The Chichiawan Stream and its tributaries in central Taiwan are the last refuge of the critically endangered Formosan landlocked salmon Oncorhynchus formosanus.  Over the past few decades, 11 check dams have been constructed in these streams to reduce sediment transport and to prevent the collapse of riverbanks. However, these dams are thought to be a primary factor in the habitat degradation that has led to a decline in salmon abundance. The dams have impacted the salmon by creating reproductive isolation, by reducing the number of accessible large boulders to provide refuge during typhoons, and by preventing salmon from returning upstream after being flushed downstream during typhoons. In addition, the sand and gravel that accumulate due to dam construction can damage salmon eggs. Typhoons, occurring primarily in spring and summer months, are a key factor in salmon population dynamics, and the salmon have adapted to seasonal typhoons in their natural habitat. However, dams have altered their natural habitat, limiting the salmon’s ability to survive typhoons. The salmon abundance began to decline in the 1960s, reaching as low as 200 individuals by 1984. The abundance has increased to over 1,200 in recent years, but the salmon have