Tag: salmon

In recent decades, dam removal has become a frequently-used strategy for restoring natural stream habitats because dams deteriorate river channels and often lead to decreased diversity of species. Taiwan has many short and steep rivers in the high mountains, where strong rainfall creates high water velocity. As a result, the government constructed many check dams to prevent the collapse of riverbanks and to lessen sediment transport to lower elevations. As of 1999, Taiwan had over 3,000 check dams. The Chichiawan Stream and its tributaries in central Taiwan are the last refuge of the Formosan salmon. Dam establishment and agricultural development have degraded this habitat.  These key factors are considered the main reason for the decline in the abundance and range of the Formosan salmon after the 1960s. The salmon population declined to about 200 individuals by 1984, at which time the Taiwanese government listed them as an endangered species. The salmon abundance in the entire Chichiawan basin has ranged between 1,000 and 5,500 since 2005. The Chichiawan Stream basin had 11 check dams in 2000, covering a length of less than 10 km. These dams have disturbed the salmon’s habitat in multiple ways. For instance, the presence of dams creates