fulbright Taiwan online journal

fulbright Taiwan online journal

Author: Laurie Battle 仈羅利

Laurie Battle 仈羅利
Laurie Battle is a professor of mathematics at Montana Tech specializing in mathematical modeling. She is a Fulbright Senior Scholar at National Chung Hsin University in Taichung, where she researches endangered Formosan landlocked salmon and teaches graduate courses on different modeling techniques.

Modeling the impact of dam removal on conservation of the Formosan landlocked salmon

           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

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Mathematical Modeling: The Formosan Landlocked 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

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Research & Reflections

fulbright taiwan online journal