Dams Cause Evolution In Fish

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Dams cause evolution in fish
Introduction
Fish migrate for habitat, reproduction, foraging, and wintering (Morita et al. 2009). Therefore, dam building affects anadromous fish and resident fish (Morita et al. 2009). Anadromous fish live in the ocean and migrate from the ocean to freshwater to lay eggs (Collins 1976, Bjornn and Reiser 1991, Limburg and Waldman 2009). Dams block fish migration pathways to freshwater for anadromous fish and affect distances. Because these fish migrate to lay eggs in spawning areas at upstream, after dam building causes shorter distance migration. Fish must migrate to complete a life-cycle that requires different habitats for each state of life (Agostinho et al. 2008, Clemento et al. 2009, Morita et al. 2009).
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2008). Therefore, plenty and diversity of fish decreases (Dudley and Platania 2007). Some fishes evolve for living in habitat change. Because water flow changes in the river affect their breeding and growing (Nilsson and Berggren 2000), but few species can adapt from a flowing water system to a still water system (Huntingford and Torricelli 1993, McCartney 2009), including salmonids (family Salmonidae) (Gharbi et al. 2006). The consequences are changing from river to catchment area of dams that the water in this area is still water. This reason disrupts many species living in the river because water flow changes in dams (McCartney…show more content…
2009). This is because dams block the river, separating the habitat into fragments (Clemento et al. 2009). This can cause smaller population, decline genetic variation, and increased genetic drift (Clemento et al. 2009). Small population can make genetic drift, leading evolution (Morita et al. 2009). Because destroying habitat will reduce the population, dams obstruct gene flow (Faulks et al. 2010). Destruction and changed habitat force fish to endure new environmental conditions, forcing evolution (Faulks et al. 2010).
When dams block rivers, fish above the dam become residents and have decreased populations. In Hokkaido, Morita et al. (2009) show the dams cause habitat fragmentation. This causes changes in populations of white-spotted charr (Salvelinus leucomaenis) (Morita et al. 2009).
McClure et al. (2008) studied habitat loss of anadromous salmonids because of dam building in west of United States. They found that habitat area declined and changing habitat distribution caused evolution in population of salmonids because of decline and changes in genetic variation. Smaller habitat cause smaller populations, leading to genetic drift.
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