Dampak Bendungan pada Migrasi Ikan

DAM`S IMPACT ON FISH MIGRATION

IN SOME RIVERS AT WEST SUMATRA PROVINCE

River is a lotic ecosystem that has various kinds aquatic organism among others that is fish. In its life cycle, fish often migrates from the downstream to the upstream of river or vice versa. The migration aims for spawning, working for diet and other activities. Lagler et. al., (1977) and Bond (1979) said that fish migration is caused by food collecting, adaptation of environment condition change, change of life cycle phase and spawning. They said again that fish do not only migrate in fresh water or river (potamodromous), but it also migrate from marine to fresh waters (anadromous) or from fresh to marine waters (catadromous). Then Cowx and Welcomme (1998) also said that fish display migratory patterns that play an important role in their ecology. To complete their life cycle, some fish species need suitable spawning sites can be quite close to the areas in which they live as adult fish. However, to optimize reproductive success, many fish species return to their natal stream or use upstream spawning grounds or tributaries which in some cases may be considerable distances away from the feeding areas. Other reasons for migration include optimum feeding strategies, avoidance of unfavourable conditions or to enhance colonization. The scale of the migration can range from tens of metres in the case of resident fish, to tens or hundreds of kilometres in potamodromous species such as Bocachica (Prochilodus sp), or even to thousands of kilometres for diadromous (anadromous and catadromous) migrants such as Salmon (Oncorhynchus sp), Eel (Anguilla sp) and Sturgeon (Acipencer sp). The migration patterns of fresh water fish can be seen on figure 1.

Figure 1. Migration Patterns of Fresh-water Fish (Cowx and Welcomme, 1998)

The result of observation have been conducted in some rivers in West Sumatera Province, i.e. Batang Anai and Batang Ulakan River at Padang Pariaman District (2000, 2001), Batang Kandis River at Padang City (2003), Batang Hari and Batang Siat River at Dharmasraya District (2006), Indropuro and Batang Kapas River at Pesisir Selatan District (2007) to indicate that there are the species such as Garing (Tor sp), Kulari (Thylognathus sp), Patin (Pangasius sp), Belanak (Mugil sp), Mingkih (Cestraceus sp) and Sidat (Anguilla sp) conducted to migrate from the down stream to upstream.

Indonesia is a developing country which the majority its inhabitant were farmer. Thus development of irrigation sector such as dam or weir construction is very important, because it related to the necessity of water to irrigate rice field. Nevertheless, weir construction did not only benefit human, but it also harm human because it can damage ecosystem that is life of fish (aquatic organism) in the mentioned river. Nakamura (1998) said that development of irrigation (dam or weir construction) have caused the fish can not migrate from down stream to upstream. Williams (1995) also said that in migration of Salmonid from ocean to upstream in Collumbia river only a little part of Salmon can pass through dam to upstream to spawning, and a large part of it was dead in mentioned passage. Then fry result of adult Salmon spawning in upstream that migrate thought dam to down stream is 100 % dead. According to Cowx and Welcomme (1998) that the fish fauna of most European countries has undergone many changes that is species decreasing as a consequence of dam constructions in rivers. Construction of dam did not only obstruct fish migration from downstream to upstream, but it also cause loss of fry (dead) during passage over or through dams from upstream to downstream.

The result of research have been conducted in dam in Elan, S. Saskatchewan River (Canada); Green, Brazos, Collorado, S. Platte, Guadalupe, Clinch rivers (USA) and Suratka River (Czech Republic) to indicated that dam constructions also cause reduced abundance of benthos (macro and micro-invertebrates) in downstream that constitute food resources for fish community. Besides, the dam constructions also effect physico-chemical of water such as gas solubility, velocity, depth, turbidity and water temperature.

References

Bond, C.E. 1979. Biology of Fish. W.B. Saunders Company, Philadelphia.

Cowx, I.G., and R.L. Welcomme. 1998. Rehabilitation of Rivers for Fish. Food and Agriculture Organization of the United Nations (FAO) and Fishing News Books, Australia.

Lagler, K.F., J.E. Bardach and R.R. Miller. 1977. Ichthyology. Jhon Wiley and Sons, New York.

Nakamura, S. 1998. Fish Passage and Instream Flow. Toyohashi University of Technology, Tempaku-cho, Toyohashi Japan. 441-8580, Japan.

Williams, J.G. 1995. Fish Passage Problems in the Columbia River, USA., and its Tributaries. In : Proceeding of International Symposium on Fishways `95 in Gifu. Publications Committee of the Internatinal Symposium on Fishways `95 in Gifu, Japan.