 |
|
In the flood season, Dau Tieng Reservoir in Tay Ninh Province can unleash water at the rate of 200cu.m per second. The improper regulation of water resources in such reservoirs has contributed to the degradation of the biodiversity, particularly fish.
|
|
Fish populations endemic to the system have been facing the loss of habitats and have been forced to adapt to new ecosystems with low biodiversity and with human regulated, instead of natural flows, according to experts at several forums held in southern DongNaiProvince and HCMCity recently.
|
These developments will lead to a severe degradation of biodiversity, which is a "crucial base for the existence and development of any country," said director Dr Hoang Nghia Son of the Institute of Tropical Biology (ITB).
Sai Gon and Dong Nai are the main rivers in the DongNaiRiver basin – the largest and only river basin lying entirely within Viet Nams territory.
The system is home to 300 species of fish, including 150 of high economic value, 130 are motile and 17 are listed in the Vietnamese Red Book of endangered species.
But "many popular fish endemic to the system have become rare, including me (tor douronensis), ngua xam (tor stracheyi), coc dam (cyclocheilichthys apogon), tren (kryptopterus) species, and lang (bagridae) family," said Nguyen Xuan Dong, an ITB researcher.
"The fishs habitat has been narrowed in both dry and rainy seasons because of the regulation of water resources in the system by the Dau Tieng and Tri An reservoirs [on Dong Nai and Sai Gon rivers respectively]," Dong said.
"Salination, in case water supply from upper parts of the rivers is limited, will favour salty, brackish water fishes to dominate habitats of freshwater species even in the middle part of the river system," he added.
In addition, the construction of dams on the system would also hinder their circulation to find sites for laying eggs, he said.
Pham Anh Duc of HCM City-based TonDucThangUniversity affirmed that the Dau Tieng, Tri An and ThacMo reservoirs are barriers to the motility of shrimps and fish from estuaries to upper parts of the rivers.
"The reservoirs as well as the development of residential zones and industrial parks have seriously changed the ecosystem in the lower parts of the rivers," he said.
Nguyen Vu Huy of the Southern Irrigation Planning Institute said many sections of the Sai Gon and Dong Nai rivers as well as their tributaries have been polluted.
"Lower parts of Dau Tieng and Tri An reservoirs have shown severe signs of pollution because of industrial development," he said.
If there was no mechanism to manage water resources in the Dong Nai river basin that takes into consideration the impacts of dams and reservoirs, biodiversity would be destroyed in the near future, speakers said at the forums.
Dong said that the Prime Ministers Decision No1497 identified Sai Gon – Dong Nai river system an important site for biodiversity protection and preservation, so the Goverment and related agencies should come up with both long and short-term plans to achieve this.
Local officials in charge of managing fresh water resources raised the alarm on the dangers posed by the domination of several imported fish species, which serve urban dwellers ornamental need.
"The peacock bass (cichla ocellaris) fish has spread to every place in the Tri An Reservoir with an average length of 30cm and width of 10cm, weighing between 400g to 500g," said Pham Ngoc Tiem, manager of the Tri An fresh water resources management team.
Experts also said the reservoir had been invaded by another strange species – the sucker-mouth catfish (hypostomus plescutomus), which is imported for cleaning glass tanks used for ornamental purposes by urban residents.
Both species are fierce predators, eating any kind of water species, and have a strong breeding capacity of 2,000 to 3,000 per egg-circle. These pose a serious threat to biodiversity in the reservoir.
Because of their habits, urban dwellers have let the fish from their tanks into the reservoir.
To cope with the situation, the Dong Nai Peoples Committee has recently requested related agencies to implement a regulation that "prohibits any release and breeding of alien fish species to and in the reservoir," said Ao Van Thinh, the committees deputy chairman.
Tiem said biodiversity in the reservoir was also affected because of the spread of a harmful plant called mimosa pigra and pollution from underwater cages used for fish breeding.
Phuoc Buu