Many farmers who breed brackish-water shrimp in the Mekong Delta have cut back on production because of high salinity this year.

Ly Thanh Dan, who has four ponds to breed shrimp in Bac Lieu Province’s Hoa Binh District, is now breeding shrimp in only one pond.

“I’ve stored water with low salinity since the last rainy season, but the water is only sufficient for breeding shrimp in one pond,” Dan said. “Shrimp will grow very slowly in water with a high level of salinity.”

The industrial shrimp area in Bac Lieu covers about 2,500ha, accounting for less than 15 per cent of the province’s total area devoted to shrimp breeding, according to the province’s Aquaculture Sub-department.

Pham Hoang Son, head of the province’s Aquaculture Sub-department, said the salinity was expected to continue to be high in the coming time.

“We have warned farmers, except those who have stored low-saline water, not to breed a new shrimp crop until the beginning of the rainy season,” he said.

Saline intrusion has entered up to 70km deep inland on rivers in many areas in the delta.

In most provinces that breed brackish water shrimp, farmers have reduced the cultivation areas by 50 per cent because of high salinity, according to the Ministry of Agriculture and Rural Development’s (MARD) Aquaculture Department.

In Soc Trang, Ca Mau, Bac Lieu and Kien Giang provinces, salinity has exceeded 30 gram per litre. When the salinity is above 30 gram per litre, shrimp are easily affected by disease.

Le Van Su, director of the Ca Mau Province Department of Agriculture and Rural Development, said hot weather had affected not only industrial and semi-industrial shrimp farming areas but also extensive shrimp farming areas.

In Ca Mau Province, which has the country’s largest shrimp cultivation area, extensive shrimp farming areas focused mostly in Dam Doi, Phu Tan and Tran Van Thoi districts.

More than 2,678 ha of extensive shrimp farming areas in Ca Mau had been affected by disease with a damage of 30-70 per cent so far this year, up 1,864 ha against the same period last year.     

Solutions

The MARD’s Animal Health Department has told provinces to increase environmental surveillance to promptly warn farmers about major changes in salinity and other environmental factors.

Provinces should instruct farmers about safe breeding techniques, focusing on factors that cause disease like salinity, temperature and water depth in ponds, said the Animal Health Department.

Farmers should follow relevant agencies’ warnings and schedules when breeding shrimp, it said.

Speaking at a seminar held in HCM City last week, Tran Dinh Luan, deputy director of the Soc Trang Province Department of Agriculture and Rural Development, said officials of the crop cultivation sector had distributed leaflets to farmers about safe production during saline intrusion. He said officials of the crop cultivation sector should also do this.

"Farmers need to be introduced to a successful aquaculture model and methods to reduce production costs and pollution," he said.

Though hot weather occurred last month, many shrimp farmers in Soc Trang’s Tran De District had a good harvest because they had large ponds, and had stored low saline water since the end of last year.

They had also bred shrimp at an average density of 30-50 shrimp per square metre, according to the My Thanh Shrimp Association in Tran De District.

In areas with high salinity, farmers should rotate aquaculture species, Luan said.

For instance, in Soc Trang’s high salinity areas, farmers were breeding yellow pomfrets in the dry season and breeding shrimp in the rainy season, he said.

Vu Van Tam, MARD Deputy Minister, has required that MARD’s Animal Health Department set up a national programme to prevent and control diseases on brackish water shrimp, considered to be one of Vietnam’s most important aquaculture species.

The country exports about US$3 billion of brackish water shrimp a year.

The delta’s natural conditions are suitable for breeding this kind of shrimp, accounting for 80 per cent of the country’s brackish water shrimp output.

Shrimp-rice farms

In the delta’s coastal areas that cannot grow rice year-round because of climate change, farmers have rotated planting of rice in the rainy season and shrimp in the dry season.

Farmers said they had earned higher profits from this shrimp-rice cultivation model than from growing only rice.

Le Thanh Son, who has rotated rice and shrimp on a 1-ha field in Kien Giang Province’s U Minh Thượng District in recent years, said this year drought and saline intrusion had been severe, so farmers with two rice crops a year had seen a lot of damage.

“When saline intrusion occurs, I keep the saline water and breed shrimp,” he said.

“I bred black tiger shrimp and earned a profit of more than VNĐ100 million (US$4,500) this year,” he said.

The shrimp-rice cultivation model has helped reduce the use of chemicals in rice fields, as well as diseases and production costs, according to farmers.

Kien Giang Province has 80,000ha of land devoted to a shrimp-rice cultivation model.

Mai Anh Nhin, deputy chairman of Kien Giang Province People’s Committee, said before the shrimp-rice cultivation model, many farmers in coastal areas were able to grow one rice crop a year with a yield of 2-3 tonnes per ha.

After the model was implemented in 2000, the yield of shrimp was 280 kilo per ha and yield of rice 4-5 tonnes per ha, he said.

Kien Giang has petitioned the MARD to allow the province to transfer 20,000 ha along coastal areas from rice monoculture to shrimp-rice rotation, he said.

Pham Khanh Ly, deputy head of the MARD’s Aquaculture Department, said responding to the effects of climate change and rising sea levels, the shrimp-rice cultivation model would be a top priority during the time of saline intrusion.

"The shrimp-rice cultivation model is considered a sustainable agricultural model," Ly said.

Shrimp-rice cultivation has expanded in the delta’s coastal provinces, reaching 160,000 ha, according to the MARD’s Directorate of Fishery.

VNS