Wei Lizhen, 59, usually casts her fishing nets on the Xijiang River around 5 am. The villager from Zhaoqing, Guangdong province, has been fishing on the tributary of the Pearl River for more than 30 years.

A boat is secured at Sanshui, Guangdong province, following a two-month fishing ban to revive declining stocks in the Xijiang River. [China Daily]

But in recent years stocks declined and her daily catch was reduced to about 5 kilograms of fish after nearly 10 hours in a tiny boat. "I caught at least 20 kg a day a decade ago," she said.

"There are fewer fish - individuals and species - due to overfishing in recent years. The common species such as carp, catfish and grass carp are now rarely seen in the river."

Overfishing has become a serious problem on the Pearl River. "It is like a small cake for many people. I can only have a tiny slice."

Wei's hope for a bigger cake might be realized in the years ahead as a result of a fishing ban, the first to encompass an entire river system, on the Pearl. The Ministry of Agriculture imposed the annual two-month restriction on April 1, the start of the peak spawning season.

The goal is to preserve biodiversity and improve water quality in China's third longest river, which includes the tributary Xijiang, Beijiang and Dongjiang rivers. The ban also covers related lakes in Jiangxi, Hunan, Guizhou, Yunnan and Guangdong provinces and Guangxi Zhuang autonomous region.

"I hope that the ban will help restore the number of fish in the river," Wei said.

A toll on the Pearl

The Pearl River, stretching 2,400 kilometers, was once home to nearly 400 varieties of fish, including such rare species as the Chinese sturgeon and the giant salamander. It contained about half of the country's freshwater species.

But years of overfishing, water pollution and increasing construction of hydro projects have led to a decline in fishing output and some rare species have not been seen for years, said Wu Zhuang, director of South China Sea Fishery Bureau under the Ministry of Agriculture.

For example, there have been no recorded catches of Chinese sturgeon in recent years. In the 1930s, some 400,000 kg of the sturgeon were produced each year in the Xijiang River alone.

According to samples collected near the biggest spawning site along the Pearl River, both the number of individual fish and the number of fish species have declined significantly during the past few years, according to a report in Guangzhou Daily.

Anadromous fish, which live in the sea but swim upriver to reproduce, "have been forced to spawn before arriving at the best sites ... because traditional grounds are blocked by hydro projects", researcher Li Xinhui was quoted as saying. "As a result, their young have slimmer chances of surviving, largely because their migration routes back to the ocean are not long enough to allow them to mature."

Li, who works for the Pearl River Fisheries Research Institute under the Chinese Academy of Fishery Sciences, also attributed the decline in the numbers of many common freshwater fish to changes in the aquatic environment.

Dealing with dams

To maintain the diversity of aquatic species in the river, Li suggested that dam projects make accommodations that allow fish to migrate and spawn. "For example, separate channels should be built in the dam projects so that fish can move upstream to their spawning sites."

Yang Shaosong, an official with the fishery bureau, said separate channels would be of little use because they are not like the natural waterways fish are accustomed to. "Fish do not know where the channels are. They may have to spawn downstream if they do not find a waterway upstream," Yang told China Daily.

An estimated 14,000 hydro projects and 96,000 water conservancy works have been constructed along the Pearl River. Most have been in the upper half of most of the tributaries, according to Yang.

"The hydro projects play an important role in supporting the economic development of cities near the river," Yang said, "but they also pose a great threat to the development of freshwater fish, hindering the propagation of some fish species.

"We cannot stop building such projects, nor ask local authorities to destroy them. So we find no way, except to ban fishing, to prevent fish species from dying in the river."

An increasing number of environmental emergencies in recent years have also polluted water and killed fish, Yang said. China's Fishery Eco-environment Report tallied 165 pollution incidents in the Pearl River in 2009, leading to economic losses totaling 56 million yuan ($8.6 million).

For example, many factories in recent years were found to have discharged industrial waste into the upper reaches of Xijiang and Beijiang river tributaries. In 2005, a serious cadmium leak from a factory in Yingde county, on the upper section of Beijiang River, killed many fish and affected nearly 100,000 local people.