Thousands of Chinese sturgeons were released into the mouth of the Yangtze River yesterday. They were implanted with microchips to study the migration patterns of the endangered species.

Among the 3,349 fish released, 600 were wild sturgeons that were mistakenly caught by fishermen. The others were artificially bred and raised in captivity. About 1,500 Chinese sturgeons were released into the river last year.

The fish were also implanted with a "pop-up tag" - the most advanced equipment used to study fish migration patterns in the world - for the first time, said Liu Jian, deputy director of the Administration Agency of the Shanghai Yangtze Estuarine Protected Area for Chinese Sturgeon.

He said the tag can collect data for 500 days. Each tag will trace the Chinese sturgeon and record information such as water pollution levels and temperature changes.

The Chinese sturgeon is endangered although scientists can't say with any accuracy how many remain in the wild. The species, believed to be 150 million years old, is viewed as a "living fossil."

"It is significant for scientists to explore the secrets of life by finding out how the fish lives," Liu said. "But now we know little about it."

Each fish also carries a small marker with a phone number - if caught it can be returned to the administration.