Chinese sturgeon spawns debate over endangered species’ ‘sexual decline’
- One team of researchers says a dam over the Yangtze is affecting the fish’s gonads while another team says the big issue is a change in water temperature
- The sturgeon was once found all over East Asia but stocks have plummeted in the last century
Is the biggest, rarest fish in the Yangtze River losing the ability to breed?
The jury is still out, with two studies on the possible degeneration of sexual organs in Chinese sturgeon – a freshwater predator that can grow as big as a shark – spawning an unusually acrimonious debate.
On one side is a team from the Ministry of Water Resources; on the other, a group of researchers from the Chinese Academy of Sciences.
In the middle is Acipenser sinensis, a rapidly dwindling fish species that can grow up to five metres (16.4 feet) long and dates back to the age of the dinosaurs, according to fossil records.
In the early 20th century, the sturgeon was found across East Asia, from the Pearl River Delta in southern China to the Korean peninsula and Japan.
But in recent decades, despite desperate efforts to save the species, the sturgeon has disappeared altogether except in the Yangtze, China’s biggest river.
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A research team led by Professor Huang Zhenli, deputy engineer-in-chief at the ministry’s China Institute of Water Resources and Hydropower Research, wondered if changes in the sturgeon’s gonads were a factor in the decline.
They used a new model to estimate the maturity of gonads in Chinese sturgeon samples collected from the early 1980s to present and found that more than 70 per cent of the samples showed various degrees of degeneration. These fish could not produce eggs or sperm when they reached the age of sexual maturity because their gonads were underdeveloped.
In a paper published in the Journal of Lake Sciences earlier this month, Huang and his colleagues said the main cause for the degradation was Gezhouba, the first dam over the Yangtze built in the 1980s, saying the issue “has been neglected or belittled”.
Each summer, the sturgeon living in the Eastern China Sea would head to the Yangtze. They would swim nearly 3,000km (1,860) miles upstream all the way to Maoshui in Meishan, Sichuan province, to spawn.
But the Gezhouba in Yichang cut this journey by almost half and the fish had no choice but to mate in strange waters, affecting the reproductive systems of the species.
In recent years, researchers failed to detect their eggs, sperm or fry in the Yangtze, raising fears about the fish’s imminent extinction.
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The other study, led by Professor Liu Huanzhang from the academy’s Institute of Hydrobiology in Wuhan, said the degeneration that Huang’s team observed was actually a change of the fish’s reproductive tissues in different stages of their life cycle.
After laying eggs or releasing sperm, the sturgeon’s sexual organs shrink, and the samples in Huang’s studies were most likely to be individuals that had mated, Liu and his colleagues said in a paper published in the journal Acta Hydrobiologica Sinica this month.
The paper said there was no evidence that the construction of the Gezhouba caused any noticeable change in the fish’s gonads, and Huang and his colleagues were “narcissists” who “cherry-picked data ... used imagination, made up stories”.
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The demise of the sturgeon, according to Liu and his team, was caused by another dam, the Three Gorges, which caused abnormal changes of temperature in the lower reaches of Yangtze.
The sturgeon is extremely sensitive to water temperature during the spawning season and ever since the Three Gorges started operation in the late 2000s, the number of the sturgeon in the lower waters has dropped sharply to only about a few hundred, according to the study.
For its part, Huang’s team said the academy “should be held responsible for serious damage to Chinese sturgeon protection caused by their negligence and contempt”.
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Zhang Boting, a Beijing-based government dam scientist who was not involved in either study, said researchers might need to consider putting the debate aside and come up with some quick, effective ways to save the fish.
Building a separate passage for the fish was not really an option because it would be so steep that probably no fish could swim upstream.
A more feasible possibility would be to change the dams’ operations to restore closer-to-nature temperatures in downstream waters during the sturgeon’s mating season.
“We can also pump oxygen into the water at the dam’s floodgates. Some evidence suggests that the surgeon’s demise is in part caused by oxygen shortage,” he said.
Human activity is believed to be the main reason behind the disappearance of the Chinese sturgeon in East Asia, but some researchers also suspect climate change is also responsible.
Beijing launched a national programme to protect the fish as dam construction spree in the 1990s prompted concern for the fish’s well-being.
Millions of artificially bred baby sturgeon have been released into the Yangtze over the last two decades, but to little effect.
The Chinese sturgeon spends 15 months in the Yangtze to mate, eating nothing until it returns to the coast.
