Is it a problem to drain more than 200,000 cubic meters of lake water to catch two alligator gar?

On July 13, a "strange fish" appeared in Yunchan Lake in Ruzhou Central Park, Henan Province. The park management confirmed that it was an invasive species, the alligator gar (Atractosteus spatula). After trying to catch it with a fishing net, they decided to release the water to catch it. In mid-to-late August, the "Ruzhou alligator gar" had evolved from a local news story to a national hot spot. At its peak, 30 million netizens watched the live broadcast of the pumping out of the water to catch fish. On the evening of the 26th, two alligator gars were caught and brought ashore in Yunchan Lake, Ruzhou.

The alligator gar caught by pumping water has been treated harmlessly | CCTV News

After the Ruzhou alligator gar was caught, news of the discovery of gars broke out in Qingdao, Shandong, Kunming, Yunnan, Zhengzhou, Henan, Xining, Qinghai, Yinchuan, Ningxia, etc. Among them, Haiyun Jiayuan Community in Qingdao, Shandong and Chuncheng Huigu Community in Kunming, Yunnan also caught gars by pumping water.

However, while pumping water can catch these ferocious fish, it also has hidden dangers.

Alligator gar suddenly appears everywhere

Alligator gar is a large freshwater fish that can grow up to 3 meters in length and weigh more than 150 kilograms. They have a long and pointed snout, a mouth full of sharp teeth, and diamond-shaped hard scales on their bodies, like an impenetrable armor. Alligator gar have survived on Earth for more than 100 million years. Apart from humans and a few large predators (such as crocodiles), and the possibility that their eggs are eaten by other aquatic animals, adult alligator gar have basically no natural enemies .

Juvenile alligator gar pounces on a forage fish being fed | The Fish Whisperer / youtube

Alligator gar and the other six species of fish in the family Gar are collectively called gars. They are mainly native to North America and Central America. For China, they are considered invasive alien species. According to the currently available data, it is generally believed that several gars entered China around 1990. At that time, gars were introduced to several farms in Guangdong as precious ornamental fish , and then gradually became a frequent visitor to the domestic ornamental fish market.

But like many ornamental fish, gar do not stay in fish tanks only, but enter China's natural or artificial water bodies through multiple channels . In 2004, an 85-centimeter short-nosed gar (Lepisosteus platostomus) appeared in the pond of Wenzhou Xiushan Park. It is speculated that this fish may have been accidentally mixed in when the park purchased a large number of ornamental fish seedlings from Guangdong, Fujian and other places in 2002. Gar larvae have also been found many times in the Dongguan section of the Dongjiang River in Guangdong. In addition to releasing them into the wild, the possibility of escaping from upstream farms into natural water bodies cannot be ruled out. Of course, the more common way is to release them into the wild and abandon them by a few aquarium enthusiasts . The gar that appear in the news are more likely to appear in this way.

Alligator gar in a fish tank. However, alligator gar in a fish tank may enter natural water bodies due to escape, release or abandonment by humans. | Raf24~commonswiki / Wikimedia Commons

Now, everyone knows about the alligator gar and knows that it is an invasive species that should be taken seriously. It should be said that the news about Ruzhou pumping water to catch alligator gar has made everyone reach this consensus.

This is very important because such a consensus had not been established before. Take the alligator gar, for example. In 2007, fishermen in Liling caught an alligator gar in the Lujiang River. Although the local fishery department mentioned in the press release that the alligator gar is a fierce foreign carnivorous fish with few natural enemies in domestic waters, they finally released the alligator gar into the natural waters " in order to preserve the fish species".

In fact, many residents have seen gar in the ponds around them, but they just don’t know what they are. According to my actual visit, in the Qingdao community where the alligator gar was found, these two big fish have lived in the shallow pond near the main entrance square of the community for at least one or two years, and it is difficult for residents not to notice their existence. However, for such a long time, no one paid much attention to them until the news of "Ruzhou alligator gar" set off the whole network. The news in Kunming, Zhengzhou, Xining and Yinchuan may be the same - it is not that the gar was suddenly discovered, but that the gar was suddenly recognized.

The alligator gar has a crocodile-like face, but with a shorter snout. | Howcheng / Wikimedia Commons

Is pumping water to catch fish the best way?

It is good to reach a consensus that invasive species should be taken seriously, but is pumping out fish a good idea?

Some believe that alligator gar have a wide range of diet, lack natural enemies in my country, and may harm humans, so they must be eliminated at all costs (such as pumping water). Others criticize the method of releasing water as too drastic, and that if water is released into natural water bodies to catch fish, the damage to native fish, benthic animals and aquatic vegetation may be more serious than the impact of the alligator gar itself.

If we only look at the landscape ponds in residential areas in Qingdao, Shandong and Kunming, Yunnan, pumping water is indeed a convenient and efficient method . These artificial ponds have limited capacity and basically no perfect natural ecology. By quickly pumping water to complete the capture, it can also completely eliminate possible breeding risks.

In a residential area in Qingdao, staff members are fishing for alligator gar in the water｜Peninsula News

But if it is Yunchan Lake in Ruzhou, the situation is different. Including Yunchan Lake, there are 5 lakes in Ruzhou Central Park. These 5 lakes are completely artificially excavated and formed by diverting water from the North Ru River. Yunchan Lake itself has a huge body of water, and there are culverts connecting the 5 lakes. How to drain more than 200,000 cubic meters of lake water? The staff introduced that they use the siphon principle to discharge the water of Yunchan Lake directly into the adjacent Danyang Lake. In order to prevent the alligator gar from escaping, they also squat at the outlet of Danyang Lake.

This massive pumping operation did catch two alligator gar and disinfected the lake bottom, which is a positive result. However, if the two alligator gar that were caught had already reproduced, it is inevitable that eggs or young fish would enter Danyang Lake through the lake water . Moreover, gars are tolerant to low oxygen and can absorb large amounts of oxygen directly from the air using their swim bladders. They may survive in low-water culverts or even in moist pond mud, and future troubles cannot be completely eliminated. Moreover, although Yunchan Lake, which was built in 2016, originated from artificial excavation, the huge water body has gradually formed a stable semi-natural ecosystem with certain ecological value. The ecological impact of the one and a half month-long pumping on underwater vegetation and benthic animals also needs to be carefully estimated.

In 2011, the Trinity River in Texas, USA, suffered a drought and a large number of fish died, but the alligator gar survived tenaciously in the mud of the dried-up river. The swimming bladder's auxiliary breathing ability is the key to its survival in low water levels｜Garzilla Guide Service

As for the gar crisis in natural water bodies, it is even more impossible to use the method of pumping water to catch gar. In recent years, gar have been found in the tributaries of the Pearl River, the tributaries of the Xiangjiang River, the Tongshan River in Fujian, the Qiantang River in Zhejiang, and the Shandong section of the Yellow River. We cannot completely drain natural rivers to catch gar. Some gar have a certain salt tolerance and can survive at the junction of fresh and salt water. No one can guarantee that they will not flow downstream into the near sea.

Drainage alone is clearly not enough to curb the proliferation of gar.

Two alligator gar caught in Ruzhou | CCTV News

In its North American homeland, the population once declined

However, the alligator gar, which is an invasive species in China, once experienced a population decline in its native North America.

For a long time, Native Americans were familiar with gars. They ate gar meat (but gar eggs and ovaries are poisonous), used fish skin to make leather goods, and used fish scales to make decorations. Due to the limited scale of fishing by the Native Americans, the population of gars was not greatly affected.

But starting in the 19th century, the distribution area of ​​gar began to shrink rapidly. Although adult gar have almost no natural enemies, gar eggs are easily eaten by other aquatic organisms. In order to improve the survival rate of fish eggs, gar rely heavily on flooded mudflats for spawning, but this breeding ground has been massively reduced due to the development of water conservancy projects in North America . From the late 19th century to the first half of the 20th century, aquaculture practitioners regarded gar as a natural enemy of the fishery and killed them indiscriminately, and even built special electric fishing boats to continuously operate in waters where gar may appear.

A giant alligator gar captured in 1910 | Dept. of Library Services, American Museum of Natural History

It was not until the second half of the 20th century that the situation of the gar, which was once condemned by everyone, slowly changed. People gradually realized that although the gar had a large appetite, it would not cause ecological disasters in its native waters, but could maintain the balance of the water ecology . In order to rebuild the gar population in its native waters, people began to release juvenile gar and imposed many restrictions on gar fishing . Texas stipulates that anglers are only allowed to catch one gar per day, and it is recommended to release the gar after fishing. It is recommended to use bronze materials for fish hooks and leader lines, so that the alligator gar can use gastric acid to corrode the fish hooks after release, ensuring its chance of survival. Some places have made detailed restrictions on the time periods and river sections for gar fishing.

It is not easy to catch gar, but its huge size and ferocious feeding habits make the fight between man and fish full of wild charm, which is an irresistible temptation for fishing enthusiasts. For gar that enter China's natural water bodies, targeted fishing may be a feasible method . Unlike most fish, gar prefer to move on the water surface. Using a float to hang large-sized fish meat can eliminate the possibility of accidentally hurting other fish.

Alligator gar caught by fishing｜Dawson Hefner / Texasmegafishingadventures.com

Of course, the gar is just one example of the growing biological invasion crisis in China and around the world. Many invasive species are more widespread and more harmful, such as the well-known Procambarus clarkii, golden apple snails, tilapia and bullfrogs. While making full use of technology to eliminate the threat of existing invasive species, we should also be vigilant against the emergence of new invasive species.

For a long time, there were no legal restrictions on human biological invasions in my country. However, since April 2021, the Biosafety Law of the People's Republic of China has come into effect. The law stipulates that if alien species are introduced without approval, in addition to the confiscation of the introduced alien species, a fine of more than 50,000 yuan but less than 250,000 yuan will be imposed. If alien species are released or discarded without authorization, they will be ordered to be captured and recovered within a time limit and fined. In serious cases, the Criminal Law also stipulates that the person shall be sentenced to fixed-term imprisonment of not more than 3 years or criminal detention.

After the Ruzhou alligator gar incident, the survey work on biological invasions in various places has generally accelerated, and the public's attention to biological invasions has also greatly increased. We sincerely hope that this will be the most significant effect of the discussion on pumping fishing.

References

[1] Lou Yundong. Current status and countermeasures of fish introduction research in my country[J]. Journal of Fisheries of China, 2000, 24(2):8.

[2] Yi Da. North American shortnose gar found in Wenzhou[J]. Fisheries Guide to Getting Rich, 2004(22):1.

[3] Lin Changhao. A highly poisonous fish, the gar, was discovered in the Lujiang River. Liling Yearbook, 2008.1.1

[4] Yuan Leyang, Zhou Zhuocheng, Zhou Jiajun, et al. Preliminary report on the fish resources survey in Tongshan Creek, Fujian Province[J]. Sichuan Animal Science, 2012, 31(6): 961-964.

[5] Tong Yongyi. Gar found in Qiantang River system[J]. Fisheries Science and Technology Information, 2001, 28(5): 238-239.

[6] Cheng Yuanhu, Gao Xiaoqin, Suo Changming. A living fossil of ancient fish, the gar, has been found in estuaries[J]. Scientific Fish Farming, 2006(11):1.

Author: A man is wandering

Editor: Mai Mai

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