Course:CONS200/2023WT2/Chinese paddlefish (Psephurus gladius): Causes of extinction and why conservation failed

Overview & History

Chinese Paddlefish side profile

Psephurus gladius, known by its common name as the Chinese paddlefish, is a now extinct freshwater fish that once flourished in its natural habitat of the Yangtze river of China, all the way to rivers flowing into the Western Pacific (Zhang et al.,2020).  Considered one of the largest freshwater megafauna in the world, a variety of factors including overfishing, construction of water dams along rivers, habitat degradation, and overfishing have led to the unfortunate declaration of its official extinction by the International Union for Conservation of Nature (IUCN) in 2022.  The Chinese paddlefish, along with the American paddlefish (Polyodon spatula) were the only two living species of paddlefish, making it an extremely unique species of freshwater fish.  Pivoting to its characteristics, the Chinese paddlefish possesses a cartilaginous skeleton and has a grey appearance, along with a white underbelly.  They also grow to lengths of up to 7 meters and are estimated to live around for 29 to 38 years (Zhang et al.,2020). As for the causes that have caused the demise of a magnificent creature such as the Chinese Paddlefish, there are a variety of driving factors that led us to this point, including habitat loss, overfishing, human activity and pollution.

Species Information

Biology

Phsephurus gladius was known to typically grow to 3 meters in length and usually weigh around 300 kilograms (661 pounds). The largest reported recorded specimen was 7 meters in length and weighed 500 kilograms (1102 pounds). Reproduction for this species occurred by males and females releasing sperm and eggs into shallow river areas and fertilization would occur if sperm came into contact with the eggs. Using its long snout it could detect electrical currents emitted by prey such as crustaceans and fish.

Behaviour

Chinese Paddlefish spawn through March and April, with spawning sites in the upper reaches of the Changjiang River, but were also reported to spawn in the lower Jinsha River. Because of how big these fish were the fully matured fish had no natural predators. However, the eggs and juvenile fish were prone to being eaten by smaller predatory fish. This fish mostly survived off of small to medium size aquatic animals that included small fish, crabs, anchovies.Using its long snout it could detect electrical currents emitted by prey such as crustaceans and fish.

Habitat

The Chinese Paddlefish, renowned as one of Earth's ancient inhabitants, owe much of their longevity to their habitat. Thriving primarily in the Yangtze River basin and its estuary, these majestic creatures favored the expansive waters of large rivers and occasionally ventured into serene lakes. Sharing similarities with salmon, they exhibited anadromous behavior, embarking on migratory journeys upstream to spawn in the upper reaches of rivers. Although their formative years were spent in the lower Yangtze, they later undertook these seasonal migrations, typically during the spring months from mid-March to mid-April. Recognizing the importance of sustaining their populations, the government has invested resources into enhancing spawning grounds. Notably, one such site along the Jinsha River stands out, offering optimal conditions with its depth of around 10 meters and sandy/loamy bottoms, providing an ideal setting for successful spawning.

Ecological Role

Before going being declared extinct in 2022, the species was a very good indicator of environmental quality and health due to the fish needing a clean and healthy waterway to live in, in order to survive.Before going being declared extinct in 2022, the species was a very good indicator of environmental quality and health due to the fish needing a clean and healthy waterway to live in, in order to survive. Chinese Paddlefish being one of the top predators, feeding on freshwater shrimp and crab, they are a essential component of the food web. Regulating and controlling the populations of small prey species, and contributing to maintaining the balance of the aquatic environment. Moreover, they played an essential role on transporting nutrients from marine environments all they way up into upper river ecosystems to spawn, enhancing other environmental factors. Furthermore, they contributed to the cultural and economic significance as they supported local fisheries and provided a food source for cultural support.

Extinction

Habitat Loss and Fragmentation

Gezhouba Dam in Yichang, Hubei Province, China

Numerous circumstances contributed to the Chinese paddlefish's extinction. The fragmentation of habitats was one of the main causes. Being a migratory and anadromous species, it needed a wide range to complete its life cycle. The first step in the Chinese paddlefish's reproductive cycle was swimming upstream. Then, as they moved back downstream to resume feeding, they would gradually mature. But starting in the 1970s, dam construction got underway, making it more difficult for the fish to get to places where they could reproduce. The Gezhouba Dam, whose construction started in 1970 and was finished in 1988, was the most notable. Situated on the Yangtze River, which is the longest river in China and the third longest globally, it was constructed.

Water Pollution

In addition to the fragmentation of the Chinese Paddlefish’s habitat, habitat degradation can also be seen through the pollution of water in the Yangtze River. As the population grew and infrastructures (dams) were built, there was an increased amount of pollutants being seeped into the water through agricultural runoffs, industrial wastewater, and domestic sewage. This degraded the habitat that the Chinese Paddlefish resided in. Since they are filter feeders in their juvenile stages, the amount of water pollution exposed to them was significant and affected their health dramatically.

Overfishing

Lastly, overfishing was already another reason for the extinction of the Chinese Paddlefish. Compared to fisheries nowadays, there is little regulation as to the gender and size of fish that can be harvested. Thus, many of the large-to-medium-sized individuals were fished. The slow growth rate could not keep up with the harvesting rate. This resulted in fishermen harvesting smaller juvenile fish, further damaging the population of Chinese Paddlefish. Furthermore, even when the Chinese Paddlefish were not targeted, they would be caught in gillnets and trawls, leading to mortality through bycatch.

Conservation Strategies

Prior to its extinction, conservation activists used a multitude of methods to mitigate the damage on the Chinese paddlefish population.  On the forefront of these changes is the Yangtze River protection strategy.   Chief amongst the strategy is the decade-long policy carried out in 2020 that prohibits fishing in the Yangtze River, which is doubled down by the Yangtze River Protection Law to help monitor illegal activity conducted by local fisherman.  The aim for the policy is to ensure the natural ecosystem as well as the fish population residing in the river ample time to recover and return to previous levels.  Moving on, as the world moves towards renewable energy, infrastructure such as hydropower plants and dams end up being built all along the main river channels across China.  The Yangtze River is no different, which has caused disturbances to breeding cycles and migratory patterns of countless fish species.  To counter this, scheduled “flood peaks”, a temporary rise in water levels at the  Xiluodu-Xiangjiaba-Three Gorges Dams  are conducted to simulate natural conditions for fish species such as the Chinese paddlefish to spawn their young.  With that being said, multiple facets of conservation have been implemented to push back the critical status of the Chinese paddlefish, though more work can definitely still be done to bring it back to its once flourishing population.

Lessons Learned

The extinction of the Chinese Paddlefish is a harsh reminder of the need to protect other sturgeon species around the world. Since the extinction the Chinese government has greatly stepped up efforts to protect aquatic species throughout the region, especially in the Yangtze river basin. This extinction is not only a wake up call to the Chinese government, but to others around the world of what can happen if you let waterways go unnoticed in terms of water health, and what it can do to the species that live within them. It turns out that many large freshwater animals around the planet are threatened with extinction due to water pollution.

Conclusion

The Chinese paddlefish was an extremely unique creature that is unfortunately now extinct, primarily due to human activity. As the main culprits of this problem, we've done too little too late to come up with conservation strategies, such as the introduction of the Yangtze River Protection Law, that aimed to oversee illicit activities on the waterfront, to help make a comeback for the Chinese paddlefish. Decades of water pollution and overfishing were loud warning signs that the ecosystem in the Yangtze river was deteriorating significantly, yet there was little action until much more recently. What we can take away from the loss of the Chinese paddlefish is the amount of work that needs to be put in order to help protect the surrounding ecosystem, so the various other freshwater fauna facing endangerment can continue residing in these waters. By preserving these fish species, it allows for the environment to gradually recuperate and return to its normal levels, and at the same time be able to provide to those that depend on the river, granted at a more regulated level.