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Threats faced
The Yangtze finless porpoise – IUCN Red List "critically endangered", China's national first-class key protected wildlife. But you know what? Most of the open waters of the former Yangtze River basin were once active with their healthy figures. Between 1984 and 1991, the total number of Yangtze finless porpoises was about 2,700, and the population of Yangtze finless porpoises has been declining year by year. According to the 2006 inspection, the total number of Yangtze finless porpoises was about 1800; In 2012, the total number of Yangtze finless porpoises was about 1,045; By 2017, there were only about 1,012 Yangtze finless porpoises left, and the sharp decline in population was a wake-up call to the world, and an endemic wildlife population was falling apart. Until 2020, the "ten-year fishing ban" plan of the Yangtze River was officially released, and under the escort of national policies, the trend of significant decline in the total population of Yangtze finless porpoises was effectively alleviated. So, what is the reason for the declining population of this species?
The multiple threats faced by the Yangtze finless porpoise are mainly as follows.
1. Busy shipping
The Yangtze River is the only waterway transportation artery running through the east, central and western parts of the mainland, and is currently the busiest and most navigable river in the world with the largest inland water transportation. While the rapid development of the shipping industry has brought huge economic benefits, it has also caused an increasingly serious squeeze on the living space of aquatic organisms.
(1) A large number of boats have encroached on the main habitat of the finless porpoise, resulting in the loss of their homes for other aquatic organisms, such as the finless porpoise and its baited fish, and the paradise suitable for them is gradually collapsing. In order to ensure navigation, the waterway department will carry out rectification construction on the waterway, and the remediation methods such as rock throwing and cement solidification will destroy the original riverbed environment and coastal wetlands of the Yangtze River, and the necessary conditions for the breeding of fish, shrimp and snail mussels will be lost, thereby destroying the food chain of the Yangtze River.
Wuhan section of the Yangtze River
(2) Due to the turbidity of the Yangtze River, cetaceans have specialized their vocal and auditory abilities in the process of long-term adaptation and evolution, and they emit and receive sound signals all the time to perceive the external environment and carry out community communication. Porpoises mainly rely on echolocation systems to survive in turbid river waters, and the noise emitted by boats interferes with porpoises predating, communicating, evading danger, etc., and even seriously damages their hearing system, resulting in their inability to identify directions underwater. After the normal communication between individuals, especially the sonar system of the juvenile dolphin is not yet developed, the underwater noise will increase the chance of the juvenile and the female dolphin being separated, resulting in the stranding or stress death of the juvenile.
Echolocation pattern diagram of finless porpoise
(3) The propeller of the boat will also cause direct damage to the finless porpoise, and some finless porpoises are disturbed underwater and do not have time to dodge, that is, they are killed or injured by the propeller.
Yangtze finless porpoise died tragically under the propeller (Photo courtesy of Zhenjiang Reserve)
Second, disorderly and excessive sand mining activities
Due to the impact on the normal navigation order of the main stream and the destruction of the Yangtze River waterway, sand mining in the main stream of the Yangtze River is currently prohibited.
(1) Sand mining will change the structure of the riverbed, resulting in changes in the underwater hydrological conditions, and in severe cases, it will lead to leakage of the riverbed, causing geological disasters and groundwater pollution.
(2) Sand mining will destroy the living environment of benthic organisms such as shrimp, crabs, snails and mussels, and submerged plants killed by sand mining activities will also destroy the spawning grounds of fish, which in turn affects the entire food chain.
(3) Intensive sand mining vessels produce strong underwater noise, which leads to the fragmentation of the habitat of aquatic animals such as finless porpoises, and hinders the migration and communication of Yangtze finless porpoises.
(4) After the sand at the bottom of the water is sucked out through the sand suction pipeline, it is directly cleaned in the rivers and lakes, and the pollutants deposited by the bottom adsorption are re-released into the water body, especially some organic pollutants that cannot be degraded in a short period of time, resulting in secondary pollution of the surrounding waters of the sand mining operation area, thereby affecting the habitat quality of aquatic organisms, and even affecting the water security of the surrounding human residents.
Working sand mining vessels
Third, the water system partition
Historically, the natural fry production of the four big fish in the Yangtze River in Hubei Province reached 20 billion, which dropped to 1.106 billion in 1982, and the resources of the four big fish fry after the Three Gorges Reservoir was impounded were about 200 million; the catch of Chinese river crabs in the Yangtze River in 1986 was 324 tons, and the current catch is less than one-tenth of it; in the 70s of the 20th century, the output of shad in the Yangtze River reached 750,000 kilograms, and the shad of the Yangtze River has been difficult to find in the past ten years, and it has almost disappeared. Connected water bodies are the basic needs of fish migration, and natural mud and sand or rivers and lakes with aquatic grass are important environments for fish to breed and feed. (1) With the completion of a large number of sluices and dams and the implementation of shoreline solidification projects, the migration of aquatic animal resources such as fish, shrimp, snails, and mussels has been blocked, and the basic regeneration capacity has been greatly reduced. (2) Interception-type wading projects such as sluice dams will themselves lead to the fragmentation of the habitat of aquatic animals such as finless porpoises, hinder the migration and genetic exchange of Yangtze finless porpoises, and the Yangtze finless porpoise population will be threatened by inbreeding. (3) In addition, the situation of cold fishing and overfishing has ensued, posing a far-reaching threat to the basic guarantee of feeding the Yangtze finless porpoise.
Shasta Dam, USA
Fourth, cool fishing and indiscriminate fishing
The catch of natural resources in the Yangtze River Basin reached 450,000 tons in 1954, dropped to more than 200,000 tons in the early eighties, and remained at about 60,000 tons around 2010. In the sixties, the main economic fish of the Yangtze River were no longer flooded, and some were on the verge of extinction, and overfishing caused a sharp decline in the natural catch of the Yangtze River fishery.
The sharp decline of fishery resources in the Yangtze River has led to food shortages for large animals such as the Yangtze finless porpoise. The decline in natural catches has given rise to extreme illegal fishing methods such as Ecstasy, rolling hooks, and electrofishing.
(1) The Ecstasy Array is a trap, consisting of a series of nets and net bags, which can stretch for hundreds of meters or even thousands of meters, after the finless porpoise enters the Ecstasy Array and is trapped, due to its strong desire to escape, there is a strong stress response resulting in choking and suffocation.
It seems to be a beautiful idyllic scenery, but it is actually a true portrayal of the "Lost Soul Array" overfishing in the middle reaches of the Yangtze River. Unsustainable fishing practices such as electric fish, poisonous fish and Ecstasy have reduced natural fish production in the region by 75%
(2) The roller hook is composed of dense nylon wire and iron hook, and the finless porpoise will struggle after being entangled in the roller hook, and the more it struggles, the more serious the injury, and finally suffocates to death. Even if you get away with it, the wound can cause the porpoise to develop sepsis due to secondary infection.
Illegal fishing gear "rolling hook"
(3) Electric fishing is a highly dangerous illegal fishing method, which can damage the reproductive system of fish at best, and drive out large and small fish in electrified waters. Porpoises that strayed into electrified waters are also doomed, and electrocuted porpoises will die directly or faint and lose consciousness and drown. Illegal fishing activities are a vicious circle, and the more depleted fishery resources are, the more rampant illegal fishing activities become, even if they cost criminals lives.
Porpoises that have been victims of illegal electric fishing
5. Water pollution
The Yangtze finless porpoise lives in water, but does not directly drink a lot of natural water, but mainly relies on food to replenish water. Therefore, water pollution in the general sense (such as nutrients, etc.) does not directly cause serious harm to the Yangtze finless porpoise. The main impact mechanism of water pollution is the decline of the food resources of the Yangtze finless porpoise, and the enrichment of pollutants in the Yangtze finless porpoise through the food chain, resulting in chronic poisoning of animals. (1) Some chemical plants directly discharge excessive sewage into natural water bodies, resulting in a decline in the quality of surrounding aquatic habitats, which in turn leads to a decrease in the food source of the Yangtze finless porpoise. (2) Organic pollutants and heavy metals that are difficult to metabolize in the water body enter the food chain and are enriched into the finless porpoise, resulting in fetal development malformation, miscarriage, and even acute poisoning death of adult finless porpoise. (3) When finless porpoises are active in the wild, they will inevitably bump and suffer minor injuries, but if they are in polluted water for a long time, the wound may not heal, and severe infection may cause sepsis and death.
Heavily polluted water
The birdsong and dolphin leap of the Yangtze River were once a good memory of a generation, but now they are very cherished, and the population recovery of the Yangtze finless porpoise is a long way to go, and protecting the Yangtze finless porpoise and protecting the life of the Yangtze River requires our joint efforts.