Baiji dolphin: is an aquatic mammal of the mammal family Cetacean order. sound jì; The media also often writes "white-tipped dolphin", a small freshwater whale endemic to China. The body is spindle-shaped, 1.5-2.5 meters long and weighs up to 230 kg. The snout protrudes forward like a bird's beak, narrow and long, with the tip of the snout slightly upturned, about 30 cm. The top of the forehead is significantly raised, the nostrils are long on the top of the head, and when breathing, the head comes out of the water first, and the spray of water is not high. The eyes are extremely small, above the back of the corners of the mouth. The ear holes are needle-eye-shaped. The dorsal fin is triangular , with broader limbs , bluntly rounded ends , and crescent-shaped caudal fins. The back of the body surface is bluish grey , the ventral surface is white , and the caudal fin is not out of water.
Mainly living in the middle and lower reaches of the Yangtze River in China and the waters of Dongting Lake, Poyang Lake, Qiantang River and other waters connected to it, usually in pairs or more than 10 heads together, like to move in the depths of the water, good at diving. The baiji dolphin is a carnivore with about 130 sharp teeth in its mouth, which are of the same type. It feeds on freshwater fish and often swims to shallow waters on the shore at dusk for predation. Also eat small amounts of aquatic plants and insects. When breathing, the head first comes out of the water, then fully exposed to the water, swimming 2 meters on the surface of the water, and then entering the water. The life span can reach more than 30 years.
The baiji dolphin evolved from terrestrial animals over a long evolutionary process and is the rarest of all cetaceans in the world. On November 14, 2018, the IUCN Red List of Threatened Species was updated and released, and the extinction of the baiji dolphin was not confirmed, maintaining the original rating of "critically endangered".
The IUCN's Dr. Sam Twee investigates along the Yangtze River in China to try to uncover the reasons behind the disappearance of the white-cum dolphin and other declining species in the Yangtze River.
As part of an intensive investigation investigating the likelihood of the extinction of the white-sided dolphin, researchers interviewed fishermen along the Yangtze River when they found the carcass of a porpoise on the bank of a river near the port of Poyang Lake. Detailed studies of dead animals can provide valuable clues to the factors that contributed to the disappearance of the white-capped porpoise, as well as the factors that contributed to the continued severe decline in the world's only freshwater finless porpoise population.
It wasn't a beautiful sight, and the researchers were told the porpoise had been lying on the riverbank for about 30 days, which was evident from the status quo. The researchers applied ointment to their noses to mask the stench emitted by animal carcasses and then began studying the autopsies of dolphins. Fortunately, it experienced extremely cold weather some time ago, so the porpoise did not seriously decay.
The animal is an adult female with a body length of 150 cm. There are no external markings to indicate that it was hit by a boat or entangled in fishing gear. From viscerally, the researchers found no broken ribs or bleeding from the sides indicating a vessel collision, or a bubble in the lungs indicating a by-catch due to a by-catch (a term used in fisheries to refer to animals that fishermen inadvertently caught while targeting other marine species. By-catch includes animals that have been caught and released and animals that have died unexpectedly as a result of fishing operations. and drowning. The animal's blubber thickness was at a healthy level, and it had several indigestioned fish in its stomach, suggesting that it had been eating normally and had been actively searching for food shortly before dying. So the finless porpoise was apparently in good physical condition before it died, which appeared to be acute and sudden, but there was no obvious evidence of trauma, as expected by-catch in the fishing gear or a boat collision. So it is likely that the animal was killed by electrocution.
Electric fishing is an illegal fishing method that was widely spread in the Yangtze River region in the 1990s. It is usually practiced by people who do not have "real" fishing skills, who work at night and use batteries to fire large amounts of electricity into rivers, collecting any dead fish floating to the surface. It is extremely destructive, with a deadly charge that can kill anything within a 20-meter range, and as fishing boats drift along the river, the charge continues to flow in the water. Professional Yangtze River fishermen despise electric fishermen. However, although local fisheries officials tell us they are concentrating on controlling electrofishing, they are limited in number and have not yet been able to conduct comprehensive "trap operations" or regularly survey river sections for control. While some clandestine operations have continued to attempt to identify fishermen in riverside communities, these operations have also been very limited.
As the researchers traveled from one riverside fishing village to another, they collected more and more data on the carcasses of fishermen and other finless porpoises that the Regional Fisheries Department has seen over the past few years. The researchers are currently analyzing all the data collected during the survey, but it appears that the finless porpoise deaths were caused by a range of different factors. As far as the researchers' investigations know, the two most common causes of dolphin deaths are boat collisions and incidental catches of fishing gear. These two factors are certainly the cause of the mass death of the Yangtze River finless porpoise. As early as 1892, a European observer reported that Yangtze River fishermen fished in the water with long lines of rolling hooks, "sometimes unfortunately, the entire line was broken by the porpoise hooks living in the Yangtze River." Throughout the 20th and 21st centuries, as the Chinese population grew, so did the fishing intensity and the number of finless porpoise deaths associated with it, and the industrialization of the Yangtze River region also led to a massive increase in ship transportation, causing the finless porpoise to lose its sense of hearing and become a dead animal on the road.
However, some causes of finless porpoise death are more pronounced than others. Non-professional fishermen are more likely to identify dolphin deaths caused by propeller impacts or entanglements in fishing gear than less obvious causes of death such as pollution or electric shock, which do not leave any external traces. Further analysis will investigate whether it is possible to tease out the relative effects of these different threat factors from the researchers' interview data.
But finless porpoises are not the only cetaceans in the Yangtze River, and the main purpose of the researchers' investigation is to investigate the disappearance of the baiji dolphin, a unique porpoise in the Yangtze River.