Baiji
The baiji is a possibly extinct species of river dolphin native to the Yangtze river system in China. It is thought to possibly be the first dolphin species driven to extinction due to the impact of humans. This dolphin is listed as "critically endangered: possibly extinct" by the IUCN, has not been definitively seen in over 20 years, and several surveys of the Yangtze have failed to find it. The species is also called the Chinese river dolphin, Yangtze river dolphin, Yangtze dolphin, and whitefin dolphin. The genus name Lipotes means "left behind" and the species epithet vexillifer means "flag bearer". It is nicknamed the "Goddess of the Yangtze" and was regarded as the goddess of protection by local fishermen and boatmen. It is not to be confused with the Chinese white dolphin or the finless porpoise. This is the only species in the genus Lipotes.
The baiji population declined drastically in decades as China industrialized and made heavy use of the river for fishing, transportation, and hydroelectricity. Following surveys in the Yangtze River during the 1980s, the baiji was claimed to be the first dolphin species in history driven to extinction by humans. A Conservation Action Plan for Cetaceans of the Yangtze River was approved by the Chinese Government in 2001. Efforts were made to conserve the species, but a late 2006 expedition failed to find any baiji in the river. Organizers declared the baiji functionally extinct. The baiji represents the first documented global extinction of an aquatic "megafaunal" vertebrate in over 50 years since the demise of the Japanese sea lion and the Caribbean monk seal in the 1950s. It also signified the disappearance of an entire mammal family of river dolphins. The baiji's extinction would be the first recorded extinction of a well-studied cetacean species to be directly attributable to human influence. The baiji is one of a number of extinctions to have taken place due to the degradation of the Yangtze, alongside that of the Chinese paddlefish, as well as the now extinct in the wild Dabry's sturgeon.
Swiss economist and CEO of the baiji.org Foundation August Pfluger funded an expedition in which an international team, taken in part from the National Oceanic and Atmospheric Administration and the Fisheries Research Agency in Japan, searched for six weeks for signs of the dolphin. The search took place almost a decade after the last exploration in 1997, which turned up only 13 of the cetaceans.
In August 2007, a Chinese man reportedly videotaped a large white animal swimming in the Yangtze. Although the animal was tentatively identified as a baiji, the presence of only one or a few animals, particularly of advanced age, is not enough to save a functionally extinct species from true extinction. The last known living baiji was Qi Qi, who died in 2002. The World Wildlife Fund is calling for the preservation of any possible baiji habitat, in case the species is located and can be revived.
Anatomy and morphology
Baiji were thought to breed in the first half of the year, the peak calving season being from February to April. A 30% pregnancy rate was observed. Gestation would last 10–11 months, delivering one calf at a time; the interbirth interval was 2 years. Calves measured around at birth, and nursed for 8–20 months. Males reached sexual maturity at age four, and females at age 6. Mature males were about long, females, with the longest specimen. The animal weighed, with a lifespan estimated at 24 years in the wild. The Yangtze river dolphin was pale blue to grey on the dorsal side, and white on the ventral side. It had a long and slightly upturned beak with 31–36 conical teeth on either jaw. Its dorsal fin was low and triangular in shape and resembled a light-colored flag when the dolphin swam just below the surface of the murky Yangtze River, hence the name "white-flag" dolphin. It had smaller eyes compared to oceanic dolphins.When escaping from danger, the baiji can reach, but usually stays within. Because of its poor vision, the baiji relies primarily on sonar for navigation. The sonar system also plays an important role in socializing, predator avoidance, group coordination, and expressing emotions. Sound emission is focused and highly directed by the shape of the skull and melon. Peak frequencies of echolocation clicks are between 70 kHz and 100 kHz.
Distribution
Historically, the baiji occurred along of the middle and lower reaches of the Yangtze, from Yichang in the west to the mouth of the river near to Shanghai, as well as in Poyang and Dongting Lakes and the smaller Qiantang River to the south. This had been reduced by several hundred kilometres both upstream and downstream, and was limited to the main channel of the Yangtze, principally the middle reaches between the two large tributary lakes, Dongting and Poyang. Approximately 12% of the world's human population lives and works within the Yangtze River catchment area, putting pressure on the river.Evolutionary history
The baiji is not closely related to any living species of dolphin, having diverged from the ancestors of the La Plata dolphin and Amazon river dolphin during the Miocene, estimated to be around 16 million years ago. The closest known relative of the baiji is Parapontoporia, native to the western coast of North America during the Latest Miocene and Pliocene. The baiji was one of five species of dolphins known to have made fresh water their exclusive habitat. The other five species, including the boto and the La Plata dolphin, have survived in the Río de la Plata and Amazon rivers in South America and the Ganges and Indus rivers on the Indian subcontinent.It is well known that the river dolphins are not a natural group. Their mitochondrial genome reveals a split of two separate lineages, Platanista and Lipotes +, having no sister relationship with each other, and the Platanista lineage is always within the odontocete clade instead of having a closer affinity to Mysticeti. The position of the Platanista is more basal, suggesting separate divergence of this lineage well before the other one. The Lipotes has a sister relationship with Inia + Pontoporia, and they together formed the sister group to the Delphinoidea. This result strongly supports paraphyly of the classical river dolphins, and the nonplatanistoid river dolphins do represent a monophyletic grouping, with the Lipotidae as the sister taxa to, and is well congruent with the studies based on short interspersed repetitive elements.
Low values of haplotype diversity and nucleotide diversity were found for the baiji of the Yangtze River. The analysis of molecular variance supported a high level of overall genetic structure. The males having a higher genetic differentiation than the females suggested a significant female-biased dispersal.
The aquatic adaptations of the baiji and other cetaceans have happened slowly and can be linked to positively selected genes and/or other functional changes. Comparative genopic analyses have uncovered that the baiji have a slow molecular clock and molecular adaptations to their aquatic environment. This information leads scientists to conclude that a bottleneck must have occurred near the end of the last deglaciation, a time that coincided with rapid temperature decrease and a rise in eustatic sea level. Scientists have also looked into PSGs in the baiji genome which are used for DNA repair and response to DNA stimulus. These PSGs have not been found in any other mammal species. Pathways being used for DNA repair have been known to have a major impact on brain development and have been implicated in diseases including microcephaly. The slow down of the substitution rate among cetaceans may have been affected by the evolution of DNA damage pathways. Over time, river dolphins, including the baiji, have had a reduction in the size of their eyes and the acuity of their vision. This probably stems from poor visibility in fluvial and estuarine environments. When analyzing the baiji genome, scientists have found that there are four genes that have lost their function due to a frameshift mutation or premature stop codons. The baiji has the lowest single-nucleotide polymorphism frequency reported thus far among mammals. This low frequency could be related to the relatively low rate of molecular evolution in cetaceans; however, considering that the decrease in the rate of molecular evolution in the baiji was not as great as the decrease in heterozygosity rate, it is likely that much of the low genetic diversity observed was caused by the precipitous decline in the total baiji population in recent decades and the associated breedings.
The reconstructed demographic history over the last 100,000 years featured a continual population contraction through the last glacial maximum, a serious bottleneck during the last deglaciation, and sustained population growth after the eustatic sea level approached the current levels. The close correlation between population trends, regional temperatures, and eustatic sea levels suggest a dominant role for global and local climate changes in shaping the baiji's ancient population demography.