Rafetus Swinhoei

The Yangtze giant softshell turtle (''Rafetus swinhoei''), also commonly known as the Red River giant softshell turtle, the Shanghai softshell turtle, the speckled softshell turtle, and Swinhoe's softshell turtle, is a critically endangered species of turtle in the family Trionychidae. It is regarded as one of the largest living freshwater turtle species. Native to eastern and southern China and northern Vietnam, the species has a known population of only two or three individuals, and the absence of fertile females has rendered it functionally extinct.

Description

The Yangtze giant softshell turtle is recognized for its deep head, pig-like snout, and dorsally positioned eyes. As a critically endangered species, it is widely regarded as the largest freshwater turtle in the world. Although comparisons are limited due to the small number of known specimens, its average and maximum sizes surpass those of other large freshwater turtles, such as the alligator snapping turtle and related giant softshell species, including other ''Rafetus'' and ''Pelochelys'' species.

Adult specimens exceed in length and in width, with weights ranging from . A study of large turtles from the Yangtze River reported an average weight of , although not all specimens were definitively identified as ''Rafetus''.

The turtle’s carapace (shell) typically measures over , with the largest recorded at in straight length. Curved carapace lengths of up to have also been reported. Exceptional specimens, primarily from Vietnam, are believed to have weighed between . The head measures over in length and in width.

Sexual dimorphism is present, with males generally smaller than females but possessing longer, more prominent tails.

Known individuals

Currently, only two or three living individuals of the Yangtze giant softshell turtle are known to exist: one in captivity in China and one or two in the wild in Vietnam.

The species' decline has been marked by significant losses in recent years. A wild individual in Vietnam was reported dead in January 2016, and the last captive female at the Suzhou Zoo in China died in April 2019 following an artificial insemination attempt.

In October 2020, a wild female was discovered in Dong Mo Lake in Vietnam, giving conservationists renewed hope. However, this individual was found dead in early 2023, further diminishing the species' chances of survival.

An additional individual is believed to have been sighted in the same area, though its exact status remains uncertain. The known surviving turtles are thought to include one at the Suzhou Zoo and potentially one in the nearby Xuan Khanh Lake.

Geographic range

The Yangtze giant softshell turtle historically inhabited the Yangtze River and Lake Tai, located on the border of Jiangsu and Zhejiang provinces in eastern China, as well as areas in southern China, including Gejiu, Yuanyang, Jianshui, and Honghe in Yunnan Province.

Two specimens captured from Gejiu in the 1970s were kept at the Beijing Zoo and the Shanghai Zoo but died in 2005 and 2006, respectively.

In Vietnam, the species has been observed in Hoan Kiem Lake in Hanoi on several occasions, including documented sightings in 1999, 2000, and 2005. The turtle captured from the lake in April 2011, which was treated for open sores potentially caused by pollution, injuries from fishing hooks, or other turtles, was later found dead in January 2016.

In recent years, individuals have been identified in Dong Mo Lake and Xuan Khanh Lake in Vietnam. A turtle discovered in Dong Mo Lake in 2020 was confirmed to be female, but it died in April 2023. Another individual of unspecified gender is thought to inhabit the same lake, while an additional turtle is believed to live in Xuan Khanh Lake.

Ecology and behaviour

Diet

The Yangtze giant softshell turtle primarily feeds on a diet of fish, crabs, snails, frogs, and aquatic vegetation such as water hyacinths and "green rice leaves."

Reproduction

The species typically lays between 20 and 80 eggs per clutch, with nesting occurring at night or during the early morning.

In an attempt to prevent extinction, a fertile female from the Changsha Zoo was transferred to the Suzhou Zoo in 2008 to breed with the only known male in captivity, a 100-year-old individual. The move, coordinated by the Wildlife Conservation Society and the Turtle Survival Alliance, involved transporting the female over 1,000 km (600 miles). Despite this effort, breeding attempts have largely failed. By 2013, six breeding seasons had produced 80 eggs, none of which were viable.

Artificial insemination was first attempted in 2015. While the process successfully fertilized a female, the eggs laid during two clutches were not viable. This female died in April 2019 after a subsequent insemination attempt.

Behaviour

Despite its large size and distinctive appearance, the Yangtze giant softshell turtle is highly elusive. It spends most of its time submerged in deep water and surfaces only briefly to breathe, which complicates efforts to observe or identify wild individuals.

Relationship with humans

Scientific description and systematics

The Yangtze giant softshell turtle was first described in 1873 by John Edward Gray, a turtle expert at the British Museum, who named it ''Oscaria swinhoei'' after English biologist Robert Swinhoe, who had sent a specimen from Shanghai. Gray described the species as "the most beautiful species of Trionychidae that has yet occurred."

In 1880, Pierre Marie Heude, a Shanghai-based Jesuit missionary, obtained multiple specimens of the species from the Huangpu River and Lake Tai. Believing the specimens exhibited significant variation, he described them as five distinct species: ''Yuen leprosus'', ''Yuen maculatus'', ''Yuen elegans'', ''Yuen viridis'', and ''Yuen pallens''. The genus name ''Yuen'' derives from the Chinese 鼋 (''yuan''), meaning "large turtle." Later, zoologists reclassified the species under different genera, including ''Trionyx'', ''Pelodiscus'', and ''Pelochelys''. In 1987, Peter Andre Meylan