A few years ago there were four species of dolphins living in freshwater ecosystems or estuaries in the world. Two of them are still distributed in South America – the Amazon River and the Plata River dolphins (Inia gophrensis and Pontoporia blainvillei, respectively) – and two lived in Asia – the Ganges and Indus River dolphin (Platanista gangetica), and the Yangtze River Dolphin, or Baiji (Lipotes vexillifer). These species were highly adapted to live in freshwater ecosystems with distinctive anatomical characteristics that differentiated them from their marine relatives, such as larger snouts (almost four times larger than the snout size of seawater dolphins), movable cervical vertebrae, and small eyes as a possible adaptation to live in muddy water.

Regrettably, the International Union for Conservation of Nature considers the Baiji the most threatened cetacean (i.e. Marine mammals commonly known as whales, dolphins and porpoises) in the world, and it is likely already extinct (IUCN Red List of Threatened Species, 2011). In 2006, a large international expedition of scientists tried to estimate the total population of this species living across its vast natural distributional area along the Yangtze River (Turvey et al. 2007). Unfortunately, after three months of intensive searches the scientists came back with absolute negative results: there was not a single sight of a Baiji. The team had to report thus the virtual or effective extinction of this species.

The implications of this possible extinction are substantial. It represents the loss of a complete lineage of mammalian evolutionary history with a geological record of approximately 20 million years of age (Isaac et al. 2007). It is also the fourth recorded extinction of an entire taxonomic family since AD 1500 and it represents the first documented global extinction of a large vertebrate (on average adults greater than 100kg) for more than 50 years, since the disappearance of the Caribbean monk seal (Monachus tropicalis) in the 1950s (Turvey et al. 2007). Interestingly, the continuous decline of Baiji populations was not caused directly by human exploitation; the collapse was the mainly the result of incidental mortality caused by fishing activities and by large perturbations of habitats.

Unfortunately, many other sympatric species [two species are considered sympatric when they exist in the same geographic area] face the same dark future as the Baiji; for example, the Chinese paddlefish (Psephurus gladius), one of the largest freshwater fish in the world, and the Yangtze finless porpoise (Neophocaena phocaenoides), which has been classified as Endangered by IUCN since 1996 (IUCN Red List, 2011).

If you are interested in knowing more about these species, or more about other endangered species, there is a wealth of information on the IUCN Red List of Threatened Species and the Encyclopedia of Life web pages.