This 2020 marks the end of the United Nations Decade on Biodiversity, a commitment that was born in 2011 with the aspiration to halt the alarming extinction of species, in compliance with the objectives of the Convention on Biological Diversity. However, despite the efforts to stop the disappearance of species in what is already considered the sixth mass extinction of the planet, according to the UN the rate of biodiversity loss is only accelerating. Here we review some of the species that in 2019 officially joined the list of Earth’s inhabitants that have disappeared forever.
In the 1970s, 25 tons of one of the world’s largest freshwater fish were caught annually. At more than three metres long and weighing 300 kilos, the Chinese paddlefish (Psephurus gladius), or Chinese swordfish, was abundant in the basins of China’s two main rivers, the Yangtze and the Yellow. However, overfishing devastated the species, coupled with the fragmentation of rivers caused by the construction of dams, which prevented spawning migrations. The last specimen was sighted in 2003, and in December 2019 a study conducted by the Yangtze River Fisheries Research Institute officially declared the species extinct between 2005 and 2010. “As no individuals exist in captivity, and no living tissues are conserved for potential resurrection, the fish should be considered extinct according to the IUCN [International Union for Conservation of Nature] Red List criteria,” the researchers wrote.
Hawaiian tree snail
The year 2019 opened with the news of an extinction: on January 1st, George, the last individual of the Hawaiian tree snail species Achatinella apexfulva, died. This mollusc, endemic to the island of Oahu, began to be considered as a threatened species in 1981. In addition to the loss of its habitat, a curious cause of its decline was a distant relative, the wolf snail Euglandina rosea, which devours other molluscs and was introduced to Hawaii in the 1950s to control agricultural pests. This invader has been responsible for the extinction of several Hawaiian snails. In 1997, the last specimens of A. apexfulva were collected from the wild in an attempt to save the species. The effort resulted in the birth of George, who in 2011 became the last member of his species, before eventually dying at the University of Hawaii at the age of 14.
A unique case is that of the so-called lost shark (Carcharhinus obsolerus), a fish native to the South China Sea. As the study that described it in 2019 pointed out, this animal was lost before it was found. When researchers examined three old museum specimens of what were believed to be smalltail sharks (C. porosus), they discovered that they were looking at a new species. The specimens, from Thailand, Borneo and Vietnam respectively, were caught more than 80 years ago. As there have been no new sightings since the 1930s, scientists believe it probably became extinct in the last century.
Bramble Cay melomys
The rodent Melomys rubicola, or Bramble Cay mosaic-tailed rat, has gone down in history as the first mammal to become extinct due to anthropogenic climate change. This animal lived exclusively on Bramble Cay, a coral sand cay in the Great Barrier Reef, where it is thought to have arrived from New Guinea on floating driftwood, or perhaps via the land bridge that once linked the two great islands. The species fed on the vegetation that covered its tiny 250-metre-long island, but increased storms due to climate change have wiped out its only livelihood. In 2009 the last specimen was sighted, and in 2019 the Australian government officially declared it extinct, although four years earlier it had already joined the IUCN list of extinct species.
In the summer of 2019, the world was shaken by the extensive fires in Brazil, which in twelve months destroyed more than 9,000 km2 of forest. Of course, this loss took its toll in terms of species. Deforestation is the cause of the disappearance of the Alagoas foliage-cleaner (Philydor novaesi), a bird that was already rare when it was first described in the Atlantic forests of the Brazilian coast in 1979. In 2011 the last confirmed sighting occurred, and in 2019 it was classified by the IUCN as extinct.
Another bird that officially left us in 2019 is the Poʻouli (Melamprosops phaeosoma), or black-faced honeycreeper, which was only found on the eastern slope of the Hawaiian island of Maui. Since its discovery in the 1970s, a rapid decline in the population has been observed due to invasive species, predation and disease. Experts began a race against time to save the species, of which only three were known at the beginning of this century. One was captured in the hope of finding a breeding partner, but it died soon after. Since 2004, there have been no confirmed sightings, and in 2019 the IUCN declared it extinct. With its disappearance, its entire genus has been lost, since it has no other relatives.
In addition to human pressure on ecosystems, there are other threats that wreak havoc on biodiversity. One of the most lethal is chytridiomycosis, a fungal disease that is decimating amphibian populations in large regions of the world. In 2019 a study published in Science estimated that the fungus has led to the decline of at least 501 amphibian species in the past half century, including 90 extinctions. In 2019 two types of frogs were added to the IUCN list of species that have left this planet, both in the same genus and in the same country, Honduras: Craugastor anciano and Craugastor omoaensis.