Fact check: A Giant fish is declared extinct — how do scientists conclude that?

Chinese paddlefish, giant fish extinct, red list extinct animals, International Union for Conservation of Nature

The Chinese paddlefish, now declared extinct, grew up to 7 m long and had existed since 200 million years ago. (Qiwei Wei et al/Science of the Total Environment)

One of the largest freshwater fish has been declared extinct in a study published in the journal Science of the Total Environment. The Chinese paddlefish (Psephurus gladius) was an iconic species, measuring up to 7 m in length, dating back from 200 million years ago, and therefore swimming the rivers when dinosaurs ruled the Earth. Its ancestral home was the Yangtze River.

But how did the study determine that it has gone extinct? Chinese researchers made this conclusion based on the Red List criteria of the International Union for Conservation of Nature (IUCN). The Red List has several categories for extinction, or for how endangered a species is. For example, “extinct in the wild” means a species survives only in a captive environment while “locally extinct” means a species has ceased to exist in a particular area but may exist in other areas. Then there is “functionally extinct”, which means the species continues to exist but it has too few members to enable to reproduce meaningfully enough to ensure survival. To be “globally extinct”, it means a species has no surviving member anywhere. Such a conclusion is reached when there is no reasonable doubt left that its last member has died.

Declaring a species extinct is an elaborate process. It involves a series of exhaustive surveys, which need to be taken at appropriate times, throughout the species’ historic range and over a time-frame that is appropriate to the species’ life cycle and form. When these surveys fail to record the existence of any individuals belonging to that species, a species may be presumed to be extinct. Once declared extinct, a species is not eligible for protective measures and conservation funding; therefore, the declaration has significant consequences.

In the case of the Chinese paddlefish, the researchers made the conclusion over long-term surveys. It was once common in the Yangtze, before overfishing and habitat fragmentation — including dam building — caused its population to dwindle from the 1970s onwards. Between 1981 and 2003, there were just around 210 sightings of the fish. The researchers estimate that it became functionally extinct by 1993, and extinct sometime between 2005-2010.