The infraorder Cetacea encompasses all whales, dolphins, and porpoises—fully aquatic mammals that inhabit nearly every aquatic environment on Earth. These creatures are currently facing unprecedented threats from human activity. While confirmed worldwide extinction of entire cetacean species has historically been rare, the modern, human-caused loss of specific dolphin species signals a profound shift. The disappearance of a single species represents a permanent reduction in biological diversity and serves as a stark warning for other vulnerable populations globally.
The Case of the Baiji (Chinese River Dolphin)
The most definitive and recent example of a human-caused cetacean extinction is the Baiji, or Chinese River Dolphin (Lipotes vexillifer), a species once unique to the Yangtze River system in China. This freshwater odontocete was the sole representative of an entire evolutionary family, meaning its loss erased millions of years of distinct evolutionary history from the planet. Its decline was rapid, driven by intense industrialization and unsustainable resource exploitation along its restricted river habitat.
The population was already severely diminished by the late 1990s, with estimates suggesting fewer than 20 individuals remained. In 2006, an intensive six-week survey failed to find a single Baiji across its entire historical range in the main Yangtze channel. Scientists subsequently concluded in 2007 that the species was functionally extinct, the first cetacean species to be driven to this status by human activity.
The designation of “functionally extinct” means the population is no longer viable, even if a few individuals persist. The numbers are too low to maintain necessary genetic diversity, and remaining individuals are too scattered to find mates, making natural recovery impossible. The primary driver of this collapse was accidental mortality from unsustainable by-catch in local fishing operations using rolling hooks, nets, and electro-fishing devices. Habitat degradation from increased shipping traffic and the construction of massive dams also contributed by fragmenting its range and reducing its prey base.
The Nuance of Marine Extinction Status
Confirming the extinction of a marine species presents a unique scientific challenge compared to terrestrial animals. The vast, three-dimensional nature of the ocean makes comprehensive population surveys extremely difficult, as animals can easily escape detection in deep or inaccessible waters. Scientists must therefore rely on a set of conservation terms to categorize the severity of a species’ decline before the final designation of “Extinct” can be made with confidence.
One category is “Extinct in the Wild,” applied when a species only survives in captivity or outside its historical range. The Baiji’s status as “functionally extinct” indicates a population is no longer large enough to play its ecological role or sustain itself through reproduction.
The Critically Endangered status is the final classification stage before a species is declared extinct in the wild, signifying an extremely high risk of extinction in the immediate future. Because of the difficulty in finding every last individual, the decision to formally declare a marine species extinct often relies on an expert assessment of data availability and the elapsed time since the last confirmed sighting. This reliance on inference means that a species may be biologically gone long before it is officially removed from the planet’s roster.
Human Drivers of Cetacean Loss
The decline of cetaceans globally is a direct result of several interwoven human activities, transitioning from historical exploitation to modern habitat degradation. The 19th and 20th centuries were characterized by commercial whaling, an industry that drove the populations of large species like the Blue Whale and Fin Whale down by as much as 98% in some areas. While international moratoriums have allowed many populations to begin slow recoveries, the threats have shifted from deliberate hunting to incidental mortality and environmental contamination.
Today, bycatch—the accidental entanglement and drowning in fishing gear—is considered the single greatest threat to small cetaceans, accounting for the deaths of an estimated 300,000 dolphins, porpoises, and small whales annually. Species like the Vaquita, which inhabit shallow coastal waters, are especially vulnerable to gillnets, which are virtually invisible and undetectable by their echolocation systems. Entangled animals often suffer severe injuries or die from asphyxiation due to their inability to surface for air.
Habitat degradation also includes acoustic pollution, which disrupts animals that rely on sound for nearly all life functions. Sources like military sonar, seismic surveys, and constant shipping traffic generate intense underwater noise that can mask communication signals used for foraging and mating. In sensitive species, such as beaked whales and narwhals, high-intensity noise can trigger panicked, deep-diving escape responses that lead to decompression sickness, similar to the “bends” in human divers.
Species on the Brink of Extinction
The lessons from the Baiji’s loss underscore the urgency of conservation efforts for other cetaceans teetering on the edge of extinction. The most precarious species is the Vaquita (Phocoena sinus), a small porpoise endemic to a tiny area in the Gulf of California. With only a few dozen individuals estimated to remain, the Vaquita is highly likely to be the next cetacean species declared functionally extinct. Its population collapse is almost entirely due to bycatch in illegal gillnets set for the totoaba fish.
Large species also face significant threats, as demonstrated by the North Atlantic Right Whale (Eubalaena glacialis), whose population is estimated to be fewer than 370 individuals. This species is under constant pressure from two primary threats: entanglements in fixed fishing gear and lethal vessel strikes. Because these whales spend significant time feeding and nursing near the ocean surface, they are highly susceptible to collisions resulting in mortal blunt force trauma or propeller cuts. The chronic stress of non-lethal entanglements also slows the calving rate of reproductively active females, crippling the population’s limited ability to recover.