An expedition searching for a rare Yangtze River dolphin ended Wednesday without a single sighting and with the team’s leader saying one of the world’s oldest species was effectively extinct.
The white dolphin known as baiji, shy and nearly blind, dates back some 20 million years. Its disappearance is believed to be the first time in a half-century, since hunting killed off the Caribbean monk seal, that a large aquatic mammal has been driven to extinction.
A few baiji may still exist in their native Yangtze habitat in eastern China but not in sufficient numbers to breed and ward off extinction, said August Pfluger, the Swiss co-leader of the joint Chinese-foreign expedition.
Lipotes vexillifer, despite living in a highly trafficked area is very poorly understood. It hasn’t been possible to maintain captive populations, and poor underwater visibility makes studies in the wild difficult. The construction of the Three Gorges Dam, along with fishing and heavier boat traffic, has driven population levels ever lower. This survey confirms what has long been expected – that this species cannot persist.
The genus name Lipotes means left behind. It is isolated in a unique habitat, and even without hunting pressure or active trade in the remains of dolphins, they are on the verge of extinction. The forces driving them to the limits also apply to a range of fish and other plants and animals that live in the Yangtze and in other rivers around the world.
Nothing hunts the baiji, even local human populations have long protected the species (though accidental deaths do happen, and the fat from killed dolphins is treated as medicinal). The dolphins are basically blind, and navigate the murky waters almost exclusively by echolocation. More traffic on the river, and more motorized traffic, has increasingly limited their ability to hunt and navigate.
On top of that, dams have changed river patterns and altered population dynamics of fish and the food the fish require. Subtle changes in the ecosystem up and down the river have been acting to drive the dolphins into danger. Reversing these changes is probably impossible, certainly impractical.
The other problem the baiji dolphin faces is even more difficult to overcome.
A dolphin lives at least 24 years (one wild dolphin was captured and accurately assessed at that age), and becomes reproductively active at 3–8 years. Females give birth to a single offspring once every couple years.
A single female could, in principle, have as many as 10 offspring in a lifetime then, though fewer is more likely. Figure in infant mortality, failures to reproduce in famine years, and other stresses, and the number of offspring reaching adulthood will get smaller. Any increase in mortality, or anything that reduces fertility, will endanger an organism that has evolved a life history that favors low birth rates. They will bounce back more slowly from any bad period, and extended bad times can drive them right to extinction.
This scenario is the same as most of the extinctions under way right now. Species are being pushed to the brink not by hunting, but by habitat degradation that affects whole swaths of life. I know it’s politically infeasible, but this is exactly why we really do need an endangered habitats act.