Ancient poems document the decline of the Yangtze finless porpoise

For at least 1,400 years, poets in China have penned pieces about the Yangtze River’s sights and sounds. Now, scientists are using those artworks to reconstruct an animal’s past.

Ancient poems can help track the vanishing range of the Yangtze finless porpoise, researchers report May 5 in Current Biology. The only known freshwater porpoise (Neophocaena asiaeorientalis asiaeorientalis) is critically endangered, with just over 1,000 estimated living in the wild.

Porpoises chased moonlight on silvered tides, as dragons summoned storm clouds looming in sight. (豚入息风银月澄，龙出听讲黑云起).

Qianlong (乾隆), emperor from 1735 to 1796 during the Qing Dynasty

“When we do conservation, we need to know the past distribution and the historical population size of the species,” says ecologist Jiajia Liu of Fudan University in Shanghai. These metrics provide a baseline and help researchers create conservation goals. But the most robust survey data on the porpoise have come from just the past few decades. To get historical information, Liu says, “we can only rely on other forms of data, like documentaries and art.”

So Liu and colleagues searched databases of ancient Chinese poems for references to the porpoise, sometimes called the “river pig” or other nicknames. After ruling out references based on abstraction rather than observation, the team identified 724 poems tracing back to the Tang Dynasty (A.D. 618–907) that mentioned the animal.

The Yangtze finless porpoise and the baiji are highly deceitful, splashing waves and leaping through the sail’s shadow. (江豚白𩷱欺人甚，喷浪跳波帆影间).

Zao Chen (陈造), Song Dynasty

Poem context and written travel records helped researchers pinpoint each writer’s location. Most poets held official positions, so details about their lives were meticulously documented, says zoologist Zhigang Mei of the Chinese Academy of Sciences in Wuhan. For instance, Qianlong, who was emperor from 1735 to 1796, wrote about the animal: “Porpoises chased moonlight on silvered tides, as dragons summoned storm clouds looming in sight.”

Combined with scientific survey data, the poems revealed that the porpoise’s range has shrunk by 65 percent since the Tang Dynasty. The disappearance was gradual throughout the five examined dynasties, which spanned through the Qing Dynasty (A.D. 1636–1912). But a sharp decrease took place between the Qing Dynasty and today. Most of the loss over the past 1,400 years occurred in the river’s tributaries and lakes, where the animal’s range has declined by about 90 percent.

Human activities are to blame, Liu says. Dam construction and land development have blocked porpoise migration. Unorthodox methods of learning about the mammal’s changing habitats can help researchers better understand and protect them.

“Poems are actually ancient citizen science,” Liu says. “These data are not perfect. … But they do have a lot of information if you use them correctly.”