古诗记载珍稀江豚在过去1400年间数量衰退的历史

"We're connecting 2,000 years of Chinese culture with biodiversity," says author Zhigang Mei of the Chinese Academy of Sciences, who grew up alongside the Yangtze River revering the porpoises; elders in his community taught that they were like spirits, predicting the weather and the fish levels, and that hurting them was bad luck. "Our work fills the gap between the super long-term information we get from fossils and DNA and the recent population surveys. It really shows how powerful it can be to combine art and biodiversity conservation."

The Yangtze is the longest river in Asia and the third longest in the world, stretching 6,300 km from the Tanggula Mountains of the Tibetan Plateau until it spills out into the East China Sea near Shanghai. Historically, people -- including many prolific poets such as Qianlong, the emperor of the Qing dynasty -- relied on the river and its tributaries to travel around the region. Along the way, many caught glimpses of the Yangtze finless porpoise, which is the world's only known freshwater porpoise and used to inhabit most of the river.

"Compared to fish, Yangtze finless porpoises are pretty big, and they're active on the surface of the water, especially before thunderstorms when they're really chasing after fish and jumping around," says Mei. "This amazing sight was hard for poets to ignore."

Indeed, as the team systematically collected, filtered, and collated their way through preserved poems dating back to the year 618, the researchers found hundreds of references to the porpoises. Mei says that the fact that a freshwater mammal like the Yangtze finless porpoise appears so often in these poems reflects the deep connection between people and nature in Ancient China.

"One of the biggest challenges in this research was just the sheer number of Chinese poems out there, and the fact that every poet had such a different style," says Mei. "We had to figure out how accurate the poets were being. Some might have been really focused on realism, describing what they saw as objectively as possible. Others might have been more imaginative, exaggerating the size or behavior of things they saw. So, once we found these poems, we had to research each poet's life and writing style to make sure the information we were getting was reliable."

By contextualizing the porpoise references within the rest of the poem and alongside historical records of the poet's life events, the researchers were able to pinpoint the chronological time and geographic location of the sightings. They found that the Qing Dynasty (1636-1912 CE) had over half of the total porpoise poetry with 477 poems mentioning the Yangtze finless porpoise, followed by the Ming Dynasty (1368-1644 CE) with 177 poems, the Yuan Dynasty (1271-1368 CE) with 27, the Song Dynasty with 38, and the Tang Dynasty (618-907 CE) with just 5 poems.

Next, the researchers used the information gathered from the poems to reconstruct the porpoise's distribution over time. They found that the sharpest habitat-range decrease occurred over the past century -- between the Qing dynasty and modern times. They also observed that the porpoise's range throughout the main part of the river has decreased by 33% since the Tang Dynasty, while its range among the tributaries and lakes that the Yangtze feeds into has decreased by 91%.

The finding that the Yangtze finless porpoise's range has declined so sharply over the past century aligns with previous research, which showed that their dwindling population can be largely attributed to human alterations to the Yangtze River -- especially through hydraulic engineering projects. The porpoises likely disappeared from the Yangtze's lakes and tributaries as a direct result of dam constructions in the 1950s that blocked off movement to and from the river's mainstem. Two other species endemic to the Yangtze -- the baiji dolphin and the Chinese paddlefish -- have gone functionally extinct over the past few decades, likely due to the same habitat changes.

"Protecting nature isn't just the responsibility of modern science; it's also deeply connected to our culture and history," says Mei. "Art, like poetry, can really spark an emotional connection, making people realize the harmony and respect we should have between people and nature."

Going forward, the authors plan to dig back into the poems they've collected to see what they can learn about what the river looked like in the past, how big the groups of porpoises used to be, and how they might have behaved before their numbers dwindled. They hope that their work can eventually help the remaining Yangtze finless porpoise population recover and potentially inspire more scientists to gain ecological insights from poetry -- as well as from other historical art forms such as novels and paintings.

"This work made me rethink the scientific value of historical literature and showed us the power of thinking across disciplines," says Mei. "Chinese poetry, this ancient art form, can be a serious scientific tool. Using the past to understand the present, 'decoding' the stories behind the art: it's not just research, it's like having a conversation with the poets of the past."