What’s Leaving Cetaceans Stranded on China’s Coasts?
The hours-long intense rescue mission of a stranded sperm whale in eastern China last month attracted global attention.
Tens of thousands of people closely watched rescuers trying to free the animal stranded on a stretch of mudflat along the coast of Xiangshan County in Zhejiang province. It took 20 hours for the 19-meter-long male to swim back into the sea on April 20 to the delight of spectators.
Nine days later, the body of a dead whale was found floating in the water near Xiangshan. It’s unclear if it was the same rescued sperm whale. Videos circulating online showed the animal had multiple cracks on its skin and fins.
Experts said cetaceans — including whales, dolphins, and porpoises — washed ashore are in distress and prone to dying.
“When we arrived, we could see that part of its skin had cracks,” Wang Zhiyuan from the Ningbo Ocean World Museum and part of the rescue team told Sixth Tone, referring to the stranded whale. “And its breathing was not good — there was a strong odor.”
Scientists have long been calling for more conservation efforts for cetaceans. As top underwater predators, their status indicates the health of the ocean’s ecosystem and they are facing growing threats from human activities and climate change, both in China and elsewhere globally.
Experts said there are various reasons for whales getting beached, adding the sperm whale is a deep-sea species that rarely comes to coastal shallow waters. Many of the animals are found on land when they’re sick, senile, injured, or while wandering into shallow waters but fail to get back.
Cetacean strandings are fatal and cause anatomical damage due to the exposure to a different environment, according to Lindsay Porter, vice-chair of the Scientific Committee of the International Whaling Commission. Beached and uncared, whales could suffer from dehydration and fractures and even be crushed by their own weight.
“When you are something as large as a whale, and you are normally in the water, your body structure is designed for the water,” she told Sixth Tone. “So, when you come on land, you do not have the same skeleton support to keep your body in the correct configuration.”
‘It’s very noisy’
An insidious threat to the cetaceans is noise pollution, experts said.
Cetaceans live in a world of sound, which travels faster in water than in air. Noise from marine traffic and mining activities could deafen them as well as interfere with their ability to communicate and navigate via sound, said Wang Zhitao, researcher of aquatic animal conservation at the Institute of Hydrobiology of the Chinese Academy of Sciences.
And that increases the likelihood of becoming stranded.
“The underwater environment is not as quiet as people might think,” Wang Zhitao told Sixth Tone. “On the contrary, it’s very noisy … Noise from human activities has now become the dominant sound source.”
Besides underwater noise, overfishing, ship collisions, and other human activities have continued to affect the survival of many aquatic creatures. For example, studies have listed their entanglement in fishing gears as one of the top causes of cetacean mortality.
Climate change is also impacting the ecology of whales, Porter said.
A warming ocean is expected to affect the geographic distribution of many whales, which are likely to move toward cooler waters, according to a report on Pacific Island whales and climate change. Ocean acidification, caused by the absorption of carbon dioxide, is causing irreversible consequences to their food chain by affecting the development of animals and plants that are important to whales.
Scientists are particularly worried that the abundance of krill, a primary food source for baleen whales, will shrink with warming oceans. This may lead to malnourishment and even a decline in the population of those whales.
Understanding strandings better
For scientists, data on stranded whales provides clues for better understanding the top predators in the sea and their habitat.
Over the past 30 years, the number of reported cetacean strandings — including mass strandings — has increased rapidly along China’s extensive coastline, according to a February study from the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences. About one-third of them have been identified as threatened species by the International Union for Conservation of Nature.
The increase in strandings could be the result of improved investment in monitoring and recording or an increase in anthropocene impacts, said Wang Zhitao. He conducts bioacoustics studies of cetaceans and was not involved in the February study.
The research from the Institute of Deep-sea Science and Engineering identified the Pearl River and Yangtze River estuaries among the coastal stranding hotspots in China. Both areas have busy shipping traffic.
The stranding hotspots tend to overlap with waters where there are a lot of human activities, according to Wang Zhitao. The sperm whale was stranded near the busy Ningbo-Zhoushan port and a Zhoushan sea farm — both estimated to be some of the world’s largest.
Wang Zhitao said his team has already identified an alarming level of noise in the Yangtze River, particularly impacting the wellbeing of the critically endangered Yangtze finless porpoise. About 90% of the monitoring sites have recorded noise levels likely to cause temporary hearing impairments to the only freshwater porpoise species in the world.
“The oceans are immense … but in the rivers, your living range is limited, and you simply cannot run away,” said Wang Zhitao.
Porter, also a senior scientist at the Hong Kong-based Southeast Asia Marine Mammal Research, has also observed changes in the behavior of Indo-Pacific humpback dolphins due to human-induced impact. Also known as the Chinese white dolphin, the threatened animal is facing multiple threats, with only around 6,000 of them alive globally, including 2,000 in the Pearl River region.
Stress caused by human activities including coastal reclamation causes lasting impacts to cetaceans, as such projects are associated with the dolphins’ low reproduction rate, according to Porter. However, she said her team recorded more calves in 2020 than in the past 20 years, as COVID-19 disrupted shipping operations around Hong Kong.
“For the first time in many years, the dolphins and porpoises didn’t have the shipping traffic around the whole time,” she said. “This is a clear indicator that stress can be related to ability to reproduce. We are hoping in some eight years’ time, this will give us a rise in the adult population.”
Wang Zhitao, the aquatic animal conservation researcher, hoped that the Yangtze River Protection Law that was enacted last year could partly relieve the human-induced pressure on the finless porpoises. As China’s first legislation on a specific river basin, the law addressed riverine noise pollution, and authorities are mulling whether to set up restricted areas that could further reduce the sonar impact of machine engines.
Meanwhile, he called for more scientific investment in China’s coastal waters to understand the status of cetacean species and guide conservation efforts. For example, coastal areas near Zhejiang — which logged at least four mass strandings last year — only have limited cetacean research and monitoring teams.
“Without sufficient understanding, conservation could also end up aimless,” said the researcher.
Editor: Bibek Bhandari.
(Header image: Rescue efforts to set the stranded sperm whale free in Xiangshan County, Zhejiang province, April 19, 2022. VCG)