This whale named "Little Guagua" died, probably because humans were too noisy

Do you remember the animal events that frequently came into our view in 2021? The collective northward migration of Asian elephants in Yunnan, the Siberian tigers entering villages in Heilongjiang, the snow leopards breaking into livestock pens in Qinghai, and the stranding of marine animals along the coast... Every piece of news about them touched our hearts. Some of these events are accidental but reasonable, and for others, we still cannot determine the cause of their occurrence, such as the frequent stranding of whale groups along the coast of my country in the second half of last year.

Recently, a melon-headed whale named "Little Guagua" may have given us the answer. Cetacean researchers from the Institute of Hydrobiology of the Chinese Academy of Sciences evaluated the stranded animal and found that the frequent stranding of whales in the second half of last year may be due to noise pollution.

Rescuers feed small fish to "Xiaoguagua"｜Linhai Municipal Party Committee Propaganda Department/China News Service

A series of mass stranding incidents

On July 6, 2021, 12 melon-headed whales (Peponocephala electra) were stranded in Taizhou, Zhejiang, including today's protagonist "Little Guagua". This is a male individual, 2.7 meters long. Based on its body length, researchers estimated that it was about 19 years old, a melon-headed whale in its prime. On July 8, except for the dead individual, all its companions were released into deep waters; and because of its poor physical condition, it has been temporarily kept for treatment, which has attracted public attention and is affectionately called "Little Guagua" by everyone.

This was not the first mass stranding of live whales that occurred along the coast of my country last summer, nor was it the last. The so-called mass stranding of whales refers to the phenomenon that more than one whale (usually excluding a single mother-child pair) of the same species is stranded on the coast and cannot return to the water on their own. The reason why mother-child pairs are not included is that whale calves are very dependent on their mothers. Once the mother is stranded, the calves will also have difficulty surviving, often "two lives are stranded".

On July 6, relevant personnel rescued the stranded "Little Guagua" and its companions｜Sina Weibo: @Xinhua News Agency (Photo provided by the Publicity Department of Linhai City, Zhejiang Province)

On June 10, 2021, six bottlenose dolphins (Tursiops truncatus) were stranded in Fuqing, Fujian, and were eventually successfully returned to deep waters. On July 6, 12 melon-headed whales were stranded in Taizhou, Zhejiang, and only six survived and were released into deep waters. On July 9, two rough-toothed dolphins (Steno bredanensis) were stranded in Ningbo, Zhejiang, and were later successfully released. On July 11, two melon-headed whales were stranded in Wenling, Zhejiang, and only one survived and was released.

On September 30, 12 melon-headed whales were found stranded in Cixi, Zhejiang, and were subsequently sent back to deep water by rescuers; however, a few days later, on the evening of October 3, another 12 melon-headed whales were found stranded in Jinshan, Shanghai. Considering that both stranding sites are located in Hangzhou Bay, facing each other across the sea, and the incidents occurred very close in time, it is likely that the group of melon-headed whales stranded in Jinshan on the 3rd were the ones in Cixi. A high tide rose late at night on the 3rd, and rescuers were unable to go into the water to rescue them. After the tide receded in the early morning of the 4th, rescuers found the bodies of 4 melon-headed whales. The other 8 may have returned to the sea successfully, or may have died, and their lives are unpredictable.

The carcass of a melon-headed whale was found in Jinshan, Shanghai, in the early morning of October 4th | Wang Haining

Mass strandings more common among toothed whales

Melon-headed whales frequently appear in these group strandings, not only with large numbers of strandings, but also with the possibility of repeated strandings in some groups. In addition, they are small toothed whales, just like other stranded bottlenose dolphins and rough-toothed dolphins.

Although the melon-headed whale is called a "whale", it is also a dolphin. Cyril di Bisceglie / Wikimedia Commons

Although toothed whales and baleen whales are both cetaceans, they have obvious differences. For example, toothed whales have cone-shaped or shovel-shaped teeth, which can emit sound waves for echolocation, use the echolocation system to find prey and avoid obstacles. Toothed whales are the protagonists of cetacean group strandings - on the one hand, toothed whales have closer social relationships and more common group activities; on the other hand, toothed whales' activities are more dependent on the acoustic environment and are more susceptible to external acoustic anomalies.

However, this cannot explain why the "little melons" are frequently stranded. Melon-headed whales do not like to visit shallow coastal waters that are heavily disturbed by humans. Instead, they mainly live in deep offshore waters and upwelling areas at the edge of the continental shelf. Even if they appear near the coast, they are often in areas with short continental shelves and great depths. What exactly caused them to frequently strand in shallow coastal waters during that period?

Mass strandings of melon-headed whales are not uncommon. On August 26, 2020, nearly 200 melon-headed whales stranded at the same time in southeastern Mauritius | Hugues Vitry and Lana Barteneva

For whales, strandings are caused by both internal and external factors. Individuals may become stranded if they are sick, aging, lost, chased by predators, or escaped from prey. External factors include both natural (such as catastrophic weather) and man-made. Among them, marine plastic pollution, toxic pollution, noise pollution, etc. caused by human activities may cause animals to become weak or lost and become stranded. When the stranding incident first occurred in early July, some experts also suggested that these melon-headed whales may have followed the food in the ocean currents and trapped themselves; or there may be problems with the echolocation system, causing them to lose their way.

In this incident, "Xiaoguagua", who was temporarily rescued due to poor physical condition, gave researchers the conditions to explore the cause of the stranding.

The answer brought by "Xiaoguagua"

The researchers plan to measure the hearing threshold of "Little Guagua" at specific frequencies and draw an audiogram to evaluate its hearing. So, how to measure its hearing threshold? The researchers used an electrophysiological method: recording its auditory evoked potential, which is the bioelectric response of the central nervous system caused by the stimulation of the auditory nervous system. This is a common and widely used method, and its results are comparable to those of other studies.

Behind the blowhole of "Little Guagua" (the hole on the top of its head that acts like a nostril, where we usually see whales spit out steam), the researchers placed two suction cup electrodes along the midline of the back, and then placed a suction cup electrode at the base of the dorsal fin to extract the signal of auditory evoked potential. Then, the researchers played a series of rhythmic sound points, set and change the frequency of these sound points, recorded the changes in "Little Guagua"'s auditory evoked potential, converted it into hearing threshold, and finally drew an audiogram.

Schematic diagram of the auditory evoked potential (AEP) method used in the study | Wang et al., 2021; Chinese translation: Miaoyujiang

By using this non-destructive auditory electrophysiological technology, the researchers measured the hearing threshold of "Little Guagua" from the frequency range of 9.5 to 181 kHz. Generally speaking, the echolocation signal range of melon-headed whales for navigation is between 25 and 32 kHz, but the hearing threshold of "Little Guagua" in this range has exceeded 120 decibels; that is, in this frequency range, other melon-headed whales can hear sounds below 120 decibels, but "Little Guagua" cannot. For "Little Guagua", which relies on echolocation for activities, it is very likely that it will make sounds but not hear the echo, so it will get lost in the sea.

Although this study only used one melon-headed whale as the research object and the research content has many limitations, it is undeniable that "Little Guagua"'s hearing was indeed damaged, and marine noise pollution does exist along the Zhejiang coast. After excluding the influence of tides, severe weather, and hearing loss caused by aging, the researchers believe that hearing damage caused by marine environmental noise is likely the reason for "Little Guagua" to be stranded; they also speculate that the stranding of other melon-headed whale groups may also be related to this.

Toothed whales rely on echolocation to find prey and determine direction. Hearing loss can seriously affect their activities｜Malene Thyssen / Wikimedia Commons

Noise pollution is inevitable

Everyone hates noise. Just ask yourself, who can sit for a whole morning under the torture of electric drills and brick cutters? The same is true for animals in the ocean. They are tired of noise, but they can't escape it. As human activities in the ocean expand and increase in frequency, whales are suffering from the double torture of instantaneous strong noise and long-term weak noise. There are countless cases of direct and indirect damage to whales caused by military activities and seismic surveys, and shipping also disturbs the lives of whales with continuous noise.

Chilean researchers use visual animations to show how blue whales avoid ships while foraging in the bay. While sailing, these ships also bring "three-dimensional surround" noise to blue whales｜Luis Bedriñana-Romano

The Yangtze River Delta is a busy place, with the world's largest cargo throughput port, Ningbo Zhoushan Port, and the world's largest container port, Shanghai Yangshan Port. In addition, the Zhoushan fishing grounds with rich fishery resources are also nearby. The frequent shipping of cargo ships and fishing boats will inevitably bring continuous noise impacts to the animals here. In addition, there may be instantaneous noise impacts that we cannot determine, but we will not discuss them here.

In my country, previously recorded incidents of melon-headed whale strandings mainly occurred along the coast of Taiwan. In neighboring Japan, there have also been many incidents of melon-headed whale strandings. Was the continuous stranding of whales in the East my country Sea from June to October 2021 the result of a single factor or a combination of factors? Does this indicate that the environment along the coast of my country has changed significantly? Although "Little Guagua" has provided us with some ideas and evidence, we still need to continue to observe in order to get a definite answer.

A stranded Cuvier's beaked whale (Ziphius cavirostris). Some deep-diving beaked whales may be frightened by the instantaneous noise underwater and quickly float to the surface, suffering from decompression sickness and eventually death. | Silver Leapers / Wikimedia Commons

Unfortunately, although "Little Guagua" had a strong will to survive, he still couldn't escape the clutches of death. The rescuers tried their best to accompany and treat him, but unfortunately, there was no hope. "Little Guagua" died in the early morning of July 28, 2021. "Little Guagua"'s help in research before his death sounded the alarm for us. The impact of human activities on whales is objective. Can we take some measures to reduce the impact of these noises on whales?

References

Zhi-Tao Wang, Alexander Ya Supin, Tomonari Akamatsu, Peng-Xiang Duan, Yi-Ning Yang, Ke-Xiong Wang, Ding Wang. Auditory evoked potential in stranded melon-headed whales (Peponocephala electra): With severe hearing loss and possibly caused by anthropogenic noise pollution. Ecotoxicology and Environmental Safety, 228 (2021), https://doi.org/10.1016/j.ecoenv.2021.113047

Author: Meow Fish Sauce

Editor: Mai Mai

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