This is based on a Xinhua Daily Telegraph and was first published in “Xinhua Daily Telegraph” Grass Weekly on August 7th, 2020. A report highlighting the experience of the first offshore cetacean survey in the South China Sea that led them to have this survey so remarkable.
How do scientists search for “whales and dolphins”?
At 6:30 a.m., two sharp alarms woke the participants of the cetacean survey team from their sleep.
An exclamation came from the bridge: “A large group of tropical spotted dolphins! Estimated at over 100!”
They saw groups of dolphins surrounded by three or four meters on either side of the bow side of the science research vessel “Tianlong”, swinging their caudal fins up and down to move forward across the sea.
The team’s chief scientist, Li Songhai, corrected, “It’s not a tropical spotted dolphin, it is a spinner dolphin.” The team member on the side said upon spotting “Spinner dolphin at 6:20 a.m, GPS position 46.” This is the 9th sighting they recorded during the cetacean survey.
History of the cetacean survey in the South China Sea
Cetaceans are collective terms for whales, dolphins, and porpoises (including finless porpoises) belonging to the order Cetacea.
Cetaceans are divided into toothed whales (Odontoceti) and baleen whales (Mysticeti).
In the 1950s, China did not ban commercial whaling.
Researcher Wang Pilie went to the ocean with the whalers and gathered some cetacean data in the South China Sea, north of Hainan Island, and included it in “Chinese Whales” and “Chinese Sea Beasts Illustrated Book.”
In 1981, China completely stopped commercial whaling activities.
Since it is expensive to organize cetacean survey separately, and the basic research awareness at that time was not strong, the research on offshore cetacean in China has since deteriorated, and the south China sea cetacean record is also not clear.
Chinese white dolphin
The fishermen not only confirmed that they had witnessed a variety of cetaceans at sea but also specially identified the endangered Chinese white dolphins with special body colors in their illustrated book!
Several studies have been carried out on the Chinese white dolphin in previous years.
Vital scientific information has been found especially on the conservation of this first-class national protected species by a relevant scientific expedition (cetacean survey) team off the coast of Hainan province.
The Chinese white dolphin is a variety of cetaceans close to the shore.
The water depth in the sea is often less than 30 meters and the distance from the shore is no more than 30 kilometers.
There are such a group of rare and endangered animals on the southwestern coast of Hainan Island.
Attention and knowledge about cetaceans are still limited.” Li Songhai said with some regret.
In 2016, the Deep Sea Institute created the “Professional Database of Cetacean Stranding Records on Hainan Island.”
Based on the information collected through the database, combined with previous visits by fishermen, Li Songhai assumed that the South China Sea was likely rich in deep diving and pelagic cetaceans.
Speculation is not enough. Li Songhai said that some cetaceans have small differences and fishermen cannot distinguish them.
The database base can simply check the types of cetaceans that have been stranded and how many, but they don’t have a clue where they came from.
Field surveys are needed to scientifically assess the diversity and distribution of cetacean species in the South China Sea.
(If you want to know about Chinese white dolphin, You can get an idea from our article on Chinese white dolphin – resource protection is not optimistic)
The first offshore cetacean survey
The “2019 South China Sea Deep Diving and Offshore Cetacean Scientific Research” organized by the Marine Mammal and Marine Biological Acoustics Laboratory of the Institute of Deep-Sea Science and Engineering has launched the first offshore cetacean survey in April 2019.
Li Songhai filled in as the leading researcher of the survey. This was the world’s first deep-diving and offshore cetacean scientific expedition (survey) in the corresponding waters of the South China Sea.
The voyage recorded a total of 8 cetacean species, including sperm whales, Cuvier’s beaked whales, and short-finned pilot whales, etc.
For the first time, it was confirmed that sperm whales, Cuvier’s beaked whales, short-finned pilot whales, and other cetaceans existed in the corresponding waters off the South China Sea.
The second offshore cetacean survey
The team set off again on July 8, 2020. The cetacean study area focused on the land slopes, seamounts, and waters of Paracel and Zhongsha Islands in the northern part of the South China Sea.
The study was more comprehensive than the previous time, and the survey content and methods used are more diverse.
This year’s scientific expedition team consists of 15 people, of which 7 were “post-95”, graduate students.
The youngest team member was only 21 years old and just graduated a few weeks ago. Some students already had extensive experience in marine mammal research.
According to a student, he studied in the Fisheries College of Undergraduate and often followed fishing boats to sea. “The fishing boat is small.
The boat was full of oil and fishy smells. It is very uncomfortable. It is the best boat I have ever followed.”
This “best boat” only hauled 450 tons and remained in the water for a very long time.
Aside from the female team members and some researchers, the other eight team members lived with the crew in the large cabin.
The large cabin had only three circular windows with a diameter of 40 cm, which was dark and damp; when sleeping on a 0.6-meter-wide wooden bed, you must be careful when turning over.
After 5 days, the team members basically used to life on the boat, and their appetites improved.
Whale encounter
This scientific expedition (cetacean survey) included visual observation, acoustic monitoring, marine floating garbage recording, and water sample collection and analysis.
Among them, the discovery tracking and recording of cetaceans by visual means is both the center and the basis of all work.
It might be different from what the outside world imagined, the main reliance on finding cetaceans is actually human eyes and telescopes.
One year ago, the group did not use any equipment, relying entirely on the naked eye, and sighted 27 groups of whales in 14 days.
Whales use their lungs for breathing. As it exhales, the breathing hole will trigger an ejection of an air column called the whale blow or spout, a cue to identify the whale from a distance.
Baleen whales have a pair of breathing holes while toothed cetaceans have one.
The difference in whale blows somewhat provides an entry point for species identification.
Often the animals are far away from the ship and cannot be directly observed. Waves and whale blows are the main focus of the whale search.
From 8.00 to 19.00, crew members were taken from the top of the cockpit to visualize the cetacean. Despite this collective shift, there were very few people on board.
Team members work in shifts about three times a day, and each time is an hour and a half uninterrupted.
In this vast expanse of tropical ocean, as soon as the sun comes out, the temperature exceeds 30 degrees Celsius.
The team members were so submerged in the sun that they couldn’t even open their eyes.
The vessel soaked in this excess air and the hull surface became moist and astringent. When you touch it, your hands are full of large salt crystals.
No matter what you are doing outside of the cabin, you should wear sun protection clothing, sun hats, and sunglasses.
One of the crew members was not wearing a sun hat and worked on the deck for less than half an hour.
The next day, his face became flushed, and then he began to peel. Sun protection clothing was poorly ventilated.
People only stand on the deck for more than ten minutes, and their backs areas fully covered with water.
The clothes are soaked in sweat and translucent, and they are wrinkled against the body.
Listening to whales and dolphins
A strong animal signal was also received and a visual group also confirmed the animal sightings. The voice of the acoustic transmission was coming from the intercom.
Compared with last year, not only search whales by visual observations but also listened to their vocal activities underwater.
Sound is the most efficient method of transmitting energy underwater.
In order to adapt to the aquatic environment, marine mammals such as cetaceans have highly developed vocal and auditory abilities during the long-term evolution.
Many of them emit underwater species-specific sounds to communicate between individuals or groups.
The sound frequencies of different cetaceans are diverse.
The peak frequency of high-frequency echolocation signals of porpoises (including finless porpoises) can reach 120-130 kHz, while that of tropical spotted dolphins is around 90 kHz, while human hearing ranges from 20 Hz to 20 kHz, which cannot be heard directly.
Such sounds of whales. The acoustic team uses instruments to monitor animal vocal activities in the daytime, towed hydrophones are used to monitor in real-time and looking for animal “traces” to help the visual team find animals faster.
At night, self-contained acoustic recorders are used for comprehensive collection and storage of various sound data for subsequent animal acoustic behavior research, and through the hydrophone array used to study the characteristics of the animal’s high-frequency echolocation signal.
Although it is known as the “acoustic group”, their work is also “expensive”.
The visual group was gathering sighting information by looking at the ocean, and the acoustic group was gathering information by looking at the spectrogram on the PC screen, together with the known attributes of the acoustic behavior of the animals to determine if there were swarming creatures.
The range of the vertical axis of the spectrogram was as high as 96 kHz.
Sometimes the acoustic sign of low frequency of animals was just between 2-3 kHz, which almost corresponds to the background noise where the main sound energy was collected in 1-2 kHz.
If you don’t pay attention, it’s easy to inadvertently miss an animal. Due to lack of experience, the acoustic team also made detours.
At the end of the first day on the job, a member enthusiastically said he had found the signal of a sperm whale.
Over the next few days, signals from the suspected sperm whales were also activated, continuous, and regular. Strangely, the signal disappeared when the ship stopped.
When the vessel started, the signal reappeared. Dong Lijun deduced that it was the sound of the engine.
The acoustic characteristics of the noise generated by the engine underwater, on the spectrogram, were similar to the signal of the sperm whale.
During this cetacean survey more than half of the whales have been heard by the acoustic team and later confirmed by the visual team.
What a sperm whale!
The team members discovered nearly 10 species of cetaceans, but there were no sightings of the sperm whales.
The Deep Sea Institute team discovered this deep-diving species in the South China Sea last year, and this year has high expectations for another sighting.
At that moment, Chief scientist Li Songhai sighted a sperm whale through his binoculars and discovered a notable whale blow somewhere far off.
It spouts to the front left at a 45-degree point.
Finally, the sperm whale was found, the whole team was relieved and the voyage was about to end in 5 days.
The sperm whales are the largest toothed whales and are a typical deep-diving animal.
They are widely distributed in warm tropical waters around the world.
They have special ecological and protection value. Historically, sperm whales have been regarded as important targets for hunting because of the widespread use of spermaceti oil on their heads.
(You can get an idea from our article on spermaceti oil – “sperm whale brings light to mankind, and mankind brings its a disaster”)
On the endless sea, the columns of air sprayed one after other, with an interval of only two or three seconds.
Li Songhai was not sure, “With so many whale spouts, it might not be a sperm whale, but the possibility is still great! Even if it is not a sperm whale, it must be a baleen whale, certainly not a dolphin!”
When the survey vessel got closer, we saw a few animals swimming slowly on the sea, like some huge driftwoods.
Their enormous heads were square, representing almost one-third of the length of the body.
“You can’t go wrong, it’s the sperm whale! Hurry up and let everyone know!”
“Ah! What a sperm whale!” There are patterns on its body!” Everyone was excited and nervous.
Once the animals are found, conditions permitting, a small boat can be set up to observe and take pictures up close, and members of the acoustic team can collect the sounds of particular animals.
The sperm whale did not evade the survey vessel and a boat carrying 6 people frees the boat, split the waves, and step by step moved towards the whale pod.
The boat is 9 meters long, which is overall shorter than the sperm whale.
In light of the large vessel, these “big guys” don’t seem to move much, but the Chief Scientist asks to follow them.
It took over 20 minutes to get close to them and the crew members reported to the large vessel that there were 7 sperm whales in total, 1 of which is a calf, and crew members found that sperm whales are molting.
Sperm whale molting is part of the natural anti-fouling mechanism, and the peeled skin can be used for gene sequencing, which is a very rare research material. The researchers were undoubtedly lucky.
Species identification
We saw an animal and it is difficult to judge if it is an melon-headed whale or false killer whale? It also has a white border on its mouth, it is a baby melon-headed whale, the scientific expedition team confirmed.
Usually, the scientific expedition team would meet every evening to identify species found during the day.
It is not an easy task to identify species onboard, individual size, dorsal fin shape, shape, and behavioral characteristics are all factors to be referred to as some species have very small differences, and if they are missing key features when taking photos, they cannot be identified.
For instance, the greatest distinction between the long-snouted spinner dolphin and the long-beaked common dolphin is that has a white spot in the focal point of the dorsal fin.
The biggest difference between the false killer whale and the baby melon-headed whale is the size difference, the melon-headed is small in size and the snout is white.
In addition to visual recognition, once a cetacean is found, members of the environmental DNA group (eDNA) will collect a sample of the sea surface water from the specially designed crossbows and are used to shoot a small dart on the animal to collect biopsy sample.
According to Li Jianlong, the head of the eDNA group and a teacher at the School of Oceanography at Hainan University, the use of vacuum filtration pumps can enrich the DNA of the water sample on the filter membrane.
Then use DNA sequencing to identify and confirm cetaceans from a molecular biology perspective and the distribution of cetacean type.
The survey was carried out for 21 days covering more than 3,000 kilometers. This study sighted 31 groups and 11 species of pelagic and deep-diving offshore cetaceans.
Deep diving cetacean species encountered such as sperm whales, curvier’s beaked whales, short-finned pilot whales, false killer whales, baby melon-headed whales.
Other pelagic cetaceans were the pantropical spotted dolphin, long-snouted spinner, Fraser’s dolphin, and stripped dolphin.
Compared with last year, the scientific expedition newly discovered and recorded four cetacean species, including false killer whales, long-snouted spinner dolphins, and melon-headed whales, indicating that the studied area has relatively rich cetacean species diversity.
Many “mother-child pairs” were also discovered during scientific research. Li Songhai introduced that whales are a highly socialized marine mammal, and the social form of many cetaceans is similar to a “matriarchal society.”
The discovery track of the “mother-child pair” indicates that the South China Sea is likely to be the nursery ground for these cetaceans.
Overview
Marine mammal conservation and marine ecological protection are crucial issues in current sustainable environmental governance.
The main objective of this offshore survey to protect the marine ecological environment and biological resources of the South China Sea, especially on cetaceans and other rare and endangered marine organism resources.
The survey of cetacean resources in the South China Sea is of great significance both from the perspective of scientific research and protection.
