GEOGRAPHY

There is new evidence that the South China Sea is a sperm whale breeding ground


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Photo courtesy of the Marine Mammal Research Team of the Institute of Deep Sea of the Chinese Academy of Sciences

At sea, while it’s not easy to catch a glimpse of sperm whales, it’s not too difficult to recognize them at a glance, and their large box-like square heads are very recognizable in large cetaceans. They are loved for their large size and cute appearance, but they are not really famous for their appearance, but for their “production” of ambergris as expensive as gold.

The value of this deep-sea animal is also that it is an important reservoir of carbon dioxide, plays a key role in regulating global climate change and carbon cycle, and has irreplaceable ecological value.

Previously, due to the lack of scientific investigation and research, the scientific information of sperm whales in China was still very scarce. To this end, the marine mammal research team of the Institute of Deep-sea Sciences and Engineering of the Chinese Academy of Sciences (hereinafter referred to as the research team of the Institute of Deep Sea) has continuously carried out a number of deep diving/far-sea cetacean scientific expeditions in the South China Sea, and found that the relevant waters of the South China Sea are most likely to be important breeding grounds for sperm whales.

Recently, the relevant research results were published in the journal “Deep Sea Research Part I: Oceanographic Research Papers” in the field of deep-sea research. This is the first time that the field of marine mammal research in China has published a research paper in a professional journal of the deep sea, marking that China’s marine mammal research has entered the “deep sea era”.

Demystify sperm whales

When it comes to sperm whales, many people are curious about the name, which is given because its intestines can form a secretion called ambergris. However, not every sperm whale can form ambergris, and only a few sperm whales are likely to form this secretion with a special fragrance by chance.

Although the sperm whale is a toothed whale, it has a large body similar to that of a baleen whale. On April 19 this year, Zhejiang Xiangshan stranded a 19.5-meter-long male sperm whale, which was close to the upper limit of male sperm whales, shocking the scene.

It is understood that a newborn juvenile whale can weigh up to 500 to 1000 kilograms and reach a body length of 3.5 to 4.5 meters. Adult males weigh 35 to 55 tonnes, while females generally weigh 10 to 20 tonnes. Adult males can reach a length of 14 to 16 m and females 10.5 to 12 m. According to the International Whaling Commission, the largest number of male individuals with bodies up to 20 meters in length and weighing 60 to 70 tons has been recorded.

It is generally believed that species with larger bodies are more inclined to feed on low-nutrient-grade organisms to reduce energy loss during the transmission of the food chain. For example, most of the large dinosaurs were “vegetarian”; the largest animals on the earth, such as blue whales and large-winged whales, filtered the smallest phytoplankton.

However, sperm whales are an exception. Supporting their bodies nearly 20 meters are not low-trophic organisms such as plankton, but deep-sea cephalopods that are also predators. This peculiar phenomenon has aroused the interest of evolutionary biologists, and it is regrettable that its evolutionary drivers are still unknown.

“Sperm whales have mysterious tracks and their habits are also very unique, with typical gender differences.” Li Songhai, the corresponding author of the paper and a researcher at the Institute of Deep Sea, introduced it in an interview with China Science News.

Sperm whales usually live in waters 500 to 1000 meters deep, and generally form two groups, one is a juvenile group and the other is a male group. The juvenile group refers to the matrilineal group of female individuals and juvenile whales and sub-adults composed of several to a dozen heads, without long-distance migration or movement, and the range of activities is not large. In the matrilineal-dominated rearing group, young male individuals will leave one after another around the age of 10 to form a highly mobile male bachelor group, and there are a few male individuals who do not move alone.

The researchers found that in adulthood, male sperm whales not only looked for food resources everywhere, but also sought out female courtship among other matrilineal groups. In order to obtain food, some males even cross the ocean and travel from tropical waters to the polar regions that do not freeze to obtain food. As a result, adult male sperm whales “travel” long distances, moving thousands to tens of thousands of kilometres, compared to juvenile populations.

Evidence of a south-sea sperm whale breeding site was found

Sperm whales are one of the most widely distributed cetacean species in the world, with a recorded presence from the unglaced polar region to the equator. During the whaling era, sperm whales were once one of the important whaling objects, providing humans with a large amount of whale meat, grease and ambergris. However, in the world whaling map published by the American Townsend in 1935, it marked the global hunting of sperm whales from 1761 to 1920, but did not give relevant information about China’s waters.

In recent decades, there have been sporadic incidents of sperm whales stranded or accidentally caught along China’s coast from south to north. In June 1993, Hainan Qionghai ran a sperm whale, in 2001, fishermen in Guangxi Beihai dragged back a dead adult individual (body length 18.4 meters), in March 2017, Guangdong Daya Bay stranded a female pregnant individual (body length 10.8 meters), and so on.

“However, these fragments of information can only indicate that sperm whales will occasionally appear in the South China Sea, which is not enough to prove that there are still settled sperm whale populations in China’s waters.” Li Songhai said.

In recent years, the research team of the Institute of Deep Sea has carried out a number of deep diving/far-sea cetacean survey voyages in the South China Sea south of Hainan Island, and in different seasons of voyage execution (March to August), sperm whale populations have been witnessed in the South China Sea (central and northern) of the South China Sea, and more than 100 groups of cetaceans and dolphins have been observed, including 9 groups of sperm whales (with an average cluster size of 5 individuals).

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South Sea sperm whale mother and child swim together Photo courtesy of the marine mammal research team of the Institute of Deep Sea, Chinese Academy of Sciences

In particular, in these 9 groups of sperm whales, researchers recorded 7 groups of juvenile groups, each containing 1 to 2 juvenile/sub-adult individuals. A total of 22 adult individuals were identified by identifying and comparing the physical features of sperm whales in the photographs (such as dorsal/caudal fin shapes, streaks, bulges, scars, etc.).

“Sperm whale juvenile populations don’t usually migrate or move widely, so we think there are sperm whale breeding and brooding groups in the deep seas of the South China Sea, and these sperm whales are likely to settle in the South China Sea.” Li Songhai said. The South China Sea is rich in cephalopod resources, and sperm whale populations are likely to also use the relevant waters of the South China Sea as their prey.

In the future, the research team of the Institute of Deep Sea will further expand the survey coverage area, accumulate observation data, and use passive acoustic monitoring, molecular genetic markers and other technical means to reveal more “unsolved mysteries” about sperm whales in the South China Sea. For example, the spatial and temporal distribution characteristics of sperm whales in the South China Sea, whether there is seasonal movement between different regions, whether there is individual communication between sperm whales in the South China Sea and sperm whales in adjacent seas, and genetic diversity.

Protect cetaceans and promote the construction of marine national parks

Deep-diving cetaceans such as sperm whales are “whale conveyor belts” in the vertical and lateral exchange of marine nutrients, and play a vital role in the energy transfer and material circulation of the underlying and surface marine ecosystems. They prey on cephalopods or benthic fish in the deep sea, and their excrement is an important bait for plankton when they return to the surface. In addition, once dead cetaceans sink to the ocean floor to form a whale-fall ecosystem, they may become “oases in the desert” in the nutrient-poor deep seas.

During marine carbon sinks, cetaceans can act as “whale carbon pumps” for carbon-oxygen exchange. All living things on Earth are made up of carbon, and the larger the organism, the longer it lives, and the more biological carbon it stores. Cetaceans are generally large and have a long lifespan, so they become an important reservoir of carbon for marine organisms.

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South China Sea deep diving / far sea cetacean expedition voyage group photo Courtesy of the marine mammal research team of the Institute of Deep Sea of the Chinese Academy of Sciences

“Large cetaceans such as sperm whales can weigh tens of tons and have a natural lifespan of more than 70 years. Each sperm whale can store tens of tons of carbon in its lifetime, is an important reservoir of carbon dioxide, plays a key role in regulating global climate change and carbon cycling, and has irreplaceable ecological value. Li Songhai said.

However, due to climate change and human activities, all cetaceans around the world have been adversely affected to varying degrees, and many species face serious existential threats and even endangerment. All cetaceans have been listed in the appendix of the CITES Convention and are all listed as national protected animals in our country. Among them, sperm whales are listed as CITES Appendix I species, assessed by IUCN as “Vulnerable vulnerable” species, and are national first-class protected animals in China.

Studies have shown that the main existential threats to sperm whales worldwide are fishing activities (net damage, entanglement, etc.), marine pollution (accidental consumption of plastic waste, noise disturbance) and ship collisions. However, specific to the existential threat of sperm whales in China’s waters, the information available to researchers is still very limited.

Li Songhai believes that more special studies and surveys are urgently needed to assess the existential threats to sperm whales that survive and haunt China’s waters. Moreover, he suggested that fishing activities in China’s territorial waters and exclusive economic zones should be further controlled and reduced, especially the overfishing of low-economic value fishery resources should be reduced, and the necessary food resources should be reserved for characteristic marine organisms such as sperm whales and endangered protected animals.

Since the 1990s, the protection of aquatic wildlife in China has mainly adopted the nature reserve system, which is suitable for the protection of rare and endangered animals in the nearshore and freshwater environments, and indeed provides a strong guarantee for the protection of nearshore and freshwater cetaceans. However, the traditional nature reserve system cannot meet the needs of protecting sperm whales and their vast habitats.

“Here, we strongly call for the construction of marine national parks in the waters near the sperm whale breeding farm in the South China Sea, and actively incorporate the protection goals of special marine habitats and characteristic marine animals such as sperm whales into the development and construction of the national park system.” Li Songhai said. (Source: China Science Daily Zhang Qingdan)

Related paper information:https://doi.org/10.1016/j.dsr.2022.103767



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