The new method makes the cetacean ecology more reliable

Background surveys of offshore ecology and rare animals have been conducted worldwide in recent years, but the results obtained by a single method are often difficult to verify their reliability.

Recently, the marine mammal research team of the Institute of Deep-sea Science and Engineering of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Deep-sea) proposed a new paradigm for integrated cetacean ecological research and demonstrated the demonstration research results. The research results were published in the academic journal Biological Conservation.

This result is conducive to cetacean researchers to carry out cetacean ecology and conservation research in waters with lack of data, better investigate the emergence, distribution and habitat utilization of cetaceans, and achieve a step-by-step, complementary and efficient and reliable survey effect.

Is there really a Chinese white dolphin in Hainan?

Historical stranding information shows that marine mammals such as cetaceans in the waters around Hainan are rich in resources and very diverse. However, due to the lack of field surveys and long-term systematic monitoring, the background data of cetaceans in Hainan is almost blank.

In the context of this lack of information, it is crucial to use a simple, efficient, fast, and low-cost method to quickly grasp the basic information of cetaceans, and local ecological awareness (LEK) surveys are a technical method to meet this need.

Li Songhai, the corresponding author of the paper and a researcher at the Institute of Deep Sea, introduced that professional fishermen are the specific occupational groups that are most frequently exposed to wild cetaceans, and through survey fishermen, they can quickly obtain their understanding, experience and views related to wild cetaceans in the process of marine fishing production, so as to provide basic direction and background information for follow-up investigation and monitoring.

Therefore, the research team conducted a survey around Hainan Island at the end of 2013. The survey selected 16 representative coastal fishing ports/villages and conducted questionnaire interviews with 510 fishermen. Thanks to the scientific and reasonable questionnaire design, the volunteer support of the Blue Ribbon Marine Conservation Association, and the strong cooperation of local management departments and communities, the entire survey was successfully completed in just over 20 days, and the research team quickly and efficiently obtained a wealth of survey data, and carried out meticulous collation and data analysis of the data.

Although the survey focused on all cetacean species that may inhabit the waters around Hainan, due to the unique body color and nearshore habits of the Chinese white dolphin, fishermen are very easy to contact and identify this species, and based on the preliminary analysis results, the researchers quickly locked a water suspected of being frequented by Chinese white dolphins – the southwest coastal waters of Hainan.

The Chinese white dolphin is a first-class protected animal in China and has high ecological, protective and research value. The results of the fishermen’s questionnaire provide exciting directions for the research team, but the fishermen’s sightings are indirect information after all, and their reliability and authenticity need to be further tested.

As a result, the research team began conducting exploratory ship-based visual surveys in the coastal waters of southwest Hainan in April 2014 to verify whether there are indeed frequent Chinese white dolphins in the area.

After months of wind and sun, the investigators’ diligent ship-based investigation work at sea finally bore beautiful fruit – on October 20, 2014, the Chinese white dolphin colony was first witnessed around Sanya Xigu Island, and the Chinese white dolphin was witnessed many times in the next two months of investigation.

“These field survey results not only verify the credibility of the results of the previous fishermen’s questionnaire, but also further confirm that there are indeed Chinese white dolphins living near the southwest coast of Hainan.” Li Songhai said.


The research team witnessed four cetacean species in the coastal waters southwest of Hainan: the Chinese white dolphin, the Indo-Pacific porpoise, the Indo-Pacific bottlenose dolphin and the pseudo-killer whale. Courtesy of The Institute of Deep-sea Sciences and Engineering, Chinese Academy of Sciences

Since then, the research team has continued to conduct month-to-month ship-based surveys and has continuously expanded the scope of the survey to all potential distribution areas of the population, with a total of 55 ship-based surveys conducted as of June 2019, each survey lasting at least 3 to 8 days. Through long-term ship-based investigation and monitoring, the investigators witnessed a total of 50 groups of cetaceans, including not only 47 groups of “regular visitors” – Chinese white dolphins, but also 2 groups of Indo-Pacific finless porpoises and some rare “passers-by” – pseudo-killer whales and Indo-Pacific bottle-nosed dolphins.

Through the analysis of the ship-based survey data, the research team had a good grasp of the composition of cetaceans in the southwest of Hainan, the habitat distribution characteristics of Chinese white dolphins, the number of individual identification, environmental preferences and other basic conditions.

Passive acoustic monitoring: they leave traces of sound

The overall sighting rate of ship-based surveys is low, and the technical approach has many limitations and deficiencies, such as being conducted only during the day and when the sea conditions are excellent, which is expensive and time-consuming.

In order to better grasp the infestation distribution of this population, the research team began to try to use underwater passive acoustic monitoring (PAM) technology. In 2016, researchers chose a location with the most frequent sightings of Chinese white dolphins on Sanya’s Xigu Island for nearly a year of exploratory experiments.

“By monitoring a typical high-frequency narrow-band signal (clicks ticking) emitted by the Chinese white dolphin, we confirmed that the Chinese white dolphin frequently appears around the monitoring site.” Li Songhai said.

Therefore, the research team further carried out a long-term and large-scale underwater passive acoustic monitoring program in 2018. The researchers selected 11 suitable sites along the coast of the Sanya-Changjiang River to carry out the deployment of the underwater acoustic monitoring platform and acoustic recorder, and then carried out instrument recovery, data download, instrument charging and re-deployment according to a cycle every 2 to 3 months.

In the monitoring cycle of more than 4 years so far, researchers have obtained acoustic data of 10 sites (no. 2 platform and acoustic equipment are lost), which has better realized the monitoring of cetaceans and various other underwater sound sources in the coverage area for a long time, large-scale, approximately continuous, day and night, and not affected by harsh sea conditions.

Li Songhai introduced that they also used some data sets to develop an automatic recognizer of clicks signals based on machine learning algorithms, and continuously optimized the recognition accuracy of the recognizer’s dolphin clicks signal to more than 96%, and then used the recognizer to detect and analyze the clicks signal of the entire underwater acoustic monitoring database.

Through passive acoustic monitoring technology, the research team has a good grasp of the habitat distribution law and spatio-temporal change mode of Chinese white dolphins in the southwest waters of Hainan, and confirmed that the acoustic monitoring results are an important supplement to the survey results of the ship.

A new paradigm for integrated cetacean ecological research

After decades of continuous development and improvement of cetacean researchers around the world, fishermen’s questionnaire surveys, ship-based visual surveys and passive acoustic monitoring have gradually become very important cetacean survey techniques, and are widely used in various types of cetacean ecological and conservation research projects.

Li Songhai pointed out that these methods have their own conditions of use, scope, requirements and limitations, which makes it difficult to verify the reliability of the survey results obtained by a single method.

In particular, it should be noted that there are many less developed countries in the world like China, and the common denominator is that cetacean background data is often very scarce. In addition, due to the very limited financial support for research and conservation, it is difficult for cetacean researchers and conservation workers in less developed countries to directly carry out targeted, large-scale, long-term, systematic field surveys and monitoring.

“In order to better carry out relevant investigation and monitoring work, for the first time, we combined the three technical methods of fishermen questionnaire survey, ship-based visual survey and passive acoustic monitoring, and demonstrated the infestation distribution and habitat utilization of Chinese white dolphins in southwest Hainan with the discovery, verification and long-term monitoring of Chinese white dolphins in Hainan.” Li Songhai introduced.

The relevant research results not only provide basic information and materials for the protection of Hainan Chinese white dolphins, but also become an important scientific support for the protection of Hainan’s coastal ecology and rare animals, but also form a set of step-by-step, mutually corroborating and complementary new paradigms of integrated cetacean ecological research.

“It also provides an important model for cetacean researchers around the world to conduct more efficient cetacean ecology and conservation research in waters where data is scarce.” Li Songhai said. (Source: China Science Daily Zhang Qingdan)

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