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A simple, non-invasive technique to measure the body length of dolphins - enhancing the conservation of a wild dolphin population

30 Sep 2022

Summary of our research

MORISAKA Tadamichi (Associate Professor, Graduate School of Bioresources, Mie University; first & corresponding author), HAMA Hiromitsu (Visiting Professor at Osaka Metropolitan University [Professor Emeritus at Osaka City University]), SAKAI Mai (Lecturer, Department of Fisheries, Faculty of Agriculture, Kindai University), and KOGI Kazunobu (Mikurashima Tourism Association) successfully measured the body lengths of 85 wild Indo-Pacific bottlenose dolphins off Mikura Island using a 3D camera with an original, simple, non-invasive method.

Wild Indo-Pacific bottlenose dolphins inhabiting the clear waters off Mikura Island are an important resource, for both sightseeing and scientific research, as it is possible to observe the dolphins underwater at close range. The individual identification study showed that around 30% of dolphins had disappeared from the area from 2008 to 2011. This prompted us to monitor population health using body length. We decided to make a "growth chart" of body length for this population in order to determine whether the nutritional status of the population was deteriorating. However, there was no simple, non-invasive technique with which to measure free-ranging wild dolphins underwater.

First, we developed a new method that requires users to take pictures of the dolphins underwater with a commercially available 3D camera in an underwater housing. Data collected over a 6-year period was then used to measure the body length of 85 individual dolphins. We then calculated length-at-age estimates and drew a "growth chart" of body size for the population. Similar to the "standard growth chart" used to assess the growth and development of human children, our method enabled us to easily identify "outlying" dolphins with smaller body lengths compared to the "growth chart," owing to a nutritional deficiency due to a reduction in prey density. We will continue to monitor population health using this system.

The study was published online in the German scientific journal "Mammalian Biology" on 22nd September 2022. Body length and growth pattern of free-ranging Indo-Pacific bottlenose dolphins off Mikura Island estimated using an underwater 3D camera

Photo of Narrow-ridged finless porpoise

Researcher information

Photo of MORISAKA Tadamichi

MORISAKA Tadamichi

Associate Professor, Cetacean Research Center, Graduate School of Bioresources

Specialized area:

Bioacoustics, Ethology, Cetology

Current research field:

Description of interesting behaviors in cetaceans, Development of the elementary techniques for cetacean conservation, Basic study for cetacean communication and society

Photo of HAMA Hiromitsu

HAMA Hiromitsu

Visiting Professor (Professor Emeritus at Osaka City University), Osaka Metropolitan University

Specialized area:

Image processing, Computer vision

Current research field:

Development of the measurement system for large mammals using image processing technique, Development of an independent living support system for elderly people.

Photo of SAKAI Mai


Lecturer, Department of Fisheries, Faculty of Agriculture, Kindai University

Specialized area:

Ethology, Marine mammalogy

Current research field:

Communication and sociality of marine mammals, Enrichment for captive marine mammals

Photo of KOGI Kazunobu

KOGI Kazunobu

Executive Director, Mikurashima Tourism Association

Specialized area:

Conservation biology, Cetology

Current research field:

Conservation of cetacean off Mikura Island, Description of fauna in Mikura Island