1. Kooyman's Homemade Recorder for Measuring Weddell Seal Dives
Kooyman, an American researcher, wanted to investigate the diving depth of Weddell seals living in Antarctica. To do this, he modified a kitchen timer used in homes to create a device that recorded depth. In the 1960s, he attached this device to a seal’s back to observe its diving behavior [3].
This homemade machine was the first unit of what is now called "biologging." The core question remains: what mechanisms were inside this simple device to capture such specific data?
2. How Biologging Works: Recording Devices Attached to Animals
In biologging, a small recording device (data logger) is attached to an animal’s body. This device contains various sensors that measure speed, depth, water temperature, and position [2].
This is somewhat similar to a "smartwatch" worn by adults, which measures exercise amount and heart rate. However, biologging devices are built much more sturdy to work underwater. While the animal swims or dives, the device continuously records data. Later, when the device is retrieved, scientists can learn where and how that animal lived.
How did this method spread to Japan and become known around the world?
3. How Japanese Researchers Named the Method "Biologging"
About 20 years after Kooyman’s work, in the 1980s, a group led by Yasuhiko Naito at the National Institute of Polar Research in Japan advanced research using Antarctic seals and penguins [4].
Then, in 2003, an international conference held in Tokyo helped spread the term "biologging" worldwide [3][6]. Today, this name is commonly used, but it actually originated in Japan. With this method now widespread, what specific discoveries have been made?
4. Underwater Facts About Seals That Only Biologging Can Reveal
Weddell seals living in the Antarctic sea have been recorded diving as deep as 904 meters and staying underwater for 96 minutes [4]. Humans cannot directly observe such deep and long dives. This was revealed through biologging.
Additionally, it was discovered that certain sea birds catch small fish around jellyfish by using the jellyfish as a tool [5]. These discoveries are not limited to large animals. Surprising facts have also been found about more familiar fish.
5. How Recorders Showed That Tuna Do Not Swim at 80 km/h
It has long been said that "tuna swim at 80 km/h." Some reference books have listed this figure. However, researchers attached recording devices to tuna to measure their actual swimming speed. They reported that the cruising speed is about 3 km/h (it is faster when swimming at full effort) [1].
The figure of 80 km/h was likely a misunderstanding. It was calculated by mistaking the speed at which the fishing line went out when a tuna was hooked during fishing for the tuna’s swimming speed [1].
Why can a small device attached to an animal reveal what large ships could not?
6. Why Researchers Collect Ocean Data From Animals
There are places like the Antarctic sea where human ships have difficulty entering. It is also not easy for a ship to follow a fish like a tuna that keeps swimming continuously. However, seals and tuna can reach those places by their own power.
If a device is attached to an animal, it collects data on water temperature and depth from the places the animal visits [6]. It is like asking the animal to run an "errand" to places humans cannot go (though the animal does not know it is being asked).
In essence, the animals themselves become tools for investigating the sea.
7. Try Investigating Biologging Ideas Yourself
Here are some ways to think about and observe it. Look at your own wristwatch or a family member’s smartwatch. If you were to attach such a device to an animal, think about what improvements would be needed (such as making it waterproof or ensuring it does not fall off).
If you visit an aquarium, watch how penguins or sea turtles dive. Try measuring how long they stay underwater using a clock.
Safety Note: At aquariums, please do not push against the glass or fences. Be careful to ensure everyone can see clearly [3].