Information Bulletin No.79

Watch Out for Tuna Belly

February 26, 1996

The Fisheries Agency has called on people involved in the nation's fishing industry to pay special attention to the bellies of bluefin tuna. The agency is requesting cooperation in retrieving electronic devices implanted in the bellies of fish released at the end of last year in an effort to record tuna migration routes and other data.

State-of-the-Art Sensors Implanted in 58 Fish
An adult bluefin, the largest tuna variety, can measure up to three meters and weigh 400 kilograms. In Japan it is considered the highest grade tuna eaten, and the fatty flesh on the underside, called toro, is especially prized for sashimi and sushi.
It is believed that bluefins are hatched near the islands of Okinawa and Amami, then swim north along the Japanese archipelago, and migrate the Pacific, but the details of their ecological niche and exact migration routes are unknown, the agency is anxious to learn about the data that is recorded.
So, in December last year, the Fisheries Agency implanted high-tech recording devices in the bellies of 58 bluefins caught off Tsushima Island and returned them to the sea. The device is a stainless steel cylinder 10 centimeters long, 1.6 centimeters in diameter, and weighing 52 grams that contains a 256-kilobyte integrated circuit and sensors. A black cable protrudes about 10 centimeters out of the fish's belly after the device is implanted.

A Ten-Year Record of Migration Routes
The device observes and records the tuna's body temperature, the intensity of light in the sea water, hydraulic pressure, and water temperature. Sunrise and sunset can be detected from the light intensity, revealing the longitude of the place where the fish is swimming. Recordings can be made every 128 seconds. Storage capacity is limited, however, so the device has been designed to reduce recordings to once a day beginning the forty-first day after the fish is released so that measurements can be continued for ten years.

Cooperation in Retrieving Devices
No matter how sophisticated the devices embedded in the fish, the data can not be analyzed unless they are retrieved. So the Fisheries Agency is using posters and other means to call for the cooperation of people throughout the country. Requests to keep the devices and notify the agency have been directed most intensively at prefectural fisheries experiment stations, fishing cooperatives, wholesale markets, and other places where these fish are most likely to be discovered.

(The above article, edited by Japan Echo Inc., is based on domestic Japanese news sources. It is offered for reference purposes and does not necessarily represent the policy or views of the Japanese Government.)