Submersible drone checks snow crab quantity off Fukui Prefecture, western Japan

The Yomiuri Shimbun

November 9, 2021

The Fukui prefectural government conducted research to determine the quantity of snow crabs off its shores using an underwater drone for the first time.

Snow crabs landed and brought to ports in the prefecture are given the brand name Echizen-gani. Such crabs are a specialty of the prefecture.

Research was unable to be conducted until now because of obstacles on the seafloor. However, the drone successfully located snow crabs in the area.

“The accuracy of our work will improve, resulting in the ability to maintain a stable volume of this marine resource,” a prefectural official said.

Echizen-gani catches totaled 1,090 tons in 1964 and plummeted to 210 tons in 1979 because of overfishing.

Work to preserve the resource has progressed, and catches have been around the 400-ton level in recent years.

The drone is 1.3 meters long, 0.7 meters wide and 0.8 meters tall.

The research was conducted Sept. 28-30 at a protected reef in an area where catching crabs is banned about 15 kilometers from the town of Echizen. The reef is about 250 meters deep.

Concrete blocks have been placed along the reef so trawls cannot be used.

The drone has multiple propellers and is equipped with sonar and lasers, so it can maneuver around the blocks.

The drone took about 15,000 photos that prefectural officials are analyzing to determine the size and sex of the snow crabs.

Every year, the prefectural government trawls for snow crabs, checks their numbers and sizes, and estimates the total volume.

However, trawling is prohibited along the protected reef. In addition, the number of crabs caught varies significantly by the area trawled and the slightest change in the net’s position. Therefore, the surveys could be inaccurate.

According to the prefectural government, using the drone is convenient because it automatically navigates along preset routes.

Officials are analyzing the photos and will estimate the quantity of snow crabs in the area.

“By sharing the research findings with other prefectures, we hope everyone involved along the Sea of Japan will preserve crabs as marine resources,” a prefectural government official in charge said.

Brand-name crab

Snow crabs landed and brought to four fishing ports in Fukui Prefecture — Echizen, Mikuni, Tsuruga and Obama — are called Echizen-gani.

The brand name is registered in the Geographical Indication Protection System administered by the Agriculture, Forestry and Fisheries Ministry. The system safeguards brand names bearing geographic names of regions and areas.

To preserve resources, the crab-catching season is limited to between Nov. 6 and March 20. Catching females is allowed only until Dec. 31 during the period.

If crabs of the same species are caught and brought to ports in the Sanin region, they are called Matsuba-gani. If they are landed and taken to ports in Ishikawa Prefecture, they are called Kano-gani.