Ghost head swordfish: Taiwan and Japan work together to promote the study of ghost head knives in the North Pacific Ocean. They like to move in the surface water.

During the production season of Guitou Dao in Xingang, the good news of Guitou Dao research also came out from the Marine Life Research Center in the east of Aquatic Research Institute and the research team of Ocean University. Based on the results of the standard release of Guitou Dao in Taiwan and Japan from 2016 to 2018, it was found that the water depth of Guitou Dao is about 70 to 90 meters and the difference of surface water temperature is 5 to 6 ℃. It can be inferred that the seasonal population distribution of Guitou Dao will be affected by the marine environment. The research results have been published in the Japanese international academic journal Fisheries Science.

In 1993, the Xingang area began to promote the "Guitou knife Fisheries improvement Program" (Guitou knife FIP). The next year, the Water Research Institute cooperated with Ocean University to conduct a "study on the identification and resources of Taiwan's Guitoudao ethnic groups." Jiang Weiquan, an associate researcher at the Marine Life Research Center in the east of the Water Test Institute, explained that at present, Guitou Dao visits Taiwan twice a year, once from April to June, Guitou Dao travels from south to north, and once from October to December, Guitou Dao swims from north to south. Because the captured sea areas of Taiwan and Japan belong to the Western Pacific Ocean, the research team not only places Guitou Dao in Taitung Chengtaigong. He also cooperated with Nagasaki University in Japan in 105 and 107 to mark Guitou Dao in the waters of Kagoshima and northern Nagasaki to record temperature, depth and illuminance, hoping to grasp the relationship between the two fishing seasons in Taiwan. to explore the structure and movement characteristics of the Guitou Dao group in the Northwest Pacific.

The research team, in cooperation with Nagasaki University in Japan, went to the custom fishing ground in northern Nagasaki, Japan, in 107 to conduct a study on exile marked by Guitou Dao, which measured the length and sex of the fish. The monitoring results show that the satellite markers are all located in the northern part of the East China Sea, recording the northward movement of Guitou Dao for 5 to 30 days.

It is found that Guitou Dao in eastern Taiwan lives in the shallow water layer with a water temperature of 25 to 29.7 degrees C and above 56.6 meters in summer and 23.2 to 29.1 degrees C and 83.4 meters in winter. Guitou Dao is only seen in winter in Japan every year. Guitou Dao in Kagoshima Bay lives in the shallow water layer of 20.5 to 23.7 degrees C and 52.4 meters, while in the northern part of Nagasaki it is 17.8 to 23.1 degrees C and 94 meters above. It can be seen that the habitat depth of Guitou knife is related to the temperature of the sea area, and the diving depth is only in the sea area with a difference of 5 to 6 degrees C from the surface water temperature, so the change of sea environment can easily affect the seasonal population distribution, and the fish catch may be affected by the change of sea environment.

Jiang Weiquan added that it is a pity that because of the strong vitality of the ghost knife, the satellite marker recorder on the fish body of the research team is easy to get rid of. At present, the longest recording time is only 30 days, so the research team has not yet mastered the path of the ghost knife back, so it is impossible to infer the relationship between Taiwan and the Japanese devil knife ethnic group. This year, we will continue to carry out the plan to mark the release of Guitou Dao in Taiwan and Japan, and we will also add a logo recorder with photography function, hoping to know the movement and predation of Guitou Dao in the sea, so as to enhance our understanding of the Guitou Dao ethnic group.

Chen Junru, director of the Water Test Institute, said that according to the statistics of the United Nations Food and Agriculture Organization (FAO), the global output of Guitoudao in 2015 was about 120000 metric tons, of which Taiwan ranked fourth, with an annual output of 9,000 tons. in response to the requirements of the export market for fishing fisheries, Taiwan promoted Guitou FIP in 103 and developed early warning strategies and catch control measures, making it the first species in China to carry out a fishery management plan. In order to implement FIP, we need rigorous scientific research to know whether there is overfishing. Therefore, the Water Test Institute will continue to cooperate with fishery scientists such as Japan and the United States, hoping to grasp the life history, ethnic movement characteristics, age structure, fishing gear and other factors, so as to evaluate the resources of Guitou Dao, and ensure the sustainable operation of domestic Guitou Dao fishing industry.

Overlap the moving path of the Guitou knife with the ocean surface water temperature map (the red triangle point is the marked wild location; the pink star is marked as the location where the marker bounces off; the blue line is the estimated location of movement). It shows that the places where the Guitou knife groups of the two places live in the sea water are similar, with a depth of about 70 to 90 meters and a difference of 5 to 6 degrees C from the surface water temperature.

Jiang Weiquan, an associate researcher at the Marine Life Research Center in the east of the Water Test Institute, demonstrated the way in which the satellite logo was inserted into the fish. Due to the strong vitality of the ghost knife, the indicator would be thrown away, resulting in a record time of up to 30 days, and it was impossible to establish the return path of the ghost knife. This is the research threshold that needs to be overcome in the next step.