Taiwan, Japan present joint research findings on shortfin mako shark

Taipei, Dec. 23 (CNA) Taiwan's Fisheries Research Institute (FRI), in collaboration with local and Japanese universities, presented their findings on the behavioral characteristics and thermoregulation mechanisms of the shortfin mako shark on Monday.

This species of shark, classified as "endangered" by the International Union for Conservation of Nature, is one of the most common bycatches of Taiwanese commercial longline and gillnet fisheries, the FRI said at a press conference.

The joint research was carried out by FRI in conjunction with Japan's Graduate University for Advanced Studies (SOKENDAI) and the National Kaohsiung University of Science and Technology.

According to SOKENDAI professor Yuki Watanabe, both Taiwanese and Japanese fishermen have helped to capture shortfin makos and tag them with custom-made data loggers, which transmitted collected data via satellite.

The loggers, which were able to take video recordings, monitored the shark's body temperature and tracked its movement in the ocean, SOKENDAI researcher Soma Tokunaga said during the press event.

Analysis of the data revealed the unique thermoregulation abilities of the shortfin mako that are not found in other shark species, one of which is the ability to regulate body temperature so it stays higher than the surrounding water, Tokunaga said.

When hunting prey even at depths of 1,000 meters where water temperatures are as low as 4 to 5 degrees Celsius, the shark can use this ability to its advantage.

FRI Deputy Director-General Yeh Hsin-ming (葉信明) said the research also shows that the shortfin mako experiences only a slight decrease in body temperature averaging about 2-4 degrees Celsius after each deep dive of several hundred meters.

This is vastly different to other types of shark, which typically keep themselves warm through a "counter current heat exchange," where blood vessels transfer surrounding heat into the body, Yeh said.

The study found that during the day, the shortfin mako shark can be found in areas from the surface to depths of 300 meters and frequently crosses the thermocline, likely related to feeding behavior, FRI associate researcher Chiang Wei-chuan (江偉全) said.

At night, it prefers to inhabit depths of between 100 m and 200 m, Chiang added.

SOKENDAI is currently working on a report to publish the findings in various international journals, Yeh said, adding that the research will also be presented at a scientific conference in January 2025.

The research will serve as a useful resource for regional fisheries management organizations (RFMOs) and others for research into the sustainability of this particular shark species, he said.

With climate change leading to variations in sea surface temperatures, the shortfin mako shark's activity will also change, and as such, the findings could provide valuable insights for future fisheries management, Tokunaga said.