Taiwan’s Fisheries Research Institute (FRI), in collaboration with local and Japanese universities, presented its findings on the behavioral characteristics and thermoregulation mechanisms of the shortfin mako shark on Monday.
The 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 told a news conference.
The joint research was carried out by FRI in conjunction with Japan’s Graduate University for Advanced Studies (SOKENDAI) and National Kaohsiung University of Science and Technology.
Photo: CNA
According to SOKENDAI professor Yuki Watanabe, Taiwanese and Japanese fishers have helped to capture shortfin mako sharks and tag them with custom-made data loggers, which transmitted the data via satellite.
The loggers, which capture video recordings, monitored the sharks’ body temperatures and tracked their movements, SOKENDAI researcher Soma Tokunaga said.
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 that it stays warmer than the surrounding water, Tokunaga said.
When hunting prey even at depths of 1km where water temperatures are as low as 4°C to 5°C, 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°C to 4°C after each deep dive of several hundred meters.
This is vastly different to other types of shark, which typically keep themselves warm through a “countercurrent heat exchange,” where blood vessels transfer surrounding heat into the body, Yeh said.
The study found that during the day, the shortfin mako shark could be found in areas from the surface to depths of 300m 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 100m and 200m, Chiang added.
SOKENDAI is working on a report to publish the findings in international journals, Yeh said, adding that the research would also be presented at a scientific conference next month.
The research would serve as a useful resource for regional fisheries management organizations and others for research into the sustainability of the species, he said.
With climate change leading to variations in sea surface temperatures, the shortfin mako shark’s activity would also change, and as such, the findings could provide valuable insights for fisheries management, Tokunaga said.
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