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Kinki University, Faculty of Agriculture
Uncovering the True Nature of the Bluefin Tunas, “the Diamonds of the Sea”

The nature of the bluefin tunas (thunnus orientalis) – large, beautiful fish known as “the diamond of the sea” – is to swim freely in the ocean. This makes close examination difficult, which is why little of their biological characteristics has been explored. Professor Tsutomu Takagi from Kinki University, Faculty of Agriculture, has been applying fluid analysis to reveal the mysterious nature of the bluefin tunas.

The Logic behind the Motion Revealed by Analyses

 According to Professor Takagi, the quantitative results generated by the fluid analysis illustrate why tunas swim up and down when moving forward. This particular style of swimming has long been noted by scientists, and has been suggested that it improves efficiency. Another theory proposed that the fish used gliding for repose, which enabled them to swim longer. However, neither theory had been confirmed until bio-logging technology became available. This technology enables live measurements on real fish by attaching sensors to the fish and monitoring their motions and environmental conditions. Using the data for water depth, degree of the body tilt, and vibration counts of the tail, Professor Takagi conducted fluid analysis and successfully confirmed the efficiency theory. Professor Takagi learned that changing the water depth while swimming increased swimming efficiency by 10-20%.

Figure 3: Analysis result of an olive flounder using SC/Tetra

(click to enlarge)

Decoding Behavioral Mechanism from Shape

 Professor Takagi first became interested in behavioral research on living organisms when he conducted an analysis of an Japanese flounder (figure 3). Originally specializing in engineering, Professor Takagi formerly conducted research simulating round purse seine nets used in tuna fisheries. Part of this work involved digitally analyzing the behavior of the Japanese flounder.

​ Using fluid analysis to calculate values of lift and drag for the Japanese flounder, Professor Takagi determined the ideal angle needed by the Japanese flounder to stably glide. He found that the calculation matched the observed results. Professor Takagi notes that he was intrigued to find that the fish behaved exactly as his calculations suggested. This is just like how vehicles function in the way they are designed.​

Using Fluid Analysis instead of Experimental Tests

 Professor Takagi has used SC/Tetra in his research for more than ten years. The software possesses easy operability and reliability. The use of fluid analysis had long been appealing, but Professor Takagi recognized that a substantial amount of time and cost would be required for him to develop his own tool. He found SC/Tetra in his pursuit of a packaged product that would be easy enough for his team to use.

Figure 4: Using SC/Tetra to analyze the bluefin tuna

 Professor Takagi is satisfied with the capability of SC/Tetra. The software is not only easy to use, but also it produces excellent computational results and includes superior technical support. Professor Takagi recognizes that computational analysis tools may not be able to perfectly simulate the complex physical phenomena occurring in nature but can be useful for drawing relative comparisons. For example, analytical methods can be used to compare the difference in drag between two angles of attacks.

 “We have not yet completely mastered the operation. For example, we are still struggling to understand turbulence that occurs on the skin surface when we compare a shark and an Japanese flounder. The analysis is tricky because results can be massively dependent on the turbulence model used. In terms of the hardware environment we have prepared for the research, the computer capability has been improved and the price has become reasonable. We benefit tremendously as the equipment we need is within our research budget,” says Professor Takagi.

 “Obtaining accurate experimental results is extremely difficult. We can only acquire approximate values from experimental measurements. Simulation is the only method that generates accurate results for us. This fluid analysis tool has become indispensable to us,” comments Professor Takagi.

Figure 5: Mr. Shin Ogawa, a second year doctoral student at Kinki University (Laboratory of Fisheries Production System, Department of Fisheries, Faculty of Agriculture) on left
Mr. Shinsuke Torizawa, a lecturer at Kinki University (in the Department of Fisheries, Faculty of Agriculture) on right

More Uses of ICT (Information and Communications Technologies): Ways to Boost Fishery

 

 Professor Takagi hopes to see more uses of ICT in the field of fishery. In the field of agriculture, ICT have become much more common, being used for environmental monitoring and crop observation. However, application of ICT to the vast and deep underwater environment is not an easy task. Professor Takagi’s research on fish behavior and simulation of round haul nets are considered significant technological advances.

 In the future, fluid analysis may make it possible to selectively capture fish of a particularly favorable size by analyzing its behavioral patterns and swim speed. Establishing the official fishing guideline is expected to improve the supply efficiency of aquatic resources and stabilize the production. The concept of combining the ICT and fishing is referred to as ‘smart fishing’ by Professor Takagi and other researchers of this field. Clearly, the use of ICT as applied to fishery, has substantial room for growth.

*All product and service names mentioned are registered trademarks or trademarks of their respective companies.
*Contents and specifications of products are as of January 1, 2014 and subject to change without notice. We shall not be held liable for any errors in figures and pictures, or any typographical errors.

Institute Details






 

Kinki University
Laboratory of Fisheries Production System, Department of Fisheries, Faculty of Agriculture
Founded 1949
Type of University  Private
Location of the Head Office Higashiosaka-shi, Osaka, Japan
URL http://www.kindai.ac.jp/

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