Are Tunas More Efficient than Mackerels or Eels?

There have been numerous studies on the energetics of fish swimming, but the question still remains which fish is the most efficient one. Tunas are one of the fastest swimmers in the ocean whereas eels and mackerels migrate thousands of miles. Comparing the efficiency of different swimmers experimentally is challenging because of lack of control over fish behavior and the environment. Numerical simulations, however, do not have such limitations and can compare fish under the same conditions (Reynolds number, tail beat frequency, etc.). Our large-eddy simulations (LES) of tuna at realistic Reynolds number (Re) reveal that Tunas are less efficient than mackerels and eels at Re 4000 and 40,000. Nevertheless, they are more efficient than mackerels and eels at Re of several hundred thousand and above. The results also reveal the need for performing simulations at realistic Reynolds numbers.