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the eagle, and the dragonfly as among the swiftest creatures 

 of their kind on earth. Most of the time, however, in tanks 

 at least, the tunas swim rather slowly. Rates reported from 

 studies at sea vary widely. 



The presence of underwater viewing ports on the Charles 

 H. Gilbert has enaVjled our Laboratory scientist Heeny S. H. 

 Yuen to make quantitative studies of the swimming speeds 

 of yellowfin and skipjack tunas in the ocean. The procedure 

 for finding these speeds is ingenious: the fish are photo- 

 graphed with a 16-mm. camera; from calculations that take 

 into account the speed of the camera, the ship's forward 

 movement, and its roll, Yuen is then able to measure suc- 

 cessive images on the film in such a way as to arrive at a 

 realistic estimate of the actual speed of a fish that may have 

 appeared within the viewing range of the camera no more 

 than half a second (fig. 6). 



In this manner, he has made 510 measurements of the 

 swimming speed of feeding skipjack tuna from four .schools 

 and 33 measurements of yellowfin from a single school. 

 These results were then treated statistically to determine 

 the validity of some of the relations suggested by the data. 



The swimming speeds of the yellowfin tuna so measured 

 were from 1.6 to 5.4 m. sec. (3.2 to 10.9 m.p.h.). These 

 results fall between those reported for yellowfin swimming 

 at a depth of about 350 feet (2 m.p.h.) and struggling at 

 the end of a fishing line (40.8 m.p.h.). 



The swimming speeds of the skipjack tuna (0.3 to 6.9 

 m. sec, or 0.6 to 13.9 m.i).h.) are much lower than those 

 found by other researchers (about 10 m. .sec, or 20.2 m.i).h.) . 

 The reason for this difference is unknown. 



Both species swam faster (covered more body lengths) 

 at the tailbeat rates measured than did the few other kinds 

 of fish studied by earlier workers. 



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