DOTSON: SWIMMING SPEED OF ALBACORE 



abrupt drop in minimum speed between 60 and 70 

 cm FL (Figure 3). 



Albacore and yellowfin tuna have very similar 

 densities (Table 2), but the pectoral fins of albacore 

 are smaller in young fish (Gibbs and Collette 1966), 

 increasing very rapidly in size as the fish mature 

 (Figure 4). Thus, small albacore have a faster 

 minimum swimming speed than small yellowfin 



120 r 



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o 100 



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 UJ 



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 z> 



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50 



40 



30 



20 



10 



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T gibccorts 



T. oiMiua 



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I 



40 50 60 70 



FORK LENGTH (cm) 



80 



Figure S.-Ttie estimated minimum swimming speed of four 

 scombrids using Magnuson's (1970) model for hydrostatic 

 equilibrium. 



400 



< 300 



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IT 



< 



p 200 



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 tt. 



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T. ot*tvt 

 T altccarii 



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0L_L 

 40 



50 60 TO 80 



FORK LENGTH (cm) 



90 



Figure 4.-Regression cunes for pectoral lifting area (A) versus 

 fork length. Curves for Thunnus obesus, T. albacares. and 

 Katsuurjnus pelamis are from Magnuson (1973). The cune for T. 

 alalunga is from Equation (2) in the text. 



tuna, and albacore over 65 cm have a slower 

 minimum swimming speed than the same size 

 yellowfin (Table 2, Figure 3) assuming similar fat 

 content and gas bladder development. 



Because bigeye tuna have a larger gas bladder 

 than albacore and also have large pectoral fins, 

 both of which grow allometrically (Gibbs and 

 Collette 1966), their estimated minimum swim- 

 ming speed is only half that of albacore at both 50 

 and 80 cm in length (Table 2). 



The minimum swimming speed necessary for 

 hydrostatic equilibrium of 50-cm albacore is 70% 

 that of 50-cm skipjack and only 40% when each is 

 80 cm long (Table 2). Unlike albacore, skipjack 

 have no gas bladder and always have small, short 

 pectoral fins; therefore, skipjack tuna must swim 

 faster as their mass increases in order to maintain 

 hydrostatic equilibrium (Figure 3). 



In Table 2 and Figure 3, density values for 

 bigeye tuna were extrapolated beyond observed 

 values and those of albacore were chosen from 

 "fat" fish; therefore, actual values shown may not 

 be exact, but the gross relationships among species 

 are expected to hold true. 



FIELD ESTIMATES OF 

 ALBACORE S^TMMIXG SPEEDS 



During August 1972, the National Marine Fish- 

 eries Sen-ice in cooperation with the American 

 Fishermen's Research Foundation tagged six 

 albacore with sonic tags and tracked their 

 movements off the coast of Monterey Bay, Calif. 

 (Laurs et al. 1972).2 



Mean speeds observed during sonic tracking of 

 three fish near 85 cm fork length were 95 cm/s 

 during daylight hours and 62 cm/s during the 

 night. These speeds are higher than the calculated 

 minimum of 42 cm/s for a fish this size. 



Each of two tagged albacore approximately 80 

 cm long, which were caught after a trans-Pacific 

 migration, had a computed minimum or straight 

 line speed (based on great circle route and time 

 free) of 26 nautical miles/day or 55 cm/s (Japanese 

 Fisheries Agency 1975). The calculated minimum 

 speed of 45 cm/s is remarkably close to the es- 

 timated minimum migration speed of these two 



2Laurs, R. M., H. S. H. Yuen, and J. H. Johnson. 1972. Study of 

 the smaU-scale movements of albacore using ultrasonic tracking 

 techniques. In Report of Joint National Marine Fisheries 

 Ser%-ice-American Fishermen's Research Foundation Albacore 

 Studies Conducted during 1971 and 1972, p. 54-72. Unpubl. Rep. 

 SWFC,NOAA,LaJolla. 



959 



