FISHERY BULLETIN: VOL. 71, NO. 2 



Table 5. — Correlations between observed speeds of 

 scombroids and the fork length, mass, required lift for 

 hydrostatic equilibrium, surface loading, and computed 

 speeds with and without the keel included in the 

 calculation. 



torals extended only about 75% of the time at 

 typical speeds. The percent of extension of 

 the pectorals varied greatly from species to 

 species. The species with the longest pectorals, 

 T. obesus and T. albacares, almost never 

 appressed their pectoral fins while swimming 

 at typical speeds. 



Typical speeds of each species over its 

 length range (Figure 8) were computed from 

 equation 1 using values for Mf, Af^ from Table 

 4, and values of Dg from Table 1, p was set 

 at 1.025 g/ml. Since the inclusion of lift from 

 the keel had little effect on computed speeds 

 (Table 3), the computations were made on the 

 basis that all lift came from the pectorals. 



The three species with the fastest predicted 

 swimming speeds — K. pelamis, Sa. chilie)isis, 

 and E. affinia — have no gas bladder (Figure 

 8), while species with the lowest predicted 

 speeds — T. albacares, T. obesus, Sa. japonicus, 

 and Ac. solanclri — have gas bladders. Ac. solan- 

 dn, the species with the lowest predicted speed, 

 has the largest gas bladder and the lowest 

 density. 



Among the three species without gas blad- 

 ders, K. pelamis is the heaviest for its length 

 and has the fastest minimum speed. The pre- 

 dicted speeds of Sa. chiUeitsis and E. affi)ns 

 are quite similar, even though E. affiiiis is 

 considerably heavier at a given length than 



100 



80 



20 40 60 80 



OBSERVED SPEED (cm /sec) 



<x 1.5 



UJ 



a. 

 </> 



Ct 

 Ml 



\- 



a. 



o 

 o 



Figure 7. — Correlation between observed swimming 

 speeds of scombroids and the computed minimum speed 

 for hydrostatic equilibrium (a) in cm/sec, and (b) in 

 body lengths/sec. Data from Table 3. Solid line shows 

 expectation for perfect agreement and dashed line is 

 the linear regression of expected speed on observed 

 speed. Correlation coefficients, /•, are given on graph. 



Sa. chiliensis (Figure 3). This difference results 

 from the difference in the lifting area of pec- 

 toral fins (Figure 6). E. affinis has lifting 

 areas twice the size of Sa. chiliensis at a 

 given length. Interestingly, the minimum 

 speeds predicted for K. pelamis were almost 

 identical to the speeds predicted by Shuleikin 



346 



