the albacore caught in July was fat loss and given 

 that fat yields about 9.4 kcal/g, less ~159f due to 

 the cost of fat mobilization (SDA), leaving about 

 8.0 kcal/g, the caloric value of the fat loss is 3,272 

 kcal. The mean length of the albacore in the July 

 sample was 63 cm with a computed mass for the 

 offshore region (from Equation (1)) of 5,030 g. As 

 this would be the weight at the initial stage, it 

 seems appropriate to use as the mass for the calcu- 

 lations the equivalent of one-half of the observed 

 loss in mass (202 g) subtracted from the computed 

 initial mass to give a value of 4,828 g. Using these 

 equations, the rate of caloric expenditure per hour 

 was estimated for a 63-cm albacore swimming at 

 54 cm/s which is the estimated minimum speed a 

 63-cm albacore can swim and maintain hydrostat- 

 ic equilibrium, V 100 (Magnuson 1970; Dotson 

 1977). Where C, plus C m is equal to the total caloric 

 expenditure (C to tai' during migration, then: 



^ total ^s "• ^m 



= 2.78 kcal/h 

 = 3.67 kcal/h. 



0.89 kcal/h 



(6) 



The caloric equivalent of the fat divided by the 

 hourly caloric utilization rate, C tota i, Equation (6) 

 yields the number of hours that swimming at 54 

 cm/s could be sustained utilizing this energy 

 source alone and is estimated to be 



3,272 kcal 

 3.67 kcal/h 



892 h or -37 days. 



The speed and time multiplied together yield the 

 linear distance traveled during this period. This 

 was calculated to be 1,730 km (935 nmi). 



Based upon sonic tracking experiments, the av- 

 erage swimming speeds of three albacore 84, 85, 

 and 87 cm in length have been observed to be 95 

 cm/s during the day and 62 cm/s at night (Laurs 

 et al. 1977). The minimum swimming speed for 

 hydrostatic equilibrium of these fish (V 100 ) is esti- 

 mated to be about 42 cm/s (Dotson 1977). Assum- 

 ing the ratio of observed speed (V ) to minimum 

 speed ( V 100 ) to be relatively constant over the size 

 range, then diurnal and nocturnal speeds can be 

 estimated where V /V 100 = 42 cm/s = 2.260 is the 

 multiplier for daylight speeds and (62 cm/s)/(42 

 cm/s) = 1.575 is the multiplier for night speeds. 

 The result of this estimation is that the daylight 

 and nighttime speeds for a 63-cm albacore are 122 

 and 80 cm/s, respectively. Assuming equal time 

 spent at each speed, about 6.08 kcalm are utilized. 



If the tracking observations are representative of 

 migratory swimming speed, and therefore caloric 

 expenditures, then the fat energy would have been 

 utilized in a period of nearly 22 days and the linear 

 distance traveled would be about 1,960 km (1,060 

 nmi). 



From the nearshore area of capture, the 

 maximum linear distance traveled using the av- 

 erage fat loss of a 63-cm albacore is indicated by 

 points A and B in Figure 1. The two values indi- 

 cated represent a) 37 days at a minimum speed of 

 54 cm/s, and b) the estimated diurnal rates of 80 

 and 122 cm/s for equal portions of 22 days. The 

 interesting result is that both the distances are 

 within the area where the offshore samples with 

 the greater length-mass relationship were col- 

 lected and compared with the onshore material. 



The maximum observed mass difference from 

 the offshore mean of an albacore caught inshore is 

 999 g or 189c of its body weight for a 65-cm fish 

 (Dotson 1977). Assuming the total weight differ- 

 ence to be fat, at its calculated minimum speed of 

 54 cm/s, this albacore could have traveled 4,200 

 km (2,270 nmi) over a period of 90 days utilizing 

 only this fat as an energy source. This would place 

 the fish well out in the mid-Pacific, as shown by 

 point C in Figure 1. Swimming at the estimated 

 day and night speeds of 122 and 80 cm/s for equal 

 parts of the day this fish could travel 4,680 km 

 (2,520 nmi) in 54 days (Figure 1, point D). 



These observations, calculations, and hypoth- 

 eses should indicate some of the potential effects 

 which can be examined in the future, given broad- 

 scale sampling and interest in the migrations of 

 tunas. Fat content is an important indicator of the 

 calories available for migration and/or spawning 

 in fish of sufficient maturity. The importance of 

 immigrants to population assessment in managed 

 fisheries is obvious. Certainly, spawning success 

 and behavior is dependent upon the available 

 caloric stores. For tunas where migration and 

 grazing up to spawning condition may be competi- 

 tive processes, a thorough examination of the fat 

 level cycles may offer insights into both periodic- 

 ity and location of the potential spawners. This is 

 an area of minimal understanding in tunas to 

 date. Considering the importance of these pro- 

 cesses in the life cycles of tunas, it seems that a 

 certain amount of importance should be placed 

 upon obtaining comprehensive data from several 

 behavioral categories of tunas where inferences 

 could be made about the relation of fat stores and 

 behavior. 



449 



