mass during the migratory period. What appears 

 to be an important question is whether or not the 

 migrations of albacore and other tunas are extra 

 demanding, meaning sufficient short-term energy 

 is required to induce fat store utilization even 

 though feeding is still accomplished. Too often the 

 concepts of growth and fat deposition are inte- 

 grated such that it is considered unlikely that 

 morphological growth can take place during fat 

 store utilization. Certainly from observations of 

 adolescent growth in mammals it is obvious that 

 there is no necessary dichotomy here. The two 

 processes require separate biochemical pathways 

 and are very likely separated temporally, well 

 within the standard day. 



In a preliminary effort to examine the question 

 of fat utilization, the length-mass relationship of 

 albacore collected offshore preceding their ap- 

 pearance in the onshore eastern Pacific surface 

 fishery has been compared with fish freshly ar- 

 rived in this fishery, and with fish which have 

 presumably been grazing and reconditioning for 

 the postsummer exodus from the onshore area. 

 Calculations from these data support the 

 hypothesis that fat stores are utilized for migra- 

 tion energy. 



We hope that these calculations and subsequent 

 inferences will stimulate further research into the 

 considerable problem of highly variable length- 

 mass information and its potential use in studies 

 of migratory fishes. 



Observations 



In June 1974, 477 albacore 463 to 794 mm long 

 were captured in the area between long. 130° to 

 140°W and lat. 30° to 40°N (Figure 1). A curve was 

 fitted by regression to the length-mass data from 

 these fish resulting in the equation ( Dotson 1977), 



M = 4.514 x 10 5 L 28746 



(1) 



where M is the mass in grams and L the fork 

 length in millimeters. Measured values fell 

 within 250 g of the regression line. 



Mass and length measurements were made on 

 14 albacore (600 to 657 mm FL, mean 631) col- 

 lected during July and 37 fish (516 to 851 mm FL) 

 collected during September 1975, in a region 110 

 km south of San Diego, Calif. ( Figure 1). The mass 

 of September-caught albacore was not different 

 from those estimated by the length-mass regres- 

 sion curve. The mass of July-caught albacore, 



however, averaged 404 g below those estimated by 

 regression (range: 172 g greater to 999 g less). 

 Analysis of body densities indicated that the mass 

 deficit of the albacore caught in July was probably 

 due to fat loss, or simply stated, as a fish of a given 

 length gets lighter its density increases (Dotson 

 1977). 



The albacore fishery near the coast commenced 

 in July 1975. The albacore in this fishery are 

 known to migrate from the offshore region (Laurs 

 and Lynn in press), and it is assumed, therefore, 

 that the mass ( fat) deficit was utilized as an energy 

 source during migration to the coast. 



Calculations and Inferences 



Using the observed mass deficits observed in the 

 July 1975 sample, it is possible to estimate the 

 migration path length assuming 1) little or no 

 growth occurs during the migration, and 2) the fat 

 utilized is the only energy source during migra- 

 tion. 



Based upon studies of swimming energetics of 

 tunas, Sharp and Francis (1976) estimated the 

 relation between swimming speed (V) in cen- 

 timeters per second, fork length ( / ) in centimeters, 

 and the swimming caloric expenditure per unit 

 time (C s ) in kilocalories per hour. The basic equa- 

 tion for this relation, in calories utilized per hour, 

 is as follows: 



C s = 8.7 x 10- 8 (I) 2 (V) 3 Cd. 



(2) 



The coefficient of drag {Cd) is estimated using the 

 relation (Sharp and Francis 1976) 



Cd = 0.262 exp [-(4.805 x 10 6 )Re] (3) 



where Re (Reynolds number) = IV I v (at#es=6.8 x 

 10 5 , Cd = 0.01), v is the kinematic viscosity of 

 seawater, approximated by the value 0.01. 



Sharp and Francis (1976) also estimated the 

 metabolic maintenance energy (C m ) (i.e. stasis 

 energy requirements) for tunas to be 1 g cal/g per 

 h. The metabolic weight (W met ) is approximated 

 by the relation 



W met = (M,) n * 



(4) 



met - UH/-) 



C m = W met x 10 3 kcal/g per h (5) 



where M f is the mass of the fish in grams. 



Assuming that the mean mass deficit of 404 g of 



448 



