FISHERY BULLETIN: VOL. 74, NO. 4 



detached left pectoral fin on a piece of paper 

 having a thickness of 0.25 mm. The outlined form 

 was cut out and w^eighed to the nearest 0.01 g on a 

 balance. Projected area was calculated from a 

 ratio of the paper weights to a standard, and 

 doubled to account for the other pectoral fin. 



Thirty-three 100 cm- pieces of the paper were 

 measured with a micrometer and weighed to 

 determine the affect of variations in paper thick- 

 ness and cutting accuracy on the calculations. The 

 thickness of the paper varied less than 1% around 

 the mean, and cutting accuracy varied by ± 2%. 

 The affect on calculations of pectoral lifting area 

 was, therefore, assumed to be negligible. 



The projected body area between the pectoral 

 fins was determined by multiplying the body 

 width at the pectorals by the width of the pectoral 

 fin at its point of attachment to the body as 

 measured on the fresh fish. Pectoral fin lifting 

 areas were determined for 42 fish caught in the 

 area described above and for 8 larger fish caught 

 off Oregon in October 1974. The following rela- 

 tionship was established between the lifting area 

 {A in square centimeters) and the fork length (L in 

 millimeters): 



4.7351 X 10- ''L-*''". 



(2) 



Albacore observed cruising under the baitboat 

 kept their pectoral fins extended continuously at a 

 sweepback angle of approximately 45°. The tips of 

 an albacore 's fins are also not rigid, and the effect 

 of this on the lifting capacity of the fin has been 

 ignored. 



A water density (7)^) of 1.025 g/ml was deter- 

 mined from temperature and salinity data from 

 the offshore region described above. This also 

 equalled the mean water density within the near- 

 shore albacore fishery. 



Fish densities were determined for three groups 

 of fish: group 1— seven fish caught during June 

 1974 in the offshore region; group 2—14 fish caught 

 60 miles south of San Diego on 23 July 1975, 

 presumably 2 wk after they appeared off the coast; 

 and group 3-37 fish caught on 13 September 1975 

 in the same region as group 2 but assumed to have 

 been near the coast for 2 mo. 



The group 1 fish were frozen immediately after 

 capture and, when returned to the laboratory, 

 thawed and weighed on a spring balance while 

 suspended in seawater to determine the density of 

 the fish in seawater (Df). 



Fish from groups 2 and 3 were weighed in 

 seawater on a pan balance immediately after 

 capture and their densities in seawater 

 determined. 



VARIATIONS IN DENSITY 



The density of group 1 fish (Figure 1) is well 

 within the range of those determined for fresh fish 

 of similar size indicating that freezing and thaw- 

 ing probably had negligible affect on density 

 determinations. All specimens were caught on or 

 near the surface by jigline or rod and reel, and 

 there was no difference in density attributable to 

 one method of capture over the other. 



Rough estimates of the development of the gas 

 bladders of 21 fish in group 3 were made im- 

 mediately after other measurements were com- 

 pleted. In specimens less than 56 cm FL (fork 

 length), the bladder was small (approximately 1 

 cm wide and 8 or 9 cm long) and contained little or 

 no gas. In specimens 60 to 70 cm FL, the bladder 

 was approximately 5 cm wide and 16 cm long and 

 filled with gas to a depth of 4 or 5 cm. Fish over 80 

 cm FL had bladders approximately 30 cm long and 

 10 cm in diameter which occupied a large volume of 



I.IIO- 



I.IOO - 



^ 1.0901- 



^ 1.0801- 



(/) 



1.070 - 



S 1.060 - 

 1.0501- 



« X 





45 50 55 60 65 70 75 



FORK LENGTH (cm) 



80 



85 



Figure 1. -Computed densities for 

 three groups of albacore: group 1 

 (triangles); group 2 (crosses); and 

 group 3 (dots). See text for explana- 

 tion of groups. 



956 



