300 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



20 contained egg remnants. None were found in 

 the North Pacific ovaries, thus giving added 

 weight to the conclusion that spawning does not 

 occur in the North Pacific. 



MINIMUM SIZE OF SPAWNING FISH 



Ueyanagi (1955) has inferred from his studies 

 that the albacore attains sexual maturity and may 

 spawn at about 90 centimeters in length. Our 

 observations are in agreement with this. 



The 12 central equatorial Pacific ovaries in the 

 late developing stage were obtained from fish 

 ranging in length from 89.1 cm. to 104.8 cm. 

 (weight, 33 to 54 lbs.) ; the 45 late developing and 

 advanced ovaries from the Hawaiian area were 

 taken from fish larger than 93.1 cm. (33 lbs.). 

 Additional evidence regarding the minimum size at 

 spawning can be found in figure 11. Although 

 egg remnants were present in ovaries at all stages 

 of maturity, none were found in fish less than 90 

 cm. in length. Therefore, our data suggest that the 

 albacore attains sexual maturity at a size of about 

 90 cm. (33 lbs.), which coincides with Ueyanagi's 

 findings. 



FREQUENCY OF SPAWNING 



The frequency distributions of egg diameters 

 (figs. 5 and 6, tables 7 and 8) show clearly two or 

 more modes which, depending on the growth rate 

 of the egg, may represent eggs that will be spawned 

 in a single season or in succeeding seasons. As 

 the data do not permit determination of the growth 

 rate of eggs, reference is again made to figure 1 1 . 

 The fact that the three advanced ovaries as well as 

 most of the late developing ovaries contained egg 

 remnants strongly indicates that the albacore 

 undergoes multiple spawning. The lack of rem- 

 nants in large, sexually inactive adults taken dur- 

 ing late winter in the North Pacific suggests that 

 remnants are not carried over from one year to 

 the next, though in the absence of any knowledge 

 regarding the rate of resorption of the unspawned 

 eggs, no definite conclusions can be drawn. The 

 presence of egg remnants together with a group of 

 eggs approaching ripeness suggest, however, that 

 albacore may spawn at least twice during a single 

 spawning season. 



FECUNDITY 



Fecundity calculations were based on the 

 assumption that all of the eggs comprising the 

 most advanced group within an ovary were 

 released in a single spawning. Eight Hawaiian 

 fish of varying sizes were selected for this study. 

 From each pair of ovaries, a random sample was 

 obtained; this was weighed to the nearest 0.001 

 gram. All of the eggs comprising the most 

 advanced group within the sample were then 

 counted. The total number of such eggs in the 

 pair of ovaries was estimated by multiplying the 

 number in the sample by the ratio of ovary- 

 weight to sample-weight. The results are shown 

 in table 9. The data are arranged in the order of 

 increasing fish size from 36 to 62 pounds. In 

 addition, two calculations made by Ueyanagi 

 (1955) are included. 



' From Ueyanagi (1955). 



There appears to be a slight tendency for 

 larger fish to have more eggs per spawning but it 

 is not as definite as that found for the yellowfin 

 (June 1953) and bigeye tuna (Yuen 1955). The 

 estimated total numbers of eggs in the most 

 advanced group were remarkably uniform, rang- 

 ing between 0.9 and 1.8 million eggs per individual 

 female. Including Ueyanagi's estimates, the range 

 is from 0.9 to 2.1 million eggs. 



OVARY SIZE AS INDEX OF MATURITY 



While the state of maturity of an ovary can be 

 determined reliably by means of egg diameter 

 measurements, a more simple and yet objective 



