140 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



-r 



ZOO 



LENGTH IN CMS AT AGE N 



Figure 7. — Combined 1948 and 1949 length data are plotted by the method of VValford (1946) and fitted with a straight 

 line. The intersect of the straight line and the line at 45° through the zero point indicates the upper asymptote 

 of the yellowfin tuna. Points mariied by O are observed vahies. 



month 37 through month 47 is the time group N 

 and is most evident in the plotted data, the mean 

 month and mean length of fish occurring in this 

 period were used as the initial point for computing 

 the relation between fish length and time. 



The reconstructed growth curve of length on 

 time and the plotted values of the original modes 

 are shown in figure 8. Since figures 7 and 8 

 indicate that the position of plotted mode values 

 are well fitted oy the calculated growth curve, 

 this serves as verification of the assumption 

 that modal group N—1 is a year younger than 



N, group N+I is a year older than N, and so on, 

 is correct. Since the original data were in terms 

 of weight, the calculated curve was also trans- 

 formed back to those terms. The growth curve 

 of weight on time is shown in figure 9. 



From the results of figures 8 and 9, it is possible 

 to determine approximate age of fishes. Ex- 

 trapolation of the curves downward suggests the 

 origin of the fish to be in year A'^— III. Ex- 

 amination of the gonads of yellowfin taken in 

 local waters indicates the spawning period to be 

 centered about the summer months. Assuming 



