22 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



spawner (see p. 16), and might therefore not have contained eggs of the larger size 

 although the fish were mature. It is considered unlikely, however, that any serious 

 error in the results is introduced by this means. 



The results from this method of studying the age at maturity indicate that 

 approximately 25 percent of the female striped bass first spawn just as they are becom- 

 ing 4 years old, that about 75 percent are mature as they reach 5 years of age, and that 

 95 percent have attained maturity by the time they are 6 years old. The average 

 lengths of individuals of these sizes are discussed in the following section (p. 30), 

 and table 10 gives the results of determining the age at maturity of 109 female striped 

 bass of known length by measurements of the diameters of the ova. 



The examination of spawning individuals in North Carolina in the spring of 1938 

 gives added evidence on the age at which female striped bass first spawn. Scale 

 samples from 25 fully ripe females of measured length (43 to 78% cm.) were collected 

 in late April and early May. The smallest of these fish was 43 cm. — a bass that was 

 just becoming 4 years old, but was somewhat smaller than the average individual of 

 this age. There were also 5 other individuals from this lot of 25 mature females that 

 were the same age as this smallest fish. Of the remaining 19 fish, 16 were just reaching 

 5, 6, or 7 years of age, while the other 3 were 8 or 9 years old. During the period when 

 these mature females were encountered, a great many hundreds of smaller females 



Figure 14. — A length-frequency curve of 85 juvenile striped bass taken in Albemarle Sound on May 11, 1938. Data smoothed 



by threes (see Table 9 for original measurements). 



from 1 to 3 years old were handled, but none were ever found to be ripe, thus offering 

 further proof that female striped bass do not arrive at maturity until they reach at 

 least 4 years of age. 



Male striped bass, on the other hand, become mature and first spawn at a much 

 earlier age. A total of 303 ripe males were encountered in late April and early May 

 in the Albemarle Sound region in 1938. The smallest of these was 21.5 cm. long and 

 was just becoming 2 years old, although it was unusually small for a fish of this age. 

 The largest was 51.5 cm. long, and was just becoming 5 years old. Of the 303 ripe 

 males examined, 150 were just becoming 2 years old, and all the remainder, except 

 the largest individual mentioned above, were becoming either 3 or 4 years old. It thus 

 becomes apparent that a large percentage of male striped bass are mature at the time 

 they become 2 years old, and it is probably true that close to 100 percent are mature 

 by the time they become 3 years old. (See Vladykov and Wallace, 1937.) 



AGE AND RATE OF GROWTH 



It has been well established in an ever increasing number of species of fish that 

 scales, since they present more or less concentric rings or annuli, may be used for age 

 determinations. It is generally assumed that the formation of a true annulus is 

 caused by the slowing down or almost complete cessation of growth in the winter, 

 resulting in the arrangement of the circuli so that an annulus appears. Actually, 

 in the striped bass, the annulus does not appear in the winter and only becomes 

 evident by April or May. Further than the determination of age, scale analysis has 

 other vitally important applications in studies on the life histories of fishes. It can 

 be used for growth calculations, is often a method for determining the geographical 



