STUDIES ON THE STRIPED BASS OF THE ATLANTIC COAST 



23 



point of origin of individual fish, and provides a means of studying migrations — e.g., 

 in salmon, Salmo salar (Masterman, 1913), and herring, Clupea harengus (Dahl, 

 1907) — age at maturity, and the number of times spawning occurs in different 

 individuals. 



In the case of the striped bass, there had been no previous work on the Atlantic 

 coast to determine the validity of the scale method for age and rate of growth studies, 

 although Scofield (1931) had applied it successfully on striped bass in California. 

 The preliminary examination of scales immediately disclosed the presence of distinct 

 annuli, which were increasingly numerous, the larger the fish from which the scales 

 were taken. Moreover, the number of annuli were normally constant on different 

 scales taken from a single individual. Also the scales taken from 17 fish that were 

 tagged in 1936 and recaptured from May to September of 1937 invariably showed that 

 the formation of an added annulus had taken place in the winter intervening between 

 the dates of release and recapture. In view of this and much other evidence, it seemed 

 that the scale method was definitely applicable to the striped bass. 



During the course of the investigation scale samples were taken from approxi- 

 mately 7,000 striped bass of measured length. Over 5,000 of these samples have been 

 mounted and studied. It is essential that all scales be taken from the same area on 

 the different fish if they are to be used for growth-rate studies, for the shape and size 

 of scales from different regions of the body vary to a marked extent and thus scale 

 measurements can only be considered comparable if the samples are homologous. 





FmuRE 16.— Diagrammatic sketch of a striped bass scale to show parts and method of measurement. 



Hence all scales were taken from the first or second white stripe above the lateral 

 line in the mid-region of the body directly below the gap between the spinous and 

 soft dorsal fins, for it was found that scales from this area were more consistently 

 suitable for study than those from any other place. A single sample generally 

 consisted of 4 or 5 scales. 



Length measurements of all striped bass were made from the tip of the lower jaw to 

 the fork in the center of the caudal fin, for it became evident in handling live fish 

 which were being tagged that measurements of this type were the easiest to make and 

 the least subject to error. All lengths given in this bulletin are to the fork in the tail, 

 unless otherwise specified. Figure 16 is a graph for the conversion of different types 

 of length measurements. A flat measuring board with vertical head-piece was always 

 used, and measurements were made to the nearest half centimeter. 



Scale samples were prepared for study by two different methods. The first 600 

 were mounted on standard 3- by 1-inch slides with %-inch cover-slips, the mounting 

 medium being corn sirup. All the remaining samples were prepared by taking the 

 impressions of the finely sculptured outer surfaces of the scales on transparent cellu- 

 loid. Lea (1918) first showed with herring scales: 



. . . that all details which are subjected to observation when the scales are used for the pur- 

 pose of age determination and growth calculations, arise from the play of light on the delicately 

 moulded relief forming the outer surface of the scales (Lea and Went, 1936). 



Lea produced casts, or imprints of the outer surfaces of scales in thin celloidin films 

 and found them ideal for study. Nesbit (1934a) devised an efficient method of pro- 



