Fishery bulletin of the Fish and Wildlife Service - NOAA

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STUDIES ON THE STRIPED BASS OF THE ATLANTIC COAST 25 character of the circuli that border it. This type occurs most commonly on scales that overlap a regenerated scale. It appears that the process of regeneration in a scale modifies the growth of adjacent scales sufficiently to form false annuli on the latter. This type was observed frequently, particularly on scale samples from tagged fish that had been recaptured and had regenerated scales in the area from which a sample was taken at the time of their original release. Regenerated scales were common in all samples, often forming at least 10 percent of those examined. Sometimes entire samples had to be discarded because there were no scales that were not regenerated. Up to 15 percent of the samples have been rejected on rare occasions because of false annuli, regenerated scales, and other factors which made the age determinations and scale measurements subject to serious errors. Scales from larger striped bass were found to be much more difficult to read for age than those from smaller individuals. Not only did the first annuli become indistinct, but there were likely to be more false annuli so that age determinations were confusing. For this reason growth calculations by the scale-measurement method have been confined to fish less than 5 years old. Particularly on scales from fish over 8 years old it was almost impossible to be sure that the age reading was correct, and on fish of this size or larger it was only feasible to make approximations as to the age of each individual. As a check on age determinations of striped bass of all sizes the growth rings on otoliths have frequently been counted, and it was found that on individuals up to 3 years old this method was satisfactory. The opercular and subopercular bones have also been examined for annular markings, which were best seen after these bones had been cleared in a half-and-half mixture of 5 percent glycerine and potassium hydroxide. On the whole such markings were found to be indistinct and irregular, and did not constitute an adequate means of making age determinations. Since the youngest striped bass taken in Connecticut waters during the course of the investigation were 2 years old, age determinations and rate of growth studies on juvenile and yearling fish were necessarily confined to material from elsewhere. The growth of the larvae has already been discussed under spawning habits and early life history (p. 19). The smallest juveniles that have been taken in their natural habitat have also been described, and, as is shown in figure 14, these fish, which were not more than 1 month old at the time they were seined in Albemarle Sound, averaged about 2.7 cm. in length. Figures 10 and 11 show the range in size of juvenile bass from the Hudson River, and of juvenile and yearling bass from Delaware Bay. It is apparent that juvenile striped bass in the Hudson averaged 5-7 cm. in length by the middle of the summer (see fig. 10). The juvenile bass taken in Delaware Bay in November 1937 formed only a small part of the curve shown in figure 11, the bulk of this sample being made up of yearling fish. The juveniles at this time, however, were from 9.5-12.5 cm. long. Growth practically ceases in the winter, and when striped bass become 1 year old in the spring they average 11-12 cm. long. Six yearling individuals taken in the Hudson River in July and August, 1936 and 1937, averaged 14.3 cm. (extremes 12.0-15.9 cm.). The yearlings in the Delaware Bay region (see fig. 11) averaged approximately 19 cm. in November 1937. By the time they become 2 years old striped bass are about 20-23 cm. in length, and it is at this age that this species probably first takes any large part in the coastal migrations. It should be mentioned at this time, however, that even in juvenile and yearling striped bass there is a tremendous variation about the mean in the measurements of any age group at any one time, as can be seen from figure 11. The subject is further complicated since the populations under consideration were from different areas where in all probability slightly different growth rates occur. Thus the lengths given for striped bass of different ages throughout can only be rough approximations. Fish 2 years old and older were sufficiently abundant to give ample material for growth-rate studies in Long Island and New England waters, particularly on the members of the dominant 1934 year-class. Figure 17 shows length-frequency curves of all striped bass measured in Connecticut waters from April through October 1936 and 1937. The prominent peaks that characterize these two curves are mainly made up of the 2-year-olds in 1936 and the 2- and 3-year-olds in 1937, and they give some idea of the relative abundance of the members of the 1934 year-class. The measurements that make up these graphs come mainly from seined individuals, but they also come from fish that were caught on rod and line and in pound-nets. Although this
26 FISHERY BULLETIN OF THE FISH AND SERVICE method of sampling the total population cannot be entirely free from error, it is probable that these curves represent the relative proportions of the different size- or agegroups to one another fairly accurately for the general region of the Niantic and Thames Rivers, Conn. The tendency of this species to school heavily, particularly among the smaller size-categories, thus making them more available and easier to catch., may have resulted in an over-emphasis on the relative numbers of the members of the 1934 year-class. And the fact that the larger fish tend to lie among the rocks in or near the surf, in places where they cannot be reached by seining, perhaps provides reason to suppose that these larger fish are not proportionately represented in these graphs. On the other hand, evidence from samplings of the striped bass population from commercial fishermen's nets in northern waters indicates that the 2-year- JC»0
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