Fishery bulletin of the Fish and Wildlife Service - NOAA

50 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
the bottom of fig. 32 are also repeated for the sake of comparison at the bottom of
fig. 33.) These provide proof that the members of the 1935 year-class that contributed
to the population summering in northern waters as 2-year-olds in 1937 came, in the
main, from the Chesapeake Bay area. Thus the middle set of curves in figure 33
are measurements of the growth zones of scales from fish that were just becoming
2-year-olds in Chesapeake Bay in 1937. They are, in other words, from bass that
had not yet migrated to any great extent, and the curve for the second growth zone
may therefore be considered typical for bass that had been born inl935 in Chesapeake
Bay. The upper set of curves in figure 33 is from measurements of the growth zones
of scales from 2-year-old fish taken from northern waters in the summer of 1937.
They are from bass of unknown origin that had migrated north along the coast in the
spring. It will be noted immediately that the curve for the second growth zone of
the scales from northern fish in the summer of 1937 compares well with the similar
curve for the bass of the same year-class known to be of Chesapeake Bay origin.
LENGTH FREQUENCIES OF GROWTH ZONES ON SCALES FROM
TWO-YEAR-OLD STRIPED BASS IN 1937
WIDTH OF GROWTH
FIGURE 33.—The length-frequencies of the growth zones on scales from 2-year-old striped bass taken In southern New England
southern Chesapeake Bay, and Currituck Sound (repeated from Figure 32 for comparative purposes), in 1937. The measurements
making up each curve have been smoothed by a moving average of threes throughout.
However, it does not compare well with the similar curve for bass of the same yearclass
known to be of North Carolina origin. (See lower set of curves, figs. 32 and
33.) There is somewhat of an overlap between the curves of the widths of the second
growth zones on scales from fish of the 1935 year-class of known origin from Chesapeake
Bay and North Carolina, so that scales from fish of the same age-group but of
unknown origin that show a second growth zone measuring from about 2.0-3.0 mm.
might have been born in either of the above-mentioned areas. It is apparent that the
majority of the widths of the second growth zones on the scales from fish taken in
northern waters in the summer of 1937 fall below 2.0 mm. Judging from these
measurements, it is possible to say that the North Carolina fish (assuming the Currituck
Sound sampling to be representative of that area) contributed at an absolute
maximum about 20 percent of the 2-year-olds summering in northern waters in 1937.
The percentage that North Carolina contributed to the northern population at this
time was probably much less. In fact, a comparison of the widths of the second
growth zones of the scales from fish of the same year-class from Chesapeake Bay and
from northern waters in 1937 (see fig. 33) shows that it is possible that North Carolina
did not contribute anything directly to the population of 2-year-olds summering in
the north in 1937, and that this population came entirely from the Chesapeake Bay
area or north of it. The latter, however, is undoubtedly an extreme view.
It is thus apparent that in 1937 North Carolina contributed directly not more than
a small fraction of the 2-year-old striped bass summering in northern waters, and that
the 2-year-old bass in northern areas in that summer came mainly from the Chesapeake
Bay latitudes and perhaps from the Delaware Bay region. There is, however,
a possibility that the fish born in North Carolina contribute indirectly to the popu-