Fishery bulletin of the Fish and Wildlife Service - NOAA

28 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
same size category. Other European investigators, however, have not found that the
same phenomenon applies in other species of fish in the North Sea. It is possible that
environmental factors, such as low temperatures in the spring and early summer of
1934, played some part in the smaller-than-average size of the members of the 1934
dominant year-class of striped bass.
It will be noted in figure 18 that the growth rate of the 2-. and 3-year-olds in
1936 and 1937 was fairly steady over the period from June through October. In
general, the modes of the length-frequency curves for the 2-year-olds progressed about
2 cm. each month. In October 1936, however, the 2-year-olds appear to have shown
an increased growth rate, the mode for this curve having progressed 3—4 cm. beyond
that for September. In October 1937 the fish of this age did not exhibit a similarly
increased growth rate, but the mode for this length-frequency curve progressed about
2 cm.—an amount about comparable to the growth during the summer months.
Since the temperature fell sharply in late September and October hi both 1936 and
1937 (see fig. 30), the normal expectation would be that the increase in length at this
time would have been less than in the summer months, assuming that the food supply
remained constant over this entire period. There are a number of possible explanations
of this apparently higher growth rate in October. There is some chance
that errors in sampling were responsible. Thus it is known that the population was
starting to change late in October (see Migrations, p. 37), and there is a slight possibility
that fish that had summered farther north, where they apparently grow faster
despite somewhat lower average temperatures (see fig. 19) were included hi the
samples at the end of this month. This does not seem likely, however, for the consistent
recapture of individuals tagged in this area from June through October gives
good evidence to the contrary. Another explanation of the apparently greater growth
rate hi the fall is suggested by the skewness of the length-frequency curve for October
1936. It will be noted hi figure 18 that in all curves for the 2-year-olds, except that
for October 1936 the peaks come about midway between the two extremes of the
range in size, or below that point. In October 1936, however, the peak falls well
above the midpoint between the extremes of size, and there is also a tendency toward
the same situation in the curve for October 1937. It may be, therefore, that this
apparently greater growth rate is possibly the result of "compensatory growth," the
name given by Watkin (1927) to the phenomenon of the smaller fish of a single age
group making up a deficiency in size between themselves and the larger fish of the
same age group hi a relatively short period after having lagged behind for some time.
The most probable explanation of the increased growth rate in the fall, however, is
that the food supply or its availability increased at this time. The analysis of the
stomach contents of striped bass is discussed in a later section of this paper, but for
the present it is interesting to consider the fact that this species is voracious in its
feeding habits and that it preys on small fish, particularly young menhaden (Brevoortia
tyrannus) and shiners (Menidia menidia notata) in Connecticut waters. Both of
these species spawn in the spring and early summer, and during July the young are
still so small and stay so close to shore that they do not form a large part of the diet
of the bass. But by late summer, and particularly early fall, they have increased in
size to such an extent that they have added enormously to the available food supply.
(For information on the growth rate of Menidia, see Food of the striped bass,
p. 53, and fig. 36.) The analysis of stomach contents during September showed
that striped bass continually gorged themselves on these small fish to the virtual exclusion
of other types of food. Furthermore, judging from the relative numbers
taken hi seme hauls in 1936 and 1937, and from the statements of local fishermen,
young menhaden were unusually abundant hi Connecticut waters in the latter part
of 1936. It is likely that these juvenile menhaden were responsible for the greater
growth rate of the striped bass in the fall of 1936, and that the increased availability
of the food supply in the late summer each year accounts for the maintenance of or
increase in the growth rate through October despite the sharp drop hi temperature
at this tune.
As will be shown subsequently, there is evidence that the growth rate of the
striped bass Varies considerably in different localities along the coast. It has already
been pointed out, however, that there was a great variation about the mean in measure-