Fishery bulletin of the Fish and Wildlife Service - NOAA

64 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
(4) Studies of the fluctuations in abundance of the species over, long-term periods
show that there has been a sharp decline in numbers. Dominant year-classes have
at times temporarily raised the level of abundance, but the intensity of the fishery is
such that their effects have been short-lived. The dominant year-class of 1934 was
the largest to be produced in the past half century, although the parental stock at this
time was probably as small as it ever has been. Evidence is presented to show that
there is a good correlation between the production of dominant year-classes of striped
bass and oelow-the-mean temperatures during the period before and immediately
after the main spawning season.
(5) The striped bass is anadromous, spawning from April through June, the
exact time depending on the latitude and temperature. The majority of spawning
takes place from New Jersey south, although there are a few isolated spawning areas
in northern waters. The development of the eggs and larvae is pictured, and the
size of the juveniles at different times of the year is discussed.
(6) Sex determinations of striped bass in Long Island and New England waters
show that the number of males in this northern range of the species seldom reaches
much over 10 percent of the population; the percentage of males apparently decreases
in the age-categories above the 2-year-olds. In waters farther south the sex
ratios are not so disproportionate. Studies of the age at maturity show that approximately
25 percent of the female striped bass first spawn just as they are becoming
4 years of age, that about 75 percent are mature as they reach 5 years of age,
and that 95 percent have attained maturity by the time they become 6 years old.
A large percentage of the male striped bass are mature at the time they become 2
years old, and probably close to 100 percent are mature by the time they become 3
years old. This difference in the age at maturity of male and female striped bass
may well account for the small percentage of males in northern waters, for the time
of the spawning season in the south coincides with the time of the spring coastal
migration to the north, which is made up mainly of immature females. (See under
migrations, p. 44.)
(7) The age and rate of growth have been studied by scale analysis and by the
average sizes of different age groups. The scale method and its applicability to the
striped bass is discussed in full. Striped bass are roughly 12 cm. long when they
become 1 year old, 24 cm. when they become 2 years old, 38 cm. when they become
3 years old. and 45 cm. when they become 4 years old. Thereafter the annual increment
in length is about 7-8 cm. up to the tenth year. The growth rate of striped
bass in the summer months in 1937 was much greater just north of Cape Cod than
it was slightly south of Cape Cod. The growth rate of 2-year-old striped bass in
Connecticut waters was approximately the same from June through October 1937,
and increased in September and October 1936, despite the drop in water temperature.
This maintenance of or increase in the growth rate in the fall was probably
due to increased food supply at this time. The growth and availability of juvenile
silversides (Menidia menidia notata) are shown to be of direct consequence in this
relation. The members of the 1934 dominant year-class averaged 2 cm. smaller than
the members of the 1933 and 1935 year-classes, neither of which were large, at similar
ages. This difference in size developed before these fish became 2 years old.
(8) A total of 3,937 striped bass have been marked by either external disc tags or
internal belly tags. Returns from these tagged fish, and the examination of commercial
catch records, show that there is a mass migration to the north in the spring and to the
south in the fall, and that the population in northern waters is stationary in the summer.
These migrations have their greatest intensity along the southern New England
and Long Island shores. They take place chiefly between Massachusetts and Virginia,
although bass north and south of these areas play some part in the migrations. The
Middle Atlantic Bight is undoubtedly the center of abundance for the striped bass over
its entire range, and tagging experiments indicate that there is little encroachment by
this stock on the populations to the north and south. Temperature undoubtedly
plays some part in the migrations, for in Connecticut waters they have been observed
to occur on each occasion when the water reached 7°-8° C. The migrations of the
striped bass, however, are not universal, for this species is caught through the summer
in southern waters and in northern waters in the winter. Those fish that stay north