Fishery bulletin of the Fish and Wildlife Service - NOAA

42 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE
populations farther south, and second, that they are made up of individuals of mixed
origin—that is, that the northern stocks are added to by the migrants from the south.
The southernmost return of a striped bass tagged in Connecticut and Long Island
waters was from the northern tip of Pamlico Sound, N. C. It is probable that the
striped bass of the Southern Atlantic Bight—that part of the coast of United States
south of Cape Hatteras—are a completely separate population, that may possibly be
added to under rare circumstances by the stock from the Middle Atlantic Bight—
Cape Hatteras to Cape Cod—and it seems reasonable to expect that the striped bass
population of the Gulf of Mexico, which presumably extends as far west as Louisiana
is entirely isolated.
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 comparatively
little encroachment by this stock on the populations to the north and south.
This is well in keeping with the conclusions of Parr (1933), who has shown that the
shallow-water fish population of the highly heterothermal Middle Atlantic Bight is
bounded on the north by a cold-water barrier in the Cape Cod-Nantucket Shoals
region in the summer, and on the south by a warm-water barrier at Cape Hatteras in
the winter. Parr (loc. cit.) has pointed out that ". . . hi neither locality are such
barriers found to be a permanent feature during all seasons." But in the case of the
striped bass they exist at those times of year when they are most effective in keeping
the bulk of the population of the Middle Atlantic Bight from encroaching on the areas
to the north or south. Thus the cold-water barrier at Cape Cod in the summer marks
the end of the northern migration in normal years, and the warm-water barrier at Cape
Hatteras in the winter may play some part in delimiting the extent of the southern
migration, and so at least partially separate the populations north and south of this
boundary.
The question as to how much temperature influences the migration of the striped
bass is one of particular interest. This is a highly eurythermal species, yet temperature
variations well within the maximum and minimum limits appear to play some
part hi determining the time of migration. It seems to be more than coincidence
that the times when the first striped bass of the year were taken—hi April 1936, 1937,
and 1938—and the times that the last ones of the year were caught—hi November 1936
and 1937—hi the Niantic River, Conn., were always when the temperature of the
water was approximately the same, 6.0° to 7.5° C. (42.8° to 45.5° F.) (see fig. 30).
Moreover, the migration of striped bass on the outer coast of North Carolina in late
March and early April 1938 was observed to take place over a period when the water
temperatures averaged 7.0° to 8.0° C. (44.6° to 46.4° F.).
The migrations north in the spring and the return to the south in the fall do not
include all striped bass, for this species is caught consistently through the summer in
southern waters and not uncommonly in northern waters in the whiter. It is a relatively
small percentage of the stock that remains north in the winter months. However,
those that do stay north are of two types—the individuals that form the resident
more or less isolated populations of the north Atlantic, and those that may have had
their origin farther south but spend an occasional winter in northern waters. The
latter may possibly bolster the northern spawning stocks, but are often composed of
individuals that are not spawning in that particular year, for this species is not necessarily
an annual spawner (see p. 16). Striped bass that do remain in the north
through the whiter months apparently become dormant and inactive hi many cases
and actually hibernate to much the same extent that has been described for the black
bass (Micropterus dolomieu) in the northern part of its range by Hubbs and Bailey
(1938). Their easy capture through the ice by scoop nets and by gigging testifies to
their sluggish state in cold water, and the outward appearance of individuals taken in
the whiter and extremely early spring often shows that they are in poor condition.
Striped bass certainly undergo partial hibernation as far south as New Jersey, the
extent of this southern limit undoubtedly being determined by the prevailing temperatures.
Dormant individuals are most commonly taken in northern waters during the
whiter hi shallow bays and in the brackish waters of estuaries. Thus it appears that
although temperatures from 6.5° to 8.0° C. play some part in causing the migrations of
this species, their effect is not universal. It may be that the first and last fish of the