Fishery bulletin of the Fish and Wildlife Service - NOAA

BIOLOGY OF THE ATLANTIC MACKEBEL 163
to be desired, present information supports the view that the present survey has covered
the most important spawning ground.
The existence of large regions with little spawning near the middle of the spawning
range of the species is a peculiarity that may be explained by hydrographie conditions.
It will be noted from the diagrammatic representation of relative intensity of spawning
in figure 3 that the regions of greatest intensity are the southern and northern quarters
of the spawning range. That of the least intensity is the middle half of the range.
The places of intense spawning, that is, the great oceanic bight between Cape Cod
MACKEREL SPAWNING ARCAS.
LITTLE SPAWNING ••• TOW3 AVERAGE-O-VO-EGU
MODERATE SPAWNING-TOWS AVERAGE «o DOO coos
MUCH SPAWNING TOWJ AVERAGC-OVEMOOOÍGSS
F шив E 3.—Relative Intensity of mackerel spawning In various regions along the Atlantic coast of North America, as Indicated
by the average number at eggs caught In plankton nets.
and Cape Hatteras, Cape Cod Bay, and the southern half of the Gulf of St. Lawrence,
have this in common: they are all bodies of relatively shoal water overlying relatively
flat bottom, where topography and circulation favor vertical stability, and vernal
warming of the upper strata proceeds rapidly, producing temperatures suitable for
mackerel spawning earlier than in the intervening areas. On the other hand, the
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