286 BULLETIN OF THE BUREAU OF FISHERIES. 
both, according to the size of the fish; at a greater or less depth, and, if not 
dormant or hibernating, that they are more or less inactive and disinclined to 
rise to the surface, where the temperature and other conditions are so variable 
and subject to sudden changes; that is to say, they are residing quietly at a 
depth of comparatively constant and uniform temperature, but of such degree 
that the fish are disinclined to activity, therefore requiring no food, but sub- 
sisting, as it were, upon the accumulated fat of the previous festal period. The 
regions, too, where, under this hypothesis, the fish reside are different for those 
of different sizes; in this instance, however, not on account of different feeding 
habits, but owing, perhaps, to the instinct of self-protection. 
It is a well-known fact, as has been previously stated, that young or small- 
sized menhaden, up to 6 or 8 inches long, linger in the bays long after the larger 
ones have disappeared. It would therefore seem that the smaller fish are either 
less susceptible to the changes due to approaching winter, or that some other 
force predominates over their inclination to leave. 
Granting, then, that the foregoing assumptions are true, when spring brings 
milder weather and less rigorous and sudden changes, the fish appear at the 
surface and their movements are again to some extent observable. 
Regarding adult mackerel, it is known that these movements or so-called 
‘‘migrations’’ precede the spawning process, but in immature fish—‘‘ blinks,” 
‘* spikes,” ‘‘tinkers,”’ etc., which have like movements—this can not be so. In 
menhaden as a whole it is not evident that the spring ‘‘migrations’’ are for 
spawning purposes. In the adult of both species the growing ova and milt 
doubtless warn the fish of the approaching ‘‘critical period,” but this can not 
be the case with the immature fish. What, then, is the impelling force that 
causes the fish to come to the surface and move about in definite or indefinite 
directions? If the previously suggested hypothesis is still followed, it may be 
reasonably assumed that the fish, having consumed their accumulated fat, are 
impelled by their desire for food. If such is the case their movements will be 
in search of food and in the line of least resistance. Their subsequent move- 
ments also, except as controlled by the breeding instinct, whether at the surface 
or below, will be for food, although they may be directly and indirectly affected 
by the same meteorological conditions, such as light, temperature, ete. When 
feeding the schools do not seem to move about very fast in any direction; there- 
fore when in rapid motion they are probably in search of ‘‘ pastures new.”” In 
support of this is the well-known fact that fish are seen going swiftly in directions 
exactly opposite to those that should be followed according to the ‘‘ migratory’’ 
or breeding instinct. Such movements are usually, and sometimes correctly, 
ascribed to enemies heading them off and driving them in that direction. But 
if this were true in every case there should be, and surely would be, some further 
evidence of the enemies; for whenever the fish have been observed to be pursued 
by predaceous animals these animals are quite conspicuously manifest. 
