THE MACKEREL AND ITS ALLIES. 165 
to extensive migrations north and south along our coasts. These migra- 
tions are believed to be carried on in connection with another kind of 
migration which I have called ‘‘ bathic migration,’’ and which consists in 
a movement, at the approach of cold weather, into the deeper waters of 
the ocean. The menhaden and many other fishes have these two kinds 
of migrations, littoral and bathic. The sea-herring, on the other hand, 
has extensive littoral migrations and probably very slight movements of a 
bathic nature. In some the latter is most extended, in others the former. 
Anadromous fishes, like the shad and the alewife, very probably strike 
directly out to sea without ranging to any great degree northward or south- 
ward, while others, of which the Mackerel is a fair type, undoubtedly 
make great coastwise migrations, though their bathic migrations may, 
without any great inconsistency, be as great as those which range less. 
Upon this point I cannot do better than to quote from a manuscript 
letter from Prof. Baird to the Hon. Hamilton Fish, Secretary of State, 
dated July 21, 1873. Having expressed certain views concerning the 
well-known phenomenon of the migration of the herring and shad, he 
continues : 
‘« The fish of the Mackerel family form a marked exception to this rule. 
While the alewife and shad generally swim low in the water, their pres- 
ence not being indicated at the surface, the Mackerel swim near the sur- 
face, sometimes far out to sea, and their movements can be readily followed. 
The North American species consist of fish which as certainly, for the 
most part at least, have a migration along our coast northward in spring 
and southward in autumn, as do the throngs of pleasure-seekers, and their 
habit of schooling on the surface of the water enables us to determine 
this fact with great precision. Whatever may be the theories of others on 
the subject, the American mackerel-fisher knows perfectly well that in the 
spring he may find the schools of Mackerel off Cape Henry, and that he 
can follow them northward day by day as they move in countless myriads 
on to the coasts of Maine and Nova Scotia.’’ 
The movements of the mackerel schools, like those of the menhaden, 
appear to be regulated solely by the temperature of the ocean. 
In my essay upon menhaden, which has just been referred to, I have 
attempted to show, in a preliminary way, the relations of the movements 
of the menhaden schools to the temperature of the water at different 
stations along the coast in accordance with certain crude observations, 
which at present constitute the only material available as a basis of such 
