THE MACKEREL AND ITS ALLIES. 165 



to extensive migrations nortli and south along our coasts. These migra- 

 tions are believed to be carried on in connection with another kind of 

 migration Avhich 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^i, 1873. Having expressed certain views concerning the 

 Avell-known phenomenon of the migration of the herring and shad, he 

 continues : 



" The fish of the Mackerel family forna 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, 

 'vvhich at present constitute the only material available as a basis of such 



