66 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



turned over into Pecouic Bay by the line of islands stretching across the 

 eastern end of Long Island Sound. 



In this same way the Chesapeake schools are said to be detained for 

 some days by the projection of Cnpe Henry. 



The hypothesis of oceanic sojourn of the menhaden. 



90, The questions of hibernation and extended migration having been 

 considered, it only remains to discuss the third alternative, that of the 

 possibility of sojourn in the warm strata of the open ocean. 



In plate XII is given diagram sections of the North Atlantic Ocean 

 between Xew York and Bermuda, showing the soundings and isothermal 

 lines obtained in Her Majesty's ship "Challenger", April 24 to May 8, 

 1873. The vertical scale is necessarily enormously exaggerated, but the 

 diagram shows the presence of strata under the Gulf Stream, and be- 

 tween it and the American coast, the temperature of which exactly meets 

 the requirements of the menhaden. At a depth of 50 to 100 fathoms 

 there is a shoreward extension of the warm stratum of 50° to 55° which 

 extends inward one hundred and twenty miles. There are no means of 

 determining the corresponding isothermal lines on the coast of North 

 Carolina, but an extension of much less degree would approach very near 

 the shore in that region. The diagram represents the condition of the 

 sea temperature near New York at the very period when the menhaden 

 are approaching the coast in April, and a similar relation not improbably 

 exists in November, at the time of their departure. The schools of fish 

 swimming out to sea when the shore waters become too cold for them, and 

 driven below the surface by the winds of November, would naturally strike 

 these temperate strata, and being kept from descending deeper by the 

 uniform coldness of the waters below, as well as by the increasing pres- 

 sure, and their efforts to approach the shores being also opposed by a tem- 

 perature barrier, they would remain in the temperate strata until they 

 were enabled by the warmth of spring to regain their feeding grounds 

 near the shores. 



No authorities can be quoted in support of this hypothesis, but, in the 

 case of the menhaden at least, it appears to exj)lain more of the difficult 

 questions in relation to periodical movements than that of hibernation 

 or that of extended migration. 



(1.) It presupposes less sudden changes of temperature than that of 

 hibernation. It has been shown that hibernation of fishes is never vol- 

 untary, but Is a state of torpidity induced like that of cestivation by a 

 change of temperature and surroundings which they have no power to 

 avoid. Before entering upon hibernation or aestivation fishes retreat 

 to the deepest water, and only become completely torpid when they are fol- 

 lowed thither by the changed conditions of existence. In the fresh 

 waters of temperate regions fishes do not become entirely torpid in cold 

 weather, but are sufiiciently active to be taken with hooks from under the 

 ice. This is also the case in very deep waters in subpolar regions. The 



