66 KEPOET OF COMMISSIONER OF FISH AND FISHERIES. 



1877 was then colder tbau that of 1876 by 2o.7 at Easti)oit; by 0o.3 at 

 Portland ; by 2o.7 at Wood's Holl ; by lo.l at New London ; and by l^.o 

 at Norfolk. July, 1877, was colder than July, 1876, at Eastport by 2o.8 ; 

 at Portland by 2o.2; at Wood's Holl by 5o.9 ; at New London by 1^.2. 

 August, 1877, was colder than August, 1876, at Eastport by 0o.3 ; at 

 Portland by 0o.6 ; at Wood's Holl by (P.9 ; at New London by 3o.l, 

 September and October of 1877 were warmer than the corresponding 

 months of 1876 at Portland, and this agrees with the fact that the cntch 

 of menhaden in Maine was entirely made in the fall months. 



General discussion as to the winter habits of summer fishes. 



86. The relations of the temperature of the water to the movements of 

 the menhaden schools having been studied, a new question is at once sug- 

 gested. When the schools disappear from our coast, driven by falling 

 temperature, where do they go ! The answer must be in the form of a 

 theory, for no one has seen them during their winter absence; at least 

 QO one has been able to identify the New England and Middle States 

 fishes after their departure in the autumn. It is evident that there are 

 but three courses open to our coast fishes when it becomes necessary for 

 them to leave inshore — 



(1.) They may swim out to sea until they find a stratum of water corre- 

 sponding in temperature to that frequented by them during their summer 

 sojourn on our coast. 



(2.) They may swim southward until they find water of the required 

 warmth. 



(3.) They may descend into the abyssal depths of the ocean, there to 

 remain for a season in partial or total torpidity. 



The last of these theories is the least plausible, from the fact that 

 it necessitates the greatest change in habits. The susceptibility of the 

 menhaden to slight changes of temperature has been pointed out. Hi- 

 bernation in the oceanic depths involves a change to a temperature 10*^ 

 to 25° colder than that preferred by them in summer, as well as other 

 important changes in respect to specific gravity and pressure. 



The theory of hibernation discussed with special reference to the habits of 



the mackerel. 



87. The hibernation theory is a favorite one with the fishermen of the 

 British Provinces, and has recently received strong support from Pro- 

 fessor Hind, in his treatise on the fisheries of North America. His argu- 

 ments refer to the mackerel, although the scup, tautog, and herring are 

 included by implication. He refers to the appearance of the mackerel 

 " with scales on tlieir eyes ami blind," and suggests that the winter sleep 

 of fishes is probably much more general than is usually supposed. He 

 takes the position that there are only two alternatives possibly open to 

 fishes which cannof live in cold water. They must migrate south or 



