552 NATURAL HISTOEY OF AQUATIC ANIMALS. 



the year when the temperature of the water is very high (from the middle of July till the middle 

 of September), or very low (January to March). The observations of the Scotch and Dutch mete- 

 orological societies made during the Scotch and Dutch summer herring fisheries have shown that 

 the temperature of the water most favorable to these fisheries is about 13 0. (55.4 P.). During the 

 Scotch winter fisheries, however, the temperature of the water ranges from 4.5 C. to 5.5 C. (40.l 

 P. to 41.9 P.), and during the Norwegian spring herring fisheries it only ranged from 3 0. to 

 4 C. (37.4 F. to 39.2 P.). But our observations are still so incomplete, and relate so exclusively 

 to the spawning Herrings, that it is impossible to say anything with absolute certainty excepting 

 the fact that the Herrings, when the temperature of the surface waters is either too high or too low, 

 go to deeper waters." 



The theory advanced by Ljunginan in this last sentence is perhaps a little premature. Is 

 it not supposable that local races of Herring exist and perform the various functions of life in 

 totally different scales of temperature? This is undoubtedly the case with sedentary fresh- water 

 species, such as the black bass, which, in its extreme northern range in North America, lives in 

 waters which in midsummer are colder than those which southern fish ever experience even in 

 winter. This view is not presented as a new one, but simply for the sake of introducing the 

 illustration. 



MIGRATIONS AND MOVEMENTS. In Ljungman's report on the fisheries of Bohuslan, already 

 quoted from, 1 is given the following recapitulation of the different scientific theories that have been 

 in the past and are now heard concerning the migrations of the Herrings : 



" In briefly recapitulating the different scientific theories regarding the migrations of the 

 Herrings, it will be found that they may all be arranged under the following heads: 



"a. The theory of a central race of Herrings, according to which all Herrings which are in the 

 world belong to one great central race, from which all kinds of Herrings, both great and small, 

 come. This theory is varied as follows: 



" 1. This central race of Herrings is supposed to live in the northern Polar Sea, from which 

 large schools emigrate every year to those coasts where herring fisheries are carried on (Anderson, 

 Pennant, and others). 



"2. This central race of Herrings is constantly moving through the Northern Atlantic Ocean 

 in a circle, whose extent is regulated by the declination of the sun (Gilpin). 



"3. Besides this great central race oi Herrings living in the Northern Atlantic Ocean, causing 

 the great herring fisheries, smaller local races having separated in course of time, causing the 

 smaller coast fisheries (Luudbeck). 



"According to the first two of these three theories there would be no regular migrations, whilst 

 such would take place according to the third. 



"&. The theory of separate races of Herrings, according to which the different fisheries are 

 caused by separate races of Herrings, each having its own locality. This theory is varied as follows : 



"1. The theory of a coast race of Herrings, considering the Herring exclusively as a bottom 

 fish. This may again be subdivided: 



"a. Some suppose that there is only one local race of Herrings in every place, which, if not 

 driven away by human agencies, always stays near the coast, There is consequently no difference 

 between coast Herrings and sea Herrings, and there are no regular migrations (Nilsson). 



" b. Others think that more than one race of Herrings may occur in one and the same place. 

 There is consequently a difference between coast Herrings and sea Herrings, and there are regular 



'Report, United States Fish Commission, part vi, p. 218. 



