504 



BULLETIN OF THE BUREAU OF FISHERIES 



they can be caught, in some numbers at least, in the pound nets all summer. There 

 is probably also a close relation between temperature and their food, but this matter 

 is not yet understood. 



It may be seen from Table 13 that the waters of Lake Superior probably never 

 become very warm, compared with those of other lakes in the same latitude. The 

 warmest temperatures, it appears, are recorded from Black Bay, Simpson Channel, 

 and Moffat Strait, where conditions are much more tempered than in the open lake; 

 but even here the highest surface reading of 16.3° is less than one of 19.5° recorded 

 from a location in Lake Nipigon some 75 miles farther north two weeks earlier in 

 the season. It is seen, also, that the temperature, even in midsummer, drops off 

 rapidly below the surface, except in Black Bay, which is so shallow and isolated that 

 its conditions approach those of an inland lake, so that at 4 fathoms in Moffat Strait 

 and Armour Harbor the temperature readings are 9.7° and 9.8°, and at 5 fathoms 

 in Simpson Channel the thermometer reads 6.6° (records 22, 25, and 15). It is 

 apparent, then, that the herring do not have to undertake a very extensive vertical 

 migration to find cold water, and that if food is present near the surface there are 

 probably no other physical factors that deter them from taking advantage of it. 



BREEDING HABITS 



The inshore fall migration is for the purpose of spawning. The grounds fre- 

 quented by the largest schools are those around the Apostle Islands and in Thunder 

 Bay. Apparently there are also favorable areas for spawning along the Minnesota 

 shore, but they must be quite restricted in area and must extend along the shore. 

 There are doubtless many grounds of less importance than these all along the lake 

 shore. The bottom frequented varies from clay and mud in Thunder Bay to gravel 

 and bowlders along the Minnesota shore. Sand is selected commonly on the south 

 shore, probably because the shoals are sandy in this area. The depth of spawning 

 varies, according to the fishermen, from a few feet to 25 fathoms. The statement 

 of James Scott that the nets are floated during the spawning season 7 fathoms below 

 the surface indicates that possibly spawning takes place off the bottom. The 

 apparent indifference of the species to the character of bottom may support this view. 

 The spawning season usually embraces about the last two weeks of November. 



VALUE AS FOOD 



The herring of Lake Superior are, in large measure, salted in kegs, but some 

 are frozen for consumption in the fresh state. The quality probably is not materially 

 different from that of the Michigan or Huron varieties. 



ABUNDANCE 



The herring fisheries around the Apostle Islands are old and are famous through- 

 out the lake region for their productiveness. Those in Canadian waters, situated 

 chiefly in Thunder Bay, are not much more than 10 years old. In years past the 

 herring have been taken in quantities sufficient only to supply the demands of a class 

 of trade that wanted cheap salt or fresh fish, and the prices paid the fishermen have 

 been so low that they could afford to fish only because fish could be captured easily 



