GREAT LAKES COREGONIDS 



429 



the catches, and the sets showed a maximum of 0.5 fish per night per thousand feet 

 ■of net. When the gangs extended from 60 fathoms to greater depths bluefins were 

 less rare. Lifts made off Marquette, Mich., on August 11, 1921, in 100 to 80 fathoms 

 (record 6), off Kossport, Ontario, on October 4, 1921, in 80 to 90 fathoms (record 20), 

 off Michipicoten Island, Ontario, on June 22, 1922, in 80 fathoms (record 23), and 

 off Alona Bay, Ontario, on June 26, 1922, in 60 fathoms (record 26), showed fromlO 

 to 21 per cent of bluefins and from 1 to 6 fish per night per thousand feet of net. 

 The records from the 4^-inch trout nets in 60 fathoms and deeper (records 2 and 4) 

 show 25 and 10 specimens per gang, while those in or bordering on shallow water 

 (records 10, 14, 15, 18, 22, and 25) took from 1 to 6 specimens per gang. 



My findings that the bluefin prefers depths of more than 60 fathoms are corrob- 

 orated by the statements of fishermen who over a period of years fished bluefins 

 exclusively out of Grand Marais, Marquette, and Ontonagon in Michigan, Grand 

 Marais in Minnesota, and off Michipicoten Island in Ontario (records 3, 9, 12, 

 19, and 24). These men all agree that the species occurred most abundantly through- 

 out the fishing season, which extended from April to November, between 60 and 100 

 or 110 fathoms. 



Whatever factors determine the vertical distribution of the bluefin, it is clear 

 that temperature is not the only one, unless it be that the species prefers to inhabit 

 a zone of practically constant temperature, such as probably obtains along the bottom 

 in the deeper waters. The data in Table 13 indicate that in mid- June and up to 

 July the bottom waters to a depth of at least 25 fathoms are not warmer than 4°, 

 the temperature of the maximum density of water, and may be even colder. During 

 August, though the thermocline appears to be relatively near the surface, there is 

 evident a slight effect of warming down to 54 fathoms. In 60 fathoms and deeper 

 there is probably no warming above 4°. The bluefins seldom are taken shallower 

 than 60 fathoms and may spend their lives in water of nearly constant temperature, 

 little influenced, at least directly, by the seasonal temperature fluctuations that 

 affect the upper layers of the water. 



It has been intimated in the preceding discussion that the bluefins are no longer of 

 commercial significance in Lake Superior, but it once occurred there abundantly. 

 It has been possible to record some facts of their history, which the various fishermen 

 who were at one time engaged in fishing them have been able to supply from memory. 

 Definite dates given in the testimony have been fixed by association with significant 

 events in the life of the narrator and have been accepted without further research. 

 The first bluefins on the American shore, so far as I can learn definitely, were taken 

 out of Ontonagon, Mich., about 1897. They are recorded in the statistics of the 

 Bureau of Fisheries for that year. The Booth Fisheries Co., according to two of 

 its pilots (McArthur and McMillan), began to take the fish out of Michipicoten 

 Island about 1900. Out of Marquette, Mich., a fishery was started by W. J. Parker 

 in 1901. At Grand Marais, Minn., James Scott first fished them in 1903. They 

 were produced out of other ports at about the same time, but no definite dates are 

 ^available. 



For several years the bluefins supported a lucrative fishery. The tugs, in a 

 gang of the 334 to 3% inch nets, which were used exclusively, often made hauls of 

 2 or 3 tons; but, strange enough, the fish ceased to be economically important at about 



