428 



BULLETIN OF THE BUREAU OF FISHERIES 



part, from the use of special 2 Yi and 2% inch nets set out of various ports on the 

 lake and are supplemented by the testimony of various fishermen. These records, 

 26 in number, show that the bluefin formerly was taken in commercial quantities 

 out of many ports on the lake and that they still occur, if only sparingly, in suitable 

 areas of the lake. 



BATHYMETRIC DISTRIBUTION 



The special nets used in the survey of the lake, which were set at depths of 15 

 to 100 fathoms (see p. 382), took at least one specimen of nigripinnis at every set 

 excepting one set off Ontonagon, Mich., and those sets made in 1923 in the bays and 

 straits along the north shore. A few specimens also have been found in the 43^-inch 

 nets set along the shore banks (records 10, 15, 18, 22, and 25). It is certain, there- 

 fore, that a few individuals, at least, stray into the shallower waters. The records 

 do not indicate the maximum depths at which the species occurs, but the testimony 

 of the commercial fishermen who at one time fished for the species establishes 100 and 

 110 fathoms as the greatest depths at which nets were set. The general chart of 

 Lake Superior shows that much of its area is overlaid by more than 100 fathoms of 

 water (a depth of 196 fathoms is known), but the fishermen do not set nets at greater 

 depths on account of the strain on them in lifting and on account of the effect of the 

 extreme pressure on their floats. It is safe, however, to predict that if fish were abun- 

 dant in the deepest water, the nets would be placed there, and it is certain, therefore, 

 that the center of abundance of the bluefin is or was in less than 100 fathoms. There 

 are various conjectures as to what may inhabit the deepest waters, but there are 

 few data on that point. Mr. Parker, of Marquette, informs me that once, north- 

 west of Stannard Rock, his gang of 4j^-inch trout nets fell into a hole that flattened 

 the corks on half a mile of his netting and that these nets caught no other fish than 

 the lawyer (Lota maculosa) , but that the lawyer was abundant. (The chart shows 

 a maximum sounding of 115 fathoms for this area, though a greater depression of 

 small extent might occur easily.) 



One may conclude from the foregoing that the bluefin ranges from 15 fathoms 

 into more than 100 fathoms, but that the maximum density is to be looked for nearer 

 the upper limit. 



RELATIVE ABUNDANCE 



In none of the lifts did the bluefin occur more than casually, but it is possible 

 that the nets employed were of too small mesh to take the fish. The fishermen in 

 Superior found that nets could not take bluefins in commercial quantities if they were 

 of smaller mesh than 334 inches, and the experience of Michigan and Ontario fisher- 

 men has been the same for the nigripinnis of these lakes. It would appear that the 

 smaller individuals of the species did not school with the largest examples or kept 

 farther above the bottom. In lifts made from gangs extending into less than 60 

 fathoms, off Iroquois Light on June 14, 1922, in 38 fathoms (record 1), off Marquette, 

 Mich., on August 8, 1921, in 42 to 65 fathoms (record 5), off Ontonagon, Mich., on 

 August 25, 1921, in 20 to 38 fathoms (record 11), among the Apostle Islands on 

 July 11, 1922, in 15 to 20 fathoms (record 13), off Duluth, Minn., on July 17, 1922, 

 in 30 to 40 fathoms (record 16), and off Grand Marais, Minn., on September 14, 

 1921, in 30 to 65 fathoms (record 17), bluefins made up not more than 3 per cent of 



