streams observed in 1953 was 143 males to 

 100 females. In the first year of operation 

 in northern Lake Michigan streams, the sex 

 ratio of 6,559 lampreys was 219 males to 100 

 females (table 6). 



Lengths and weights of sea lampreys in 

 spawning runs entering index streams of Lake 

 Superior and from one stream on Lake Michi- 

 gan (tables 7 and 8) permit a number of com- 

 parisons. The average total length for 3,939 

 Lake Superior specimens (sexes combined) 

 was 18.1 inches in 1954- -0.4 inch above the 

 mean 17.7 inches for 263 lampreys measured 

 in 1953 . The average length of 572 lampreys 

 taken in 1954 from Rapid River, tributary to 

 Lake Michigan, was 17.7 inches. In 1954, 

 the mean weight of 2,474 lampreys from Lake 

 Superior streams was 225.6 grams (7.9 ounces), 

 which was closely similar to the average weight 

 of 226.8 grams (8.0 ounces) for 279 lampreys 

 from the Chocolay Riverain 1953 . The average 

 weight of 572 specimens from Rapid River on 

 Lake Michigan was 174.2 grams (6. 1 ounces). 



The differences in weight of the sea lam- 

 preys from the two lake basins is probably 

 due to the loss of the principal food species 

 (lake trout) in Lake Michigan. The abundance 

 of lampreys in Lake Michigan has reached the 

 point where lack of food prohibits maximum 

 growth of the lamprey. This phenomenon was 

 noted in Lake Huron in 1951 (Applegate, Smith, 

 and Patterson, 1$52). As the population of 

 sea lampreys increases in Lake Superior, a 

 reduction in their size should become apparent. 



Electrical features of streams 

 and related problems 



Each stream appears to have its own elec- 

 trical characteristics, and problems of control 

 vary accordingly. These characteristics af- 

 fect the power consumption, the intensity of 

 the electrical field, and the dispersion of the 

 field relative to the, electrodes and the trap. 

 They do not prohibit the establishment of an 



effective barrier in the water with one of 

 the three standard types of electrode arrays. 

 In all of the streams, the electrical field 

 remained an absolute barrier to the up- 

 stream passage of sea lampreys regardless 

 of changes or fluctuations in the electrical 

 characteristics. 



Information collected to date on 

 electrical fields at the barriers has added 

 little to the data discussed by Applegate, 

 Smith, and Nielsen (1952). The same 

 equipment (as described by them) was used 

 to obtain the information . Electrical data 

 from 31 streams included measurements 

 of current flow around and between elec - 

 trodes, intensity of the field, ratio between 

 resistivities of the stream bottom and of 

 the water, conductivity of water, and power 

 consumption. Preoccupation with problems 

 of installation and operation of structures 

 during the season prevented a scheduling of 

 measurements at selected index streams. 

 Failure to obtain these periodic measure- 

 ments makes it necessary to speak only in 

 generalities . 



Fluctuations of temperature, volume, 

 conductivity of the water, and immersed 

 surface area of electrodes influence the 

 electrical field in the streams. Changes 

 in these factors appear usually to compen- 

 sate for one another. For example, as 

 water levels decrease in streams with Type 

 A and Type B electrode arrays, the con- 

 ductivity of the water increases; but the 

 intensity of the electrical field remains 

 nearly constant because of reduction in the 

 surface area of the immersed electrode . 



The change in water conductivity also 

 results in a change in the ratio between 

 bottom and water resistivities . It would 

 seem best to install a control device where 

 the bottom resistance exceeds that of the 

 water. Information obtained to date, how- 

 ever, indicates that a satisfactory electrical 



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