±o Nonsjcisten:.,, 



2o Crnsidered frotr or'-'^lrlnary examination as not s-Jiitable for 

 the reproduction of sea lampreys. 



3o Tributaries not in need of examination because extensive 

 potential spawning habitat had already been found in the 

 watershed. 



Detailed data were collected for all of the 178 streams examined 

 in 19^1 (tables 17-22). The 1951 survey was less extensive than that 

 of 19^0 in that most of the minor tributaries of each watershed were 

 not examined. 



However, all of the 3l5 watersheds flowing directly into Lake 

 Superior from the Tahquamenon west of the Michigan-Wisconsin border 

 (1950 and 1951 survey areas) have now been examined in sufficient 

 detail for the purposes of this surveyo 



Streams with a large productive potential (Space for more than 



' ~~ " "^ 75 nests) t 53 



Streams with a medium productive potential (Space for 6 to ?5 nests) s 11? 



Streams with a small productive potential (Space for 1 to 5 nests) s 75 



The standards on which the above groupings are based are, of course^ 

 arbitrary and are intended only to provide a convenient s3''stem of classi- 

 fication. Productive potential is defined as the capacity of a stream 

 to produce sea lampreys, expressed as the number of nests which may be 

 constructed on the spawning sites available when; 



1. Certain less variable factors such as quality of gravel 

 (Spawning material), gradients, velocities, and stream 

 sizes are believed to be satisfactory for reproduction. 



.2. Highlj/- variable factors such as temperature and effects of 

 freshets^ which cannot be accurately evaluated (in m.ost 

 situations) on the basis of available information, are 

 considered as favorable. 



3. S'jrvival of larvae from the nests may be anticipated to be 

 normal. 



Streams in which adult sea lampreys were observed or reported (see also 

 table 2377 



1950 survey areas 7 (Additional records available from 1951 

 rechecks will be presented in a later report.) 



1951 survey areas none (Most of the streams were examined after 

 the spawning season.) 



