S oandai'ds and methods 



Criteria used i;. esoiraating the productive potentials of Lake 

 Superior basin streams were established during a studj'- of the life 

 history of -".re sea lamprey by Applegate (1950), 



The life history of the sea lamprey in the Great Lakes can be 

 summarized a.s follows « In the spring the adults ascent streams and 

 spawn on gravels After a short period of incubation the eggs hatch 

 and the larvae emerge,, These larvae, carried downstream by the current, 

 dive for and burrow into the bottom when quiet water is reachedo 

 Metamorphosis takes place after a larval life of about h years « The 

 resulting sexually immature adults are carried by high water to the 

 lakes where the parasitic life of 12 to 20 months begins « 



For successful completion of the stream phases of the life cycle, 

 certain known basic conditions among others must prevail in the streams. 

 Suitable larval habitat consisting of soft (sand or silt) bottom 

 material must be present in the streams proper or in their estuaries. 

 In order to spawn, adult lampreys req-ulre (1) water temperatures of 

 about 53° Fo or above, (2) water velocities of 1 to 5 feet a second, 

 and (3) the presence of suitable gravel formations (or other hard 

 elements such as clam shells) for nest building (Applegate 19^0) « 

 These factors were found to be of optimum quality in certain streams 

 when (1) water temperatures were between 60° Fo and 70° ¥<,; (2) water 

 velocities ranged from 1 to 3 feet a secondj (3) stream-bed formations 

 consisted of concentrated grav^tel of ideal size (3/it inch to 3 inches in 

 diameter) in bars or ridges which formed riffle areas » These criteria 

 are based on studies of lampreys in streams flowing into Lakes Huron and 

 Michigano It is suspected that spaiming may be inhibited in many Lake 

 Superior streams by certain conditions which are common in that area, 

 such as colder water temperatures, steep gradients, sudden freshets, and 

 heavy turbidity due to lake clay. 



The streams were examined by walking or canoeing along their courses 

 for the distance required to determine their productive potentials j if 

 abundant spawning habitat or an obvious barrier was found in a stream 

 section just above the mouthy, examination of that stream was discontinued! 

 streams in which gravel was lacking were surveyed from mouths to head- 

 waters to make certain of the lacko 



Standardized methods and techniques were employed so far as it was 

 practical to do soo The necessity for covering a large amount of terri- 

 tory demanded deviation from preferred methods (usually the employment 

 of visual estimates instead of measurements) often enough to wai-rant an 

 explanation of those actually used in this particular survey. 



