average, to-'cal length of the runs in Carp Creek has decreased 9 percent 

 (1,6 inches) from a maximum of 17.1!. inches in 19U7 to 1^.6 inches in 

 1951. In samples from both Carp Greek and the Ocqueoc River, the aver- 

 age total length declined betvreen O08 sxid 0.9 inch in the period I9I1.9 to 

 19.5l-» The average \veight of migrar.ts entering Cai'p Creek has decreased 

 about 33 percent (approximately 70 g.cmi3) during the ^--year period. 



Arjy further decline in the size of mature spawning migrants -will 

 profoimdly affect any proposed control program based on the operation of 

 T/eirs and traps. Further reduction of 'tveir screen or grate aperatures 

 below the l/2-inch spacing now required will create e:5rtremely difficult 

 operational problems during spring flox.s. 



The spaivning runs in Carp Creek and the Ocqueoc River in 19^1 did 

 not differ in character or in their response to cer-t.ain factors in the 

 environraent vary from these vane occu.';"::';j.ig in the same str-eans in pru- 

 vioiis years. Data pertaining to the runt, in these tvro streams in 19^1 

 are presented in tables 9} 10, and 12; s^jnilar information for the runs 

 occurring in 1950 has been presented by Applegate and Smith (19^1) and 

 for the years 19l;7, 19U8, and I9U9 by Applegate (19^0) . Strict compai-i- 

 sons of the character of the Ocqueoc River run in 19bl in relation to 

 time of migration and response to variov.s environmental factors should 

 not be made T/ith those runs of former years. Daily and periodic catches 

 in this i-iver (as detailed in table IC) were strongly influenced b3- the 

 operation of an e^rper-imental electromechanical weir and trap located below 

 the permanent Ocqueoc River installatioxi. Experimentation with this new 

 de\ace was carried on intermittentlly fi'om May 1 to June l5« During the 

 periods of effective operation of the eJ.ectromechanical iveir, many or all 

 lampreys "vvBre blocked below the electrodes and did not enter the traps in 

 the pe;:Tiianent installation until the ele^jtrical device became 5_noperative . 



New developments and furt her evaluation of mechanical 

 control devi 'c'-fis 5/ 



Barrier dams. — The experimental bar:-ier dam in the Black River, 

 Mackinaw Coimty, Michigan, which was designed to block aiid divert spawn- 

 ing runs of sea lampreys was rebuilt by the Michigan Department of Conser- 

 vation during the winter of 19^0-51 (fig';"'. 3 and i;)o A trap, which was 

 installed in the wall of the original c'am, was removed and the cur-vod 

 steel lip attached to the face of the dan was extended further across the 

 strear.1. These changes enabled the str-.ir/jure to handle ivith greater facil- 

 ity the large discharge of the Black Riv'?-;r during the spring runoff. 



5/Fi.ve types of mechanical control de'Ticos have been developed to date: 

 Xl) large, permanent type weirs and tri.ps for capturing spawning i-uns, 

 (2) and (3) portable-type iveirs for use in medium- and small-sized streams 

 for capturing spawning runs, (li) dams ai:d inclined-screen trap units for 

 captiiring 7/^oung, downstream migrants, aiid, (5) barrier dams for blocking 

 and diverting spa-vming runs. The essential characteristics and the liiTiita- 

 tions of these devices have been described in an earlier report (Applegate 

 and Sirdth, 19^1). 



31 



