total catchj 32,171 individuals were taken in Control Zone H-1, 

 I|.2,930 were captured in the Wisconsin control devices, and the remain- 

 ing 321 lampreys were taken from the two streams tributary to Lake 

 Superior. Biological data were reviorded for many of these lampreys 5 

 all individuals were subsequently dcjstroyed. These catches ccre siim- 

 marized in table 1 iiriiere the jJidividvAi totals by strean and by iaK:e 

 basin are given. 



Relative abundance r.f sea lampreys 



Lake Huron. — The sea-lamprey population in northern Lalce Hurori., as 

 Indicated by the size of the spawnlig runs captured, apparently conbin- 

 ued to maintain itself at the pealc level of its abundance ior a:tiother 

 season. The total run in the Ocqueoc River was 19,393 sea lampreys in 

 the 1951 season as compared to 18,822 in 1?50 and 2l|.,6l4.5 in 19U9. As 

 in 1950, a considerable number of migi'ants from the adjacent lake ar-ea 

 was "siphoned-off" by trappijng operations in other streams in the virgin- 

 ity; this reduced the total catch in the Ocqueoc River to a cer-^-.ain ex- 

 tent. Consideration of all factors would indicate that, numerically 

 spealcing, the runs in the three seas./ns were of comparable sise. 



Most of the catches in the snail .streams of Control Zone H-l were 

 considerably less than for the previ.ou3 year. At first thought this de- 

 crease would seem to indicate a declij.ne in the sea-lamprey population. 

 Actually, these small catches were the I'esult of the blcoking of the 

 stream mouths by sand ba::'s sevei-al t?jr.es during the period of upstreejn 

 migration. High lake levels, ?-ow stream disch.arges, and strong w3.nds 

 all contributed to unusual bari'ier-ba:'" formations during the 19^1 season. 



All available records of spaivirLig runs of sea lampreys into the 

 streams of northern Lake Huron (Uriited States -viraters) arre assembled in 

 table 2. Those records for the Ocqucioc River demonstrate the phenomenal 

 increase in the population in the yea:;'f 19W-i- to 19li.9 and the st!.bsequent 

 leveljjig-off of that population -when fish stocks in the nci'^/heiT. areas 

 of the lalce were reduced almost to the point of disappeai'anca (fig. 2). 



Lalce Michigan. —In the streams ti'ibutaj:y to noi'thwfistem La.ke Mich- 

 igan, ~tvelr"~an3~trap catches coutinuec. to ?.'eflect the explosive increase 

 of the species in these waters. In 19^1, sea-lamprey spaTjning runs in 

 six Wisconsin streams were nearly thiree times as lai-ge as those dntei-- 

 ir.g the same streams the previous yea::'. In 19^0, I6jli.l0 spawning mi- 

 grants were taken in six control devices; in 1951^ U2,980 inoAi^-iduals 

 vrere captured. All available records of spawning runs entering thes'5 six 

 streams are presented in table 3« The spa'swriing runs captur^sd :ji Hibbards 

 Creek, Door County, Wisconsin demonstrate most dramatically the enonnous 

 increase in the nujabers of sea lampreys in the lalce since 191;.'? (babla 3 

 arid fig. 2). 



The data collected in 19^1 give no indication that the sea lamprey 

 population in Lake Michigan has yet c>tf.ained the peak of its ab-o:adancft, 

 Maxjjn'om abundance and a leveling-off in tiumbers of the lam-prey popula- 

 tion in northern Lake Hui-on followed by several years the vix'^mal 



