dczTOC of Ecarrin;: in coiijunction vlth a '..locllns in abundance of 

 these species provides sx-:e circumstantial evidence that t'le sea 

 lainpreys are currently increasin'-; in nirnbers. TirVO factors must be 

 considered^ hovrever, in evaluatinr this latter ei,idence: (1) 

 suckor populations are reportedly sufferinr a cyclic decline in 

 abundance at the present tb:o in vrhicli the la-ipreys r.iay onlj be an 

 acceleratin:; factor; and, (2) lake trout, upon Tri;ich la:'.preys seem 

 to prefer to feed are now relatively scarce in Lake Huron. 17ith 

 the reduction in nuinbers oi this species and -srith lamprey stocks 

 increasing.;, there vrould naturally f ollov; some diversions of la-!- 

 preys to other fishes, 3vidence collected both at ^veirs and in the 

 co.::ercial fisheries indicate that the Lalce Iharon suc'cer population 

 r;ay noT."- be bearing; the brunt of such a shift, 



So"e biological charr^cteristi zs of spaTmin; runs 



(1) Se:: ratio and differential- r.i: ration of sexes 



Of the 1,617 sea lar-preys talcen in the Carp Creek iveir in 1/U7, 

 se:c data iTcre obtained fron 1,600 specimens. Of these 1,600 sea 

 lar.ipreys, 997 or 62,3 percent -.TOre r.ales and 603 or 37.7 percent 

 vrere females. This is a ratio of 165 "ales : 100 fem.ales. Of 2,939 

 sea laiipreys taken in tlrie same vreir in 19)43, se;: data vrsre obtained 

 from 2,931 specii-iens. Of these, l,32li. or 62,9 percent vrere 

 males and 1,039 or 37,1 percent T;ere females. This is a ratio of 

 169 males : 100 females. In 19h9, the sex of all sea lampreys com- 

 prising the run, 2,763 individuals, vras determined. Of these, 1,366 

 or 67,!? percent were riales and 397 or 32.5 percent were females. 

 The resultant ratio is 2O0 m.ales : 100 females. 



In the Ocqueoc Pdver in 19U7, 679 sea lampreys were examined 

 for sex data. Of these, 36U or 53^6 percent were males and 315 or 

 kSth percent were females. This ratio of 116 males : 100 females 

 is open to question since data on the sex composition of the entire 

 run and any differential migration by sexes is lackinr;. Of 2li,6U3 

 sea lampreys taken in the Ocqueoc River in 19U9, 16,793 or 68.2 

 percent were males and 7^314.5 or 31^ 8 percent vrere females. The 

 sex I'atio v/as 2lh males : 100 females. 



A trend tov^ard an increasing proportion of males amonc mature 

 lamprey's composing the rvms is evident in these fi;Tjres. The 

 sli:;ht proportionate increase in the numbers of males betv/een 19U7 

 and 19U8 is not necessarily sicnificant but that increase occurrinc 

 between 19i|.8 and 19U9 most certainly is indicative of a i;;rovri.ng 

 im.balance in the population. I do not believe that even the 

 earliest sex ratio recorded (Carp Greek, I9I1.7 — 165 males : 100 

 females) is a natural ratio for the species, v;hich if their spav.n- 

 inc habits are any indication, must possess ■under noiTial circujiistances 

 a near-balanced or balanced sex ratio. In support of this contention, 

 is a sample of 52 ocean-run sea la::iprey3 talcen in the Sheepscot River 

 in I-aine (19h9) vrhich I had the opportunity of examininr. This sample 

 had a sex ratio of 79 m.ales : 100 females. 



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