Their activities may acco\mt, in pajr-t, for the seecing scarcity 

 in scEie spawning areas, of djanc and dead lanprejs which have 

 completed their spaiming acti-'/ities . 



Migratory sea lampreys, even in areas of deep water, are 

 preyed upon by the gulls. Several enpH-oyees of the IJanistique 

 Pulp and Paper Co. and Mr. Howard Loeb of the Fish Di-'.n.^ion 

 reported observing (in 19h7) "sea gulls" capturing migratory sea 

 lampreys as they came to the surface in. "boils" beloiv the tail- 

 race of the paper mill on the Manistique .River. This phenomenon 

 is so common during the pealc of migration in that river and the 

 actions of the gulls so comical as they attempt to swallow 11;- to 

 18-inch lampreys that they provide consistent amusement for mill 

 employees during this period. 



Of all avian and terrestrial predators, gulls apparently 

 constitute the only significant natural enemy of the sea lamprey 

 during its migration and spavming in Michigan streams. However, 

 the total effect of the activities of these birds has not kept 

 this lamprey from becoming more abundant up to the present or 

 from increasing its range. 



The basic source of references in the literature to natural 

 enemies of adult sea lampreys is the study of Surface (1395) for 

 the Cayuga Lake region. New York. Sui-face presented records of 

 predation upon adults by: (Mammals) raccoons, muskrats, rats, 

 minli;, weasels, foxes; (Birds) havidcs, owls, herons, bitterns; and 

 (Reptiles) the water snake. He reported also having seen a bowfin 

 eat an adult sea lamprey in an aquarium. All of these kinds of 

 animals, along with other potential predators, are present in 

 Michigan and probably feed occasionally on migrant or spawning sea 

 lampreys . 



(8) Reproductive potential of sea lampreys 



(a) Collection of materials 



All field observations upon which this study of the repro- 

 ductive potential of the sea ^lamprey is based were made between 

 April 9 and July 10, 19U7, on the Ocqueoc River and Carp Creek. 

 The degree of maturity of nearly all sea lampreys entering Carp 

 Creek in that year was estimated as was that of large samples of 

 specimens taken from the Ocqueoc River. The entire ovaries were 

 rem.oved from 70 migrant females and preserved in F-A-A (a solution 

 CI formalin, acetic acid and alcohol) . Fifty-eight of these speci- 

 mens were taken in Carp Creek, eight in the Ocqueoc River, one in 

 Ocqueoc Lake (talcen in a gill net, presumably -vrfiile migrating through 

 the lake to the spawning grounds in the river upstream from the lake), 

 and three were captured in the Cheboygan River below the power dam 

 in the city of Cheboygan, Cheboygan County. Pertinent mens"ural 

 data "vvere collected on a.11 specimens at the time of capture. The 



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