a fleshy keel ventrally from the anus to the caudal fin. The 

 lower margin of the tail fin liketvise becomes somewhat thickened. 

 Females may also be indentified from some distance by the swell- 

 ing of the body proper by the egg mass lAich malces it bulge 

 beyond the lines of the head and branchial region. In spawning 

 males, the branchial region becomes somaivhat distended and has 

 a greater diameter than the rest of the body. 



(2) Spavming behavior ; the spaTniing act 



The spawning behavior of sea lampreys observed in the Ocqueoc 

 River was primarily monogamous, occasionally polygamous, and veiy 

 infrequently promiscuous. On certain visits to the sample spavm- 

 ing areas studied in 19hQ, 9$h nests upon which sea lampreys were 

 present were studied. In 2U^ of these nests, spawning had not 

 yet begun and tiie lampreys present were engaged solely in the 

 construction of the nest. In 393 nests, spaivning had been com- 

 pleted and only spent individuals, primarily males, were there. 



Spawning was observed in 338 nests. It was undertalcen by a 

 single pair in 261 nests or 77.2 percent of all instances observed. 

 All observations of the complete spawning activities of pairs 

 indicated that they remained mated for the entire spawning venture. 

 In hh nests or 13.0 percent of the total observed, one male was 

 spaTsning v/ith two females. Other polygamous combinations observed 

 ■vvith one male vrere: three females (6 nests); four females (2 nests); 

 and five females (1 nest) (Total: 9 nests— 2.7 percent of total). 

 Promiscuous spawning was observed in 6 nests (1.6 percent of total). 

 Combinations of sexes present were two males and two females 

 (1 nest); two males and three females (1 nest); two males and 

 seven females (1 nest); three males and t'-vo females (2 nests); 

 and four males and two females (1 nest) (Appendix G, Table U). 

 Polygamous and promiscuous spawning ivere generally observed after 

 the peak of spawning activity and may be attributed to having the 

 females outnumber the males on some spaivning areas during the late 

 part of the season, and/or to local overcrowding of the spawning 

 beds. 



Polyandrous spawning, i.e., one female Td.th several males, 

 was observed in 18 nests. In almost all of these, various degrees 

 of antagonism were exhibited by the males toi'/ards one another. 

 This was usually expressed in attempts by one male to drive 

 another from the nest. The aggressor ivould usually succeed in 

 fastening his mouth firmly to the victim. The latter would reply 

 in kind, and firmly locked together, they wo-ald go thrashing 

 downstream with the current. This antagonism ivas particularly 

 marked in males of a single spasming pair. Mien casual males in- 

 truded upon their spawning activities, they were promptly driven 

 away in the manner described above. I consider this further evi- 

 dence that under optimum conditions, spa'wning among sea lampreys is 

 undertaken by pairs -vtiich remain mated for the entire spaiming 

 period. 



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