586 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Size of Upstream Migrants 



Early arrival of the larger sea lampreys in the 

 spawning migration was observed by Surface 

 (1899) in Cayuga Inlet and by Applegate (1950) 

 for Lake Huron stocks. During 1950, 1951, and 

 1952 the early upstream-migrants in Cayuga Inlet 

 were again found to be both longer and heavier 

 than late migrants (tables 27, 28). Comparison 

 of average lengths of early with late migrants re- 

 veals that the former averaged 0.2 to 0.7 inch 

 longer. In weight, the early migrants averaged 

 0.2 and 0.6 ounce heavier in 1950 and 1952, re- 

 spectively, but in 1951 their weight averaged 0.4 

 ounce less than that of late migrants. Although 

 the sex ratio of upstream-migrants changed during 

 the season, this change had no effect on the size of 

 early and late migrants as the sexes had the same 

 mean size. 



Table 27. — Mean lengths of adult sea lampreys taken early 

 and late in the spawning migration in Cayuga Inlet 



Body Color 



Recently transformed sea lampreys are bluish- 

 black 6 dorsally and laterally and silvery-white 

 ventrally. With increasing age the epidermis be- 

 comes dark olive. The body is mottled by black 

 pigment in the dermal layer, especially on the 



• Color standards employed In this description are those given by Rldg- 

 way (1912). 



dorsal surface; the ventral surface is nonpig- 

 mented. At the height of the spawning season 

 the dark-olive epidermal layer changes to a medal- 

 bronze on the majority of individuals, although 

 there is much variation. A few lampreys, often 

 the largest and most mature, develop a xanthine- 

 orange coloration. Others, often the smallest and 

 least mature, remain bluish-black or dark-olive. 



Pigmentation on the dorsal fin is sparse and 

 rather indistinct in comparison with that on the 

 trunk. A band of skin along the base of both 

 dorsal fins is pigmented much the same as the 

 trunk. An indistinct band, approximately one- 

 fourth the fin height, on the margin of the dorsal 

 fins is nonpigmented. The caudal fin bears dark 

 pigmentation on its posterior portion which dimin- 

 ishes anteriorly. A ridgelike continuation of the 

 ventral portion of the caudal fin forward to the 

 urogenital opening is nonpigmented. 



In 1951 a study was made of the correlations 

 between color and size, sex, and time during the 

 spawning period. To facilitate the recording and 

 calculation, five color categories were established 

 and given index numbers as follows: (1) xanthine 

 orange; (2) raw sienna; (3) medal bronze; (4) dark 

 olive; and (5) bluish -black. This series is listed 

 here in reverse order of color changes that occur as 

 sexual maturity is approached. Numbers of speci- 

 mens were: 183 males and 110 females captured on 

 the spawning run in Cayuga Inlet during the 

 period April 26-30, 1951; 152 males and 144 fe- 

 males taken during the period May 13-16, 1951. 



The linear regressions of color on length (fig. 13) 

 illustrates the tendency for large lampreys to be 

 lighter and more colorful than small ones. Males 

 were lighter and a more golden color than females 

 of similar size. Early migrants were approxi- 

 mately one color category lighter than late mi- 

 grants. A measure of closeness of the relation be- 

 tween color and total length is provided by the 

 correlation coefficient. Correlation coefficients for 

 the April collections, as shown in the tabulation, 

 indicate considerable variation. Correlation co- 

 efficients for the May collections are rather high, 

 indicating relatively little variation ; however, only 

 the females in the May collections have a sig- 

 nificantly high value (indicated by asterisk). 



Individual records of 20 specimens whose color 

 was recorded when they were captured on their up- 

 stream migration and tagged, and again recorded 

 after spawning was completed, were used as an 



