88 Fred C. Rohde and Rudolf G. Arndt 



50-81 mm TL. Hann (1927) stated that sexual maturity in Michigan is 

 attained by two years of age, at 45-70 mm SL. Koster (1936) found that 

 first spawning in a stream-dwelling population near Ithaca, New York, 

 occurred at the end of the second year of life (age group II), while some 

 specimens of a lake-dwelling population from nearby Cayuga Lake 

 apparently matured at the end of the first year of life (age group I). This 

 early maturity may result from a genetic or an environmental difference 

 between these populations. 



Butler Mill Branch sculpins reached sexual maturity at a smaller size 

 than any other population of C. bairdi (x SL = 37.4 mm, range 22-64, N = 

 225). Mean length of 33 Butler Mill Branch adults taken in 1981 was 44.7 

 mm SL (range 35-65 mm). Adults from the new localities in Caroline and 

 Dorchester counties, Maryland, were of similar size (x SL = 38.7 mm, 

 range 29-62, N = 48), and Franz and Lee (1976) noted small size in the 

 other Caroline County population. 



Mature males in the March and May 1978-80 samples were larger (x 

 SL = 47.6 mm, range 37-64, N = 38) than mature females (x SL = 38.9 

 mm, range 32-59, N = 86), a highly significant difference (P<0.001). 

 However, there was no significant difference at the 0.05 level in the 

 January, February, and March 1973-75 samples (mature males, x SL = 

 33.7 mm, range 25-47, N = 31; mature females, x SL = 31.7 mm, range 

 22-40, N = 70). The reason for the size difference of 1978-80 is not appar- 

 ent. Such sexual dimorphism was also observed by Hann (1927), Bailey 

 (1952), Ludwig and Norden (1969), and Nagel (1980), but not in New 

 York sculpins by Koster (1937). 



Regressions for the weight-length relationship derived for males and 

 females from both sampling periods are: (1973-75) males, Log W = 

 - 10.8985 + 3.0585 Log L, r = 0.99; females, Log W = -10.3999 + 2.8814 

 Log L, r = 0.99; (1978-80) males, Log W = -1 1.8313 + 3.3681 Log L, r = 

 0.99; and females, Log W = -1 1.0505 + 3.1412 Log L, r= 0.99. Analysis of 

 covariance reveals significant differences (P<0.05) in slope between sexes 

 and between years. A slope greater than 3.00, indicating that relative 

 weight increased faster than length (Ricker 1971), is noted in three of four 

 regressions. Only females in 1973-75 showed a slightly faster increase in 

 length when compared to weight. 



There is a strong, and expected, positive correlation between SL and TL: 

 SL= 1.21 + 0.76 TL, r= 0.93. 



Condition factor (K) for both sexes is lowest during the coldwater 

 months preceding spawning (Table 6). Highest K values were recorded 

 during the warmwater period subsequent to spawning. With the excep- 

 tions of October and November, males were more robust than females. 



