Cottus Life History in Delaware 83 



venter was smoky-gray with fine black stippling, and the breast and 

 abdomen dull whitish. The normally prominent black saddles were indis- 

 tinct. On 14 March, seven of eight males were so colored, while one had 

 the more typical tan background color with prominent chocolate-brown 

 saddles. On each subsequent date, through 29 March 1981, some males 

 had the dark coloration described above, but the number of such males 

 then found per date never exceeded those with the brown body. Even 

 some males guarding eggs on and after 14 March 1981 were brown. 



Water temperature during the spawning period ranged from 7.5° to 

 12.5° C in March 1975, and from 6.5° to 11.0° C in March 1980. 

 Temperatures from other years were within these ranges. Koster (1937) 

 reported spawning in upper New York State at 10° C, Bailey (1952) in 

 Montana at 7.8° to 12.8° C, Ludwig and Norden (1969) in Wisconsin at 

 8.9° to 13.9° C, and Nagel (1980) in Tennessee at 12° C and 14° C. Water 

 temperature fluctuates considerably during egg development. Tempera- 

 tures (°C) at Butler Mill Branch in 1981, from the date before the first 

 eggs were found (22 February) through the date after the last were found 

 (18 April), were: 10.0, 9.0, 7.5, 8.0, 7.0, 11.0, 11.5, 13.5, 12.0, and 16.0. 

 Eggs in 1980 (two dates) were found at 8.0° C and 6.5° C. 



The difference between number of males (69) and females (156) 

 collected during the reproductive season was highly significant (chi- 

 square, P<0.001, expected ratio 1:1). The observed values may be a 

 sampling artifact. However, as a male is known to spawn with more than 

 one female, it is also possible that the observed values reflect a real 

 difference. Ludwig and Norden (1969) noted a reduction in number of 

 males at commencement of the spawning season, and suggested it 

 resulted from competition for nesting sites and some segregation of sexes. 

 Koster (1936) found no significant difference in the proportion of males 

 to females. 



Age and Growth 



The Butler Mill Branch sculpins are more short-lived than reported 

 for any other Cottus species. This may be related to early onset of sexual 

 maturity. Further, only few Butler Mill Branch C. bairdi that reach age 

 group I survive to spawn twice. Length-frequency distributions based on 

 the total sample through 1980 indicate the existence of three age groups: 

 O, I, and a presumed II (Figs. 4,5). In 1974, group I fish were present from 

 January to September, but none was collected in November. Of later 

 samples, some group I fish were still present in November 1978. A few 

 may have survived the winter, as indicated by the large specimens Q> 50 

 mm SL) collected in March and July 1979, which would then have been 

 in age group II. Fish corresponding to this age group were also present in 

 the 1980 samples. Of the 403 sculpins collected in 1980, 262 (65.0%) were 



