Cottus Life History in Delaware 87 



Table 5. Monthly mean standard lengths, by sex, for 1973 and 1974 year classes 

 of Cottus bairdi from Butler Mill Branch, Sussex County, Delaware. 

 Number of specimens in parentheses. 



Date 



1973 Year Class 



1974 Year Class 





Male 



Female 



Unsexed 



Male 



Female 



28 Oct., 













4 Nov. 1973 



32.5 (6) 



27.7(10) 









20 Jan. 1974 



36.6 (5) 



33.8(21) 









17 Feb. 1974 



41.5(2) 



38.7 (3) 









17 Mar. 1974 



41.0(3) 



38.0 (2) 









20 Jul. 1974 



46.7 (3) 



41.5 (8) 



21.1 (83) 



- 



- 



8 Sep. 1974 



43.5 (6) 



40.5(13) 



24.2 (82) 



- 



- 



30 Nov. 1974 



- 



41 (1) 



30.0(121) 



- 



- 



2 Mar. 1975 



- 



- 



- 



30.7(18) 



29.8 (37) 



23 Mar. 1975 



- 



- 



- 



35.0 (3) 



30.4 (7) 



(Table 5). By next March these fish, now in age group I, were mature and 

 had spawned. Males (N = 21) now averaged 31.3 mm SL and females (N = 

 44) 29.9 mm. 



Growth in the 1973 year class was at first similar, with a combined 

 October-November sample mean length of 29.5 mm SL. However, 

 growth did not decrease pronouncedly or cease in winter as noted in the 

 1974 year class and as reported for a population by Bailey (1952). Rather, 

 sculpins of the 1973 year class apparently continued to grow from 

 November to March. For combined February-March 1974 samples, both 

 sexes (5 males, 5 females) averaged some 10 mm longer than those taken 

 in early March 1975. The reason for this difference is not known; it may 

 be an artifact of small sample size. Nagel (1980) also noted such between- 

 year variation in growth rate. The 1979 year class (age group I) exhibited 

 little growth, if any, from June through August (Table 4). A few fish 

 presumed of the 1978 year class (age group II) were also present in the 

 1980 samples. These were 10 to 15 mm longer than those collected the 

 previous spring, interpreted as growth continuing during the second year 

 of life. 



Cottus bairdi in Montana exhibited a growth rate comparable to 

 Butler Mill Branch specimens during age group 0, but none matured until 

 in age group II and when usually longer than 74 mm TL (Bailey 1952). 

 Ludwig and Norden (1969) observed growth similar to Sussex County 

 Cottus in age groups to II, but reported earliest maturity in Wisconsin 

 sculpins in age group II (x SL = 54.5 mm, range 37-70). Nagel (1980) 

 noted reproduction in Tennessee at the end of the second year of life, at 



