Life History of a Coastal Plain Population of the 

 Mottled Sculpin, Coitus bairdi (Osteichthyes: Cottidae), 



in Delaware 



Fred C. Rohde 



Charles T. Main, Inc., 

 Prudential Center, Boston, Massachusetts 02199 



AND 



Rudolf G. Arndt 



Faculty of Natural Sciences and Mathematics, 

 Stockton State College, Pomona, New Jersey 08240 



ABSTRACT. — Aspects of the biology of a Coastal Plain population 

 of Cottus bairdi in a lowland forest stream in Delaware were examined 

 during 1973-81. Cottus bairdi occurs primarily over a gravel substrate; 

 naturally-occurring rocks are absent. Individuals are shorter-lived and 

 attain sexual maturity at a smaller size than in other studied popula- 

 tions. Two age groups, and a presumed third, were found. Only 33% of 

 age group survives to spawn in age group I. Spawning occurs in 

 February and March at a water temperature of 6.5° to 12.5° C, and 

 mean ovum diameter is 2.15 mm. There is a strong relationship 

 between ova number and standard length (Y = -157.11 + 6.80 SL). 

 Fecundity is lower than that reported for most populations of C. 

 bairdi. Most eggs are deposited in single-spawn clusters, with a mean 

 egg number of 134.2 per cluster. Condition factor indicates that males 

 are generally more robust than females. Most growth in length occurs 

 in age group 0, males are longer than females, and there is a highly 

 significant difference in sex ratio of mature specimens taken. 



Dominant food is trichopteran and dipteran larvae, and plecopte- 

 ran nymphs; crustaceans, ephemeropteran nymphs, and coleopteran 

 larvae are of minor importance. There is seasonal variation in food 

 items. Diet differs only slightly as a function of sculpin size. 



INTRODUCTION 



The mottled sculpin, Cottus bairdi, is widely distributed in the United 

 States and Canada (Lee 1980) and there are numerous studies of aspects 

 of its life history (Gage 1878; Smith 1922; Hann 1927; Koster 1936, 

 1937; Bailey 1952; Daiber 1956; Ludwig and Norden 1969; Patten 1971; 

 Nagel 1980). There are, however, only four known Atlantic Coastal 

 Plain populations, all located in the Nanticoke River system, Chesa- 

 peake Bay drainage. We studied one of these, in Butler Mill Branch and 



Brimleyana No. 7:69-94. July 1 98 1 . 69 



