Cottus Life History in Delaware 



73 



i 



N 



.5 1.0 



Kl LOMETERS 



...... indicates distri- 

 bution of Cottus bairdi 

 in Butler Mill Branch 

 and tributaries 

 • •• — indicates sampling 



SEAFORD 



-no 



7T\ 



SAMPLING 



Fig. 1. The Butler Mill Branch system near Seaford, Sussex County, Delaware, 

 showing Cottus bairdi distribution and sampling area. 



clear, is turbid after rain. Temperature in the sampling area ranged from 

 5.5° C (February) to 20.0° C (July), pH from 5.7 to 7.0 (typically 6.5), 

 and dissolved oxygen concentrations from 9.1 to 12.8 ppm. 



Stream flow data were taken in the sampling area on 22 dates 

 between 30 June 1955 and 16 April 1969 by the U.S. D.I. Geological 

 Survey, Water Resources Division (Robert H. Simmons, pers. comm.) at 

 low-flow conditions (after periods of no rain for four or five days). Aver- 

 age stream cross-section area was 0.76 m 2 (range 0.20-2.17), mean flow 

 0.16 m 3 /sec (0.04-0.46), and mean water velocity 0.21 m/ sec (0.10-0.29). 

 The lowest values were from summer, the highest from spring and late 

 fall. 



Fifteen fishes were taken with C. bairdi (number of times in paren- 

 theses) in a total of 26 collections made in the sampling area during 

 1973-80: Lampetra aepyptera (20), Anguilla rostrata (18), Umbra pyg- 

 maea (11), Esox americanus (1), Esox niger (6), Notemigonus crysoleucas 

 (4), Erimyzon oblongus (17), Ictalurus natalis (2), Ictalurus nebulosus (1), 



