Life History of the Mottled Sculpin, Cottus bairdi, in 
Northeastern Tennessee (Osteichthyes: Cottidae) 
Jerry W. Nagel 
Department of Biological Sciences, East Tennessee State University, 
Johnson City, Tennessee 37614 
ABSTRACT. ^Cottus bairdi in northeastern Tennessee spawns for the 
first time at the end of its second year. Mature males are larger than 
mature females. Spawning occurs in early April and is completed within 
a one week period. Comparison with northern and western populations 
indicates lower fecundity, larger eggs, and larger hatchlings for C. bairdi 
in northeastern Tennessee. Population estimates revealed that immature 
fish were concentrated in disturbed, exposed habitats, whereas mature 
fish were evenly distributed between disturbed and undisturbed 
habitats. 
INTRODUCTION 
Several studies reported on the life history and ecology of the mot- 
tled sculpin, Cottus bairdi, in the northern and western parts of its range 
(Hann 1927; Koster 1936; Bailey 1952; Zarbock 1952; McCleave 1964; 
Ludwig and Norden 1969; Patten 1971). This study presents information 
on the life history of C. bairdi in the southeastern part of its range. 
MATERIALS AND METHODS 
Specimens of C. bairdi (N = 795) were collected from a 2.5 km sec- 
tion of Straight Creek, a tributary to the Nolichucky River, 7.5 km south 
of Johnson City, Washington County, Tennessee. Stream width in this 
section ranges from 0.5 to 2.0 m and averages 1.0 m. The stream has a 
gravel and rubble substrate and is 95% riffle (depth = 5-15 cm) with 5% 
pool habitat (depth =0.5- 1.0 m). Streamside canopy is either 100% in un- 
disturbed areas or 0% in areas disturbed by road construction 15 years 
prior to this study. Stream gradient in this section is 39 m km-' . Water 
temperatures were recorded with a mercury thermometer at the time of 
collection; highest recorded temperature was 19°C on 11 July 1977 and 
on 5 August 1977. 
Collections were made by electrofishing at monthly intervals from 
March 1977 to April 1978. All specimens were preserved in 10% formalin 
(buffered with CaC 03 ) within one hour of capture. 
A supplementary collection of C. bairdi (N = 102) was made from 
North Indian Creek in Unicoi County, Tennessee on 25 February 1978 to 
provide comparative information from a larger stream. North Indian 
Creek at this collection site is 5 to 10 m wide, 0.2 to 0.5 m deep in riffle 
areas, and 2 to 3 m deep in pools. 
Total length (TL) of all specimens was measured to the nearest 1.0 
mm and gonads from all specimens greater than 45 mm TL were weighed 
Brimleyana No. 4: 115-121. December 1980. 
115 
