Life History and Ecology of the Sculpin Cottus bairdi punctulatus in Southwestern Montana

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Abstract
In the West Gallatin River, Prickly Pear Creek, and Wolf Creek, Mont., bottom-dwelling aquatic insects comprised 99.7% of the total number of food organisms in 903 sculpin stomachs. Diptera and Trichoptera larvae and pupae constituted 55.5 and 36.7%, respectively, while Ephemeroptera and Plec-optera nymphs together made up 5.9%. Trichoptera were consumed in greatest numbers in the fall and least in spring, while Diptera were taken most in spring and least in fall. The max. amount of food per stomach occurred during winter mos. while the min. was found in summer. Sculpins were most abundant in rubble riffle areas and least abundant where the bottom was entirely sand or clay. The 1951 spawning season was from June 5 to 30 and hatching occurred from July 3 to 21, indicating an incubation period of 21-28 days. Some individuals matured at the age of 2 years and all females over 74 mm. total length were sexually mature. Development of ovaries was determined by calculating ripeness factors based on the ovary volume and the cube of the total body length. The number of eggs per female ayeraged 203 and many nests were used by more than one female. The nests were prepared and attended by the males. Length-frequency data in general agreed with growth data based on otolith studies.

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