Population dynamics of introduced flathead catfish in Lake Mitchell, South Dakota

Abstract

The introduction of flathead catfish (Pylodictis olivaris) into Lake Mitchell presented a unique opportunity to study the population dynamics of this species in a South Dakota impoundment. We collected flathead catfish using daytime, low-frequency electrofishing during June 2013, 2014, and 2015 and July, August and October of 2014 to examine population characteristics including abundance, recruitment, mortality, growth, condition, and diet. The flathead catfish population in Lake Mitchell was estimated at 1348 individuals (95% CI = 459–1455; density = 4.97/ha) in 2014 and 1197 individuals (95% CI = 931–1461; density = 4.42/ha) in 2015. Individuals from 11 year classes ranging from 1 to 13 years old were present. The population exhibited consistent recruitment, and annual mortality was estimated at 39%. Flathead catfish grew quickly exceeding stock length at age 3 and quality length at age 5; however, growth slowed in 2015. Similarly, condition of substock and stock-quality length fish declined in 2014 and 2015, respectively. The decline in growth and condition coincided with the recruitment of a large 2012 year class and may be an early indicator of intraspecific competition. Diets of Lake Mitchell flathead catfish primarily consisted of crayfish (Orconectes spp.) and fish with flathead catfish shifting to piscivory at approximately 400 mm. The high percentage of centrarchids in flathead catfish diets along with an increase in flathead catfish abundance coinciding with a decrease in bluegill abundance may indicate that flathead catfish are negatively impacting the bluegill population in Lake Mitchell.

Keywords

• Pylodictis olivaris
• flathead catfish
• population dynamics
• predation
• South Dakota