Potential Effects of Double-crested Cormorants on Largemouth Bass in Lake Chicot, Arkansas

Fisheries managers and anglers are concerned about the effects that increasing over-wintering populations of piscivorous double-crested cormorants Phalacrocorax auritus have on sport fishes across North America. We estimated the mortality of the largemouth bass Micropterus salmoides population due to predation by cormorants on a 2024-ha oxbow lake in southeastern Arkansas. Cormorants consumed an estimated 0.05%-6.20% of the largemouth bass population in 2001. Consumption ranged widely because of the variability associated with our estimates of the number of days per year that cormorants spent on the lake and the instantaneous estimate of number of cormorants feeding on the lake. Potential for competition between cormorants and largemouth bass was examined by determining diet overlap for fall, winter, spring, and all seasons combined. Diet overlap was greater than 60% only in the fall, but cormorant and largemouth bass diets were never significantly correlated. Managers concerned with cormorant-sport fish interactions should focus their efforts on obtaining accurate cormorant counts, as opposed to elaborate and expensive diet studies. Key words: double-crested cormorant, diet, largemouth bass, Lake Chicot

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