Common Carp - Uncommon Predator!

Authors: Eric Frye, David Ward

Year: 2022

Abstract

Predation by common carp (Cyprinus carpio) on humpback chub (Gila cypha) has the potential to be high with negative impacts to humpback chub recruitment. We evaluated predation effects of common carp on humpback chub eggs, larvae and juveniles in the laboratory. We extracted and fertilized humpback chub eggs from captive reared adult chub and placed 1 ml of fertilized eggs onto cobble in each of 9, 150-gallon tanks at 20°C with either 2 common carp (6 replicates), or no carp (control, 3 replicates). Eggs were exposed to these treatments for 24-hours and then fish were removed. After 10 days, humpback chub larvae were counted. Treatments with common carp experienced a 97% reduction in humpback chub egg and larval survival. Experiments were then scaled-up in size to verify that this effect was not the result of small tank size. An additional 12 trials (6 with carp and 6 without carp) were conducted in 500-gallon raceways with similar results. Humpback chub eggs and larvae again experienced over 90% reduction in survival when compared to control trials with no carp present. Additional 24-hr laboratory predation trials were conducted using captive reared juvenile bonytail (Gila elegans) (22-70 mm TL) humpback chub (21-49 mm TL) and razorback sucker (Xyrauchen texanus) (47-98 mm TL) as prey. Chubs and suckers both experienced unexpectedly high predation mortality with the smallest sizes being most vulnerable. These results demonstrate that common carp are not just a threat to eggs and larval native fish, but also to juveniles. This information gives context about potential management actions designed to conserve Colorado River native fishes. Additional carp-focused management actions within the Little Colorado River may be warranted to conserve imperiled native fishes.