Science: The Carp-Bass Relationship

Carp get fingered for a lot of negative aquatic issues, but a recent study** took a new look at one particular aspect of an old issue. Researchers asked what happens on a large scale (~6500 sq. ft.) when you put carp, bass and bluegill together in the same area.

As expected, turbidity was substantially higher in enclosures containing common carp than those without. What was unexpected though was successful spawning by both bluegill and bass at rates equivalent to non-carp enclosures. In fact, survival of juvenile largemouth bass was higher in enclosures with carp than in those without, and larval abundance of both bass and bluegill were equivalent to non-carp enclosures. This suggested little if any feeding by carp upon the eggs or nests of both species, a commonly held belief among bass anglers. Higher survival rates of larval and juvenile largemouth bass were theorized as possibly attributable to the increase in turbidity making young fish less susceptable to predation, as they might have used stained or muddy water as a form of cover or camouflage.

That said, the news wasn’t all good. While survival of larvals was equal to or greater than non-carp enclosures, and growth was also equivalent in that age group, growth of older juveniles suffered strongly. While they couldn’t pinpoint a specific reason, theories included either elimination of a specific food source or type required at a critical stage of development due to turbidity or vegetative removal, or possible intraspecific competition between juveniles due to an increased survival rate and a potentially limited food supply.

Ultimately, researchers summarized, “Although common carp did not directly reduce reproductive output or initial survival of largemouth bass and bluegills, the reductions in observed growth of juveniles may have long-term implications for centrarchid population abundance and size structure”, and that “negative effects of common carp on centrarchid populations may persist over several generations, eventually impairing sport fisheries and making improvements to population size structure difficult.”

** Effects of Common Carp on Reproduction, Growth, and Survival of Largemouth Bass and Bluegills. Matthew D. Wolfe, Victor J. Santucci, Lisa M. Einfalt & David H. Wahl. Transactions of the American Fisheries Society. Volume 138, Issue 5, 2009. pages 975-983.