Document: NAT-3-74-5

Effects of crayfish on fish recruitment and invertebrate size-structure in ponds.

DORN, N.J.* and G.G.MITTELBACH

W.K. Kellogg Biological Station, Hickory Corners, MI 49060, USA ¹

Abstract:
We examined the potential for a native crayfish (Orconectes virilis), to influence pumpkinseed sunfish (Lepomis gibbosus) recruitment success in a set of 6 experimental ponds (1.5m deep, 25m diam.) in southern Michigan. In June of 1999, all ponds received 6 adult fish of each sex. Half of the ponds were stocked with crayfish at a density of 1.5/m² (24g/m²). Fish, littoral invertebrates, and macrophytes were sampled intermittently throughout the summer. Nest failure via crayfish egg predation was observed on a number of occassions, and total young-of-year fish biomass, was significantly lower in crayfish ponds. Mean size of young-of-year fish was also significantly lower in crayfish ponds. Final snail and macrophyte biomass tended to be lower in the crayfish ponds, however high inter-pond variability precluded statistical significance. Across all littoral invertebrate taxa (excluding crayfish), mean invertebrate size in August was significantly greater in ponds with crayfish. We interpret this affect of crayfish on mean invertebrate size as an indirect effect mediated through fish density, as mean invertebrate size was negatively correlated with young-of-year fish biomass and young-of-year fish size.

Keywords: fish, crayfish, indirect effect, egg predation

This abstract is being presented at: 10:30 AM in session:
Poster Session #9: Fish, Lakes, Streams and Wetlands.