Seasonal prey shifts and bioenergetics Daniel D. Magoulick Arkansas Cooperative Fish and Wildlife Research Unit Department of Biological Sciences University of Arkansas - Fayetteville

Zebra Mussel Dreissena polymorpha

Zebra Mussels on a Native Mussel

Lock Gate with Zebra Mussels

Freshwater Drum Aplodinotus grunniens

Questions What fish species prey on zebra mussels in Lake Dardanelle and the Arkansas River? Do fish predators prefer zebra mussels over other prey? Is this affected by fish size or season? Are zebra mussels a profitable prey item for fishes in Lake Dardanelle?

Potential Predators and Prey Preference

Zebra Mussels in Blue Catfish

Blue Catfish Prey Selection Lake Dardanelle Percentage of Fish (%) 7/969/96*1/973/974/979/97*12/971/983/985/986/988/989/981/99 Sample Dates ZM Shad Other Empty Percent prey use JASONDJFMAMJJASONDJFMAMJJASONDJ

Gizzard Shad (Dorosoma cepedianum) Winter Die-Off

Buoy and Sample Plates Summer 1996

Blue Catfish Prey Selection Lake Dardanelle Percentage of Fish (%) 7/969/96*1/973/974/979/97*12/971/983/985/986/988/989/981/99 Sample Dates ZM Shad Other Empty Percent prey use JASONDJFMAMJJASONDJFMAMJJASONDJ

Zebra Mussel Die-off Summer 1997 and 1998

Zebra Mussels Consumed by Blue Catfish Predator Size Classes Number of Fish >711.2 Blue Catfish Size Classes (mm) Fish Containing Zebra Mussels Total Number of Fish/Size Class (N = 463)

Length of Zebra Mussels Ingested by Blue Catfish Length (mm) Blue Catfish Size Class (mm) (N = 140)

Zebra Mussel Clusters

Zebra Mussels in Blue Catfish

Major Points Blue catfish are a new and important predator of zebra mussels. –53% of blue catfish contained zebra mussels Blue catfish show seasonal prey shifts, consuming zebra mussels in summer and shad in winter. –Alternation between native species and introduced species All size classes of blue catfish consume zebra mussels extensively.

Energetics Caloric Analyses of Primary Prey Species

Gizzard Shad Dorosoma cepedianum

Threadfin Shad Dorosoma petenense

Asiatic Clam Corbicula fluminea

Zebra Mussels Dreissena polymorpha

Drying Oven

Muffle Furnace

Ash Determination and Correction

Zebra Mussel Consumption and Growth of Freshwater Drum in Lake Erie Graph From Study by French and Bur (1991) Mean back-calculated total length (mm) Age present study (1991) 1978 (Bur 1984) 1958 (Edsall 1967)

Major Points Energy content of bivalves was significantly less than that of shad. Energy content showed a significant interaction between prey species and season. Shad had significantly greater energy content than bivalves in any season. –Whole organism energy content of shad was order of magnitude greater than bivalves. Quantity vs. quality?

Conclusions Zebra mussels have become an important prey item for freshwater drum, redear sunfish, and blue catfish in Lake Dardanelle and the Arkansas River. –Adult blue catfish forage extensively on all sizes of zebra mussels. –Blue catfish show a seasonal prey shift, feeding on zebra mussels in summer and shad in winter. Zebra mussels and asiatic clams are significantly lower in caloric value than gizzard and threadfin shad. –Quantity vs quality? –Prey profitability? (Capture success, handling time, evacuation rates, prey density, season)

36 Energy Budget in Individual Fish P=C-(F+U)-R or C=P+F+U+R

37 Abiotic Factors affect Bioenergetics Temperature affects all of the budget variables

38 Blue Catfish Prey Consumption based on Bioenergetics Model Greater biomass of zebra mussels than shad were consumed by all size classes

39 Blue Catfish Production and Prey Use Gross production tracks shad consumption