1. Seasonal prey shifts and bioenergetics
Daniel D. Magoulick
Arkansas Cooperative Fish and Wildlife Research Unit
Department of Biological Sciences
University of Arkansas - Fayetteville
Had large selection to choose from, but presenting this because:
It focuses on fish and invertebrates in same study
Shows my approach to addressing applied questions using basic research approaches
Highlights my approach to science
Comparative field studies
Manipulative field experiments
Lab experiments and studies
Does not get into my work on disturbance, stream drying and habitat relationships (ask me later)
Put Lindsey on talk to highlight he was grad student doing work and to show hard work can pay off in good job

2. Zebra Mussel Dreissena polymorpha
The focus of my talk for today is the zebra mussels that were introduced into the Great Lakes in the late 80’s and have since moved down the Mississippi River and up the Arkansas River.
Ringed crayfish slide. Other species introductions are accidentatl. Unfortunately there are numerous opportunities to study the effects of introduced species on native species in the US, including Arkansas. This is a ringed crayfish native to the Ozarks, but my graduate students and I have found that it has invaded the Spring River drainage and appears to be negatively impacting a rare native species of crayfish in this same drainage. I recently received a grant from the US Fish and Wildlife Service to study the effect of this introduced crayfish on the native crayfish community in the Spring River drainage.

3. Zebra mussels moved down the Ohio and Mississippi Rivers and into the Arkansas River. They are well up into Oklahoma and may be in Kansas.

4. Zebra Mussels on a Native Mussel
Zebra mussels also affect ecosystem structure and function directly and indirectly. Tremendous densities of 1000’s/m2.
Affect native fish, inverts. and algae, some pos. and some neg.
Filter tremendous volumes of water so affect:
nutrient cycling
Reduce turbidity
Increased primary production
Another exotic species in Arkansas that has become a nuisance species is the Zebra Mussel. Zebra mussels moved from the Great Lakes to the Mississippi River and up the Arkansas River and are found in very high densities in Lake Dardanelle.
This is Lake Dardanelle, which now has a substantial population of zebra mussels. Zebra mussels have impacted native species, as well as causing other problems.

5. Lock Gate with Zebra Mussels
Also, cause much economic impacts such as clogging intake pipes, affecting navigation structures.
Zebra mussels act as nuisance species, not only because they negativley impact native species, but also because they clog water intakes, alter navigation systems and affect ecosystem function. For example, they have been shown to significantly increase primary production in Lake Erie, which has cascading impacts throughout the system.

6. Aplodinotus grunniens
Freshwater Drum
Aplodinotus grunniens
Freshwater drum, a native molluscivorus fish species studied in Great Lakes,
prey extensively on zebra mussels.
do not control zebra mussel populations.
Zebra mussels appeared to negatively impact these populations.
reduced food quality?
Three major questions are of great concern regarding introduced species.
How do they affect native species?
Can the introduced species be controlled?
Abiotic
Biotic
Can we predict which species will become nuisance species and which ecosystems are more easily invaded?
My students and I have examined the first question for much of the past several years in different systems and with different species. For the rest of todays talk I would like to discuss questions one and two as they relate to zebra mussels and native fish predators. Specifically, we'll be examining the reciprocal influences of fish predators and zebra mussels (i.e., abiotic control will not be examined).

7. 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?

8. Potential Predators and Prey Preference

9. Another species that has been introduced into US freshwaters is the zebra mussel. This species was first discovered in the Great Lakes in 19? and is thought to have been transported into the US in the ballast water of a transatlantic freighter.

10. Zebra Mussels in Blue Catfish
These relationships may be explained by the way blue catfish forage for zebra mussels and they way that zebra mussels grow and congregate. Unlike most other bivalves, zebra mussels are exposed on hard substrates, rather than being buried down in soft substrates. They also form dense clusters with all size classes occurring in any given cluster. Blue catfish grab clusters and consume them whole.
Capture success, handling time, and prey density favor use of zebra mussels as prey.

11. Three predators on zebra mussels:
Previously known molluscivores
freshwater drum
redear sunfish
Previously not known
blue catfish
No zebra mussels in other species including channel catfish and common carp

12. Blue Catfish Prey Selection
Lake Dardanelle
100
100 80 80 60 ZM 60
Percent prey use
Percentage of Fish (%)
Shad 40 40
From previous work in the Great Lakes, we know that a few species of native fish predators consume zebra mussels, but at levels that were too low to impact zebra mussel population dynamics. All species that were known predators of zebra mussels were molluscivores with pharyngeal teeth that can crush mollusc shells (like freshwater drum).
Seasonal shifts in prey use by blue catfish:
zebra mussels in summer
shad in winter
Other 20 20
Empty J
7/96 A S
9/96* O N
1/97 D J
3/97 F M
4/97 A M
9/97* J J A
12/97 S O
1/98 N D
3/98 J F
5/98 M A
6/98 M J
8/98 J A
9/98 S O N
1/99 D J
1996
1997
1998
Sample Dates

13. Gizzard Shad (Dorosoma cepedianum)
Winter Die-Off
From previous work in the Great Lakes, we know that a few species of native fish predators consume zebra mussels, but at levels that were too low to impact zebra mussel population dynamics. All species that were known predators of zebra mussels were molluscivores with pharyngeal teeth that can crush mollusc shells (like freshwater drum).

14. Buoy and Sample Plates Summer 1996
Notice the lack of zebra mussels being prey on by blue catfish after June 1998.

15. Blue Catfish Prey Selection
Lake Dardanelle
100
100 80 80 60 ZM 60
Percent prey use
Percentage of Fish (%)
Shad 40 40
From previous work in the Great Lakes, we know that a few species of native fish predators consume zebra mussels, but at levels that were too low to impact zebra mussel population dynamics. All species that were known predators of zebra mussels were molluscivores with pharyngeal teeth that can crush mollusc shells (like freshwater drum).
Note no zebra mussels after July 98 and increased Other and Empty at this point.
Other 20 20
Empty J
7/96 A S
9/96* O N
1/97 D J
3/97 F M
4/97 A M
9/97* J J A
12/97 S O
1/98 N D
3/98 J F
5/98 M A
6/98 M J
8/98 J A
9/98 S O N
1/99 D J
1996
1997
1998
Sample Dates

16. Zebra Mussel Die-off Summer 1997 and 1998
This was related to mass zebra mussel mortality in Summer 98 due to increased water temperature.
Notice normal zebra mussels on buoys and sample plates from summer 1996.

17. Zebra Mussels Consumed by Blue Catfish
Predator Size Classes
(N = 463) 40 30
Number of Fish 20
Due to high summer water temperatures, zebra mussels experienced a massive die-off in the summer of 1997 and again in 1998. 10
203.2
254
304.8
355.6
406.4
457.2
508
558.8
609.6
660.4
>711.2
Blue Catfish Size Classes (mm)
Fish Containing Zebra Mussels
Total Number of Fish/Size Class

18. Length of Zebra Mussels Ingested by Blue Catfish30 25 20 15
Length (mm) 10
This graph shows that zebra mussels are being consumed by all size classes in proportion to their abundance. There is no signficant difference (p=0.12) between the two distributions. Unlike many fish predator-prey interactions, zebra mussel prey are consumed throughout the size class range of blue catfish. This increases the chance that any reciprocal influence between the two populations will be great. We did not effectively sample the smallest individuals in the population, but based on our observations and those of others 5
228.6
254
279.4
304.8
330.2
355.6
381
406.4
431.8
457.2
482.6
508
533.4
558.8
584.2
609.6
635
Blue Catfish Size Class (mm)

19. Zebra Mussel Clusters
Not only do all size classe of blue catfish collected prey on zebra mussels, but we also don't see the typical positive correlation between fish predator size and prey size. All size classes of blue catfish are consuming all size classes of zebra mussels. This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass.

20. Zebra Mussels in Blue Catfish
These relationships may be explained by the way blue catfish forage for zebra mussels and they way that zebra mussels grow and congregate. Unlike most other bivalves, zebra mussels are exposed on hard substrates, rather than being buried down in soft substrates. They also form dense clusters with all size classes occurring in any given cluster. Blue catfish grab clusters and consume them whole.
Capture success, handling time, and prey density favor use of zebra mussels as prey.

21. 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.

22. Caloric Analyses of Primary Prey Species
Energetics
Caloric Analyses of Primary Prey Species
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

23. Gizzard Shad Dorosoma cepedianum
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

24. Threadfin Shad Dorosoma petenense
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

25. Asiatic Clam Corbicula fluminea
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

26. Zebra Mussels Dreissena polymorpha
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

27. Drying Oven
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

28. This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

29. Muffle Furnace
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

30. Ash Determination and Correction
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.

33. Zebra Mussel Consumption and Growth of Freshwater Drum in Lake Erie
Graph From Study by French and Bur (1991)
375
present study (1991)
1978 (Bur 1984)
325
1958 (Edsall 1967)
275
This is likely a function of how the blue catfish consume zebra mussels. Zebra mussels are attached to hard substrates and are essentially grazed, like a cow eating grass. Small and large zebra mussels occur together in clusters, which leads to the lack of size-selectivity by the blue catfish. You often find the clusters of zebra mussels still intact in the stomachs of the blue catfish predators.
Mean back-calculated total length (mm)
225
175 2 3 4 5 6 7
Age

34. 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?

35. 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 36

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

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

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