1. What caused a regime shift in the Wabash River? Indiana AFS Feb 28, 2014 Mark Pyron, Jesse Becker, Dawn DeColibus, Kevin Wyatt, and Allison Rober Center of Aquatic Biology and Fisheries Environmental Science

2. Previous results: regime shift Regress body size on size bins Negative slope = inefficient transfer

3. Wabash River Regime Shift Body size distribution of fishes changed: 1974-2008

4. Abundances in trophic groups

5. Potential causes of regime shift? Large flood / severe drought Point-source pollution Over-harvesting fish Excess nutrients, increased algae, diet change in upper trophic levels

6. Diet of fishes change? Pilot analysis Isotope analyses: 13C and 15N ratios Museum archives 1960-2008 Predator = spotted bass, drum, sucker Omnivores = spotfin shiner Detritivore = gizzard shad

7. One trophic level ~ 3 ppt d15N http://sofia.usgs.gov AlgaeMacrophytes

8. INHS archival fishes: Wabash River

9. Gizzard shad now consume additional sources NANFA.ORG

10. Gizzard shad consume additional sources Shiner consume lower trophic sources NANFA.ORG

11. Upstream individuals consume at lower trophic levels

12. ISOTOPE RESULTS Change in diet of consumer fishes (planktivore / omnivore) in 1990s Different algae? Different nutrients? Impact of Asian carp?

13. STOMACH CONTENTS GIZZARD SHAD Has diet changed?

16. Summary Fish diets changed 1960-2000 Gizzard shad consume less algae, low quality Algal assemblage changed – cause?

17. Summary Fish diet changedFish diet changed Algal assemblage changedAlgal assemblage changed Asian carp / Higher nutrients?Asian carp / Higher nutrients?