What caused a regime shift in the Wabash River?

Indiana AFSFeb 28, 2014

Mark Pyron, Jesse Becker, Dawn DeColibus, Kevin Wyatt, and Allison Rober

Center of Aquatic Biology and FisheriesEnvironmental Science

Previous results: regime shift• Regress body size on size bins

• Negative slope = inefficient transfer

Wabash River Regime Shift• Body size distribution of fishes changed:

1974-2008

Abundances in trophic groups

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

Diet of fishes change?Pilot analysis

• Isotope analyses: 13C and 15N ratiosMuseum archives 1960-2008

Predator = spotted bass, drum, sucker

Omnivores = spotfin shiner

Detritivore = gizzard shad

One trophic level ~ 3 ppt d15N

http://sofia.usgs.gov

Algae Macrophytes

INHS archival fishes: Wabash River

• Gizzard shad now consume additional sources

NANFA.ORG

• Gizzard shad consume additional sources• Shiner consume lower trophic sources

NANFA.ORG

Upstream individuals consume at lower trophic levels

ISOTOPE RESULTS

• Change in diet of consumer fishes (planktivore / omnivore) in 1990s

• Different algae? • Different nutrients?• Impact of Asian carp?

STOMACH CONTENTS GIZZARD SHAD

• Has diet changed?

Summary

• Fish diets changed 1960-2000

• Gizzard shad consume less algae, low quality

• Algal assemblage changed – cause?

SummarySummary

• Fish diet changedFish diet changed• Algal assemblage changedAlgal assemblage changed• Asian carp / Higher nutrients?Asian carp / Higher nutrients?