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?
