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
Previous results: regime shift Regress body size on size bins Negative slope = inefficient transfer
Wabash River Regime Shift Body size distribution of fishes changed:
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 ratios Museum archives Predator = spotted bass, drum, sucker Omnivores = spotfin shiner Detritivore = gizzard shad
One trophic level ~ 3 ppt d15N AlgaeMacrophytes
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 Gizzard shad consume less algae, low quality Algal assemblage changed – cause?
Summary Fish diet changedFish diet changed Algal assemblage changedAlgal assemblage changed Asian carp / Higher nutrients?Asian carp / Higher nutrients?