**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

River Discharge as a Predictor of Lake Erie Yellow Perch Recruitment

Stuart Ludsin¹, Kevin Pangle¹, Lucia Carreon-Martinez², Nicholas Legler², Julie Reichert², Daniel

Heath², Brian Fryer², Timothy Johnson³, Jeffrey Tyson⁴, Tomas Höök⁵, George Leshkevich⁶, Doran

Mason⁶, David Bunnell⁷, Chris Mayer⁸, Tom Johengen⁹, Henry Vanderploeg⁶, and Alison Drelich¹

¹ The Ohio State University, Dept of Evolution, Ecology, and Organismal Biology, Aquatic Ecology

Laboratory, Columbus, OH

² University of Windsor, Great Lakes Institute for Environmental Research, Windsor ON

³ Ontario Ministry of Natural Resources, Glenora Fisheries Station, Picton, ON

⁴ Ohio Department of Natural Resources, Division of Wildlife, Sandusky, OH

⁵ Purdue University, Department of Forestry and Natural Resources, West Lafayette, IN

⁶ NOAA Great Lakes Environmental Research Laboratory, Ann Arbor, MI

⁷ U.S. Geological Survey, Great Lakes Science Center, Ann Arbor, MI

⁸ University of Toledo, Department of Environmental Sciences and Lake Erie Center, Toledo, OH

⁹ University of Michigan, Cooperative Institute for Limnology and Ecosystems Research, Ann Arbor, MI

March 2011

ABSTRACT:

The Laurentian Great Lakes support numerous fisheries that are of recreational and commercial importance, yet our understanding of the recruitment process for any species is limited. Toward improving our understanding of yellow perch (Perca flavescens) recruitment in western Lake Erie, as well as enhancing the management of this ecologically and economically important species, we used a hypothesis-driven, field-, laboratory-, and modeling based research approach to explore the mechanisms underlying a strong positive relationship between Maumee River discharge during spring (March-May) and yellow perch recruitment to the fishery at age-2 (i.e., high discharge leads to strong future recruitment events). We evaluated two hypotheses regarding this relationship. Hypothesis 1 argued that springtime Maumee River discharge regulates yellow perch recruitment via bottom-up control of food (zooplankton) production for pelagic larvae, whereas Hypothesis 2 argued that Maumee River discharge benefits yellow perch recruitment via enhanced turbidity that reduces predation mortality on larvae. Our collective findings from 2006-2009 field sampling and simulation modeling demonstrate that Maumee River discharge benefits larval yellow perch through formation of a plume in the open lake. Using individual-based modeling, we found that survival during the larval stage was greater in the Maumee River plume (MRP) than in non-MRP waters during all study years, while otolith microchemical and molecular genetics approaches conducted on field-collected larvae and juvenile survivors demonstrated that MRP larvae recruited to the new year-class in August (when recruitment to the fishery is set at age-2) disproportionately more than non-MRP larvae during 2006-2008 (but not 2009, where survival probabilities were equal between water masses). The primary mechanism underlying enhanced survival and contributions of larvae to the new year-class from the MRP (relative to non-MRP waters) related more to top-down (predation; Hypothesis 2) than bottom-up (production of zooplankton prey; Hypothesis 1) processes. Multiple lines of evidence support this conclusion: 1) although growth and condition of larvae were generally higher in the MRP than non-MRP waters, only seemingly minor differences were found in temperature and zooplankton biomass/production between water masses (field observations) and no obvious difference in the consumption of zooplankton prey was evident (field observations); 2) higher predator densities and water clarity were found in non-MRP waters than in the MRP (field observations); 3) a higher degree of size-selective mortality against slow-growing larvae occurred in non-MRP waters than in the MRP (field observations); and 4) differential larval yellow perch survival was more sensitive to predation mortality than starvation mortality (modeling observation). These findings confirm the importance of short-lived (pulsed) tributary-driven inputs of sediments and nutrients from the watershed to the yellow perch recruitment process, the results of which can been seen in the fishery for a long time afterwards. From a management perspective, our research points to the need for Lake Erie management agencies to not only consider the role that predation by white perch (Morone americana), an invasive species, plays in the Lake Erie larval yellow perch recruitment process, but also the value of using state-of-the-art DNA-based techniques (versus traditional visual analysis) to quantify predation mortality on young individuals such as larval fish. Further, our findings support the Great Lakes Fishery Commission’s missions of 1) implementing ecosystem-based fishery management strategies and 2) expanding physical-biological coupling research in the basin, as the recruitment of our study species is clearly driven by processes operating external to Lake Erie proper, including physical forcing by the Maumee River.