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For more recent research updates - please see my USGS profile

Recreational fisheries harvest dynamics

Recreational fisheries, especially in freshwaters, are increasingly recognized for their cultural, economic, and ecological importance.  But inland recreational fisheries are being threatened by the rapid pace of environmental change which is increasing the vulnerability of these fisheries to overharvest and collapse. Therefore, much of my research focuses on understanding the magnitude of recreational fisheries harvest and the effect this harvest has on ecosystems.

PC: Riley Steinbrenner

Holly Embke walleye

Ecosystem response to whole-lake sunfish removal

Northern temperate lake walleye populations have been declining in recent decades. As an economically, ecologically, and culturally important fishery in northern Wisconsin, identifying the mechanisms behind these declines is critical. A potential influencing factor may be increasing numbers of warm-water species, such as largemouth bass, whether through predation pressure or indirectly via food web interactions. In an effort to understand these relationships, we are performing a whole-lake removal of basses and sunfishes (i.e., centrarchids) in a northern Wisconsin lake. In addition to measuring food web dynamics and limnological changes in the experimental lake, we are monitoring a nearby control lake. This research has the potential to inform management of these vital fisheries as well as clarify energy flow dynamics in northern temperate lakes. To find out more about this project, visit our website:

Grass Carp spawning in Lake Erie

Grass Carp are an herbivorous species native to China and Russia but have become increasingly invasive in the United States after being introduced for vegetation control. Adults have been collected in all of the Great Lakes except for Lake Superior, but no self-sustaining populations have been found, although naturally reproducing populations are present in the Mississippi River basin. Due to their voracious appetite, there is increasing concern that if populations were to establish in the Great Lakes, Grass Carp could drastically alter ecosystems. I focused my research on the Sandusky River, a tributary to Lake Erie, to determine if Grass Carp were spawning in the Great Lakes basin. After collecting multiple viable eggs in 2015, I developed a modeling framework to estimate the spawning and hatching locations of these eggs. I also looked at the relationships between spawning evidence and abiotic factors, most importantly hydrology. As this was the first direct confirmation of invasive carp spawning in the Great Lakes basin, this information was used to inform targeted management actions for this species.
Holly Embke grass carp

Macroinvertebrate communities in Quebec reservoirs

During my undergraduate degree at McGill University in the lab of Dr. Irene Gregory-Eaves, I researched the effects of varying water drawdown levels on macroinvertebrate communities in multiple Quebec reservoirs. For this project, I analyzed sediments as well as macroinvertabrates to examine relationships between community composition and abiotic factors. We determined that winter drawdown and thermal regime were significant predictors of macroinvertebrate abundance as well as community diversity. 
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