Project: Seasonal food web impacts on variable sportfish recruitment
Advisor: Stu Ludsin
- Aquatic Ecology
- Fisheries Biology
- Conservation Biology
Prey availability often plays an essential role in driving sportfish growth and subsequent recruitment. The central goals of our project are to help improve the ability of the Ohio Department of Natural Resources – Division of Wildlife (ODNR-DOW) to (1) better understand the ecological mechanisms that might underlie seasonal variation in zooplankton (ZP) availability to larval and juvenile (pre-recruited) sportfishes, and (2) better assess prey-fish availability (i.e., Gizzard Shad, Dorosoma cepedianum) to large-bodied top predators in Ohio reservoirs. Our project will largely focus on the role of a common macroinvertebrate (i.e., Chaoborus spp.) in influencing availability of both prey-fish and ZP. Chaoborus is a macroinvertebrate that migrates daily between dark hypoxic bottom waters (during the day) and more oxygenated surface waters (during the night) where it feeds on mesozooplankton. This movement pattern is potentially problematic for two reasons. First, Chaoborus holds great potential to reduce ZP prey availability to pre-recruited sportfishes (e.g., Saugeye, Sander canadensis x S. vitreus; Pomoxis spp.; Lepomis spp.) by migrating into the dark surface waters at night to consume ZP that otherwise would be consumed by larvae and juveniles sportfish, and then returning to bottom waters before daybreak, where it can use the less-illuminated hypoxic zone as a refuge from visual fish predators that also are hypoxia-intolerant. At present, a comprehensive assessment of whether Chaoborus limits ZP availability to pre-recruited sportfishes is lacking. Second, because the gas bladders of Chaoborus resonate well at the hydroacoustic sampling frequency (~200 kHz) used by the ODNR-DOW when estimating prey-fish availability to large-bodied predators at night, these estimates might be biased high by the presence of Chaoborus in the water column. At present, we have little understanding of the magnitude of this bias, including how it varies across reservoirs that differ in their physical (e.g., size, thickness of bottom hypoxic layer) and biological (e.g., Chaoborus and Gizzard Shad densities) characteristics. Our project will address both of these information gaps by (1) determining how food web interactions and physicochemical conditions combine to influence ZP prey availability to pre-recruited sportfishes, and (2) quantifying the bias introduced by Chaoborus into hydroacoustics estimates of available prey-fish biomass and developing a model to correct for this bias.
To learn more about Rebecca's work, check out her CV: Dillon_2015_CV.pdf
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