Short- and Long-Term Effects of Changing Food Quality on Early Life Stages of Walleye in the Western Basin of Lake Erie

Increased nutrient runoff and climatic changes are altering the composition of algae and other primary producers in aquatic systems worldwide. Changes in primary producers have the potential to affect an entire food web by altering the available nutrients. This may particularly impact early life stages due to direct effects on survival and development, but also due to indirect effects that may persist and alter adult survival, growth, or reproductive success. In the western basin of Lake Erie, the algae community is becoming dominated by species with poor fatty acid content such as cyanobacteria. Fatty acids are vital in fish development and reproduction. A decline in available essential fatty acids may greatly affect fishes like walleye, an important predator and sport fish. Our research on the short- and long-term effects of poor food quality at vulnerable early life stages of walleye will allow for better understanding of changes to walleye physiology, walleye populations, and the fish community throughout the western basin of Lake Erie. To examine this question, we are collecting samples from Lake Erie, conducting laboratory experiments, and creating a demographic model of the walleye population.

 

Defining a Biologically Relevant Definition of Hypoxia

Hypoxia, or low oxygen concentration, is often defined at dissolved oxygen levels below 2.0 mg/L. Hypoxia develops naturally in many systems, but it occurs more frequently and becomes more severe in response to added nutrients from human-sources. Hypoxic zones, like those in the Gulf of Mexico, Lake Erie, and the Baltic Sea, are often referred to as “Dead Zones” because most aquatic organisms leave the area or are killed by the low oxygen concentrations. The concentration of 2.0 mg/L is lethal for some fish species, however, fish begin to be negatively affected by hypoxia at higher concentrations. To identify an ecologically relevant threshold of hypoxia for fish, my coauthors and I (lead author: Allison Hrycik) performed a meta-analysis of laboratory experiments examining at which point fish growth and consumption were negatively affected by low dissolved oxygen concentrations. Defining a more relevant definition of hypoxia for a broad range of fish species may help with identification and management of hypoxic habitats.

Check out our article <here>

 

Nutrient Loading Trade-offs for Fish Habitat Quality between Production and Hypoxia

In some bodies of water, hypoxia, or low dissolved oxygen concentrations, develops more frequently and becomes more severe (lower) when extra nutrients enter the water. However, the additional nutrients can also increase food available to many fish species, which may increase fish biomass (through reproduction and growth), aka fish production. We explored this balance between hypoxia and production using a computer model of habitat quality in the central basin of Lake Erie. Understanding how aquatic habitat responds to varying nutrient concentrations will help better predict ecosystem responses to increased nutrient loading, as well as help improve understanding of how ecosystems may respond during nutrient reduction programs.

Read more about this in technical bulletin No. 3 published by the Old Woman Creek National Estuarine Research Reserve

 

Yellow Perch Behavioral and Physiological Responses to Moderate Hypoxia

Fish are affected by aquatic hypoxia (the depletion of oxygen to relatively low levels) at varying concentrations of dissolved oxygen depending upon species tolerances, temperature, and other environmental conditions. Often, the effects of hypoxia on fish are studied at lethal or close to lethal concentrations (< 2 mg/L). However, hypoxia can negatively affect fish behavior (including food consumption) and physiology (including growth) at higher concentrations as well. To examine the responses of a species that is regularly exposed to moderate to low concentrations of dissolved oxygen, we conducted a series of behavioral and physiological experiments on yellow perch. Yellow perch have been found to forage into hypoxic zones for preferred prey items, and may not abandon an area if oxygen concentrations are are moderate levels. Their responses to moderate hypoxia may help us further understand the effects of developing and persistent hypoxia on aquatic populations.

See our article <here> or our blog post on The Fisheries Blog <here>.

 

Eurasian Perch Morphology and Niche Use in Swedish Lakes

Eurasian perch develop different body-shapes (morphologies) depending on which habitat they utilize during growth and maturation. Fish that use open water habitat develop more stream-lined bodies which allow for higher swimming speeds, whereas fish that use near-shore, vegetated habitat develop stockier bodies which allow for greater maneuverability. This has been prominently observed in Swedish glacial lakes. Seasonal hypoxia (low oxygen concentrations) develops in some Swedish lakes in the late summer coincident with peaks in prey resources associated with the lake bottom. We collected Eurasian perch from lakes across Sweden to determine if morphologies and habitat usage may differ between perch from lakes that develop seasonal hypoxia and those in lakes where late-summer hypoxia does not occur. Elimination or partial elimination of the deep-water lake habitat during peak prey densities may affect the development of perch morphologies and demonstrate further ways in which hypoxia alters ecosystems.

 

Predator Responses to Yellow Perch Egg Skeins

Yellow perch are one of few fish that produce a gelatinous skein around their eggs. There are many hypothesized benefits of the skein including increasing aeration, increasing fertilization success, and protecting the eggs from infection and predation. To determine how predators respond to yellow perch egg skeins, I worked with an undergraduate intern to assess predator preference for different egg types, including yellow perch eggs. Additionally, we performed a preliminary molecular analysis to see what potential molecules within the skein may provide protection. Yellow perch have a high rate of egg survival, and the molecular composition of the skein may be an important cause of this by providing one or more protective benefits.

Check out the article <here> or read about it on The Fisheries Blog <here>.