Cleaner water may pose risk to some Lake Erie fish species

A recent study suggests that efforts to reduce nutrient runoff in Lake Erie aimed at curbing harmful algal blooms and alleviating low-oxygen dead zones, might inadvertently affect fishery health.

Researchers, led by Don Scavia, professor emeritus at the University of Michigan School for Environment and Sustainability, utilized a variety of models to highlight the necessity of monitoring multiple aspects of an ecosystem at the same time, particularly as climate change results in increased temperatures and rainfall.

During their investigation, the researchers discovered an unexpected trade-off for fisheries; as nutrient inputs were curtailed to enhance water quality, the catch of the highly sought-after yellow perch species was notably reduced alongside the decrease in dead zones.

“What we’re finding is that as you clean up the lake by reducing nutrients, the ability to support important contemporary fisheries might also decline,” said Stuart Ludsin, professor of evolution, ecology and organismal biology at The Ohio State University and a co-author of the study.

The modeling indicates that anticipated warming will expand the area of the dead zone caused by nutrient overload, suggesting that there is no inclination to relax restrictions; the study also offers projections for future nutrient reduction targets. However, researchers emphasize that nutrient management decision-makers must prioritize fisheries alongside these targets to ensure a balanced approach.

Current federal water-quality guidelines aim to reduce nutrients – primarily phosphorous – in Lake Erie by 40% compared to 2008 levels through strategies such as improving wastewater treatment processes, restoring wetlands, and adopting agricultural and urban practices to reduce runoff. Excess nutrients lead to hypoxia, resulting in diminished dissolved oxygen levels that can devastate aquatic life, creating extensive dead zones.

Ludsin’s lab previously conducted a 2023 study that paved the way for this research, revealing that historical fishery harvests of lake whitefish, yellow perch, and walleye peaked at various water quality levels in Lake Erie. The team identified this situation as a “wicked” management challenge, characterized by complex trade-offs that must be skillfully navigated.

In the recent study, researchers associated predictive modeling of nutrient and temperature impacts on hypoxia in Lake Erie with data from commercial fishery harvests over the last century and climate forecasts for 2030-2099. The findings indicated that an increase in nutrients and warmer air contributes to enhancing hypoxic conditions, highlighting that the rise in temperatures due to climate change should be considered in water quality management.

Although nutrient loads have not yet reached the target reduction of 40%, there has been significant progress over the past decade, according to Ludsin, who is also the co-director of the Aquatic Ecology Laboratory at Ohio State.

Additionally, the influence of dead zones on fish populations has not historically been a significant consideration in water quality management strategies. The results revealed that the larger dead zones in the 1960s and 1970s led to decreased harvests of lake whitefish and walleye, coinciding with a peak in yellow perch catches. Lake whitefish seem to require the cleanest water, while walleye can adapt to lower nutrient levels but have varied dietary options, whereas yellow perch thrive when nutrient levels are elevated.

“When you clean up the lake, you might get rid of zones of low dissolved oxygen, but the loss in food production that comes from reduced nutrients seems to have a more negative impact on yellow perch,” Ludsin said. “So whatever nutrient loading target we move to, there are going to be potential winners, such as lake whitefish, and there could be potential losers, especially for yellow perch and even walleye to some degree.

“The punchline of our research is that there didn’t seem to be any single level of nutrient loading that is going to maximize the production of all three species.”

The authors of the paper advocate for implementing ecosystem-based management approaches that utilize straightforward predictive models to highlight the trade-offs between water quality and fisheries. They emphasize the importance of encouraging interaction between managers from both sectors, who historically have not collaborated effectively.

“When you manage water quality, you should be considering more than just water quality. You need to consider impacts on fisheries, too,” Ludsin said. “Likewise, when you manage for fisheries, it’s not sufficient just to measure catch statistics. You need to be considering the state of the ecosystem and the broader environment.”

With newly acquired long-term funding, Ludsin aims to aid agencies in establishing targets for water quality control while taking into account the effects on fishery resources.

Journal reference:

1. Donald Scavia, Stuart A. Ludsin, Anna M. Michalak, Daniel R. Obenour, Mingyu Han, Laura T. Johnson, Yu-Chen Wang, Gang Zhao, and Yuntao Zhou. Water quality–fisheries tradeoffs in a changing climate underscore the need for adaptive ecosystem–based management. PNAS, 2024; DOI: 10.1073/pnas.2322595121