Doctoral Student Revives a Multi-Agency Research Collaboration to Assess Why the Yellow Perch in the Rivers of the Chesapeake Bay are Struggling

Research examines the health of yellow perch as an indicator of the health of the Chesapeake Bay, urbanization, and even changing weather patterns

Alex MacLeod holding a yellow perch

Image Credit: Lena McBean, University of Maryland

October 24, 2019 Samantha Watters

With a new grant from the Maryland Sea Grant program, Alexander MacLeod, a doctoral student in the department of Environmental Science & Technology (ENST), has earned another piece of funding to address a largely unexplored phenomenon in the rivers that feed into the Chesapeake Bay - struggling yellow perch populations. As a more in depth investigation of initial studies conducted through the United States Geological Survey (USGS), the Maryland Department of Natural Resources (DNR), and the United States Fish and Wildlife Service (USFWS), MacLeod is leading the collaboration and pooling resources together across each of these agencies among other supporters to create his own doctoral research program to examine why yellow perch reproduction is in decline and egg hatch rates are as low as 10%. Known as the harbingers of spring, these fish are not only an important commercial and recreational fishery in the Bay, but act as an indicator of overall Bay and ecosystem health.

“As far as the Chesapeake Bay is concerned, yellow perch are a relatively understudied species,” says MacLeod. “When I was considering a PhD, I decided that if I can study this phenomenon, I’d do the PhD because it is a real world problem that has been largely ignored, and it is truly rare for fish populations to be in precipitous decline even after fishing pressure was eliminated. This is a far more complex challenge than overfishing, and it is worth rising to the occasion. Yellow perch aren’t crabs or oysters, or even the rockfish that garner so much attention in the Bay, and yet the consistent environmental and reproductive challenges these populations have been facing for decades may be indicative of serious issues for those iconic Bay fisheries in the future.”

Recreational fishing was closed for twenty years between 1989 and 2009 in many rivers of the Bay, primarily on the Western Shore, to try to revitalize the yellow perch population. The rockfish fishery in the Bay was completely closed for five years in 1985, resulting in a major recovery. However, with yellow perch, there was no change to the population when fishing was limited, so recreational fishing was reopened in 2010.

In initial studies conducted by MacLeod’s collaborators at USGS, USFWS, and DNR from 2007 to 2009, researchers examined urbanization (impervious surfaces like parking lots and roads that cause runoff and pollution in waterways) in relation to yellow perch reproduction. The results showed abnormalities in egg viability, ovaries, and testes, particularly in these urbanized watersheds. “This was a profound result that clearly showed there is something very wrong with the development of the eggs, and we didn’t know exactly what was going on there,” says Fred Pinkney, USFWS.

Collaborative sampling
Collaborative sampling

Unfortunately, the results of these studies didn’t immediately translate into additional research until MacLeod picked up the torch with his current work. MacLeod set some lofty goals for his research, hoping to identify what chemicals may be making it into the waterways and affecting yellow perch, working under Lance Yonkos in ENST, and partnering with Pinkney in the Environmental Contaminants Program at USFWS. In order to do this, MacLeod is examining nearly the entire lifecycle of the fish, looking at egg viability, genetics in the brain, liver, and ovaries, hormones in the blood, and tissue changes to see if certain genes or hormones explain differences in reproductive health in weaker and stronger yellow perch populations across the Bay. To facilitate this work, he is also partnering with Vicki Blazer, a fish pathologist with USGS specializing in reproductive health, and Steve Minkkinen, a fish biologist and project leader in conservation at USFWS. USGS, USFWS, and DNR are all helping with the sampling, processing fish samples, contributing expertise, and providing MacLeod access to their laboratories and instruments for his work. The USGS Environmental Health program is providing passive samplers and chemical analyses to identify potential chemical contaminants.

“A lot of times we do these studies and we are in a scientific bubble, but I know a lot of people along the river are very interested in having a healthy population, especially with yellow perch because it is such a historical fishery,” says Pinkney.

Yellow perch laying an egg chain, or ribbon
Yellow perch laying an egg chain, or ribbon

As a relatively active commercial fishery in the upper Bay equating to about 50,000 pounds annually and an iconic recreational fishery elsewhere in Maryland, the yellow perch are the earliest spawning fish in the Bay - hence their unofficial title, harbingers of spring. As a predominantly freshwater fish, Bay populations of yellow perch are one of the few that report “runs” similar to salmon. They live as adults in the saltier water closer to the Bay, and then run up the rivers and tributaries to lay their eggs in a freshwater environment. Unlike other fish, their long strands or “ribbons” of eggs float in the water, making them an attraction to local communities, as well as an indicator that it is time to fish for yellow perch. This local ritual kicks off the fishing season for the spring.

While unique and attractive, yellow perch egg strands are extremely sensitive to environmental and water conditions since the eggs float in the water, clinging to woody debris. “Different fish seem to be good indicators of exposure to various stressors related to the health of the ecosystem,” says Blazer, USGS. “What we see in yellow perch is these reproductive effects on the eggs, which could have links to contaminants and hormones in the water.”

“A lot of work has been done in the Great Lakes on yellow perch,” explains Yonkos, “but there has been less focus in the Bay. Contaminants in the water directly link to contaminants in eggs, and this is the first investigation of chemical contaminants in this population.”

Alex MacLeod examining a yellow perch sample
Alex MacLeod examining a yellow perch sample

MacLeod adds, “Filling in the gaps with genetics, hormones, and tissue studies, we can start to try to see what is actually going on with this population. Genetics to hormones to tissue - it’s a cascade of potential toxicological effects. But, we can’t ignore that ecology might explain what contaminants do not.”

Ecology and environmental factors are a large piece of the puzzle, with a focus on impervious surfaces and urbanization as it not only relates to contamination, but physical changes in the ecosystem. In highly urbanized areas along the Severn River for example, waterways have been transformed from traditional river systems that moderate water flow, salinity, and temperature into essentially canals, with no buffer between land and water. These transition areas not only provide wildlife with food and shelter, but are ideal for protecting egg chains - without this buffer, there is less opportunity for effective spawning. Additionally, this makes these waterways more susceptible to extreme runoff from increasingly intense weather, and all of these factors can affect health, egg viability, hatch rates, and offspring survival.

“The more and more impervious surface you have, suddenly you start to see these whole species effects where the populations are greatly reduced,” says Minkkinen, USFWS. “Having these different river systems - the Choptank still being more agricultural versus the Mattawoman and Severn seeing more urban development - if we see big differences in these populations and can draw some inferences that man is having some influence on the health of fish, that’s an important thing for people to try to understand, just by us being there and changing the environment.” MacLeod reiterates, “We have to change the way we move water across the landscape, and that’s very complicated.”

MacLeod is looking forward to sharing his data with not only the scientific community, but with local communities that care about their local rivers and yellow perch populations as well as the overall health of the Bay. “People think about the health of the Bay more than they think about the health of the rivers, but these are the arteries that keep it alive, so if you treat those poorly, it undermines overall Bay health. It took the past three years to build up the momentum and funding for this work, but every little bit counts, and we’ve pulled together a lot of smaller grants and leveraged the invaluable partnerships we’ve formed to get to where we can make an impact.”

MacLeod will be sharing perspectives on this work and preliminary findings with a poster presentation at the upcoming AGNR Cornerstone Event: Ensure a Clean and Healthy Chesapeake Bay on October 29, 2019. For more information or to register (free), visit