Scientists examine blue catfish caught harvested by electrofishing during cooperative monitoring work with commercial harvesters .Photo by Maryland Department of Natural Resources staff.
Two recent studies by Maryland Department of Natural Resources scientists – one about underwater grass habitat and another on a major invasive threat – highlight how research findings can inform fisheries management.
A study led by DNR biologist Dr. Joseph W. Love, published in Ecological Modelling (May 2024), modeled the effects of habitat and catch-and-release mortality on largemouth bass populations. Another study by Dr. Love and coauthors Branson D. Williams, Tim Groves, Ross Williams, and Mary Groves examined the movement of blue catfish and was published in Estuaries and Coasts (May 2025).
“DNR’s fisheries management strategies are rooted in science,” said DNR Fishing and Boating Services Associate Director Tony Prochaska. “These two publications provide data that inform how we can manage two very different species, one we work to conserve and another we are trying to control.”
A GIS-based Approach for Managing Catch-and-Release Fisheries
The conservation of largemouth bass, the state’s most popular recreational sportfish, has been a priority for anglers and the Maryland Department of Natural Resources for decades. More than 20 years of monitoring data on largemouth bass populations in the upper Chesapeake Bay watershed were compared with habitat data to model the roles that habitat and angling have on protecting the fishery.
DNR’s habitat suitability model predicts quality of habitat and helps identify patches of fish, allowing managers to predict what happens to a fishery when adverse conditions affect one or more patches of fish.
Model scenarios showed that populations increase with greater levels of submerged aquatic vegetation, which provides protective habitat for juveniles and foraging areas. During periods with lots of grass, largemouth bass abundance remained stable even when more bass mortality, or deaths, occurred during and after catch-and-release, because of high levels of suitable habitat for reproduction and growth.
Conversely, modeling results showed that when habitat conditions declined, catch was predicted to decline or become more variable, and only improve when both catch-and-release mortality decreased and habitat conditions improved.
This research showed catch-and-release fisheries should be managed by protecting and improving essential habitat conditions, when possible, and if not, then by preventing periodic spikes in annual mortality.
This year, the department is working with its Black Bass Advisory Committee to develop a survey of bass tournaments to better monitor and reduce conditions associated with catch-and-release mortality. DNR also routinely monitors the health of submerged aquatic vegetation and conducts an environmental review of in-stream projects that could negatively affect that habitat. The department works with partners to promote best management practices in its permits, the Maryland Fishing and Crabbing Guide, and bass conservation webpage in order to prevent disruption of spawning and to minimize bycatch mortality associated with other fisheries.
Movement and Habitat Use by Invasive Blue Catfish in a Tidal Freshwater River
Blue catfish surgically implanted with a radio tag to track movement within Patuxent River. Fish were also tagged with an orange floy tag asking anyone who catches it to call the Maryland Department of Natural Resources. Photo by Maryland DNR staff
Blue catfish are an invasive species in Maryland, and lowering their biomass will help protect Maryland ecosystems. Since the introduction of blue catfish in Virginia in the 1970s and 1980s, they have spread to all major tidal rivers of Maryland’s portion of Chesapeake Bay. Determining whether localized control can succeed for a species that can swim many miles within a year and repopulate other rivers is a key question for fisheries managers.
To answer that question, Maryland Department of Natural Resources scientists conducted research using dual acoustic-radio tags to learn where blue catfish go during winter and spring in the Patuxent River.
Blue catfish were found in specific, upstream areas during winter, but tended to move more in spring. About two-thirds of tracked fish moved less than one-tenth of a mile per day. Movement into downstream, brackish water occurred during June, but was uncommon.
The authors concluded that river-wide actions underway by the department could help lower biomass in that river. However, coordinated bay-wide efforts in multiple rivers will be needed to prevent future repopulation.
The department is conducting a pilot project this year to work with commercial harvesters to assess populations and remove blue catfish biomass from major rivers using boat electrofishing. DNR and researchers at Salisbury University are also studying whether removing large fish affects population structure, while DNR and the U.S. Geological Survey are developing forecast models to explore how reducing specific size classes in a population could influence long-term population trends.
Members of the public can contribute to this effort by fishing for and harvesting blue catfish or selecting it at restaurants or seafood markets when available.
