Raising oysters along the bed of the Potomac River could lower pollution and improve water quality, according to new findings that show “farm-raised” shellfish are a promising method of managing nutrients.
Image courtesy Robert Rheault/Flickr
Nutrient pollution from urban, suburban and agricultural runoff has long plagued the Potomac, whose watershed spans four states and the District of Columbia and has the highest population in the Chesapeake Bay region. Excess nutrients like nitrogen and phosphorous can fuel the growth of algae blooms, which block sunlight from reaching underwater grasses and create low-oxygen dead zones that suffocate marine life. While filter-feeding oysters were once plentiful in the river—capable of removing nutrients from the water—their numbers have dropped due to overfishing and disease.
In a report published in Aquatic Geochemistry, scientists with the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) show that cultivating shellfish on 40 percent of the Potomac’s bottom would remove all of the nitrogen now polluting the river. While conflicting uses—think shipping lanes, buried cables and pushback from boaters and landowners—mean it is unlikely that such a large area would be devoted to aquaculture, putting even 15 to 20 percent of the riverbed under cultivation would remove almost half of the incoming nitrogen. The combination of aquaculture and restored reefs could provide even greater benefits.
Image courtesy Virginia Sea Grant/Flickr
Shellfish aquaculture could also have benefits outside the realm of water quality: the shellfish could serve as a marketable seafood product, while the practice could provide growers with additional income if accepted in a nutrient trading program. Even so, the report notes that aquaculture should be considered “a complement—not a substitute” for land-based pollution-reducing measures.
“The most expedient way to reduce eutrophication in the Potomac River estuary would be to continue reducing land-based nutrients complemented by a combination of aquaculture and restored oyster reefs,” said scientist and lead study author Suzanne Bricker in a media release. “The resulting combination could provide significant removal of nutrients… and offer innovative solutions to long-term persistent water quality problems.”
At present, there are no aquaculture leases in the Potomac’s main stem. But in 2008, Maryland passed a plan to expand aquaculture in the region, and in 2009, NOAA launched an initiative to promote aquaculture in coastal waters across the United States.
Over the last decade, American shad abundance in the Potomac River has continued its consistent rise, driving the overall upward trend of shad abundance in the Chesapeake Bay.
Image courtesy MTSOfan/Flickr
While shad spend most of their adult lives in the ocean, the anadromous fish migrate into freshwater rivers and streams to spawn. Since 2000, shad abundance in the Bay has increased from 9 percent of the goal to 41 percent of the goal, with the Potomac seeing the most consistent rise in returning shad. Between 2000 and 2013, shad abundance in the Potomac rose from 12.4 percent to 129.4 percent of the target. Scientists attribute this increase to a series of factors, including improvements in water quality; a resurgence in underwater grass beds; the installation of a fish passageway at Little Falls Dam; a moratorium on recreational shad harvest; stocking efforts that reprinted fish to the river and kick-started the population; and the overall suitability of the Potomac as shad habitat.
“While there are several factors behind the shad recovery in the Potomac River, improved water quality is the cornerstone,” said Jim Cummins, director for living resources at the Interstate Commission on the Potomac River Basin (ICPRB) and co-chair of the Chesapeake Bay Program’s American Shad Indicator Action Team. “Without cleaner waters in the Potomac River, we would never have seen such a boost in returning shad. We’ve reached the sustainable fishery target for the river, but we are still working to achieve a more robust goal: to see the shad population healthy and fit, and to see the river run silver again. That’s not a ‘pristine river’ goal—that’s a goal we can achieve.”
The Bay Program tracks the abundance of shad in the James, Potomac, Rappahannock, Susquehanna and York rivers as an indicator of watershed health. Collectively, these five waterways account for about 90 percent of the Bay’s shad population, and each has its own population target.
While shad abundance is relatively high in the Rappahannock River—reaching 92.7 percent of the target in 2012 but falling to 88.9 percent of the target in 2013—abundance remains negligible in the upper James and Susquehanna and variable in the lower James and York. Some variability is natural, but the continued scarcity of shad in the upper James and Susquehanna can be attributed to large dams that block fish passage and mute some of the natural cues that send migratory fish upstream.
Once one of the most valuable fisheries in the Bay, shad populations have declined in recent decades due to pollution, historic overfishing and the construction of dams that block the fish from reaching their spawning grounds. Commercial shad harvest is now closed across most of the region, and Bay Program partners are working to remove dams, install passageways that allow shad to reach upstream habitats and restock waterways with hatchery-raised fish. In addition, students in Maryland, Virginia and the District of Columbia are raising shad and releasing them into the Potomac River, bringing public attention to the importance of the once-forgotten fish.
Overall, shad abundance in the Bay has increased from 8 percent of the goal in 2000 to 41 percent of the goal in 2013.
The Maryland Department of Natural Resources (DNR) has launched a state-wide campaign to teach citizens about the impact of blue and flathead catfish and encourage anglers to remove the invasive species from local rivers and streams.
Native to the Mississippi, Missouri and Ohio river basins, blue catfish were introduced to the James, Rappahannock and York rivers in the 1970s and ‘80s as a sport fish. Flathead catfish were introduced to the James in the 1960s for the same reason. Over time, the natural movement and purposeful introduction of the fish into new waters have hastened their establishment in Chesapeake Bay tributaries.
This concerns scientists, who fear the fast-growing and long-lived blue catfish, in particular, could impact the region’s ecologic and economic resources. Because of its opportunistic feeding habits, the blue catfish has become an apex predator, disrupting the structure of the Bay ecosystem and eating up critical aquatic species.
Indeed, “gut content analyses” of the fish have found American shad, Atlantic menhaden, freshwater mussels and blue crabs in their stomachs. Peyton Robertson, director of the National Oceanic and Atmospheric Administration’s Chesapeake Bay Office and chair of the Chesapeake Bay Program’s Sustainable Fisheries Goal Implementation Team, compared the blue catfish to a Bengal tiger, noting that the fish eats “just about anything.”
“If left unchecked, [blue catfish] could, as top predators, start to impact other parts of our ecosystem,” Robertson said.
But its eradication isn’t feasible, and experts believe the invasive fish is here to stay. So managers hope to mitigate their spread and minimize their impact on native fish.
With support from the Bay Program, DNR has established more than 150 signs at water access points and kiosks around the state to help anglers identify, catch and keep the species, while Maryland Seafood has escalated its efforts to market the fish to restaurants and boost consumer demand.
“[Humans] are great at overfishing things,” said Maryland Seafood Marketing Director Steve Vilnit. “And [the blue catfish] is a species that we want to overfish.”
The Chesapeake Bay Program has submitted a report to Congress outlining the health of the Chesapeake Bay and the effectiveness of the partnership’s management strategies.
Under Section 117(h) of the Clean Water Act, the administrator of the U.S. Environmental Protection Agency (EPA) must submit the report every five years in coordination with the Chesapeake Executive Council.
While the Bay remains in poor health, the report highlights several signs that indicate certain strategies will work to restore the treasured resource. The report notes, for instance, that the Chesapeake Bay Total Maximum Daily Load (TMDL) and Executive Order 13508 have been integral in spurring collaboration among cities, states, federal agencies, nongovernmental organizations and citizens. The Chesapeake Bay Watershed Agreement that Bay Program partners plan to sign this summer will use clear goals and outcomes and increased transparency and accountability to continue this positive momentum.
“The… Chesapeake Bay Watershed Agreement is our preparation for the future—a future where the Chesapeake Bay watershed remains an economic engine for the region, rebuilds a thriving and diverse ecosystem and reclaims its status as a celebrated treasure for the citizens who live in the watershed and throughout the nation,” writes Bay Program Director Nick DiPasquale in the report.