I enjoy eating fish. I also enjoy catching them. And after learning about the impact that a couple of recent invaders have had on the Chesapeake Bay, I’ve added two new fish species to my catch list.
About a year ago, I sat in a meeting (which I do a lot) and listened to a presentation on yet another threat to the Chesapeake Bay’s aquatic environment. This threat came in the form of the blue and flathead catfish, the finfish equivalent to the invasive zebra mussel that has upset the aquatic ecosystem of the Great Lakes.
Blue catfish are considered “apex predators”; they sit at the top of the food chain. They consume not only other finfish, but shellfish as well. They have no predators. Introduced to Virginia’s James, Rappahannock and York rivers as a sport fish in the 1960s, ‘70s and ‘80s, they have multiplied and extended their reach into other parts the Bay. Apparently, they are here to stay.
Recently, the Maryland Department of Natural Resources (DNR) launched a public awareness campaign to promote a “catch and cook” movement in place of the usual “catch and release” program. The agency is working with restaurants and fish processors to market these catfish. During the campaign’s April kick-off event, we were treated to samples of what these demons of the deep might taste like. I went back for seconds (several times). This is a great source of protein for those who rely on fishing for both sustenance and subsistence. And while catfish are bottom feeders, I’ve been assured that, as long as we eat fish that are smaller than 32 inches, there shouldn’t be any concern about the bioaccumulation of toxins. Good to know.
The Bay has become home to other invasive fish, as well. We all remember the northern snakehead! While this critter isn’t as pervasive as the blue catfish, it is another species that has pushed portions of the Bay ecosystem out of balance. But let me recommend a snakehead ceviche. If you can’t beat ‘em, eat ‘em! Bon apetit!
Note: The opinions expressed above are those of the author and do not necessarily reflect U.S. EPA policy endorsement or action.
Underwater grass abundance in the Chesapeake Bay increased 24 percent between 2012 and 2013, reversing the downward trend of the last three years.
Because underwater grasses are sensitive to pollution but quick to respond to water quality improvements, their abundance is a good indicator of Bay health. Aerial surveys flown from last spring to last fall showed an almost 12,000-acre increase in grass abundance across the Bay, which scientists attribute to the rapid expansion of widgeon grass in the saltier waters of the mid-Bay and the modest recovery of eelgrass in shallow waters where the species experienced a “dieback” after the hot summers of 2005 and 2010. Scientists also observed an increase in the acreage of the Susquehanna Flats.
“The mid-Bay has seen a big rise in widgeon grass,” said Robert J. Orth, Virginia Institute of Marine Science (VIMS) professor and coordinator of the school’s Submerged Aquatic Vegetation Survey, in a media release. “In fact, the expansion of this species in the saltier waters between the Honga River and Pocomoke Sound was one of the driving factors behind the rise in bay grass abundance. While widgeongrass is a boom and bust species, notorious for being incredibly abundant one year and entirely absent the next, its growth is nevertheless great to see.”
Underwater grasses, also known as submerged aquatic vegetation, are critical to the Bay, offering food to invertebrates and waterfowl and providing shelter to fish and crabs. Like grasses on land, underwater grasses need sunlight to survive. When algae blooms or suspended sediment cloud the waters of the Bay, sunlight cannot reach the bottom habitat where grasses live. While healthy grass beds can trap and absorb some nutrient and sediment pollution—thus improving water clarity where they grow—too much pollution can cause grass beds to die. Indeed, poor water clarity remains a challenge for eelgrass growth in deeper waters.
Until this year, the Bay Program mapped underwater grasses by geographic zone. Now, abundance is mapped in four different salinity zones, each of which is home to an underwater grass community that responds differently to strong storms, drought and other adverse growing conditions. This reporting change “makes more ecological sense,” said Lee Karrh, program chief at the Maryland Department of Natural Resources (DNR) and chair of the Bay Program’s Submerged Aquatic Vegetation Workgroup.
“Reworking our historic data was hard work, but doing so makes it easier to understand patterns in grass growth,” Karrh said.
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.