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.
For close to a decade, scientists and volunteers have spent their springs at the Nanticoke Shad Hatchery, working to rebuild populations of American shad.
In this small building near Bethel, Del., hundreds of thousands of American shad are raised each year before they are returned to their native spawning grounds in the Nanticoke River. This spring, the hatchery stocked about 558,000 fish to the waterway.
In the early 1900s, excessive commercial harvests took a heavy toll on American shad. Over the past century, poor water quality and the construction of dams that restrict the anadromous fish’s access to upstream spawning grounds have caused shad populations to decline.
Image courtesy Library of Congress
Today, restoration efforts are giving American shad a much-needed population boost. Restocking programs across the Chesapeake Bay watershed—combined with harvest restrictions, improved water quality and the removal of dams—are critical to the re-establishment of the species.
American shad spend most of their lives in brackish and saltwater before returning to their birth waters to spawn. The Nanticoke Shad Hatchery collects its brood stock directly from the Nanticoke River and its Deep Creek tributary to ensure adult fish will return to the waterway and to preserve the genetic integrity of the local shad population.
Throughout the spring spawning season, which runs from mid-March through April, mature shad that are held in the hatchery’s closely monitored, 3,500-gallon spawning tanks periodically release eggs and sperm.
On the morning after an overnight spawning event, pea-sized eggs are filtered into an egg collection tank.
“Bad eggs” are removed from the tank before fertilized eggs are measured by volume and placed in incubation jars to grow.
Eggs that survive to the “eyed” stage are moved to one of four culture tanks, where they will hatch into larval fish within a week.
After a few more days spent in the safety of the culture tanks, the larval fish absorb their nutritive yolk sac and transform into fry that are ready to feed on their own in their natural habitat.
Before the hatchery-produced fish are released into the Nanticoke River, scientists mark them with oxytetracycline. Tracking the fish will allow scientists to gauge their survival and stocking success over time.
Six years of sampling surveys on the Nanticoke River show that adult American shad abundance has increased, while the number of hatchery-produced juveniles has decreased. According to hatchery manager Mike Stengl, this suggests the hatchery is succeeding in its long-term goal: to reduce the percentage of hatchery-grown fish in the river and encourage the wild population to spawn on its own.
Success at the Nanticoke Shad Hatchery and at other hatcheries across the region are giving American shad a second chance at survival in the watershed.
View more photos on the Chesapeake Bay Program Flickr page.