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American Shad Abundance

Data from the James, Potomac, Rappahannock, Susquehanna and York rivers show the abundance of American shad in the Chesapeake Bay fell from 39 percent to 38 percent of the goal in 2016.

Each river from which shad abundance data is collected has its own restoration target. Between 2015 and 2016, relative shad abundance dropped to the lowest index values ever reported in the Rappahannock, York and Lower James rivers, reaching 21 percent, 9 percent and 2.7 percent of the targets, respectively. Abundance remained negligible at Bosher’s Dam on the Upper James River and at York Haven Dam on the Susquehanna River. Relative abundance has increased and surpassed the restoration target in the Potomac River—the only waterway in which abundance is represented with the running average of the catch rate since data collection began—over the course of data collection.



Shad Abundance




July 22, 2011

What are American shad and why are they important to the Chesapeake Bay? Bruce Vogt from the National Oceanic and Atmospheric Administration (NOAA) explains how the watershed’s shad population has changed over time and what scientists are doing to restore the anadromous fish to our waterways.

Learn more about shad in the Chesapeake Bay Program’s online Field Guide.

Importance

American shad (Alosa sapidissima) form an important link in the Chesapeake Bay’s food web. The return of the migratory fish from the ocean to freshwater rivers each spring brings food to the Bay in the form of protein-rich eggs, adult shad that can be captured during the spawn and a new generation of shad that can offer forage to striped bass, bluefish and other species when they return to the sea. But pollution, historic overfishing and the construction of dams that block the migratory fish from reaching their upstream spawning grounds have critically lowered shad populations. Shad recovery is progressing, but can be hampered by natural predation and commercial bycatch. Commercial harvest is closed across most of the region and our partners are working to remove dams and restock rivers with hatchery-raised fish.

Goal

Between 1989 and 2013, more than 2,570 miles of fish passage were opened in the Chesapeake Bay watershed to help American shad and other migratory fish move between freshwater rivers, the Bay and the ocean. In 2014, the Chesapeake Bay Program set a goal to open an additional 1,000 stream miles to migratory fish and a goal to improve our capacity to understand the role forage fish populations play in the Bay ecosystem.

This indicator incorporates shad abundance data from five of the watershed’s rivers. Each river has its own restoration target. While the targets of two rivers are measured by the amount of shad that pass a certain dam each year, the rest are measured in “catch per unit effort” or catch rate.

  • Lower James River Target: 34.66 catch per unit effort (CPUE)
  • Upper James River Target: 500,000 shad passing Bosher’s Dam annually
  • Potomac River Target: 31.1 CPUE running average
  • Rappahannock River Target: 7.85 CPUE
  • Susquehanna River Target: two million shad passing York Haven Dam annually
  • York River Target: 17.4 CPUE

The Upper James target is based on the number of shad that can be supported by the 137 miles (or 11,930 acres) of habitat available above the Bosher’s Dam fishway. The Susquehanna target is based on the number of shad that can be supported by the habitat available above the York Haven Dam and was developed for the 1981 Federal Energy Regulatory Commission hearings during the dam’s relicensing. The Lower James, Potomac, Rappahannock and York targets are based on shad abundance levels during the 1950s.

Long-term trend (2000-2016)

Between 2000 and 2016, American shad abundance in the Chesapeake Bay increased from 11 percent to 38 percent of the goal. The Potomac River—the only waterway in which abundance is represented with the running average of the catch rate since data collection began in 1999—has seen a positive trend in progress as it is measured toward the population target and is responsible for driving the overall Bay-wide trend since 2000. Shad abundance has been variable in the Lower James, Rappahannock and York rivers and remained negligible in the Upper James and Susquehanna rivers. Scientists attribute the increases in the Potomac population to a series of factors, including: improvements in water quality; a resurgence in underwater grass beds; moratoriums on shad harvest; the installation of a fish passageway at Little Falls Dam and the removal of Embry Dam; stocking efforts that reprint fish to rivers and kick-start local populations; and the overall suitability of the Potomac as shad habitat.

If current trends continue, shad abundance will decline and stabilize at a lower percentage of the overall goal. At that point, increases will only occur if shad return to other river systems.

  • James River: Abundance has varied, with peaks of 14 percent of the target in 2003 and 2011 and a low of about 1.5 percent in 2016. Abundance estimates for the James are a weighted combination of data collected in the upper and lower portions of the river. In the Upper James, abundance has remained negligible at less than one percent of the target. In the Lower James, the abundance index has fluctuated between 2.7 and 27 percent of the target.
  • Potomac River: The abundance index has increased from 21 percent to 139 percent of the target. Unlike other waterways, abundance estimates for the Potomac are a running average of the catch per unit effort for all years since 1999.
  • Rappahannock River: The abundance index has seen notable highs, reaching 90 percent of the target in 2003 and 2004, 93 percent of the target in 2012 and 110 percent of the target in 2014. The index value fell to an all-time low of 21.4% in 2016. 
  • Susquehanna River: Abundance has remained negligible at less than one percent of the target. Only a small portion of the thousands of shad that pass the Conowingo Dam reach and pass the York Haven Dam, above which is optimal spawning habitat.
  • York River: The abundance index peaked at 75 percent of the target in 2001 and hovered around 50 percent for the next three years. Between 2005 and 2013, the abundance index remained between 20 and 30 percent of the target. In 2014, it peaked at 58 percent, but in 2015, it fell to a low of 11 percent, and in 2016, it reached a new low of 9 percent.

Change from previous year (2015-2016)

Between 2015 and 2016, American shad abundance in the Chesapeake Bay decreased from 39 to 38 percent of the goal.

  • James River: Abundance fell from 2 percent to 1.5 percent of the target. In the Upper James, abundance remained minimal at less than 1 percent of the target (with 36 shad passing Bosher’s Dam). In the Lower James, the abundance index fell from 3.6 to 2.7 percent of the target (1.56 to 0.96 CPUE).
  • Potomac River: The abundance index rose from 133 percent to 139 percent of the target (41.4 to 43.3 CPUE running average).
  • Rappahannock River: The abundance index fell from 65 percent to 21 percent of the target (5.1 to 1.7 CPUE).
  • Susquehanna River: Abundance remained negligible at less than 1 percent of the target (with 178 shad passing York Haven Dam).
  • York River: The abundance index fell from 11 percent to 9 percent of the target (1.9 to 1.5 CPUE).

Additional Information

Collecting data

Spawning stocks of American shad are monitored in the James, Potomac, Rappahannock, Susquehanna and York rivers. Values for the Upper James and Susquehanna are determined by fish passage data from Bosher’s Dam and York Haven Dam, respectively. Values for the Lower James, Rappahannock and York are determined by gill net data from the Virginia Institute of Marine Science. Values for the Potomac are determined by pound net bycatch and discard data from the Potomac River Fisheries Commission.

Shad are also monitored in other parts of the watershed—including the Upper Bay and several Maryland tributaries—but because these areas lack established restoration goals, these data are not included in this indicator.

Because these data are collected for multi-jurisdictional resource management, shad monitoring efforts are relatively cost-effective. The long-term datasets can be compared to data from previous time periods, and trends show managers where conservation efforts have been successful and where further study and restoration are needed.

While no Maryland tributaries are featured in this indicator, the Maryland Department of Natural Resources has monitored the shad population in its portion of the Susquehanna River since 1984 through an annual hook and line survey conducted just below the Conowingo Dam. In June of 2017, the state provided a summary of these efforts.

Restoring American shad

Several challenges persist both in and outside of the Chesapeake Bay watershed for restoring American shad. Inside the watershed, dams, culverts and other structures built across rivers and streams continue to block the migratory fish from reaching their upstream spawning grounds. Along the Atlantic coast, predation and bycatch can lower shad abundance.

Because shad are a coastal species, the Atlantic States Marine Fisheries Commission (ASMFC) makes management decisions (like harvest moratoriums or allowable bycatch). Local jurisdictions have closed commercial shad harvest across most of the watershed and our partners are working to remove dams and restock rivers with hatchery-raised fish.

Source of Data

Chesapeake Bay Program

Related Indicators

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