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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 reached 44 percent of the goal in 2014.

The Potomac River has seen the most consistent rise in returning shad, reaching 130 percent of its population target in 2014. The Rappahannock River has also seen notable highs, and reached 110 percent of its target in 2014. Shad abundance remains variable in the lower James and York and negligible in the upper James and Susquehanna.



Shad Abundance


Shad Abundance (2014)

Map: Shad Abundance (2014)

Date created: Mar 25 2015 / Download

American shad were once the most abundant and economically important species in the Chesapeake Bay. Shad are anadromous fish and spend most of their lives in the ocean, returning to freshwater rivers to spawn after they reach maturity. Data for the York, Potomac, Rappahannock and lower James Rivers were provided by the Virginia Institute of Marine Science via an ongoing Catch per Unit Effort (CPUE) study involving American Shad gill-netting. Data for the Susquehanna and upper James Rivers represent published fishway passage values for Conowingo and Boshers Dams, respectively.




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 population 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.

  • Upper James River Population Target: 500,000 shad passing Bosher’s Dam annually
  • Lower James River Population Target: 34.66 catch per unit effort (CPUE)
  • Potomac River Population Target: 31.1 CPUE running average
  • Rappahannock River Population Target: 7.85 CPUE
  • Susquehanna River Population Target: two million shad passing York Haven Dam annually
  • York River Population 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 (2000-2014)

Between 2000 and 2014, American shad abundance in the Chesapeake Bay increased from 11 percent to 44 percent of the goal. The Potomac River has seen the most consistent rise in returning shad and is responsible for driving the positive Bay-wide trend. Shad abundance is also high in the Rappahannock, but negligible in the upper James and Susquehanna and variable in the lower James and York. Scientists attribute the increases in the Potomac and Rappahannock populations 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
  • The overall suitability of the Potomac as shad habitat

If current trends continue, abundance will decline and stabilize without reaching our goal. At that point, further increases will only occur if shad begin to return to those rivers that have seen consistently low spawning stocks.

  • James River: Abundance has hovered around 10 percent of the target, with peaks of 14 percent in 2003 and 2011 and a low of 2 percent in 2006. 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 minimal at less than 1 percent of the target. In the Lower James, abundance has fluctuated between 4 and 27 percent of the target.
  • Potomac River: Abundance has increased from 21 percent to 130 percent of the target. Abundance estimates for the Potomac are a running geometric mean of the catch per unit effort for all years since 1999.
  • Rappahannock River: Abundance 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. 
  • Susquehanna River: Abundance has remained minimal at less than 1 percent of the target. Only a small portion of the shad that pass the Conowingo Dam reach and pass the York Haven Dam, above which is optimal spawning habitat.
  • York River: Abundance peaked at 75 percent of the target in 2001 and hovered around 50 percent for the next three years. Between 2005 and 2013, abundance remained between 20 and 30 percent of the target, but in 2014 it reached 58 percent

Change from previous year (2013-2014)

Between 2013 and 2014, shad abundance in the Bay increased from 40 percent to 44 percent of the goal.

  • James River: Abundance rose from 7 to 12 percent of the target. In the Upper James, abundance remained minimal at less than 1 percent of the target (from 192 to 24 shad passing Bosher’s Dam). In the Lower James, abundance rose from 13 to 21 percent of the target (4.5 to 7.4 CPUE).
  • Potomac River: Abundance rose from 127 percent to 130 percent of the target (39.4 to 40.3 CPUE running average).
  • Rappahannock River: Abundance rose from 89 percent to 110 percent of the target (7 to 8.7 CPUE).
  • Susquehanna River: Abundance remained minimal at less than 1 percent of the target (from 202 to 8 shad passing York Haven Dam).
  • York River: Abundance increased from 23 percent to 58 percent of the target (4 to 10 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 abundance 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.

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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