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American Shad Abundance

Based on the most recent data from the James, Potomac, Rappahannock, Susquehanna and York rivers, the estimate of Chesapeake Bay-wide American shad abundance increased in 2013 to 41 percent of the goal.

The Potomac River has seen the most consistent increase of returning shad, reaching 129 percent of that river’s target. The York River’s shad abundance is at 23 percent of the target, the lower James is at 13, the Rappahannock is at 89 while the upper James and Susquehanna rivers remain at less than 1 percent.



Shad Abundance


Shad Abundance (2013)

Map: Shad Abundance (2013)

Date created: Mar 24 2014 / 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

Produced by Steve Droter
Stock Footage: Photography by Michelson, Inc. and Jim Thompson, MD DNR
Photos: Library of Congress, LC-DIG-ggbain-18896, LC-DIG-hec-06375
Music: “A Moment of Jazz” by Ancelin

Importance

American shad form an important link in the Bay food web. Shad feed on zooplankton and are preyed upon by larger fish, including bluefish, weakfish and striped bass.

Historically, local economies flourished from the annual shad run in the spring, when the fishes’ upriver migration begins. But shad populations were decimated in the 1970s by overfishing, pollution, and dams and other blockages that prevent the fish from reaching their upstream spawning grounds.

Goal

Spawning shad stocks are tracked in five major river systems, each with its own numeric target to meet or exceed:

James River:

  • Lower: 34.66 Catch per Unit Effort (CPUE)
  • Upper: 500,000 shad passing Boshers Dam annually

Potomac River: 31.1 CPUE running average

Rappahannock River: 7.85 CPUE

Susquehanna River: Two million shad passing York Haven Dam annually

York River: 17.4 CPUE

Long-term trend (2000-2013)

Bay-wide: As a whole, Chesapeake Bay American shad abundance has steadily increased from 8.6 percent to 40.6 percent of the goal.

  • The shad abundance trend in the Potomac is responsible for driving the overall upward Bay-wide trend since shad passage at York Haven and Boshers dams remains negligible, and since shad abundance trends on the York, Rappahannock, and lower James are variable.
  • If the current trends continue then goal achievement will decline and stabilize at a lower level. At that point, further increases can only occur if American shad abundance begins to increase in the other river systems.

James River: Abundance has remained around 10 percent of the target, with a peak of 14 percent in both 2003 and 2011 and a low of 2 percent in 2006.  Abundance estimates for the James River are a weighted combination of the upper James (Boshers Dam) and lower James data.

  • Upper James: Abundance at Bosher’s Dam has remained minimal at less than 1percent of the target.
  • Lower James: Fluctuated between 4-27 percent of the target.

Potomac River: Unlike the other rivers, the Potomac’s abundance measurement is a running geometric mean calculated for all years since 1999. Abundance has steadily increased from 12.4 percent to129.4 percent of the target.

Rappahannock River: Abundance peaked to approximately 90 percent of the target in 2003 and 2004, declined to a minimum of less than 30 percent in 2010and peaked again to approximately 90 percent in 2012.

Susquehanna River: Abundance has remained minimal at less than 1 percent of the target. Only a small portion of the shad that pass Conowingo Dam reach and pass York Haven Dam. There is optimal spawning habitat above York Haven Dam.

York River: Abundance reached a peak of 75 percent of the target in 2001 then stabilized at approximately 50 percent. Since 2005, shad abundance has declined to levels between 20-30 percent of the target.

Change from previous year (2012-2013)

Bay-wide: Increased from 38.5 percent to 40.6 percent of goal achieved.

James River: Decreased from 9.6 percent to 7.1 percent of the target. Abundance estimates for the James River are a weighted combination of the upper James (Boshers Dam) and lower James data.

  • Upper James: Remained below 1 percent of the target (slight increase from 184 to 192 shad passing Boshers Dam).  Boshers Dam data for 2013 are considered provisional (as of March 2014).
  • Lower James: Decreased from 17.5 percent to 12.9 percent of the target (6.1 to 4.5 CPUE).

Potomac River: Increased from 119.5 percent to 129.4 percent of the target (36.6 to 39.4 CPUE)

Rappahannock River: Decreased from 92.7 to 88.9 percent of the target (7.3 to 7 CPUE).

Susquehanna River: Remained below 1 percent of the target (slight decrease from 224  to 202 shad passing York Haven Dam)

York River: Increased from 18.2 percent to 22.8 percent of the target (3.2 to 4 CPUE)

Additional Information

American Shad Restoration

Three of the rivers (James, Potomac and Susquehanna) have fish passage systems in place so shad can bypass dams and other blockages.

Several challenges persist for restoration of American shad. American shad use the Chesapeake Bay for spawning and nursery habitat, and reside along the Atlantic Coast (outside the Bay) for most of their life. If the shad abundance trend reverses from increasing to decreasing, this suggests that there may be factors external to Chesapeake Bay affecting American shad such as predation influences and/or bycatch in coastal fisheries.

  • Since American shad are a coastal species the Atlantic States Marine Fisheries Commission (ASMFC) makes management decisions, such as the harvest moratorium and allowable bycatch.
  • Low shad abundance in the Bay and along the Atlantic coast is thought to be the partial result of bycatch issues in offshore fisheries (located in the Exclusive Economic Zone, or EEZ).

American Shad Restoration Goals

The James River restoration goal of 500,000 American shad above Boshers Dam is based upon the number of shad that can be supported by the 137 miles (11,930 acres) of habitat that became available following construction of the Boshers Dam fishway.

  • The number of acres was multiplied by 50 shad per acre, which is consistent with the Susquehanna River methodology and studies of the Connecticut and Columbia rivers.
  • A total of 568,200 shad can be supported between Boshers Dam and Lynchburg, Virginia, including tributaries in between.
  • The Boshers Dam fishway was sized to pass 500,000 shad annually.

The Susquehanna River restoration goal of two million American shad above the York Haven Dam was developed for the 1981 FERC hearings during hydro-project relicensing.

  • Research in the Connecticut and Columbia rivers estimated up to 50 American shad per acre during the spawning run.
  • Acres of available spawning habitat in the Susquehanna River were estimated and then multiplied by 50 shad per acre.
  • The resulting estimate of two million shad represents how many spawning shad can be supported above the York Haven Dam, assuming effective fish passage downstream.

Benchmark restoration goals established via the 2007 ASMFC American Shad Stock Assessment are the targets for each tributary.

  • The goals for the Potomac, York, Rappahannock, and lower James Rivers are based on 1950s population levels. Catch data for this period is available for the Potomac and York Rivers, but not for the Rappahannock and lower James. The ratio of the York 1980s data the 1950s data was calculated, and this ratio was used to back calculate 1950s catch indices from available Rappahannock and lower James 1980s data. The major assumption is that the lower James and Rappahannock showed the same declining trend as the York from the 1950s to the 1980s.
  • Fish passage count goals previously established by Pennsylvania and Virginia are the targets for the York Haven Dam and Boshers Dam respectively.

American Shad Abundance Data

The Susquehanna and James river counts are determined by fish passage data at York Haven and Boshers Dams, respectively.

  • Assessment of the Susquehanna River changed from shad passage at Conowingo Dam to shad passage at York Haven Dam to reflect the goal of two million shad passing the York Haven Dam annually.
  • On the James River, American shad passage at Boshers Dam is compared to a passage goal of 500,000 shad.

Values for the lower James, Rappahannock and York rivers are determined using gill-net data from the Virginia Institute of Marine Science. Values for the Potomac River are determined using pound net bycatch and discard data from the Potomac River Fisheries Commission. To determine goal achievement, the 1950s commercial Catch per Unit Effort (CPUE) is compared to the current commercial (Potomac River pound net) or fishery-independent CPUE monitoring.

The number of shad passed at the York Haven and Boshers dams and the CPUE of shad caught via gill net and pound net are long term datasets that can be used for comparison with data from previous time periods. The data trends inform managers where efforts have been successful further study and restoration efforts are needed. Furthermore, these data are collected for other multi-jurisdictional management needs making these monitoring efforts relatively cost effective.

Source of Data

Chesapeake Bay Program

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