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Appendix U. Filter Feeders White Paper

This appendix is a deliberative document related to options for incorporating the effects of filter 

feeders into the Chesapeake Bay total maximum daily load (TMDL) and implementation plans.
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Strategies for Allocating Filter Feeder Nutrient 

Assimilation into the Chesapeake Bay TMDL

Prepared for U.S. Environmental Protection Agency

Prepared by Tetra Tech, Inc., 10306 Eaton Place, Suite 340, Fairfax, VA 22030

1. Introduction

Filter feeders play an important role in the uptake of nutrients from the Chesapeake Bay and have the 

potential to significantly improve water quality if present in large numbers. The current goal for the 

Chesapeake Bay is to increase the native Eastern oyster, Crassostrea virginica, population tenfold. A 

population increase of that magnitude could remove 10 million pounds of nitrogen annually (Cerco

2005). Menhaden fish, Brevoortia tyrannus, are another filter feeding organism in the Chesapeake 

Bay. This paper explores the options for incorporating the effects of filter feeders into the Chesapeake 

Bay TMDL and implementation plans. As a way of fostering management and restoration of filter 

feeders, the U.S. Environmental Protection Agency (EPA) intends to investigate future monitored 

levels of filter feeder populations and incorporate that into EPA’s model-based tracking of state 

progress in achieving the 2-year milestones.

2. Current Harvest Situation

The Atlantic States Marine Fisheries Commission (ASMFC) reports that the reduction fishery 

harvested 85,000 metric tons of menhaden from the Chesapeake Bay in 2008 and 21,150 metric tons 

from bait landings (ASMFC 2009b). The vast majority of the catch is in the Virginia portion of the 

Chesapeake Bay using the purse seining method. Purse seining has been banned in the Maryland 

portion of the Chesapeake Bay for decades, so menhaden are primarily harvested via pound nets.

Addendum IV to Amendment 1 to the Atlantic Menhaden Fishery Management Plan (Chesapeake Bay 

Reduction Harvest Cap Extension) extends the annual harvest cap established under Addendum III at 

109,020 metric tons on reduction fishery harvests from the Chesapeake Bay (ASMFC 2009a). That 

will extend the cap through 2013. The cap was extended to allow further investigation into the 

abundance of menhaden in the Chesapeake Bay. There is concern that localized depletion of menhaden 

in the Bay is occurring. Stock assessments are conducted on a coast-wide basis and not on the Bay 

individually, so the Bay population is unknown.

According to the National Marine Fisheries Service (NMFS) Annual Commercial Landings Statistics 

(NMFS 2010), 249,485 pounds of eastern oyster were harvested in Maryland in 2008, and in Virginia, 

352,678 pounds of eastern oysters were harvested. Current oyster populations are about 1 percent of 

the historic population. This is because of a number of factors including, historical overharvesting, 

disease, loss of habitat, excess sedimentation from deforestation, agricultural practices, urban 

development, and natural predation (CBP 2009).
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3. Strategies to Increase Filter Feeder Populations in the Chesapeake 

Bay

Menhaden Nutrient Assimilation

According to Brush et al. (2009), the Chesapeake Bay larval menhaden appear to feed on zooplankton, 

then transition to phytoplankton as juveniles and return to higher zooplankton consumption rates as 

adults (age 1+). Given calculated consumption rates for menhaden, based on age, “adults are unlikely 

to significantly impact phytoplankton biomass and production on a baywide basis” (Brush et al. 2009). 

Juvenile consumption of algae is estimated to be a few percent of the daily phytoplankton biomass in 

the summer and fall, and up to 5 percent and 20 percent of daily productivity in the summer and fall, 

respectively” (Brush et al. 2009). Menhaden might influence water quality on a smaller scale, such as 

an individual tributary, Bay segment, or menhaden school (Brush et al. 2009). A menhaden simulation 

is fully operational in the CBP wWater Quality and Sediment Transport Model of the Chesapeake Bay, 

and the model corroborates the findings of Brush et al. (2009). Although the influence of menhaden 

ion water quality is estimated to be less than that of oyster filter feeders, even a small percentage of 

nutrient assimilation or chlorophyll reduction in the Chesapeake Bay would ease the pressure in 

meeting 2-year milestones.

Oyster Nutrient Assimilation

Research shows that 700 to 5,500 pounds of total nitrogen are removed annually per 1,000,000 marketsized oysters. That is a wide range of biomass needed for offsets. Assuming the 2:1 reduction 

requirement under Virginia’s trading program, 3.6–28.5 million oysters would be needed to offset 

10,000 pounds of total nitrogen (Stephenson 2008).

Stephenson (2009) estimates the cost of total nitrogen reduction at $0–$100 per pound. In comparison, 

agricultural best management practices (BMPs) costs in Virginia range from $4 to $200 per pound and 

urban stormwater BMPs can be $25 to more than $1,000 per pound or more (Stephenson 2009).

Oyster Restoration and Preservation

Sanctuaries are already part of the planning process in the Virginia Oyster Restoration Plan and 

Maryland Priority Restoration Areas. Sanctuary areas could provide spawning areas to increase the 

population of wild oysters.

The 2009 Maryland Oyster Restoration and Aquaculture Development Plan would increase sanctuary 

areas from 9 percent to 24 percent of the remaining quality habitat (36,000 acres) in certain locations: 

Magothy River, Chester River, the area between Patapsco and Back Rivers, Upper St. Mary’s River, 

Point Lookout, Little Choptank River, Upper Patuxent River, and the area between Hooper Strait and 

Smith Island.

The Maryland Oyster Restoration and Aquaculture Development Plan also outlines 600,000 acres 

newly available for bottom leasing, including 95,524 acres of formerly off-limits natural oyster bars, 

and develops Aquaculture Enterprise Zones, which are areas preapproved for leasing (MDNR 2009).

Challenges to Increasing Oyster Populations

A limited amount of bottom is suitable/available as oyster habitat. The Oyster Management Plan (CBP 

2004) suggests that there are 10,000 to 20,000 acres of restorable habitat in Maryland and about 28,500 
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acres in Virginia. Even within suitable habitat areas, disease mortality and reduced fecundity are major 

inhibitors to population expansion.

There is a need to provide greater incentives for aquaculture of native oysters. Oyster aquaculture is 

limited by the supply of disease-resistant seed oysters. Expansion of aquaculture investment is not 

likely until more seed is available, which is limited by cost-effective market production from seed 

(CBP 2004).

4. Accounting for Filter Feeders in the TMDL

EPA’s intention is to base the TMDL on the current population of filter feeders. Potential future 

population changes would not be accounted for in the TMDL. If future monitoring data indicate 

changes in the filter feeder population, the 2-year milestone delivered load reductions can be adjusted 

accordingly. The adjusted loads will be compared to the 2-year milestone commitments to ensure each 

state is meeting its obligations.

5. Crediting Filter Feeder Benefits

During the 2-year milestone evaluation of filter feed populations, credits or debits for changes in 

populations and associated nutrient assimilation can be assigned in one of two ways that EPA is 

considering.

Under Option A, only the state responsible for the filter feeder changes would obtain a credit/debit 

towards reaching its 2-year milestones. It would be possible for any state or the District of Columbia to 

receive credit toward increasing filter feeder populations. Maryland and Virginia can implement their 

programs directly. Nontidal states and the District of Columbia could pay into Maryland and Virginia 

programs to increase filter feeder populations. Maryland and Virginia would have to ensure that any 

projects funded by other jurisdictions are in addition to activities planned by Maryland or Virginia or 

both. To eliminate double counting, each project credit must be properly assigned to the jurisdiction 

paying for the project.

Under Option B, any nutrient credit/debit associated with a change in filter feeder populations would 

be distributed proportionally across all the states and the District of Columbia, regardless of the 

jurisdiction responsible for funding or implementing the project.

Under both options, the changes in filter feeder populations would be based on monitoring data. To 

accurately assign credits to the appropriate jurisdiction and ensure milestones are reached, restoration 

activities and population increases must be tracked and verifiable. Regardless of the crediting option 

chosen, Maryland and Virginia should address filter feeder management in their watershed 

implementation plans.

6. Other Issues of Concern

While increasing filter feeder populations can provide nutrient assimilation to mitigate the effects of 

excess nutrients, it is not a method of pollutant source reduction. Because nutrient assimilation can be 

considered an in-stream treatment technology by some regulators, there is some concern that it cannot 

be used in lieu of advanced wastewater treatment technologies (Stephenson 2009). Additionally, 

because pollutants are not reduced at or near the source, this strategy could create a problem with 
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meeting local water quality standards in the upstream jurisdictions. Further consideration should be 

given to address these issues.

7. References

ASMFC (Atlantic States Marine Fisheries Commission). 2009a. Addendum IV to Amendment 1 to the 

Atlantic Menhaden Fishery Management Plan, Chesapeake Bay Reduction Harvest Cap 

Extension. Atlantic States Marine Fisheries Commission, Washington, DC.

ASMFC (Atlantic States Marine Fisheries Commission) Atlantic Menhaden Plan Review Team. 

2009b. 2009 Review of the Fishery Management Plan and State Compliance for the 2008 

Atlantic Menhaden (Brevoortia tyrannus) Fishery. Atlantic States Marine Fisheries 

Commission, Washington, DC.

Brush, M.J., R.J. Latour, E.A. Canuel, P.J. Lynch, and E.D. Condon. 2009. Modeling Atlantic 

Menhaden in Support of Nutrient and Multispecies Management – Draft. College of William 

and Mary, Virginia Institute of Marine Science, Gloucester Point, VA.

Cerco, C. 2005. The Chesapeake Bay Environmental Model Package. Presentation to the Chesapeake 

Bay Program Office Modeling Quarterly Review. October 2005, Annapolis, MD.

CBP (Chesapeake Bay Program). 2004. Oyster Management Plan. Chesapeake Bay Program, 

Annapolis, MD.

CBP (Chesapeake Bay Program). 2009. Oyster Harvest. 

<http://www.chesapeakebay.net/oysterharvest.aspx?menuitem=14701>. Accessed January 26, 

2010.

MDNR (Maryland Department of Natural Resources). 2009. Maryland Oyster Restoration and 

Aquaculture Development Plan—Presentation. Maryland Department of Natural Resources, 

Shellfish Division, Baltimore, MD.

Stephenson, K. 2008. Nutrient Offsets in Virginia: Update and Alternatives Analysis. Presented at 

Virginia Rural Water Association Conference. March 18, 2008, Williamsburg, VA.

Stephenson, K. 2009. The Economics of Nutrient Harvest: Overview of Alternatives and Challenges to 

Creating Incentives. Presented at Bioextractive Technologies for Nutrient Remediation 

Workshop, December 14, 2009, Stamford, CT.

NMFS (National Marine Fisheries Service) National Oceanic and Atmospheric Administration. 2010. 

Annual Commercial Landings Statistics. 

<http://www.st.nmfs.noaa.gov/st1/commercial/landings/annual_landings.html>. Accessed 

January 26, 2010.