United States Region III

Environmental Protection Agency Chesapeake Bay Program Office

Biological Evaluation

for the Issuance of Ambient Water

Quality Criteria for Dissolved

Oxygen, Water Clarity and

Chlorophyll a for the Chesapeake Bay

and Its Tidal Tributaries
Biological Evaluation

for the Issuance of Ambient Water Quality Criteria 

for Dissolved Oxygen, Water Clarity and Chlorophyll a

for the Chesapeake Bay and Its Tidal Tributaries

April 25, 2003

U.S. Environmental Protection Agency

Region III
i

CONTENTS

Page

Background ................................................................. 1

Summary of the Proposed Regional Criteria Guidance .............................. 4

Water Quality Standards ...................................................... 5

New and Refined Tidal Water Designated Uses

Chesapeake Bay Water Quality Criteria

Dissolved oxygen criteria

Water clarity

Chlorophyll a

Evaluation Area ............................................................. 10

Federal Listed Species Within the Evaluation Area ................................ 10

Plants

Mammals

Birds

Fish

Reptiles

Mollusks

Insects

Status of Listed Species ....................................................... 17
ii

Manner in Which Regional Criteria Guidance May Affect the Shortnose Sturgeon ..... 18

Water clarity

Chlorophyll a

Dissolved oxygen

Chesapeake Bay oxygen dynamics

Derivation of Chesapeake Bay dissolved oxygen criteria

Shortnose Sturgeon dissolved oxygen sensitivity

Dissolved oxygen criteria protective of shortnose sturgeon

Tidal Water Designated Use Habitats

Chesapeake Bay low oxygen: historical and recent past

Historical and potential sturgeon tidal habitats

Deep-channel habitats

Deep-water habitats

Salinity tolerances

Distribution studies

Chesapeake Bay salinity distributions

Life history of shortnose sturgeon

Status of shortnose sturgeon in the Chesapeake Bay

Delaware Chesapeake migratory corridor

Genetic findings

Field study results

Habitat quality benefits from dissolved oxygen criteria attainment

Recovery of the shortnose sturgeon

Findings .................................................................... 42

Summary and Conclusion ..................................................... 43

References .................................................................. 46

Tables and Figures

Table 1 ...................................................................... 8

Chesapeake Bay dissolved oxygen criteria

Table 2 ...................................................................... 9

Summary of Chesapeake Bay water clarity criteria for application to shallow-water bay

grass designated use habitats.

Table 3 ..................................................................... 10
iii

Chesapeake Bay narrative chlorophyll a criteria.

Figure 1 ..................................................................... 2

Illustration of the nutrient, sediment and dissolved oxygen impaired waterbodies in the

Chesapeake Bay watershed from the 1998 303(d) list.

Figure 2 .................................................................... 11

Chesapeake Bay and its tidal tributaries.

Figure 3 .................................................................... 28

Map of all U.S. Fish and Wildlife Service sturgeon capture location stations where

shortnose sturgeon were caught during June 1-September 30 between 1994- March 2003.

Figure 4 .................................................................... 29

Map of all U.S. Fish and Wildlife Service sturgeon capture location stations where

shortnose sturgeon were caught year-round between 1994 and March 2003.

Figure 5 .................................................................... 32

Map of summer averaged bottom water salinities <5 ppt based on Chesapeake Bay water

quality monitoring program data from 1996-2000.

Figure 6 .................................................................... 33

Map of summer averaged bottom water salinities <15 ppt based on Chesapeake Bay

water quality monitoring program data from 1996-2000.

Figure 7 .................................................................... 34

Long-term averaged spatial distribution of deep-water designated use habitats for

comparison only with figures 5 and 6 salinity distributions. Actual deep-water designated

use habitats will be determined based on pycnocline delineation using monthly

monitoring cruise data.

Figure 8 .................................................................... 39

Locations of all the U.S. Fish and Wildlife Service fisheries-independent sturgeon

sampling stations where no sturgeon were caught.

Appendices

A. Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and

Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional Criteria

Guidance).

B. Technical Support Document for the Identification of Chesapeake Bay Designated

Uses and Attainability. 

C. List of Federally Endangered Species for Maryland, Virginia, Delaware and the

District of Columbia.
 Biological Evaluation

for the Issuance of Ambient Water Quality Criteria 

for Dissolved Oxygen, Water Clarity and Chlorophyll a

for the Chesapeake Bay and Its Tidal Tributaries

U.S. Environmental Protection Agency

Region III

April 2003

The U.S. Environmental Protection Agency’s (EPA) Region III Ambient Water Quality

Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its

Tidal Tributaries (Regional Criteria Guidance) is being evaluated. The EPA is voluntarily

continuing consultation with NOAA National Marine Fisheries Service in accordance with

Section 7 of the Endangered Species Act by issuing this biological evaluation.

The NOAA National Marine Fisheries Service, which is the federal agency with

responsibility for the shortnose sturgeon (Acipenser brevirostrum) under the Endangered Species

Act (ESA), has advised the EPA that shortnose sturgeon have been documented in various areas

of the Chesapeake Bay and its tidal tributaries and are, therefore, considered to be present in the

Bay.

BACKGROUND

The Administrator of the U.S. Environmental Protection Agency (EPA); the governors of

Maryland, Virginia and Pennsylvania; the Mayor of the District of Columbia; and the Chair of a

tri-state legislative body known as the Chesapeake Bay Commission signed the Chesapeake Bay

Agreement in 1987 (Chesapeake Executive Council 1987). A principal goal of that agreement

was a 40 percent reduction of nutrients (nitrogen and phosphorus) entering the Bay tidal waters

by the year 2000 from controllable point and nonpoint sources in the entire 64,000-square-mile

Bay watershed from levels being discharged in 1985. The agreement provided that once

achieved, this level would be maintained thereafter. Implementation of this goal was conducted

in a cooperative manner including actions under state laws primarily for best management

practice (BMP) implementation, and voluntary reductions from both point and nonpoint sources

encouraged by cost share grant programs. The EPA is participating in these activities pursuant

to Section 117 of the Clean Water Act.

Yet in spite of these efforts, nutrient and sediment enrichment related water quality

problems have persisted throughout the Chesapeake Bay and tidal tributaries (Figure 1) (U.S.

Environmental Protection Agency 2003b). Maryland’s portion of the Chesapeake Bay and its

tidal tributaries were listed on its 1996 and 1998 Clean Water Act (CWA) Section 303(d) lists of

impaired waters. In May 1999, EPA Region III identified Virginia’s portion of the Chesapeake

Bay and portions of several tidal tributaries on Virginia’s 1998 CWA Section 303(d) list. 

Delaware’s tidal portion of the Nanticoke River and the District of Columbia’s tidal Anacostia 
Figure 1. Illustration of the nutrient, sediment and dissolved oxygen impaired waterbodies in

the Chesapeake Bay watershed from 1998 303(d) list.

Source: U.S. EPA http://www.epa.gov/owow/tmdl/
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and Potomac rivers have also been listed on the Section 303(d) list. Shortly thereafter, a new

agreement, entitled Chesapeake 2000 was adopted by the Chesapeake Bay Executive Council in

response to a comprehensive assessment of the Bay’s restoration needs and delineated an ambitious

list of new restoration commitments (Chesapeake Executive Council 2000). New York, Delaware

and West Virginia have been brought in as watershed partners committed to these Chesapeake Bay

water quality restoration goals through a six state memorandum of understanding with the EPA

(Chesapeake Bay Watershed Partners 2001). 

Chesapeake 2000 lists the following specific actions as steps to achieve its water quality

goals for nutrients and sediment:

1. By 2001, define water quality conditions (i.e., criteria) necessary to protect aquatic

living resources and then assign load reductions for nitrogen, phosphorus and

sediment to each major tributary;

2. By 2002, complete a public process to develop and begin implementation of revised

Tributary Strategies to achieve and maintain the assigned loading goals;

3. By 2003, the jurisdictions with tidal waters will use their best efforts to adopt new or

revised water quality standards consistent with the defined water quality conditions.

Note that, though the actions still apply, the schedule has changed as follows:

C Final definitions of water quality conditions (i.e., criteria)–April 2003;

C Complete revisions to tributary strategies–April 2004; and

C Adoption of revised water quality standards–July 2005.

To implement and coordinate the above actions, the Chesapeake Bay Program formed a

Water Quality Steering Committee composed of senior water management policy representatives

from all seven watershed jurisdictions–New York, Pennsylvania, Maryland, District of Columbia,

Delaware, Virginia and West Virginia–EPA Region II, Region III and Headquarters, Chesapeake

Bay Commission, Interstate Commission on the Potomac River Basin, and the Susquehanna River

Basin Commission. A wide range of stakeholders including: regional governmental organizations,

the environmental advocacy community and wastewater treatment facility owners and operators

actively participated with the Committee. These partners and stakeholders have been meeting

several times a month over the past three years to meet the water quality commitments set forth in

Chesapeake 2000.

The “water quality conditions necessary to protect aquatic living resources” are being

defined through the development of EPA guidance for Chesapeake Bay specific water quality

criteria for dissolved oxygen, water clarity and chlorophyll a under the direction of the Chesapeake

Bay Program’s Water Quality Steering Committee. Collectively, the EPA believes these three

water quality parameters provide the best and most direct measures of the impacts of too much

nutrient and sediment pollution on the Bay's aquatic living resources–fish, crabs, oysters, and

underwater bay grasses. The criteria are being published by EPA Region III as Chesapeake Bay

specific water quality criteria guidance (U.S. Environmental Protection Agency 2003a).

The criteria are being issued pursuant to the Chesapeake Bay Program’s statutory mandate
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under Section 117 (b)(2)(B) of the Clean Water Act to “implement and coordinate science, research,

modeling, support services, monitoring, data collection and other activities that support the

Chesapeake Bay Program.” These criteria provide EPA’s recommendations to states for use in

establishing water quality standards consistent with Section 303 (c) of the Clean Water Act,

focusing on the recovery and protection of aquatic life resources. 

SUMMARY OF THE PROPOSED REGIONAL CRITERIA GUIDANCE

In order to achieve and maintain the water quality conditions necessary to protect the aquatic

living resources of the Chesapeake Bay and its tidal tributaries, EPA Region III has developed the

Regional Criteria Guidance. The EPA is issuing this guidance in accordance with Section 117(b) of

the Clean Water Act and in accordance with the water quality standards regulations (40 CFR Part

B1). This document presents EPA’s regionally-based nutrient and sediment enrichment criteria

expressed as dissolved oxygen, water clarity and chlorophyll a criteria, applicable to the Chesapeake

Bay and its tidal tributaries. This guidance is intended to assist the Chesapeake Bay states,

Maryland, Virginia and Delaware, and the District of Columbia in adopting revised water quality

standards to address nutrient and sediment-based pollution in the Chesapeake Bay and its tidal

tributaries.

EPA Region III has identified and described five habitats (or designated uses) that, when

adequately protected, will ensure the protection of the living resources of the Chesapeake Bay and

tidal tributaries. Those five uses (summarized below and described in detail in Appendix A and B)

provide the context in which EPA Region III derived adequately protective Chesapeake Bay water

quality criteria for dissolved oxygen, water clarity and chlorophyll a, which are the subject of the

Regional Criteria Guidance. Accurate delineation of where to apply these tidal water designated

uses is critical to the Chesapeake Bay water quality criteria (U.S. Environmental Protection Agency

2003a). 

The Chesapeake Bay dissolved oxygen criteria vary significantly across the five refined tidal

water designated uses to fully reflect the wide array of species living in these different Bay habitats,

as reflected in Table 1. 

The water clarity criteria reflect the different light requirements for underwater plant

communities that inhabit low salinity versus higher salinity shallow water habitats throughout the

Bay and its tidal tributaries. Table 2 provides an overview of the recommended light requirements

for water clarity criteria. 

The EPA is providing the states with a recommended narrative chlorophyll a criteria

applicable to all Chesapeake Bay and tidal tributary waters (Table 3). The EPA encourages the

states to adopt numerical chlorophyll a criteria for application to those tidal waters where algal

related designated use impairments are likely to persist even after attainment of the applicable

dissolved oxygen and water clarity criteria. The Regional Criteria Guidance contains technical

information to support quantitative interpretation of the narrative chlorophyll a criteria. 

The Regional Criteria Guidance is the product of a collaborative effort among the

Chesapeake Bay Program partners. They represent a scientific consensus based on the best
5

available scientific findings and technical information defining water quality conditions necessary to

protect Chesapeake Bay aquatic living resources from effects due to nutrient and sediment overenrichment. Various stakeholder groups have been involved in their development, with

contributions from staff of federal and state government, local agencies, scientific institutions,

citizen conservation groups, business and industry.

 The EPA conducted three reviews of the Regional Criteria Guidance. The third and final

public review of the Regional Criteria Guidance document was completed in January 2003 in

parallel to the second and final independent scientific peer review. The Regional Criteria Guidance,

comments from reviewers and responses to reviewers’ comments will be available on the web on

April 25, 2003 at: http://www.chesapeakebay.net/baycriteria.htm. A full copy of the Regional

Criteria Guidance is attached as Appendix A.

In addition to the Regional Criteria Guidance, EPA Region III distributed a draft Technical

Support Document for the Identification of Chesapeake Bay Designated Uses and Attainability

(Technical Support Document) for public review. The Technical Support Document provides

additional information for states to consider in the refinement of designated uses and modifications

of state water quality standards.

The Technical Support Document was made available for review and comment on

December 16, 2002. Comments received and response to reviewers’ comments are available on the

web at: http://www.chesapeakebay.net/baytsd.htm. A full copy of the draft Technical Support

Document was included in the draft BE previously submitted to NOAA National Marine Fisheries

and the U. S. Fish and Wildlife Service as part of the informal consultation. The final document is

expected to be completed on May 30, 2003. A full copy will be provided, upon publication next

month, as Appendix B.

WATER QUALITY STANDARDS

Water quality standards consist of 1) designated uses for the water body, 2) narrative or

numerical water quality criteria to protect those uses, and 3) an anti-degradation policy. Currently,

each state across the Chesapeake Bay and tidal tributary jurisdictional waters in the current

Maryland, Virginia, Delaware and the District of Columbia designated aquatic life uses to be

protected as part of their water quality standards. The Regional Criteria Guidance enables the states

to consider more specific, and in general, more protective aquatic life use refinements into criteria. 

The Chesapeake Bay watershed states with tidally influenced Bay waters–Maryland, Virginia,

Delaware and the District of Columbia–are ultimately responsible for defining and formally

adopting a refined set of designated uses into their respective water quality standards.

New and Refined Tidal Water Designated Uses

The five new and refined Chesapeake Bay tidal water designated uses are proposed to more

fully reflect the different aquatic living resources communities inhabiting a variety of habitats and,

therefore, the different intended aquatic life uses of those tidal habitats. The tidal water designated

uses provide the context for deriving the Chesapeake Bay dissolved oxygen, water clarity and

chlorophyll a water quality criteria. Accurate delineation of where to apply these tidal water

designated uses is critical to effective application of the Chesapeake Bay water quality criteria. See
6

the Technical Support Document (U.S. Environmental Protection Agency 2003b) for a more

detailed explanation of new and refined uses.

The migratory fish spawning and nursery designated use shall support the survival, growth

and propagation of balanced indigenous populations of ecologically, recreationally and

commercially important anadromous, semi-anadromous and tidal-fresh resident fish species,

including the federally listed shortnose sturgeon, inhabiting spawning and nursery grounds from

February 1 through May 31. It protects migratory fish during the late winter to spring spawning and

nursery season in tidal freshwater to low-salinity habitats. Located primarily in the upper reaches of

many Bay tidal rivers and creeks and the upper mainstem Chesapeake Bay, this use will benefit

several species including striped bass, perch, shad, herring and sturgeon.

The shallow-water bay grass designated use shall support the survival, growth and

propagation of rooted, underwater bay grasses necessary for the propagation and growth of

balanced, indigenous populations of ecologically, recreationally and commercially important fish

and shellfish inhabiting vegetated shallow-water habitats.

The open-water fish and shellfish designated use shall support the survival, growth and of

balanced, indigenous populations of ecologically, recreationally, and commercially important fish

and shellfish species inhabiting open water habitats. It is focused on surface-water habitats in tidal

creeks, rivers, embayments and the mainstem Bay, and protects diverse populations of sportfish,

including striped bass, bluefish, mackerel and sea trout, as well as important bait fish such as

federally listed shortnose sturgeon and important bait fish such as menhaden and silversides.

The deep-water seasonal fish and shellfish designated use shall support the survival,

growth and propagation of balanced, indigenous populations of ecologically, recreationally, and

commercially important fish and shellfish species inhabiting deep-water habitats from June through

September. It protects animals inhabiting the deeper transitional water-column and bottom habitats

between the well-mixed surface waters and the very deep channels. This use protects many bottomfeeding fish, crabs and oysters, and other important species such as the bay anchovy.

The deep-channel seasonal refuge designated use shall protect the survival of balanced,

indigenous populations of ecologically important benthic infaunal and epifaunal worms and clams,

which provide food for bottom-feeding fish and crabs from June through September. Naturally low

dissolved oxygen conditions prevail in the deepest portions of this habitat zone, during the summer.

Chesapeake Bay Water Quality Criteria

Dissolved Oxygen Criteria

Current numeric state water quality criteria for tidal Chesapeake Bay waters aquatic life

protection require 5 mg liter -1 dissolved oxygen concentrations at all times (instantaneous or daily

minimum) throughout the year throughout all of tidal Bay waters – from the deep trench extending

down the center of the mainstem Chesapeake Bay to the shallows lining thousands of miles of

shoreline. Based on in-depth analyses of natural conditions and human-caused conditions that can

not be remedied, there are portions of deep-water Chesapeake Bay and its tidal tributaries that can

not achieve the current state dissolved oxygen standards during the June 1 through September 30

time frame (U.S. Environmental Protection Agency 2003b). Based on the scientific information set
7

forth in the Regional Criteria Guidance and the Technical Support Document, the EPA has found

that the aquatic life uses in the deep-water and deep-channel habitats (summer only) have not and

will not require a 5 mg liter -1 dissolved oxygen levels for protection (see Appendix A and B and

discussions below). At the same time, the EPA found that migratory fish spawning and nursery

habitats require higher levels of dissolved oxygen (>5 mg liter -1) to sustain aquatic life use during

the late winter to early summer time frame than provided by the current state water quality

standards. The Chesapeake Bay dissolved oxygen criteria are based on the clear scientific

evaluations of the specific needs of the aquatic living resources, where they live, and during which

time of the year they live there (the designated uses or habitats) and the level of oxygen needed

within each of the designated uses of the Bay tidal waters.

The Chesapeake Bay dissolved oxygen criteria vary significantly across the five refined tidal

water designated uses to fully reflect the wide array of species living in these different Bay habitats. 

Table 1 summarizes the Chesapeake Bay dissolved oxygen criteria. For more detailed information,

including scientific data used in the development of the criteria, please review Chapter III in the

Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll A for the

Chesapeake Bay and Its Tidal Tributaries (Appendix A; U.S. Environmental Protection Agency

2003a). To review the recommended implementation procedures for this criteria, see Chapter VI in

the same document.

Water Clarity

Currently there are no numeric state water quality criteria that exist for water clarity with the

exception of the District of Columbia. The primary causes that have contributed to the loss of

underwater bay grasses in the Chesapeake Bay are nutrient over-enrichment and increased

suspended sediments in the water, and associated reductions in light availability. By applying

appropriate numeric water clarity criteria to the shallow-water bay grass designated use, attainment

of this criteria will improve the health and survival of underwater plant communities and, thus, the

quality of life and diversity of the fish and invertebrate species supported by these shallow-water

vegetated habitats (U.S. Environmental Protection Agency 2003a). 

The Technical Support Document proposes that water clarity criteria should apply to

varying depths from 0.5 meters up to 2 meters (approximately 6.5 feet) depending on the area of the

Bay and tidal tributaries (U.S. Environmental Protection Agency 2003b). Areas where natural

factors (e.g. strong currents, rocky bottoms, shipping terminals) or permanent physical alternations

to shoreline (e.g., shipping terminals) would prevent underwater bay grass growth would be

excluded (Appendix B; U.S. Environmental Protection Agency 2003b).

The water clarity criteria reflect the different light requirements for underwater plant

communities that inhabit low salinity versus higher salinity shallow water habitats throughout the

Bay and its tidal tributaries (Table 2). For more detailed information, including scientific data used

in the development of the criteria, please review Chapter IV in the Ambient Water Quality Criteria

for Dissolved Oxygen, Water Clarity and Chlorophyll A for the Chesapeake Bay and Its Tidal

Tributaries (Appendix A; U.S. Environmental Protection Agency 2003a). To review the

recommended implementation procedures for this criteria, see Chapter VI in the same document.
8

Table 1. Chesapeake Bay dissolved oxygen criteria.

Designated Use Criteria Concentration/ Duration Protection Being Provided T

Migratory fish

spawning 

and 

nursery use

7-day mean > 6 mg liter-1

(tidal habitats with 0-0.5 ppt salinity)

Survival/growth of larvae/juvenile tidal fresh residentfish; protective of threatened/endangered species. 

Instantaneous minimum > 5 mg liter-1 Survival and growth of larvae/juvenile migratory fish;

protective of threatened/endangered species.

Open water designated use criteria apply 

Shallow-water bay

grass use

Open water designated use criteria apply 

Open-water fish and

shellfish use

30 day mean > 5.5 mg liter-1

(tidal habitats with 0-0.5 ppt salinity)

Growth of tidal fresh juvenile and adult fish; protective

of threatened/endangered species.

30 day mean > 5 mg liter-1

(tidal habitats with >0.5 ppt salinity)

Growth of larval, juvenile and adult fish and shellfish;

protective of threatened/endangered species.

7 day mean > 4 mg liter-1 Survival of open-water fish larvae.

Instantaneous minimum > 3.2 mg liter-1 Survival of threatened/endangered sturgeon species.1

Deep-water seasonal

fish and shellfish use

30 day mean > 3 mg liter-1 Survival and growth of Bay anchovy eggs and larvae.

1 day mean > 2.3 mg liter-1 Survival of open-water juvenile and adult fish.

Instantaneous minimum > 1.7 mg liter-1 Survival of Bay anchovy eggs and larvae.

Open water designated use criteria apply 

Deep-channel

seasonal refuge use

Instantaneous minimum > 1 mg liter-1 Survival of bottom-dwelling worms and clams. 

Open water designated use criteria apply 

1. At temperatures considered stressful to shortnose sturgeon (>29oC), dissolved oxygen concentrations above an instantaneous minimu

protect survival of this listed sturgeon species.

Source: U.S. Environmental Protection Agency 2003a.
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Table 2. Summary of Chesapeake Bay water clarity criteria for application to shallow-water bay grass designat

 Salinity

Regime

Water Clarity

Criteria as 

Percent Lightthrough-Water

Water Clarity Criteria as Secchi Depth

Water Clarity Criteria Application Depths

0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0

Secchi Depth (meters) for Above Criteria Application Depth

Tidal fresh 13% 0.2 0.4 0.5 0.7 0.9 1.2 1.3 1.4 Oligohaline 13% 0.2 0.4 0.5 0.7 0.9 1.2 1.3 1.4 Mesohaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 Polyhaline 22% 0.2 0.5 0.7 1.0 1.2 1.4 1.7 1.9 

Sep

Source: U.S. Environmental Protection Agency 2003a.
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Chlorophyll a

Maryland, Virginia, Delaware and District of Columbia’s current water quality standards

do not include numeric chlorophyll a criteria. Chlorophyll a is an integrated measure of primary

production as well as an indicator of water quality. Chlorophyll a plays a direct role in reducing

light penetration in shallow-water habitat, thereby negatively affecting underwater bay grasses. 

Uneaten by zooplankton and filter feeding shellfish, the microbial process that breaks down

excess dead algae removes oxygen from the water column. Phytoplankton assemblages can

become dominated by single species which represent poor food quality or even produce toxins

that impair the animals that feed directly on them. From a water quality perspective, chlorophyll

a is the best available, most direct measure of the amount and quality of phytoplankton and the

potential for reduced water clarity and low dissolved oxygen impairments.

The EPA is providing the states with a recommended narrative chlorophyll a criteria

applicable to all Chesapeake Bay and tidal tributary waters (Table 3). The EPA encourages the

states to adopt numerical chlorophyll a criteria for application to those tidal waters where algal

related designated use impairments are likely to persist even after attainment of the applicable

dissolved oxygen and water clarity criteria. The technical information supporting states’

quantitative interpretation of the narrative chlorophyll a criteria is published within the body of

the Chesapeake Bay water quality criteria document. For a full description and detailed

technical supporting documentation, please review Chapter V in the Ambient Water Quality

Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll A for the Chesapeake Bay and Its

Tidal Tributaries (Appendix A; U.S. Environmental Protection Agency, 2003a). To review the

recommended implementation procedures for this criteria, see Chapter VI in the same document.

Table 3. Chesapeake Bay narrative chlorophyll a criteria.

Concentrations of chlorophyll a in free-floating microscopic aquatic plants (algae) shall not

exceed levels that result in ecologically undesirable consequences–such as reduced water

clarity, low dissolved oxygen, food supply imbalances, proliferation of species deemed

potentially harmful to aquatic life or humans or aesthetically objectionable conditions–or

otherwise render tidal waters unsuitable for designated uses.

EVALUATION AREA

The area evaluated for application of the EPA’s recommended Regional Criteria

Guidance is the Chesapeake Bay and its tidal tributaries to the fall line (Figure 2). 

FEDERAL LISTED SPECIES WITHIN THE EVALUATION AREA

Appendix C contains a listing of all Federally threatened and endangered species

compiled by the U.S. Fish and Wildlife Service and the NOAA National Marine Fisheries

Service in the four jurisdictions with tidal influenced Chesapeake Bay waters–Maryland,

Virginia, Delaware and the District of Columbia. The species listed include plants, mollusks,

fishes, reptiles, birds, insects and mammals. The level of information for each species varies. 

Only a limited number of threatened or endangered species are aquatic dependent organisms. 

For this evaluation the following aquatic and aquatic dependent species that still occur in the
Chesapeake Bay and Major Rivers

Figure 2. Chesapeake Bay and its tidal tributaries.

Potomac

Patuxent

Pocomoke

Nanticoke

Choptank

Chester

Susquehanna

York

Pamunkey

Mattaponi

Rappahannock

James

Appomattox

Elizabeth
12

region and have been identified through correspondence with the Services were considered: 

• Plants–sensitive joint-vetch, swamp pink; 

• Mammals–humpback whale, finback whale, blue whale, right whale, sei whale,

sperm whale, West Indies manatee;

• Birds–bald eagle, piping plover;

• Fish–shortnose sturgeon, Atlantic sturgeon (state listed);

• Reptiles–loggerhead sea turtle, Kemp’s ridley sea turtle, leatherback sea turtle,

hawksbill sea turtle and green sea turtle;

• Mollusks–dwarf wedge mussel; and

• Insects–Puritan tiger beetle, northeastern beach tiger beetle.

Plants

The sensitive joint-vetch (Aeschynomene virginica) is found in Maryland and Virginia

(U.S. Fish and Wildlife Service 1992). It is an annual legume native to the eastern United States,

growing on the fringe of marshes or shores. The species occurs within the intertidal zone of

freshwater tidal river systems where populations are flooded twice daily. Its aquatic dependence

is, therefore, intertidal habitat. Its presence in a given marsh may be a factor of displacement by

aggressive, non-native plant species, hydrological conditions, salinity tolerances, and/or other

parameters. Sensitive joint-vetch seems to favor micro habitats where there is a reduction in

competition from other plant species. Bare to sparsely vegetated substrates appear to be a

habitat feature of critical importance for establishment and growth of this species. Almost every

population of sensitive joint-vetch is susceptible to hydrological changes (e.g., water withdrawal

projects), habitat loss and modification (e.g., through bank erosion), or other stressors caused by

development.

The swamp pink (Helonias bullata) is endangered in Maryland and Virginia, and

threatened in Delaware. The swamp pink is a distinctive perennial plant with thick stocky

rhizomes. It inhabits a variety of freshwater non-tidal wetlands, including spring seepages,

swamps, bogs, wet meadows and margins of small streams. The swamp pink does not usually

inhabit tidal wetland areas (L. Arroyo, personal communication, 2002). The major threat to the

species is loss and degradation of its wetland habitat due to encroaching development,

sedimentation, pollution, succession and wetland drainage. Activities that increase

sedimentation, pollutant runoff, or cause flooding of habitat should, therefore, be avoided. 

Human foot traffic or vehicle traffic, as well as beaver dam building constitute other threats to

the swamp pink. Site conservation is the primary recovery plan for the swamp pink. 

Mammals

Various marine mammals such as the blue whale (Balaenoptera musculus), sei whale

(Balaenoptera borealis), sperm whale (Physeter catodon), right whale (Balaena glacialis),

humpback whale (Megaptera novaeangliae) and finback whale (Balaenoptera physalus) occur

in ocean waters off the coast of Maryland and Virginia (NOAA National Marine Fisheries
13

Service 1991a, 1991b, 1998b, 1998c). There is some evidence that healthy whales occasionally

use bay waters. For example, in 1994, two humpback whales were reported lunge fishing under

the Chesapeake Bay Bridge, according to David Scofield, Manager of Ocean Health Programs at

the Baltimore Aquarium (D. Scofield, personal communication, 2002). While whales are indeed

occasionally seen in the Chesapeake Bay, it is not considered critical habitat for them. Recovery

plans include maintaining and enhancing whale habitats, and identifying and reducing death,

injury or disturbance to whales caused by humans. 

The West Indies manatee (Trichechus manatus latirostris) is another endangered

mammal species that sometimes visits the Chesapeake Bay. Typically manatees live in warm

marine/estuarine waters, and eat aquatic grasses, algae, mangrove leaves, and water hyacinths.

They usually migrate because of water temperature and salinity. In 1994, a manatee left the area

near Jacksonville, Florida on June 15, entered the Chesapeake Bay on July 4, and was spotted in

Rhode Island’s waters on August 13. While water temperatures in these regions were unusually

warm in 1994, David Scofield at the Baltimore Aquarium says that there has been a manatee

sighting in the Bay every year since 1994 (D. Scofield, personal communication, 2002). Enough

of the sightings have been confirmed that scientists believe this wandering behavior may not be

as unusual as once thought. The major causes of mortality are from colliding with watercraft,

and getting stuck in flood gates and canal locks. 

Birds

The bald eagle (Haliaeetus leucocephalus) is listed as threatened (U.S. Fish and Wildlife

Service 1990). Its aquatic dependence is due to the use of aquatic foraging areas for

consumption of aquatic organisms. Chesapeake Bay region bald eagles occupy shoreline habitat

of the Chesapeake and Delaware bays and their tributaries. Populations of bald eagles in the Bay

region have continued to increase since the recovery plan was written in 1990 (A. Moser,

personal communication, 2002). However, the eagle requires large blocks of undisturbed mature

forested habitat in proximity to aquatic foraging areas. The principal threat to its continued

recovery is habitat loss due to shoreline development and other land use changes. Chesapeake

Bay region eagles are also threatened by acute toxicity caused by continued use of certain

contaminants, shooting, and accidents. Recovery actions include protection of existing nesting,

foraging, and roosting habitat and reduction of mortality from environmental contamination.

The piping plover (Charadrius melodus melodus) is listed as threatened federally, and

also state listed as threatened in Virginia (U.S. Fish and Wildlife Service 1988). Approximately

100 pairs of piping plovers nest on Virginia’s Atlantic barrier islands. They are uncommon

transients along the southern mainland coast and lower Chesapeake Bay. Plovers are rare

transients inland along the Potomac River and rare winter residents in Virginia. Piping plovers

arrive at breeding grounds in Virginia around mid-March and lay eggs from mid-April to early

July. They breed on sandy, gravel and/or cobbled coastal beaches in areas with little or no

vegetation. Piping plovers forage in intertidal zones and wrack lines of ocean beaches, washover

areas, mudflats, sandflats, coastal ponds, lagoons and salt marshes, eating marine worms, fly

larvae, beetles, crustaceans, mollusks and other invertebrates. Its numbers were drastically

reduced in the 20th century because of uncontrolled commercial and recreational hunting and egg

collecting in the 1900s, and dune stabilization and beachfront development after World War II. 

Loss of habitat along with increased recreational use of beaches has caused further population
14

declines. Today the populations are limited by predators (including dogs and cats), flooding of

the nest by rain or tidal overwash, development and beach stabilization, and pedestrian and Off

Road Vehicle traffic that inadvertently crush eggs or chicks. Continued protection of Virginia’s

barrier islands for nesting is essential for recovery of this species in Virginia. 

Fish

The Atlantic sturgeon (Acipenser oxyrhynchus oxyrhynchus) is listed as state

endangered in Delaware. Federally, the Atlantic sturgeon was placed on the candidate species

list in 1988 and again in 1998, though it was never listed (NOAA National Marine Fisheries

Service 1998d). It is being considered here due to the moratorium on all Atlantic sturgeon

harvests, adopted in 1997 by the Atlantic States Marine Fisheries Commission (Colligan et al.

1998).

The Atlantic sturgeon is an anadromous species, migrating from the ocean to fresh water

to spawn. It can live up to 60 years, and reach lengths of up to 14 feet, and weights of over 800

pounds. Sturgeon are typically bottom dwellers, using their snouts to root along the bottom for

benthic organisms such as molluscs, insects and crustaceans, which it sucks up with its

protrusive mouth. Currently, these sturgeon can be found in 32 rivers from Maine to Georgia,

with spawning occurring in at least 14 of these rivers. 

The status of the Atlantic sturgeon in the Chesapeake Bay is not certain. There has been

no evidence of reproduction in the Maryland portion of the Chesapeake Bay for over 25 years

(Speir and O’Connell 1996). Recent evidence suggests limited spawning in the James and York

Rivers (NOAA National Marine Fisheries Service 1998d). The initial and most significant threat

to the Atlantic sturgeon was commercial fishing, since sturgeons are sought for their eggs

(caviar) as well as their flesh. Increased prevalence of hypoxia in the 20th century due to postWorld War II agricultural practices and residential development has caused sturgeon habitat

degradation in the 1900s (Secor and Niklitschek 2001). All sturgeon fisheries are now closed. 

The shortnose sturgeon (Acipenser brevirostrum) is a Federally listed species. 

Shortnose sturgeon was listed as endangered on March 11, 1967 (32 FR 4001), and they

remained on the endangered species list with the enactment of the Endangered Species Act in

1973 (NOAA National Marine Fisheries Service 1998a, 2002).

The National Oceanic and Atmospheric Administration’s National Marine Fisheries

Service Shortnose Sturgeon Recovery Plan (Recovery Plan) indicates reports of its occurrence in

the Chesapeake system in 1876 (NOAA National Marine Fisheries Service 1998a). The

National Marine Fisheries Service Biological Opinion for the Washington Aqueduct Permit

(NOAA National Marine Fisheries Service 2002) states that other historical records of shortnose

sturgeon in the Chesapeake Bay include: the Potomac River (Smith and Bean 1899), the upper

Chesapeake Bay near the mouth of the Susquehanna River in the early 1980s, and the lower Bay
1

 The EPA believes there is a potential that the Dadswell et. al. 1984 referenced observations at the mouths of the

James and Rappahannock are incorrect. The authors misidentify the York (as the James) on the map presented in

Figure 7 and give two markings, represented by dots in very up-estuary regions (one in York, one in the Mattaponi). 

No details were given on the number of observations or source.

15

near the mouths of the James and Rappahannock rivers in the late 1970s (Dadswell et al. 1984).1

The U.S. Fish and Wildlife Service Reward Program for Atlantic Sturgeon began in

1996. Shortnose sturgeon have been incidentally captured via this program. As of July 2002, 50

shortnose sturgeon were captured via the reward program in the Chesapeake Bay and its

tributaries–four from the lower Susquehanna River, two in the Bohemia River, six in the

Potomac River, two south of the Bay Bridge near Kent Island, one near Howell Point, one just

north of Hoopers Island, one in the Elk River, and two in Fishing Bay (Mangold 2003; Spells

2003; Skjeveland et. al. 2000). The remaining 31 shortnose sturgeon were captured in the upper

Chesapeake Bay north of Hart-Miller Island. These fish were captured alive in either

commercial gillnets, poundnets, fykenets, eel pots, hoop nets, or catfish traps (Mangold 2003;

Spells 2003; Skjeveland et. al. 2000).

In many river systems, Shortnose sturgeon appear to spend most of their life in their natal

river systems, only occasionally entering higher salinity environments. They are benthic

omnivores and continuously feed on benthic and epibenthic invertebrates including molluscs,

crustaceans and oligochaete worms (Dadswell 1979).

Shortnose sturgeon depend on free-flowing rivers and seasonal floods to provide suitable

spawning habitat. For shortnose sturgeon, spawning grounds have been found to consist mainly

of gravel or ruble substrate in regions of fast flow. Flowing water provides oxygen, allows for

the dispersal of eggs, and assists in excluding predators. Seasonal floods scour substrates free of

sand and silt, which might suffocate eggs (Beamesderfer and Far 1997).

Shortnose sturgeon spawn in upper, freshwater sections of rivers and feed and overwinter

in both fresh and saline habitats. In populations that have free access to the total length of a river

(absent of dams), spawning areas are located at the farthest accessible upstream reach of the

river, often just below the fall line (NOAA National Marine Fisheries Service 1998a). 

Tributaries of the Chesapeake Bay that appear to have suitable spawning habitat for the

Chesapeake Bay shortnose sturgeon include the Potomac, Rappahannock, James, York,

Susquehanna, Gunpowder and Patuxent rivers (J. Nichols, personal communication, 2002). Still

other scientists believe that very little if any suitable spawning habitat remains for shortnose

sturgeon due to past sedimentation in tidal freshwater spawning reaches (Secor, personal

communication 2003; J. Musick, personal communication, 2003)

According to the Recovery Plan shortnose sturgeon are affected by habitat degradation or

loss (resulting, for example, from dams, bridge construction, channel dredging, and pollutant

discharges) and mortality (resulting, for example, from impingement on cooling water intake

screens, dredging and incidental capture in other fisheries) as principal threats to the species’

survival (NOAA National Marine Fisheries Service 1998a). The recovery goal is identified as

delisting shortnose sturgeon populations throughout their range, and the recovery objective is to
16

ensure that a minimum population size is provided such that genetic diversity is maintained and

extinction is avoided.

Reptiles

Marine sea turtles include the loggerhead sea turtle (Caretta caretta), Kemp’s ridley

sea turtle (Lepidochelys kempi), leatherback sea turtle (Dermochelys coriacea), hawksbill sea

turtle (Eretmochelys imbricata), and green sea turtle (Chelonia mydas). Sea turtles are

migratory; they enter the Chesapeake Bay in late May to early June when water temperatures

rise and depart between late September to early November. An estimated 3,000 to as many as

10,000 loggerhead turtles, and perhaps 500 Kemp’s ridley sea turtles, use the Chesapeake Bay (J.

Musick, personal communication, 2002). Approximately 95 percent of the loggerheads found in

the Chesapeake Bay are juveniles, and the area from the mouth of the Bay to the Potomac River

serves as an important foraging area for this life stage. Loggerhead sea turtles tend to forage

along channel edges in the Bay and tidal rivers while Kemp’s ridley sea turtles feed in the water

flats. Sea turtles in the Chesapeake Bay (mostly loggerheads and Kemp’s ridleys) forage on

crustaceans (e.g., crabs) and mollusks. Threats to the turtles include, incidental takes, poaching,

pollution and marine habitat degradation. Recovery plans include protection of nesting habitats,

eliminating mortality from incidental catch in commercial fishing, and reduction of marine

pollution (NOAA National Marine Fisheries Service and U.S. Fish and Wildlife Service 1991a,

1991b, 1992, 1993; U.S. Fish and Wildlife Service and NOAA National Marine Fisheries

Service 1992). 

Mollusks

The dwarf wedge-mussel (Alasmidonta heterodon) is endangered in Virginia and was

listed as Federally endangered in 1990. The dwarf wedge mussel is an Atlantic Coast freshwater

mussel, usually found in sand, firm muddy sand, and gravel bottoms in rivers of varying sizes

with slow to moderate current. To survive they need silt-free, stable stream beds and welloxygenated water that is pollutant free. No host fish are known for this species, but it is thought

that in some locations the host fish may be anadromous since these mussel populations have

been eliminated in rivers with dams. These mussels are found in Aquia Creek and the South

Anna and Nottoway rivers. The dwarf wedge mussel filter feeds on suspended detritus and

zooplankton. The dwarf wedge-mussel is salinity intolerant and, therefore, is mainly found in

freshwater habitats. They are mainly found in Connecticut and are not found in tidal areas (E.

Davis, personal communication, 2002). Habitat degradation is the greatest cause of this species’

decline. Industrial pollution, intensive recreational development, urban and agricultural

development, and siltation have adverse effects on this species. 

Insects

The Puritan tiger beetle (Cicindela uritana) was listed as Federally threatened in 1990,

and is endangered in Maryland (U.S. Fish and Wildlife Service 1993). It is found in Kent, Cecil,

and Calvert counties. It occurs on open sand flats, dunes, water edges, beaches, woodland paths

and sparse grassy areas. Populations have declined due to habitat alterations associated with

human population growth, as well as inundation and disturbance of its shoreline habitat from

dam construction, riverbank stabilization, and other human activities. The beetle larvae, in

particular, are sensitive to natural and human-induced changes to beaches and bluffs, as well as

human traffic and water-borne pollution.
17

The northeastern beach tiger beetle (Cicindela dorsalis dorsalis) is listed as threatened

in Maryland, and proposed threatened in Virginia (U.S. Fish and Wildlife Service 1994). It

occurs in over 50 sites within the Chesapeake Bay region. Northeastern beach tiger beetles are

rare beach-dwellers that occur on open sand flats, dunes, water edges, beaches, woodland paths,

and sparse grassy areas. The beetle is most vulnerable to disturbance during the larval stage,

which lasts two years. Larvae live in vertical burrows, generally in the beach intertidal zone

where they are particularly sensitive to destruction by high levels of pedestrian traffic, Off Road

Vehicles, and other changes due to coastal development and beach stabilization structures. It is

tolerant to aquatic changes and is more dependent on beach conditions for survival (B. Knisley,

personal communication, 2002)

STATUS OF LISTED SPECIES

For the reasons stated below, the EPA has determined through consultation with the U.S.

Fish and Wildlife Service and the NOAA National Marine Fisheries Service, that the issuance of

the Regional Criteria Guidance is not likely to adversely affect the listed species below (K.

Mayne, written correspondence, April 22, 2003, 2003; M. Ratnaswamy, written correspondence,

2003; M. Colligan, written correspondence, 2003). Therefore no further consultation is

necessary with respect to these species:

• The swamp pink (Helonias bullata) does not usually inhabit tidal wetland areas. The

Chesapeake Bay and its tidal tributaries (evaluation area) are not considered important

habitat for this species.

• Blue whale (Balaenoptera musculus), sei whale (Balaenoptera borealis), sperm whale

(Physeter catodon), right whale (Balaena glacialis), humpback whale (Megaptera

novaeangliae), finback whale (Balaenoptera physalus), and West Indies manatee

(Trichechus manatus latirostris) have been known to occasionally wander into the

Chesapeake Bay waters, however, it is not considered important habitat for them. The

major threat to these species is direct human physical contact.

• The dwarf wedge-mussel (Alasmidonta heterodon) is not found in the evaluation area.

• The northeastern beach tiger beetle (Cicindela dorsalis) is dependant on beach

conditions for survival.

• The Puritan tiger beetle (Cicindela uritana) is mainly threatened by human activities

such as population growth, disturbance of its shoreline habitat and construction of dams.

• Loggerhead sea turtle (Caretta caretta), Kemp’s ridley sea turtle (Lepidochelys

kempi), leatherback sea turtle (Dermochelys coriacea), hawksbill sea turtle

(Eretmochelys imbricata), green sea turtle (Chelonia mydas) mainly use the Bay for

foraging during juvenile life stages. Sea turtle prey species will benefit from the Regional

Criteria Guidance.

• The bald eagle (Haliaeetus leucocephalus) is a predator, and scavenger, exploiting a

variety of food sources such as birds, mammals, fish (consisting primarily of menhaden,

large gizzard shad, white perch and catfish) and waterfowl depending upon food

abundance. The Regional Criteria Guidance would encourage improved conditions for

these species of fish, particularly spawning habitat.

• The piping plover (Charadrius melodus melodus) are mainly found on the Atlantic coast

and are mainly threaten due to the depletion in prime nesting habitat areas.
18

• The sensitive joint-vetch (Aeschynomene virginica) are mainly susceptible to water

withdrawal projects or habitat loss, modification, or degradation caused by development.

Therefore, the only endangered or threatened species under the NOAA Fisheries

jurisdiction in the evaluation area that will potentially be affected is the endangered shortnose

sturgeon (Acipenser brevirostrum) (K. Mayne, written correspondence, 2003; M. Ratnaswamy,

written correspondence, 2003; M. Colligan, written correspondence, 2003). No critical habitat

has been designated for the shortnose sturgeon (NOAA National Marine Fisheries Service

1998a).

MANNER IN WHICH REGIONAL CRITERIA GUIDANCE MAY AFFECT THE

SHORTNOSE STURGEON

Water Clarity

The recommended Chesapeake Bay water clarity criteria, if adopted by each state and

approved by the EPA would establish the minimum level of light penetration required to support

the survival and continued propagation of underwater bay grasses in both lower and higher

salinity communities (U.S. Environmental Protection Agency 2003a). The Regional Criteria

Guidance provides documentation which supports that attaining water clarity at the proposed

levels will improve underwater bay grass survival, growth and propagation, thus improving

habitat to fully support a diverse shallow water habitat. Based on the recommended criteria and

the evaluations for each listed species described above, which includes the habitat and spawning

areas of the species and threat to species recovery, the EPA has determined that the

recommended water clarity criteria will not likely adversely effect the listed species evaluated in

this document. Furthermore, the EPA has determined that the proposed water clarity criteria will

beneficially affect preferred habitat, spawning areas and food sources that will add substantially

in the recovery of the shortnose sturgeon. 

Chlorophyll a

The recommended Chesapeake Bay narrative chlorophyll a criteria and technical

information supporting states’ quantitative interpretation of the narrative criteria provides

concentrations characteristic of desired ecological trophic conditions and protective against

water quality and ecological impairments (U.S. Environmental Protection Agency 2003a). 

These recommended concentrations are given to prevent reduced water clarity, low dissolved

oxygen, food supply imbalances, proliferation of species deemed potentially harmful to aquatic

life or humans, or aesthetically objectionable conditions. The Regional Criteria Guidance

provides documentation which indicate that water clarity and dissolved oxygen improve when

excess phytoplankton measured as chlorophyll a are significantly reduced, thus improving water

quality and critical aquatic habitat in the waters of the Chesapeake Bay and its tidal tributaries. 

The EPA has determined that the recommended chlorophyll a criteria will not likely adversely

affect the listed species evaluated in this document. Furthermore, the EPA has determined that

the recommended chlorophyll a criteria will beneficially affect preferred habitat, spawning areas

and food sources that the listed species depends on.

Dissolved Oxygen

A set of dissolved oxygen criteria have been derived to protect Chesapeake Bay estuarine
19

species based on the EPA’s conclusions and scientific research on the different Bay habitats (see

chapters III and VI in Appendix A; U.S. Environmental Protection Agency 2003a). Oxygen

dynamics and natural low- to no-oxygen conditions were also fully considered in the

development of the refined tidal water designated uses (see Appendix B; U.S. Environmental

Protection Agency 2003b) which factor in natural conditions leading to low dissolved oxygen

concentrations.

Chesapeake Bay Oxygen Dynamics

Taking into account the natural processes that control oxygen dynamics is critical to

identifying the different Bay aquatic life habitats and establishing criteria reflective of natural

conditions and protective of each habitat. The Chesapeake Bay tends to have naturally reduced

dissolved oxygen conditions in its deeper waters because of its physical morphology and

estuarine circulation. As in other estuarine systems (e.g., Boynton et al. 1982; Nixon 1988;

Caddy 1993; Cloern 2001), the Chesapeake’s highly productive waters combined with sustained

stratification, long residence times, low tidal energy and tendency to retain and recycle nutrients

set the stage for lower dissolved oxygen conditions. The mesohaline mainstem Chesapeake Bay

and lower reaches of the major tidal rivers have a stratified water column, which essentially

prevents waters near the bottom from mixing with more oxygenated surface waters. Recycling

of nutrients and water-column stratification leads to severe reductions in dissolved oxygen

concentrations during the warmer months of the year in deeper waters within and below the

pycnocline.

This reduction in dissolved oxygen generally results from a host of additional biological

and physical factors (e.g., Kemp and Boynton 1980; Kemp et al. 1992; Sanford et al. 1990;

Boynton and Kemp 2000). The annual spring freshet delivers large volumes of fresh water to

the Chesapeake Bay. The contribution of significant quantities of nutrients in the spring river

flows, combined with increasing temperatures and light, produces a large increase in

phytoplankton biomass. Phytoplankton not consumed by suspension feeders (such as

zooplankton, oysters and menhaden) sink to the subpycnocline waters, where they are broken

down by bacteria over a period of days to weeks (e.g., Malone et al. 1986; Tuttle et al. 1987;

Malone et al. 1988). This loss of oxygen due to bacterial metabolism is exacerbated due to the

onset of increased stratification, which restricts mixing with surface waters.

The Chesapeake Bay’s nearshore shallow waters periodically experience episodes of low

to no dissolved oxygen, in part because bottom water has been forced into the shallows by a

combination of internal lateral tides and sustained winds (Carter et al. 1978; Tyler 1984; Seliger

et al. 1985; Malone et al. 1986; Breitburg 1990; Sanford et al. 1990). Low dissolved oxygen

conditions in shallow waters of the tidal tributaries are more often the result of local

production/respiration than the incursion of bottom waters. Climatic conditions such as calm

winds and several continuous cloudy days in a row can contribute to oxygen depletion in these

shallow water habitats. These habitats can be exposed to episodes of extreme and rapid

fluctuations in dissolved oxygen concentrations (Sanford et al. 1990). In depths as shallow as 4

meters, dissolved oxygen concentrations may decline to 0.5 mg liter-1 for up to 10 hours

(Breitburg 1990).

Diel cycles of low dissolved oxygen conditions often occur in non-stratified shallow
20

waters where water-column respiration at night temporarily reduces dissolved oxygen levels

(D’Avanzo and Kremer 1994). In nearshore waters of the mesohaline mainstem Chesapeake

Bay, near-bottom dissolved oxygen concentrations are characterized by large diel fluctuations

and daily minima during the late night and early morning hours of July and August (Breitburg

1990). 

The timing and extent of reduced dissolved oxygen conditions in the Chesapeake Bay

vary from year to year, largely driven by local weather patterns, the timing and magnitude of

freshwater river flow and concurrent delivery of nutrients and sediments into tidal waters, and

the corresponding springtime phytoplankton bloom (Officer et al. 1984; Seliger et al. 1985;

Boynton and Kemp 2000; Hagy 2002). In the Chesapeake Bay’s mesohaline mainstem, these

conditions generally occur from June through September but have been observed to occur as

early as May and may persist through early October, until the water column is fully mixed in the

fall. The deeper waters of several major Chesapeake Bay tidal tributaries can also exhibit

hypoxic and anoxic conditions (Hagy 2002). 

Derivation of Chesapeake Bay Dissolved Oxygen Criteria

The derivation of these criteria followed the methodologies outlined in the EPA’s

Guidelines for Deriving Numerical National Water Quality for the Protection of Aquatic

Organisms and their Uses (U.S. Environmental Protection Agency 1985), the risk-based

approach used in developing the Ambient Aquatic Life Water Quality Criteria for Dissolved

Oxygen (Saltwater): Cape Cod to Cape Hatteras (U.S. Environmental Protection Agency 2000)

and the Biological Evaluation on the CWA 304(a) Aquatic Life Criteria as part of the National

Consultations, Methods Manual (National Consultation) (U.S. Environmental Protection

Agency, U.S. Fish and Wildlife Service and National Marine Fishers Service, in draft). The

resulting criteria specifically factored in the physiological needs and habitats of the Bay’s living

resources and were structured to protect five distinct tidal water designated uses (U.S.

Environmental Protection Agency 2003a, 2003b).

Criteria for protecting the migratory fish spawning and nursery, shallow-water bay grass

and open-water fish and shellfish designated uses were set at levels to protect the growth,

recruitment and survival. Criteria applicable to deep-water seasonal fish and shellfish designated

uses were set at levels to protect shellfish and juvenile and adult fish, and to foster the

recruitment success of the bay anchovy. Criteria for deep-channel seasonal refuge designated

uses were set to protect the survival of bottom sediment-dwelling worms and clams. These

summer season deep-water and deep-channel designated uses take into account the limited

aquatic life uses due to the natural historic presence of low oxygen in these habitats and the

likelihood that such conditions may persist although significantly improved over present

conditions (U.S. Environmental Protection Agency 2003b).

Shortnose Sturgeon Dissolved Oxygen Sensitivity

Sturgeon in the Chesapeake Bay and elsewhere are more sensitive to low dissolved

oxygen conditions than most other fish. In comparison with other fishes, sturgeon have a limited

behavioral and physiological capacity to respond to hypoxia (multiple references reviewed and

cited by Secor and Niklitschek 2001, 2003). Sturgeon basal metabolism, growth, consumption

and survival are all very sensitive to changes in oxygen levels, which may indicate their
2

 The authors report that dissolved oxygen levels were monitored every 30 minute throughout the 6 hour

tests, and state that each parameter remained at ‘satisfactory levels’. The dissolved oxygen values reported

are 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 and 7.5 mg liter-1. Since up to five replicates were used with as many as

12 measurements, it seems very unlikely that these exact dissolved oxygen concentration values were

maintained consistently throughout all the tests.

21

relatively poor ability to oxyregulate. In summer, temperatures greater than 20°C amplify the

effect of hypoxia on sturgeon and other fishes due to a temperature-oxygen ‘habitat squeeze’

(Coutant 1987). Deep waters with temperatures that sturgeon prefer tend to have dissolved

oxygen concentrations naturally below the minimum that they require. Sturgeon are therefore

either forced to occupy unsuitable habitats or have a reduction in habitat.

Several studies have directly addressed the lethal effects of hypoxia on sturgeon species

important to the Chesapeake Bay. Jenkins et al. (1993) examined the effects of different

salinities and dissolved oxygen levels on juveniles of the shortnose sturgeon (Acipenser

brevirostrum). The dissolved oxygen tests were all conducted at a mean temperature of 22.5°C.

The authors state:

Due to various constraints including limitations of facilities and test animals,

strictly controlled and standardized methods could not be followed in all tests.

The findings reported should be considered as preliminary until such time as

more rigorous testing can be accomplished.

In addition, the authors report nominal2

 oxygen levels rather than those specific D.O.

levels experienced during each replicate experiment. All experiments were conducted in

freshwater. Still, there was strong evidence presented that younger fish were differentially

susceptible to low oxygen levels in comparison to older juveniles. Fish older than 77 days

experienced minimal mortality at nominal levels š2.5 mg/L, but at 2.0 mg liter-1 experienced 24

to 38 percent mortality. Younger fish experienced 18 to 38 percent mortality in the 3.0 mg liter-1

and >80% mortality in the 2.5 mg liter-1 treatment. Mortality of juveniles  ̃77 days at treatment

levels š3.5 mg liter-1 was not significantly different than control levels. Because only nominal

levels were reported, the EPA could derive LC50 values based upon responses reported by

Jenkins et al. (1993).

Dissolved Oxygen Criteria Protective of Shortnose Sturgeon

More rigorous tests with shortnose sturgeon were recently performed using young-of-theyear fish 77 to 134 days old (Campbell and Goodman 2003). Campbell and Goodman (2003)

present four 24-hr LC50 values for shortnose sturgeon (Acipenser brevirostrum). Three of these

are from tests with non-stressful temperatures (22-26°C) for this species. The fourth test was

conducted at 29°C and was considered to be a stressful temperature by the authors (L. Goodman,

personal communication, 2003). Fish from this fourth test also were exposed to temperatures as

high as 31°C during the acclimation period immediately preceding their exposure to hypoxia. 

Since the data from the fourth test also include an effect due to temperature stress they should be

considered separately from that of the other three tests.

The most latest draft (December 2002) of the National Consultation on threatened and
3

Based on daily dissolved oxygen data provided by the lead author, Dr.David Secor, University of Maryland Center

for Environmental Studies, Chesapeake Biological Laboratory, Solomons, Maryland.

22

endangered species (being negotiated between the U.S. EPA, the U.S. Fish and Wildlife Service

and the National Marine Fisheries Service) states:

Where acute toxicity data are available for the species of interest, only these data will be

used for designating the LC50 for this species. If these data include more than one test,

the geometric mean of the LC50s of these tests will be used in risk calculations. If only

one toxicity test has been conducted, the lower 95% confidence interval of the LC50 from

this test will be used.

Following this guidance the final LC50 for shortnose sturgeon under ambient conditions

of non-stressful temperatures would be the geometric mean of 2.2, 2.2 and 2.6 mg liter-1 —2.33

mg liter-1. Under stressful temperatures the LC50 value that should be used would be 3.1 mg

liter-1 (this is the LC50 of the 29/C test, since the 3.1 mg liter-1 treatment resulted in exactly 50

percent mortality there was no 95 percent confidence interval) (Campbell and Goodman 2003). 

Long-term exposures (10 days) of Atlantic sturgeon, Acipenser oxyrinchus, young-ofthe-year (150 to 200 days old) to 2.8 to 3.3 mg liter-1 at 26°C resulted in complete mortality over

a 10-day period in three of four replicates (Secor and Gunderson 1998). The fourth replicate

experienced 50 percent mortality. At 19°C and 2.3 to 3.2 mg liter-1, only 12 to 25 percent

mortality was recorded. There was insufficient data to calculate an LC50 for 19/C (was less than

2.70 mg liter-1, but could not determine how much less). However, based on survival data

present in Secor and Gunderson (1998), a 96-hr LC50 of 2.89 mg liter-1 3

 was estimated for

Atlantic sturgeon at 26°C. This value is very similar to the ‘high temperature’ value of 3.1 mg

liter-1 calculated for shortnose sturgeon by Campbell and Goodman (2003). Data from

Niklitschek and Secor (2001) show that shortnose sturgeon are more tolerant of higher

temperatures than Atlantic sturgeon, which could explain why 26°C is not a stressful

temperature for shortnose sturgeon (Campbell and Goodman 2003), but is for Atlantic sturgeon

(Secor and Gunderson 1998). Alternately, the temperature difference between the two species

could be because the shortnose sturgeon were from Savannah River progeny and were held at

higher temperatures than the Atlantic sturgeon which came from Hudson River progeny.

Using the above data, the EPA calculated acute criteria for the protection of sturgeon

survival in the Chesapeake Bay under both non-stressful and stressful temperatures for habitats

appropriate for sturgeon use. The only LC50 value available for non-stressful temperatures that

meets the requirements for criteria derivation based on EPA’s 1985 guidelines (U.S.

Environmental Protection Agency 1985) is the 24-hr 2.33 mg liter-1 calculated above from

Campbell and Goodman (2003). To be consistent with EPA guidelines, this value was used with

the original EPA Virginian Province saltwater dissolved oxygen criteria acute data set to

recalculate the Final Acute Value (FAV). The new FAV, 2.12 mg liter-1, is more protective than

the 1.64 mg liter-1 from the Virginian Province document, but not as protective as the 2.33 mg
4

This value is the geometric mean of the LC5/LC50 ratios from the Virginian Province document. The ratio for the

shortnose sturgeon tests from Campbell and Goodman (2003) was 1.30 (based on an analysis of raw data provided

by the co-author Larry Goodman, U.S. Environmental Protection Agency, Office of Research and Development,

Gulf Ecology Division, Gulf Breeze, Florida). To be consistent with the Virginian Province document, the EPA

applied the 1.38 ratio.

23

liter-1 value. Therefore, we default to the 2.33 mg liter-1 value, multiplying it by 1.384 to arrive at

a new CMC, 3.2 mg liter-1 (rounded to two significant figures). This value is expected to be

protective of sturgeon survival at non-stressful temperatures. Campbell and Goodman (2003)

indicate that most of the mortality for shortnose sturgeon occurs within the first 2 to 4 hours of a

test. Therefore, using this value as an instantaneous value should protect sturgeon under most

conditions.

A higher dissolved oxygen criterion would be needed in areas and times of the year

where sturgeon are to be protected and temperatures are likely to be considered stressful (e.g.,

29°C and above for shortnose sturgeon). The simplest approach is to use the LC50 value of 3.1

mg liter-1 from the fourth test of Campbell and Goodman (2003). Multiplying this by 1.38

results in a high temperature CMC for shortnose sturgeon of 4.3 mg liter-1.

To determine a criterion value that would also protect sturgeon from nonlethal effects in

the habitats for sturgeon use, bioenergetic and behavioral responses were considered which had

been derived from laboratory studies conducted on juvenile Atlantic and shortnose sturgeon

(Niklitschek 2001; Secor and Niklitschek 2001). Growth was substantially reduced at 40 percent

oxygen saturation compared to normal oxygen saturation conditions (greater than or equal to 70

percent saturation) for both species at temperatures of 20o

 C and 27o C. Metabolic and feeding

rates declined at oxygen levels below 60 percent oxygen saturation at 20o C and 27o C. In

behavior studies, juveniles of both sturgeon species actively selected 70 percent or 100 percent

oxygen saturation levels over 40 percent oxygen saturation levels. Based on these findings, a 60

percent saturation level was deemed protective for sturgeon. This corresponds to 5 mg liter-1 at

25o

 C. Therefore, a 5 mg liter-1 Chesapeake Bay dissolved oxygen criterion protecting against

adverse growth effects would protect sturgeon growth as well.

Tidal Water Designated Use Habitats

The migratory spawning and nursery and open-water designated uses are by their very

design and definitions protective of shortnose sturgeon. The deep-water and deep-channel

designated uses are seasonally applied to open-water habitats where and when water column

stratification prevents the free exchange of oxygenated waters with the surface mixed layer. 

These two designated uses were not established to be protective of oxygen sensitive species like

sturgeon during the summer months in recognition of natural processes that make this habitat

unsuitable for such species during the June through September time frame as discussed below.

Chesapeake Bay Low Oxygen: Historical and Recent Past

Dissolved oxygen levels vary naturally in lakes, estuaries and oceans over varying

temporal and spatial scales due to many biological, chemical and physical processes. In

estuaries such as the Chesapeake Bay, freshwater inflow that influences water-column

stratification; nutrient input and cycling; physical processes such as density-driven circulation;
24

and tides, winds, water temperature and bacterial activity are among the most important factors. 

These processes can lead to large natural seasonal and interannual variability in oxygen levels in

many parts of the Chesapeake Bay and its tidal tributaries.

Superimposed on this natural dissolved oxygen variability is a progressive increase in the

intensity and frequency of hypoxia and anoxia over the past 100 to 150 years, most notably since

the 1960s. This human-induced eutrophication is evident both from instrumental data and

geochemical and faunal/floral ‘proxies’ of dissolved oxygen conditions obtained from the

sedimentary record.

The instrumental record, while incomplete prior to the inception of the multi-agency

Chesapeake Bay Monitoring Program in 1984, suggests that as early as the 1900s to 1930s (Sale

and Skinner 1917; Newcombe and Horne 1938; Newcombe et al. 1939) and especially since the

1960s (Taft et al. 1980; Hagy 2002), summer oxygen depletion has been recorded in the

Chesapeake Bay. Officer et al. (1984), Malone (1992), Harding and Perry (1997) and Hagy

(2002) provide useful discussions of the instrumental record of dissolved oxygen and related

parameters such as chlorophyll a across this multi-decadal data record.

At issue is whether, and to what degree, dissolved oxygen reductions are a naturally

occurring phenomenon in the Chesapeake Bay thereby creating habitats at certain times of year

that are unsuitable for species including the sturgeon. Long sediment core (17 to greater than 21

meters in length) records indicate that the Chesapeake Bay formed about 7,500 years ago

(Cronin et al. 2000, Colman et al. 2002) when the rising sea level after the final stage of

Pleistocene deglaciation flooded the Susquehanna channel. The modern estuarine circulation

and salinity regime probably began in the mid- to late Holocene epoch, about 4,000-5,000 years

ago (in the regional climate of the early Holocene, the Chesapeake Bay’s salinity differed from

that of the late Holocene). This is based on the appearance of ‘pre-colonial’ benthic

foraminiferal, ostracode and dinoflagellate assemblages. It is against this mid- to late Holocene

baseline that we can view the post-European settlement and modern dissolved oxygen regime of

the Chesapeake Bay. 

During the past decade, studies of the Chesapeake Bay’s late Holocene dissolved oxygen

record have been carried out using several proxies of past dissolved oxygen conditions, which

are preserved in sediment cores that have been dated using the most advanced geochronological

methods. These studies, using various indicators of past dissolved oxygen conditions, are

reviewed in Cronin and Vann (2003) and provide information that puts the monitoring record of

the modern Chesapeake Bay into a long-term perspective and permits an evaluation of natural

variability in the context of restoration targets. The following types of measurements of oxygensensitive chemical and biological indicators have been used: nitrogen isotopes (Bratton et al.,

2003); biogenic silica and diatom communities (Cooper and Brush 1991; Cooper 1995; Colman

and Bratton 2003); molybdenum and other metals (Adelson et al. 2000; Zheng et al., 2003); lipid

biomarkers; acid volatile sulfur (AVS)/chromium reducible sulfur (CRS) ratios; total nitrogen

and total organic carbon (Zimmerman and Canuel 2000); elemental analyses (Cornwell et al.

1996) and paleo-ecological reconstructions based on dinoflagellate cysts (Willard et al. 2003);

and benthic foraminiferal assemblages (Karlsen et al. 2000). Although space precludes a
25

comprehensive review of these studies, and the time period studied and level of quantification

vary, several major themes emerge, which we summarize here. 

First, the 20th century sedimentary record confirms the limited monitoring record of

dissolved oxygen, documenting that there has been a progressive decrease in dissolved oxygen

levels, including the periods of extensive anoxia in the deep-channel region of the Chesapeake

Bay that have been prominent during the last 40 years. Most studies provide strong evidence

that there was a greater frequency or duration of seasonal anoxia beginning in the late 1930s and

1940s and again around 1970, reaching unprecedented frequencies and/or duration in the past

few decades in the mesohaline Chesapeake Bay and the lower reaches of several tidal tributaries. 

Clear evidence of these low dissolved oxygen conditions has been found in all geochemical and

paleo-ecological indicators studied principally through their great impact on benthic and

phytoplankton (both diatom and dinoflagellate) communities. 

Second, extensive late 18th and 19th century land clearance also led to oxygen reduction

and hypoxia, which exceeded levels characteristic of the previous 2,000 years. Best estimates

for deep-channel mid-bay seasonal oxygen minima from 1750 to around 1950 are 0.3 to 1.4-2.8

mg liter-1 and are based on a shift to dinoflagellate cyst assemblages of species tolerant of low

dissolved oxygen conditions. This shift is characterized by a four- to fivefold increase in the

flux of biogenic silica, a greater than twofold (5-10 milliliter-1) increase in nitrogen isotope ratios

(

15N) and periods of common (though not dominant) Ammonia parkinsoniana, a facultative

anaerobic foraminifer. These patterns are likely due to increased sediment influx and nitrogen

and phosphorous runoff due to extensive land clearance and agriculture.

Third, before the 17th century, dissolved oxygen proxy data suggest that dissolved oxygen

levels in the deep channel of the Chesapeake Bay varied over decadal and interannual time

scales. Although it is difficult to quantify the extremes, dissolved oxygen probably fell to 3-6

mg liter-1, but rarely if ever fell below 1.4-2.8 mg liter-1. These paleo-dissolved oxygen

reconstructions are consistent with the Chesapeake Bay’s natural tendency to experience

seasonal oxygen reductions due to its bathymetry, freshwater-driven salinity stratification, high

primary productivity and organic matter, and nutrient regeneration (Boicourt 1992; Malone

1992; Boynton et al. 1995).

In summary, the main channel of the Chesapeake Bay most likely experienced reductions

in dissolved oxygen before large-scale post-colonial land clearance took place, due to natural

factors such as climate-driven variability in freshwater inflow. However, this progressive

decline in summer oxygen minima, beginning in the 18th century and accelerating during the

second half of the 20th century, is superimposed on past and present interannual and decadal

patterns of dissolved oxygen variability. Human activity during the post-colonial period has

caused the trend towards hypoxia and most recently (especially post-1960s) anoxia in the main

channel of the Chesapeake Bay and some of its larger tributaries. The impact of these patterns

has been observed in large-scale changes in benthos and phytoplankton communities, which are

manifestations of habitat loss and degradation.
26

Historical and Potential Sturgeon Tidal Habitats

Atlantic and shortnose sturgeon probably most recently colonized the Chesapeake Bay

5,000-8,000 years ago after the last glaciation, when climate and the watershed’s hydraulic

regime became more stable (Custer 1986; Miller 2001). The Chesapeake Bay during this period

already exhibited the two-layer circulation pattern. Thus, we should expect that deep-channel

habitats during periods of strong stratification were hypoxic during the past 5,000 years, albeit

not at the same spatial extent or severity that has occurred over the past 50 years (Officer et al.

1985; Cooper and Brush 1991). Atlantic sturgeon in other estuarine and coastal systems will use

habitats greater than 15 meters in depth (see below), but these other systems do not exhibit the

same characteristics of estuarine circulation, watershed areal extent and bathymetry that

contributes to natural deep-water and deep-channel hypoxia in the mesohaline Chesapeake Bay. 

Deep-Channel Habitats

The geochemical, paleoecological, and instrumental record of the 20th century indicates

that deep-channel regions have not served as potential habitats for sturgeon because seasonal

(summer) anoxia and hypoxia have occurred most years, reaching and sustaining levels below

those required by sturgeon. Hypoxia, and probably periodic, spatially-limited anoxia, occurred

in the Chesapeake Bay prior to the large-scale application of fertilizer, but since the 1960s

oxygen depletion has become much more severe, prohibiting sturgeon use of this habitat during

summer months (Hagy 2002).

Analysis of recent U.S. Fish and Wildlife Service sturgeon capture location data showed

absence of sturgeon occurrences in deep-channel habitats during summer months (June 1

through September 30), but substantial numbers of occurrences in these same habitats during

other seasons (U.S. Environmental Protection Agency 2003b). Based upon the recent relevant

history of the Chesapeake Bay ecosystem, the deep-channel regions in summer are not

considered sturgeon habitats. 

Deep-Water Habitats

Deeper water-column regions may continue to support foraging, temperature refuges, and

migration corridors for sturgeons during times in the absence of strong water-column

stratification which naturally result in dissolved oxygen concentrations well below saturation due

to restrictions in mixing with the well-oxygenated surface mixed layer. In other estuarine and

coastal systems where strong water-column stratification does not occur to the degree observed

in the Chesapeake Bay and its tidal tributaries, both sturgeon species are known to use deepwater habitats in summer months as thermal refuges (see section titled “Life History of

Shortnose Sturgeon”). 

The water column in the mesohaline Chesapeake Bay mainstem and the mesohaline

lower tidal reaches of several major tributaries (Chester, Patapsco, Patuxtent, Potomac and

Rappahannock river) stratifies to the point where within pycnocline (deep-water) and below

pycnocline (deep-channel) waters are effectively prevented from receiving oxygenated waters

from the overlying surface mixed layer (open-water) during the summer months. These

mesohaline (>5-18 ppt) waters are also far enough removed from the free flowing rivers and the

ocean to prevent re-oxygenation through the inflow of oxygenated bottom waters. During the

period 1990-1999, very little summer time deep-water habitat was predicted to support sturgeon
27

production based upon a bioenergetics model, due principally to pervasive hypoxia (Niklitschek

and Secor, in review). Further, sturgeons are able to behaviorally respond to favorable gradients

in dissolved oxygen (Secor and Niklitschek 2001) and, thus, will avoid the naturally lower

dissolved oxygen waters.

 

Recent fisheries dependent and independent data synthesized by the U.S. Fish and

Wildlife Service (Mangold 2003; Spells 2003; Skjeveland et. al. 2000) did not show substantial

overlap during summer months between deep-water regions and shortnose sturgeon occurrences. 

The EPA recognizes this data base contains fisheries dependent data collected through

incidential catch by gear (i.e., pound nets) deployed generally in waters less than 7 meters in

depth.

Figure 3 illustrates shortnose sturgeon capture locations during the June 1 through

September 30 timeframe with Figure 4 illustrating the locations of all 50 shortnose sturgeon

captures in Chesapeake Bay throughout the year since 1994 through March 2003. Outside of the

June 1 through September 30 time frame, shortnose sturgeon captures were reported across all

tidal water habitats, including habitats seasonally designated as deep water or deep channel, but

protected as open-water habitats from the beginning of October through the end of May. 

Through an in-depth analysis of the 400 station, 1400 individual sturgeon (both Atlantic and

shortnose sturgeon) U.S. Fish and Wildlife Service captures database, no recorded shortnose

sturgeon captures overlapped with the seasonally defined deep-water habitat.

Based upon this analysis, it does not appear likely that habitat found within pycnocline

deep water would comprise ‘potential’habitats for sturgeons during periods of strong water

column stratification limiting exchange with overlying, more oxygenated waters. In the absence

of strong water column stratification, these deeper depth water column habitats are considered

open water habitat and comprise ‘potential’ habitats for sturgeons.

Salinity Tolerances

During their first year of life, shortnose sturgeon tend to occur in fresh water (Dovel et al.

1992; Haley 1999) but can tolerate salinities up to 15 ppt (Jenkins et al. 1993; Niklitschek 2001). 

Extensive observational and experimental evidence points toward shortnose sturgeon

concentrating in habitats with less than 5 ppt for all life history stages during summer months

(Dadwell 1984; Dovel et al. 1992; Geogehan et al. 1984; Brundage and Meadows 1982; Collins

and Smith 1996; Bain 1997; Haley 1999). Laboratory experiments also showed that young-ofthe-year Atlantic sturgeon are more likely to survive in salinities greater than or equal to 15 ppt

(Niklitschek 2001). Based on distributional evidence, older juvenile and adult shortnose

sturgeon are limited to oligohaline and low mesohaline regions of estuaries (<15 ppt), while by

their second year of life, Atlantic sturgeon fully tolerate salinities ranging from 0 to 35 ppt 

(Dovel and Berggen 1983; Dovel et al. 1992; Kieffer and Kynard 1993; Colligan et al. 1998).

Jenkins et al. (1993) exposed shortnose sturgeon young-of-the-year (age 22-330 days) to

acute transitions in salinity for periods of 18-96 hr. Larvae (22 d ays old) showed >50 percent

mortality at 9 ppt exposure for 48 hours. Juveniles (63 days [48 hr] and 76 days old[96 hr]) 
28

Figure 3. Map of all U. S. Fish and Wildlife Service sturgeon capture location stations

where shortnose sturgeon were caught from June 1-September 30, 1999-March 2003.

Sources: Mangold 2003, Spells 2003, Skeveland et al. 2000.
29

Figure 4. Map of all U.S. Fish and Wildlife Service sturgeon capture location stations where

shortnose sturgeon were caught year-round between 1994-March 2003.

Sources: Mangold 2003, Spells 2003, Skjeveland et al. 2000.
30

showed reduced survival (~60 percent) at 13-15 ppt. At 96 hours exposure, 76 days old

juveniles experienced complete mortality at 15 ppt. Yearlings (330 days old) exposed to 25 ppt

showed 100 percent survival during an 18 hr trial, but were extremely stressed and probably

would have succumbed past the experiment’s end (Jenkins et al. 1993). No yearlings survived

acute exposures to 30 or 35 ppt. 

Niklitschek (2001), in dissertation research, exposed shortnose sturgeon juveniles (~6-12

months in age) to salinity conditions after more gradual periods of acclimation (1 ppt/day). In 10

day trials at 0 to 22 ppt, he observed comparatively lower growth and higher routine metabolism

rates for shortnose sturgeon than Atlantic sturgeon. In spatially explicit habitat models, these

bioenergetic differences contributed to habitat curtailments in lower tributaries and the mainstem

of the Chesapeake Bay due to high salinity effects there. Salinity was predicted to be a chief

factor contributing to lower (often negative) production of shortnose sturgeon in lower

Chesapeake Bay habitats in comparison to tidal fresh habitats (<0.5 ppt) in the upper Chesapeake

Bay and major tidal tributaries (e.g., Potomac, Rappahannock, James, and Nanticoke Rivers. In

behavioral studies (Niklitschek 2001), juvenile shortnose sturgeon (as well as Atlantic sturgeon)

did not discriminate between salinities of 0 and 8 ppt, nor did they exhibit preference between 8

and 15 ppt. Juvenile shortnose sturgeon showed a stressed behavioral response and reduced

survival at 29 ppt in comparison to salinities 0, 8, 15, and 22 ppt.

Distribution Studies

Distribution studies and laboratory experiments support the view that shortnose sturgeon

show preference for riverine and estuarine habitats over marine ones (e.g., Secor 2003). 

Shortnose adults have been reported occasionally in coastal waters up to 31 ppt, but typically

occur within several kilometers of their natal estuaries (Dadswell et al. 1984; Kynard 1997). As

an example, shortnose sturgeons recorded in Sandy Hook Bay are believed to be part of Hudson

River population (Dadswell et al. 1984). Kynard (1997) described the life cycle of shortnose

sturgeon as freshwater amphidromous, which specifies freshwater as spawning location but

occasional forays into estuaries and coastal regions that are unrelated to spawning. This

contrasts with the sympatric Atlantic sturgeon, which are considered true anadromous fishes that

must migrate into coastal waters to complete their life cycles (Kynard 1997; Dovel and Berggren

1983; Dovel et al. 1992). Freshwater amphidromy has also been termed semi-anadromy, which

also typifies the life cycle of Chesapeake Bay white perch. 

The life cycle for shortnose sturgeon in regions north of South Carolina has been

generalized by several authors (Dadswell et al. 1984; Bain 1997; Kynard 1997). 

1. Adults move from brackish wintering grounds to head of estuary for spawning;

2. Adults feed in freshwater tidal portion during summer months and move back down

estuary for winter; and 

3. Juveniles disperse from tidal freshwater (where they originated) to brackish winter

grounds during their first year of life. 

In general, shortnose sturgeon do not invade salinities greater than 15 ppt, with centers of

concentrations at less than 5 ppt for all life history stages during summer months (Dadswell et al.
31

1984; Brundage and Meadows 1982; Dovel et al. 1992; Geogehan et al. 1992; Collins and Smith

1996; Bain 1997; Haley 1999). There are at least two ‘landlocked’ populations of shortnose

sturgeon that can complete their life cycles in freshwater – the Santee Cooper and Holyoke Pool

sub-populations (Kynard 1997). 

Kynard (1997) hypothesized that there occurred latitudinal trends in the propensity of

individuals of a population to move outside the natal estuary into coastal waters. Fish from the

most northerly populations (St. John River, New Brunswick) would emigrate into coastal regions

during winter months to avoid stressful temperatures. Shortnose from systems between

Merrimack River and Delaware Bay were the least likely to migrate to coastal waters since

temperature conditions were favorable in these estuaries year-round. In systems from South

Carolina to Florida (St. Johns Estuary), summer temperatures may drive shortnose adults to use

down-estuary and coastal areas. 

The issue of coastal occurrence of shortnose remains controversial. Past studies have

misidentified Atlantic sturgeon juveniles as shortnose sturgeon (Kynard 1997). Physiological

salinity limits on adult shortnose sturgeon are not fully understood at this time. Genetic

evidence strongly indicates limited straying among natal estuaries (Wirgin et al. in press). 

Indeed, Kynard (1997) concludes, “The lack of marine movements by most adults suggests that

the recolonization rate of shortnose...would be slow.” Still, some records of shortnose in coastal

waters (up to 31 ppt; Dadswell 1984) cannot be questioned. An interesting case in point is the

recent ‘invasion’ of hatchery shortnose sturgeon stocked into the Savanna River yet recaptured

in lower South Carolina estuaries (Smith et al. 2002). Clearly these fish must have left Savanna

River and emigrated into waters that approached marine salinities in the inter-coastal waterway.

Chesapeake Bay Salinity Distributions

Maps of long-term averaged bottom salinity distributions document a lack of overlap of

the preferred (<5 ppt) and a limited overlap with the likely upper salinity tolerance (<15 ppt) of

shortnose sturgeon and deep-water and deep-channel designated use habitats during the summer

months (figures 5, 6 and 7, respectively).
32

Figure 5. Map of summer averaged bottom water salinities <5 ppt based on

Chesapeake Bay Water Quality Monitoring Program data from 1996-2000.
33

Figure 6. Map of summer averaged bottom water salinities <15 ppt based on

Chesapeake Bay Water Quality Monitoring Program data from 1996-2000.
34

Figure 7. Long-term averaged spatial distribution of deep-water designated use habitats for

comparison only with figures 5 and 6 salinity distributions. Actual deep-water designated use

habitats will be determined based on month by month delineation of the pycnocline depths

using Chesapeake Bay water quality monitoring cruise data.
35

Life History of Shortnose Sturgeon

Shortnose sturgeon are benthic fish that feed on a variety of benthic and epibenthic

invertebrates including molluscs, crustaceans (amphipods, chironomids, isopods), and

oligochaete worms (Vladykov and Greeley 1963; Dadswell 1979). Shortnose sturgeon are longlived (30 years) and, particularly in the northern extent of their range, mature at late ages. In the

north, males reach maturity at 5 to 10 years, while females mature between 7 and 13 years. 

In the northern extent of their range, shortnose sturgeon exhibit three distinct movement

patterns. These migratory movements are associated with spawning, feeding, and overwintering

activities. In spring, as water temperatures rise above 8oC, pre-spawning shortnose sturgeon

move from overwintering grounds to spawning areas. Spawning occurs from mid/late March to

mid/late May depending upon location. In populations that have free access to the total length of

a river (e.g., no dams within the species’ range in a river: Saint John, Kennebec, Altamaha,

Savannah, Delaware, and Merrimack Rivers), spawning areas are located at the farthest

accessible upstream reach of the river, often just below the fall line (NOAA National Marine

Fisheries Service 1998a). Shortnose sturgeon spawn in upper, freshwater sections of rivers and

feed and overwinter in both fresh and saline habitats. Shortnose sturgeon are believed to spawn

at discrete sites within the river (Kieffer and Kynard 1996).

Adult shortnose sturgeon typically leave the spawning grounds soon after spawning. 

Non-spawning movements include rapid, directed post-spawning movements to downstream

feeding areas in spring and localized, wandering movements in summer and winter (Dadswell et

al. 1984; Buckley and Kynard 1985; O’Herron et al. 1993). Kieffer and Kynard (1993) reported

that post-spawning migrations were correlated with increasing spring water temperature and

river discharge. Young-of-the-year shortnose sturgeon are believed to move downstream after

hatching but remain within freshwater habitats (Dovel 1981). Older juveniles tend to move

downstream in fall and winter as water temperatures decline and the salt wedge recedes.

Juveniles move upstream in spring and feed mostly in freshwater reaches during summer.

Shortnose sturgeon occur at depths between 1 and 12 meters (Kieffer and Kynard 1993;

Savoy and Shake 2000: Welsh et al. 2000). 

Status of Shortnose Sturgeon in the Chesapeake Bay

In the final recovery plan, the NOAA National Marine Fisheries Service identified 19

separate distinct populations occurring in New Brunswick Canada (1); Maine (2); Massachusetts

(1); Connecticut (1); New York (1); New Jersey/Delaware (1); Maryland and Virginia (1); North

Carolina (1); South Carolina (4); Georgia (4); and Florida (2) (NOAA National Marine Fisheries

Service 1998a). The NOAA National Marine Fisheries Service stated that loss of a single

shortnose sturgeon population segment may risk the permanent loss of unique genetic

information that is critical to the survival and recovery of the species and that, therefore, each

shortnose sturgeon population should be managed as a distinct population segment or recovery

unit for the purposes of Section 7 of the Endangered Species Act (NOAA National Marine

Fisheries Service 1998a). The NOAA National Marine Fisheries Service concluded in the

Biological Opinion for the Washington Aqueduct Permit that because of this policy, actions that

could adversely affect a DPS or recovery unit would be evaluated in terms of their potential to

jeopardize the continued existence of an individual population segment (as opposed to the
36

existence of shortnose sturgeon range-wide) (NOAA National Marine Fisheries Service 2002). 

The NOAA National Marine Fisheries Service recovery plan indicates that shortnose

sturgeon found in the Chesapeake Bay and its tributaries are considered part of the Chesapeake

Bay distinct population segment. Welsh et al. (1999) summarizes historical and recent evidence

of shortnose sturgeon presence in the Chesapeake Bay. The first published account of shortnose

sturgeon in the Chesapeake system was an 1876 record from the Potomac River reported in a

general list of fishes of Maryland (Uhler and Lugger 1876). Other historical records of

shortnose sturgeon in the Chesapeake Bay as reviewed by Dadswell et. al. (1984) are not

conclusive, as most likely these species were misidentified Atlantic sturgeon and possibly misidentified tributaries as well (D. Secor, personal communication, 2003).

Delaware/Chesapeake Migratory Corridor

The issue of whether shortnose sturgeon naturally populates the Chesapeake Bay through

local reproduction or immigration centers on the role of C&D Canal as a migration corridor. The

Delaware population has long been noted for having a viable and moderately large shortnose

sturgeon population. Brundage and Meadows (1982) reviewed all literature and reports for the

period 1817-1979 and concluded that the center of distribution of adults during summer months

was 1-3 ppt. For the more recent period 1973-1979, a small concentration of shortnose sturgeon

was observed in proximity to the C&D Canal, prompting them to conclude that “...interchange

between the two estuaries [Delaware and Chesapeake] would seem highly probable.” Hastings

et al. (1987), estimated a moderately large population (in comparison to Hudson River and St.

John River Canada) of 6,000-14,000 sturgeons in the upper tidal estuary for the period 1981-

1987. Several authors have speculated that the range of the Delaware population was probably

contracted during much of 20th Century due to an anoxic/hypoxic zone of water occurring

between Philadelphia and Wilmington (Brundage and Meadows 1982; Kynard 1997), but that

recent improvements in water quality may have contributed to a range expansion into areas

including the vicinity of C&D Canal. Kynard (1997) in particular, called attention to the

likelihood that the C&D Canal may in recent times (since improvement in water quality and

range expansion in the Delaware Bay) serve as a corridor for emigration by Delaware population

shortnose sturgeon into the Chesapeake Bay.

In contrast to the Delaware Bay, there is little evidence that shortnose sturgeon occur in

abundance in the Chesapeake Bay or in fact remain viable. In the early publication, Fishes of

Chesapeake Bay, Hildebrand and Schroeder (1927), called into question whether shortnose

sturgeon remained in the Chesapeake Bay and believed that the very rare observations of

shortnose sturgeon in the 20th Century may have been due to taxonomic misidentifications.

Modern ichthyologists continue to debate whether shortnose sturgeon historically occurred in

Chesapeake Bay tributaries, or whether their abundances approached those observed elsewhere

(J. Waldman, personal communication, 2003; J. Musick, personal communication, 2002).

It is unknown at this time whether there is a reproducing population of shortnose

sturgeon in the Chesapeake Bay. Kynard (1997) suggests that no reproducing populations of

shortnose sturgeon exist between the Delaware and Cape Fear estuaries, but may be related to

shared qualities of the Chesapeake Bay and North Carolina estuaries including shallow water

bathymetries (Paul 2001), large historical inputs of sediment and nutrients to these systems
37

(Cooper 1995; Brush 2001; Secor and Austin, in review), and the low volume of suitable

spawning habitats (clean rubble, cobble and other substrate needed for egg attachment).

Dadswell et al. (1984) and Welsh et al. (2002) documented occurrence of shortnose

sturgeon in the Chesapeake Bay in the vicinity of C&D Canal for the periods 1976-1981 and

1996-2001, respectively. Both these periods contained a set of anomalously wet years

(http://md.water.usgs.gov/monthly/bay.html), which would be expected to favor emigration

through the canal by Delaware population sturgeons. Further, an unusually strong spring freshet

in 1996 altered salinity structure throughout most of the Chesapeake Bay for much of the spring

and summer. This would have facilitated dispersal of shortnose sturgeon to regions away from

the upper Chesapeake Bay (C&D Canal) and could account for recent occurrences in Potomac

River. 

The Federal Recovery Plan for Shortnose sturgeon (NOAA National Marine Fisheries

Service 1998a) noted these post-1996 occurrences, and in a precautionary framework, used the

occurrence data as evidence for listing the Chesapeake Bay as a Distinct Population Segment. 

Recent genetic data, however, indicates that shortnose sturgeons captured in the Chesapeake Bay

since 1996 represent a sub-set of the Delaware Bay’s gene pool (Wirgin et al., in review). If the

Delaware population continues to expand in abundance and range, we should expect increased

emigration of shortnose sturgeon through the C&D Canal and into other parts of the Chesapeake

Bay, particularly in wet years.

Genetic Findings

Research conducted by the New York University School of Medicine involving

mitochondrial DNA (mtDNA) analysis of shortnose sturgeon populations suggests that shortnose

sturgeon captured in the upper Chesapeake Bay may have migrated from the Delaware River to

the upper Chesapeake through the Chesapeake and Delaware Canal (Grunwald et al. 2002). In

this study, genetic comparisons were made among all shortnose sturgeon populations for which

tissue samples were available. All population comparisons exhibited clear and significant

differences in haplotype frequencies except for comparisons between the Upper/Lower

Connecticut River and Delaware/Chesapeake. There were no unique haplotypes in the

Chesapeake Bay fish. Samples from four fish from the Potomac River were analyzed and results

indicate that these fish exhibited the same haplotypes as fish found elsewhere in the Chesapeake

Bay and in the Delaware River. These results suggest that some or all of the sturgeon captured

in the Chesapeake Bay and its tributaries may not be part of the Chesapeake Bay, but rather

transients from the Delaware population. 

However, the Washington Aqueduct Permit biological opinion concluded that

mitochondrial DNA (mtDNA) represents only a fraction (less than 1 percent) of the genetic

material and is maternally inherited. Therefore, in order to obtain conclusive results, it is

necessary to look at nuclear DNA (nDNA), which represents greater than 99 percent of the

genetic material and is biparentally inherited (NOAA National Marine Fisheries Service 2002). 

In the absence of stronger evidence to the contrary, the NOAA National Marine Fisheries

Service presumes that shortnose sturgeon captured in the Chesapeake Bay and its tributaries are

part of the Chesapeake Bay distinct population segment (NOAA National Marine Fisheries

Service 2002).
38

Field Study Results

The U.S. Fish and Wildlife Service conducted a sampling study sponsored by the U.S.

Army Corps of Engineers between 1998 and 2000 in the Maryland waters of the Chesapeake

Bay to determine the occurrence of shortnose and Atlantic sturgeon in areas of proposed dredgefill operations (Skjeveland et. al. 2000). This study included fishing at a total of 24 sites within

the Chesapeake Bay, five of which were located in the middle Potomac River approximately 30

to 74 miles downstream of the Washington Aqueduct discharge site. During this study, no

shortnose sturgeon were captured in the Potomac or Susquehanna rivers. An additional study by

the U.S. Fish and Wildlife Service was performed in the Potomac River and included sampling

at two areas in the vicinity of Little Falls, Virginia, which are environments that are consistent

with the preferred spawning habitat of shortnose sturgeon and are located near the Aqueduct

discharge sites (Eyler et. al. 2000). No shortnose sturgeon were captured during this study

either. 

 A separate U.S. Fish and Wildlife Service sampling study was also conducted in the

upper Chesapeake Bay mainstem, lower Susquehanna River and Chesapeake/Delaware Canal

during 1998 and 2000 in conjunction with a Section 7 consultation for the Baltimore Harbor and

Channels Federal Navigation Project (as cited in NOAA National Marine Fisheries 2002). This

study involved bottom gillnetting at 19 sites within the upper Chesapeake Bay mainstem and

lower Susquehanna River, and tracking of sonically tagged sturgeon within the upper Bay and

the Canal. No shortnose sturgeon were captured at any of the 19 sites. Figure 8 illustrates the

gill netting sites from these three U.S. Fish and Wildlife Service studies where no sturgeon were

caught.

The U.S. Fish and Wildlife Service Atlantic Sturgeon Reward Program has documented

the incidental captures of 50 shortnose sturgeon from various locations in the Bay over the six

year duration of the program (Mangold 2003; Spells 2003; Skjeveland et. al. 2000) (see Figure

4). The majority of these fish were tagged and tissue samples were taken from 36 fish in order

to determine the genetic characteristics of the individuals. The shortnose sturgeon have been

incidentally captured via this program from the lower Susquehanna River (4), the Bohemia River

(2), Potomac River (6), south of the Bay Bridge near Kent Island (2), near Howell Point (1), just

north of Hoopers Island (1), the Elk River (1) and Fishing Bay (2). The remaining 31 shortnose

sturgeon were captured in the upper Bay north of Hart-Miller Island. These fish were captured

alive in either commercial gillnets, poundnets, fykenets, eel pots, hoop nets, or catfish traps.

According to the NOAA National Marine Fisheries Service Washington Aqueduct Permit

biological opinion, the U.S. Fish and Wildlife Service studies may not have been comprehensive

enough to determine the presence or absence of sturgeon in the upper tidal Potomac River

(NOAA National Marine Fisheries Service 2002). Sampling sites may have been too deep with

too strong a current and timing and duration of the sampling events and the type of nets

employed may not have been appropriate for targeting shortnose sturgeon (NOAA National

Marine Fisheries Service 2002). This finding was reported at the same time as documenting no

captures of shortnose sturgeon during a 2 year U.S. Fish and Wildlife Service bottom gill netting 
39

Figure 8. Locations of all the U.S. Fish and Wildlife Service fisheries-independent sturgeon

sampling stations where no sturgeon were caught.

Source: Skjeveland et al. 2000.
40

study on the Potomac River which included a total of 4,590 fishing hours. Furthermore, it should

be noted that it is the opinion of the National Marine Fisheries Service that the U.S. Fish and

Wildlife Service studies should not be used as conclusive indicator of shortnose sturgeon

absence in the upper tidal Potomac River (NOAA National Marine Fisheries Service 2002).

A 2000 NOAA National Marine Fisheries Service report, entitled “A Protocol for Use of

Shortnose and Atlantic Sturgeons” identified a minimum sampling protocol for use in north

central rivers (Chesapeake drainages to the Merrimack River) to confirm shortnose sturgeon

presence or absence. The NOAA National Marine Fisheries Service Washington Aqueduct

Permit biological opinion indicated that the U.S. Fish and Wildlife Service studies did not follow

this desired protocol, which was published after the studies commenced. That report cited that 

the U.S. Fish and Wildlife Service sampling sites may have been too deep, in areas with too

strong a current to adequately document the presence of shortnose sturgeon (NOAA National

Marine Fisheries Service 2002). In addition, the timing and duration of the sampling events and

the type of nets employed may not have been appropriate for targeting shortnose sturgeon habitat

in question (NOAA National Marine Fisheries Service 2002). 

Lacking conclusive data, the NOAA National Marine Fisheries Service’s Washington

Aqueduct Permit biological opinion assumed the presence of shortnose sturgeon based on the

documented presence of this species and suitable spawning habitat in the Potomac River system. 

The NOAA biological opinion cited evidence from the life history attributes of shortnose

sturgeon which suggests that fish from the Chesapeake Bay distinct population segment were

also spawning in at least the Susquehanna, Gunpowder, and Rappahannock river systems

(NOAA National Marine Fisheries Service 2002). 

Habitat Quality Benefits from Dissolved Oxygen Criteria Attainment

Recent adoption of new Chesapeake Bay basinwide caps on nitrogen, phosphorus and

sediment loads by all seven watershed jurisdictions–New York, Pennsylvania, Maryland,

Virginia, West Virginia, Delaware and the District of Columbia–and the EPA will result in

significant improvements in tidal water quality (U.S. Environmental Protection Agency 2003b). 

Restoration of sturgeon habitat is among the many benefits that will be achieved. Open-water

designated use habitats currently unsuitable for sturgeon will be restored. Upon attainment of

the 175 million pounds total nitrogen loading cap (110 million pound reduction from 2000 loads)

and the 12.8 million pound total phosphorus loading cap (6.3 million pound reduction from 2000

loads), dissolved oxygen levels last observed in the 1950s and early 1960s will become the

norm. Bay shorelines will likely see over 185,000 acres of underwater bay grasses, more than

double the acreages mapped today. 

The adoption of the new loading caps underscores the commitment of the Chesapeake

Bay watershed partners to restoring the Bay. These loading caps are the greatest, most

challenging and stringent that have ever been established. According to the Chesapeake Bay

Commission’s The Cost of a Clean Bay, the jurisdictions will need an additional 12.8 billion

dollars to achieve these goals (Chesapeake Bay Commission 2003).

 Attainment of these challenging yet feasible loading cap goals and the resultant restored

water quality conditions will mean a substantial improvement to the Bay. Nevertheless, the
5

The entire Chesapeake 2000 agreement is available on the web at: www.chesapeakebay.net.

41

seasonal designated deep-water and deep-channel habitats in the mesohaline Chesapeake Bay

and lower rivers will still not be suitable for sturgeon during the summer months.

Recovery of the Shortnose Sturgeon

The Recovery Plan provides a strategy to protect shortnose sturgeon populations and

habitats. The recovery outline includes three shortnose sturgeon recovery objectives: 1.

Establishing Listing Criteria; 2. Protect Shortnose Sturgeon Population and Habitats; and 3.

Rehabilitate Habitats and Population Segments (NOAA National Marine Fisheries 1998a). In

addition to the Regional Criteria Guidance the Chesapeake Bay Program partners have been

initiating programs and policies throughout the Chesapeake Bay, which incorporate many of the

elements of the Rehabilitate Habitats and Population Segments recovery strategy. In fact, the

partners spend millions of dollars a year on the restoration of the Bay. The Chesapeake 20005

agreement outlines some of these commitments which improve habitat for the Bay and are

consistent with the Recovery Plan for the Shortnose Sturgeon. Some of these include:

• Restoring fish passage for migratory fish to more than 1,357 miles of currently blocked

river habitat by 2003 and establishing monitoring program to assess outcomes;

• Work with local governments, community groups and watershed organizations to

develop and implement locally supported watershed management plans in two-thirds of

the watershed to address the protection, conservation and restoration of stream corridors,

riparian forest buffers and wetlands for the purposes of improving habitat and water

quality;

• Correct the nutrient- and sediment-related problems in the Chesapeake Bay and its tidal

tributaries sufficiently to remove the Bay and the tidal portions of its tributaries from the

list of impaired waters under the Clean Water Act (the Regional Criteria Guidance is

part of this commitment);

• Through continual improvement of pollution prevention measures and other voluntary

means, strive for zero release of chemical contaminants from point sources, including air

sources to the Bay;

• Ensure that measures are in place to meet our riparian forest buffer restoration goal of

2,010 miles by 2,010;

• Assess the effects of airborne nitrogen compounds and chemical contaminants on the Bay

ecosystem and help establish reduction goals for these contaminants;

• Establish appropriate areas within the Chesapeake Bay and its tributaries as ‘no discharge

zones’ for human waste from boats;

• Strengthen programs for land acquisition and preservation within each state that are

supported by funding and target the most valued lands for protection;

• Reduce the rate of harmful sprawl development of forest and agricultural land in the

Chesapeake Bay watershed by 30 percent;

• Make education and outreach a priority in order to achieve public awareness and personal

involvement on behalf of the Bay and local watersheds.
42

• Enhance funding for locally-based programs that pursue restoration and protection

projects that will assist in the achievements of the goals of this and past agreement;

FINDINGS

The EPA has determined through consultation with the U.S. Fish and Wildlife Service

and the NOAA National Marine Fisheries Service, that the only endangered or threatened

species under the NOAA Fisheries jurisdiction in the evaluation area that will potentially be

affected is the endangered shortnose sturgeon (Acipenser brevirostrum). All the other federal

listed species within the Chesapeake Bay and its tidal tributaries would either not be affected or

would be beneficially affected by the issuance of the Regional Criteria Guidance.

The EPA has determined that the recommended water clarity criteria will not likely

adversely effect the listed species evaluated in this document. Furthermore, the EPA has

determined that the proposed water clarity criteria will beneficially affect preferred habitat,

spawning areas and food sources that the listed shortnose sturgeon depends on.

The EPA has determined that the recommended chlorophyll a criteria will not likely

adversely affect the listed species evaluated in this document. Furthermore, the EPA has

determined that the recommended chlorophyll a criteria will beneficially affect preferred habitat,

spawning habitat and food sources that the listed species depends on.

The EPA has determined that the collective application of dissolved oxygen criteria for

the migratory fish spawning and nursery and open-water fish and shellfish designated uses are

fully protective of shortnose sturgeon survival and growth for all life stages. 

• The migratory spawning and nursery 6 mg liter -1 7-day mean and 5 mg liter - 1

instantaneous minimum criteria will fully protect spawning shortnose sturgeon. 

The February 1 through May 31 application period for the migratory spawning

and nursery criteria fully encompasses the mid-March through mid-May

spawning season documented previously from the scientific peer reviewed

literature.

• The individual components of the open water criteria protect shortnose sturgeon

growth (5 mg liter -1 30-day mean), larval recruitment (4 mg liter -1 7-day mean)

and survival (3 .2 mg liter -1 instantaneous minimum). A 4.3 mg liter -1

instantaneous minimum criterion applies to open waters with temperatures above

29o

C considered stressful to shortnose sturgeon.

• The open water criteria applied to tidal fresh waters includes a 5.5 mg liter -1 30-

day mean criterion providing extra protection of shortnose sturgeon juveniles

inhabiting tidal freshwater habitats.

The EPA has determined that adoption of the proposed dissolved oxygen criteria into

Maryland, Virginia, Delaware and the District of Columbia’s state water quality standards and

their eventual attainment will beneficially affect shortnose sturgeon spawning, nursery, juvenile

and adult habitats and food sources by driving widespread nutrient reduction loading actions

leading to increasing existing ambient dissolved oxygen concentrations. This determination is
43

consistent with and pursuant to Endangered Species Act provisions that state that the EPA is to

use its authority to further the purpose of protecting threatened and endangered species (see 16

U.S.C. § 1536(a)). It is also consistent with the NOAA National Marine Fisheries Recovery

Plan (1998a) for shortnose sturgeon which recommends working cooperatively with states to

promote increased state activities to promote best management practices to reduce non-point

sources. 

The EPA has determined that adoption, implementation and eventual full attainment of

the states adopted dissolved oxygen water quality standards will result in significant

improvements in dissolved oxygen concentration throughout the tidal waters to levels last

observed consistently over four to five decades ago in Chesapeake Bay and its tidal tributaries.

The EPA recognizes that dissolved oxygen criteria for June through September for the

deep-water seasonal fish and shellfish and the deep-channel designated use are at or below levels

that protect shortnose sturgeon. The EPA believes there are strong lines of evidence that

shortnose sturgeon historically have not used deep-water and deep-channel designated use

habitats during the summer months due to naturally pervasive low dissolved oxygen conditions.

• Published findings in the scientific literature regarding salinity preferences (tidal

fresh to 5 ppt) and salinity tolerances (<15 ppt) clearly indicate shortnose

sturgeon habitats are unlikely to overlap with the higher salinity deep-water and

deep-channel designated use habitats.

• The EPA has concluded, based on extensive published scientific findings and indepth analysis of the 1400 record U.S. Fish and Wildlife Service Reward Program

database, that these same deep-water and deep-channel regions have not served as

potential habitats for sturgeon during the June through September time period

when there is a natural tendency for low dissolved oxygen conditions to occur.

• The EPA recognizes the potential limitations of the U.S. Fish and Wildlife

Service data set. However, the EPA believes the significant extent of the capture

records–400 stations and 1400 individuals caught–provides substantial evidence

for the lack of a potential conflict between shortnose habitat and seasonally

applied deep-water and deep-channel designated uses.

The EPA had determined that the recommended dissolved oxygen criteria for the refined

designated uses will not likely adversely effect the listed species evaluated in this document. 

Furthermore, the EPA has determined that the Chesapeake Bay dissolved oxygen criteria will

beneficially affect critical habitat and food sources that the listed species is dependent on. 

SUMMARY AND CONCLUSION

Shortnose sturgeon are endangered throughout their entire range (NOAA National

Marine Fisheries Service 2002). According to NOAA, in the Final Biological Opinion for the

Washington Aqueduct, this species exists as 19 separate distinct population segments that should

be managed as such; specifically, the extinction of a single shortnose sturgeon population risks

permanent loss of unique genetic information that is critical to the survival and recovery of the
44

species (NOAA National Marine Fisheries Service 2002). The shortnose sturgeon residing in the

Chesapeake Bay and its tributaries form one of the 19 distinct population segments.

Adult shortnose sturgeon are present in the Chesapeake Bay based on the 50 captures via

the U.S. Fish and Wildlife Service Atlantic Sturgeon Reward Program. However, the presence

and abundance of all life stages within the evaluation area itself are unknown. Preliminary

published scientific evidence suggests that the shortnose sturgeon captured in the Chesapeake

Bay may be part of the Delaware distinct population segment using the C & D Canal as a

migratory passage. However, the NOAA National Marine Fisheries Service recommend more

studies utilizing nuclear DNA need to be conducted before this can be proven conclusively. 

Section 9 of the Endangered Species Act and Federal regulations pursuant to section 4(d)

of the Endangered Species Act prohibit the take of endangered and threatened species,

respectively, without special exemption. ‘Take’ is defined as to harass, harm, pursue, hunt,

shoot, wound, kill, trap, capture or collect, or to attempt to engage in any such conduct. Harm is

further defined by NOAA National Marine Fisheries Service to include any act which actually

kills or injures fish or wildlife. Such an act may include significant habitat modification or

degradation that actually kills or injures fish or wildlife by significantly impairing essential

behavioral patterns including breeding, spawning, rearing, migrating, feeding, or sheltering. 

Harass is defined by U.S. Fish and Wildlife Service as intentional or negligent actions that create

the likelihood of injury to listed species to such an extent as to significantly disrupt normal

behavior patterns which include, but are not limited to, breeding, feeding or sheltering. 

Incidental take is defined as take that is incidental to, and not the purpose of, the carrying out of

an otherwise lawful activity.

The Shortnose Sturgeon Recovery Plan (NOAA National Marine Fisheries Service

1998a) further identifies habitat degradation or loss (resulting, for example, from dams, bridge

construction, channel dredging, and pollutant discharges) and mortality (resulting, for example,

from impingement on cooling water intake screens, dredging and incidental capture in other

fisheries) as principal threats to the species’ survival. The recovery goal is identified as delisting

shortnose sturgeon populations throughout their range, and the recovery objective is to ensure

that a minimum population size is provided such that genetic diversity is maintained and

extinction is avoided.

Considering the nature of the proposed Regional Criteria Guidance, the effects of the

recommended criteria, and future cumulative effects in the evaluation area, the proposed

issuance of Regional Criteria Guidance is not likely to adversely affect the reproduction,

numbers, and distribution of the Chesapeake Bay distinct population segment in a way that

appreciably reduces their likelihood of survival and recovery in the wild. This contention is

based on the following: (1) the adoption of the recommended dissolved oxygen criteria into state

water quality standards and subsequent attainment upon achievement of the Chesapeake Bay

watershed’s nutrient loading caps will provide for significant water quality improvements to the

tributaries to the Chesapeake Bay (such as the Susquehanna, Gunpowder, and Rappahannock

rivers) where the shortnose sturgeon would most likely spawn and spend their first year of life;

(2) the main channel of the Chesapeake Bay most likely experienced reductions in dissolved

oxygen before large-scale post-colonial land clearance took place, due to natural factors such as
45

climate-driven variability in freshwater inflow; and (3) there is strong evidence that shortnose

sturgeon have historically not used deep-water and deep-channel designated use habitats during

the summer months due to naturally pervasive low dissolved oxygen conditions.

Based on the evaluation conducted in this document it is the EPA’s conclusion that the

proposed issuance of the Regional Criteria Guidance would not adversely affect the continued

existence of the Chesapeake Bay DPS of shortnose sturgeon. No critical habitat has been

designated for this species, and therefore, none will be affected. In fact, the EPA believes state

adoption of the criteria into water quality standards will directly lead to increased levels of

suitable habitat for shortnose sturgeon.
46

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APPENDICES

Appendix A Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and

Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries.

Appendix B Technical Support Document for the Identification of Chesapeake Bay

Designated Uses and Attainability.

Appendix C. List of Federally Endangered Species for Maryland, Virginia, Delaware and the

District of Columbia.
1

APPENDIX C

Endangered Species in Maryland, Delaware, Virginia, and the District of Columbia.

Listings by State and Territory as of October 24, 2002

Notes:

 Displays one record per listing entity. 

 Includes experimental populations and similarity of appearance species. 

 Pertains to the range of a species, not the listing status within a State/Territory. 

 Includes non-nesting sea turtles and whales in State/Territory coastal waters. 

 Includes species under the sole jurisdiction of the National Marine Fisheries Service.

Source : U.S. Fish and Wildlife website http://ecos.fws.gov/webpage/

Maryland – 26 listings

Animals – 19

Status Listing 

E Bat, Indiana (Myotis sodalis)

E Darter, Maryland (Etheostoma sellare)

T Eagle, bald (lower 48 States) (Haliaeetus leucocephalus)

T Plover, piping (except Great Lakes watershed) (Charadrius melodus)

E Puma, eastern (Puma concolor couguar)

T Sea turtle, green (except where endangered) (Chelonia mydas)

E Sea turtle, hawksbill (Eretmochelys imbricata)

E Sea turtle, Kemp's ridley (Lepidochelys kempii)

E Sea turtle, leatherback (Dermochelys coriacea)

T Sea turtle, loggerhead (Caretta caretta)

E Squirrel, Delmarva Peninsula fox (Sciurus niger cinereus)

E Sturgeon, shortnose (Acipenser brevirostrum)

T Tiger beetle, northeastern beach (Cicindela dorsalis dorsalis)

T Tiger beetle, Puritan (Cicindela puritana)

T Turtle, bog (northern) (Clemmys muhlenbergii)

E Wedgemussel, dwarf (Alasmidonta heterodon)

E Whale, finback (Balaenoptera physalus)

E Whale, humpback (Megaptera novaeangliae)

E Whale, right (Balaena glacialis)

Plants – 7 

Status Listing 

T Joint-vetch, sensitive (Aeschynomene virginica)

E Gerardia, sandplain (Agalinis acuta)

T Amaranth, seabeach (Amaranthus pumilus)

T Pink, swamp (Helonias bullata)
2

E Dropwort, Canby's (Oxypolis canbyi)

E Harperella (Ptilimnium nodosum)

E Bulrush, Northeastern (Scirpus ancistrochaetus)

Virginia – 70 listings

Animals – 56

Status Listing

E Bat, gray (Myotis grisescens)

E Bat, Indiana (Myotis sodalis)

E Bat, Virginia big-eared (Corynorhinus (=Plecotus) townsendii virginianus)

XN Bean, Cumberland (pearlymussel) AL; free-flowing reach of the Tennessee

River below the Wilson Dam, Colbert and Lauderdale Counties, AL (Villosa

trabalis)

E Bean, purple (Villosa perpurpurea)

E Blossom, green (pearlymussel) (Epioblasma torulosa gubernaculum)

T Chub, slender (Erimystax cahni)

T Chub, spotfin (Cyprinella monacha) – Entire

E Combshell, Cumberlandian (Epioblasma brevidens) – Entire Range; except where

listed as Experimental Populations 

XN Combshell, Cumberlandian AL; free-flowing reach of the Tennessee River 

below the Wilson Dam, Colbert and Lauderdale Counties, AL (Epioblasma

brevidens)

E Darter, duskytail (Etheostoma percnurum) – Entire Range 

T Eagle, bald (Haliaeetus leucocephalus) – Lower 48 States

E Fanshell (Cyprogenia stegaria)

E Isopod (Lirceus usdagalun) – Lee County cave

T Isopod, Madison Cave (Antrolana lira)

E Logperch, Roanoke (Percina rex)

XN Madtom, yellowfin (Noturus flavipinnis) – Holston River, VA, TN 

T Madtom, yellowfin (Noturus flavipinnis) – Except where XN 

E Monkeyface, Appalachian (pearlymussel) (Quadrula sparsa)

E Monkeyface, Cumberland (pearlymussel) (Quadrula intermedia) – Entire Range; 

except where listed as Experimental Populations 

XN Monkeyface, Cumberland (pearlymussel) (Quadrula intermedia) AL; Freeflowing reach of the Tennessee River below the Wilson Dam, Colbert and 

Lauderdale Counties, AL 

E Mucket, pink (pearlymussel) (Lampsilis abrupta)

E Mussel, oyster (Epioblasma capsaeformis)– Entire Range; except where listed as 

Experimental Populations 

XN Mussel, oyster (Epioblasma capsaeformis) AL; Free-flowing reach of the 

Tennessee River below the Wilson Dam, Colbert and Lauderdale Counties, AL 

E Pearlymussel, birdwing (Conradilla caelata) – Entire Range; except where listed 

as Experimental Populations 
3

E Pearlymussel, cracking (Hemistena lata) – Entire Range; except where listed as 

Experimental Populations 

E Pearlymussel, dromedary (Dromus dromas) – Entire Range; except where listed 

as Experimental Populations 

E Pearlymussel, littlewing (Pegias fabula)

E Pigtoe, finerayed (Fusconaia cuneolus) – Entire Range; except where listed as 

Experimental Populations 

XN Pigtoe, finerayed (Fusconaia cuneolus) AL; free-flowing reach of the Tennessee

River below the Wilson Dam, Colbert and Lauderdale Counties, AL 

E Pigtoe, rough (Pleurobema plenum)

E Pigtoe, shiny Entire Range; Except where listed as experimental populations 

(Fusconaiacor)

XN Pigtoe, shiny (Fusconaia cor) – AL; free-flowing reach of the Tennessee River 

below the Wilson Dam, Colbert and Lauderdale Counties, AL 

T Plover, piping (Charadrius melodus) – Except Great Lakes watershed 

E Puma, eastern (Puma concolor couguar)

E Rabbitsfoot, rough (Quadrula cylindrica strigillata)

E Riffleshell, tan (Epioblasma florentina walkeri (E. walkeri))

E Salamander, Shenandoah (Plethodon shenandoah)

T Sea turtle, green (Chelonia mydas) – Except where endangered

E Sea turtle, hawksbill (Eretmochelys imbricata)

E Sea turtle, Kemp's ridley (Lepidochelys kempii)

E Sea turtle, leatherback (Dermochelys coriacea)

T Sea turtle, loggerhead (Caretta caretta)

E Snail, Virginia fringed mountain (Polygyriscus virginianus)

E Spinymussel, James (Pleurobema collina)

E Squirrel, Delmarva Peninsula fox (Sciurus niger cinereus) – Except Sussex

County, Delaware 

E Squirrel, Virginia northern flying (Glaucomys sabrinus fuscus)

E Sturgeon, shortnose (Acipenser brevirostrum)

E Tern, roseate (Sterna dougallii dougallii) – Northeast U.S. nesting population 

T Tiger beetle, northeastern beach (Cicindela dorsalis dorsalis)

T(S/A) Turtle, bog (Muhlenberg) (southern) (Clemmys muhlenbergii)

E Wedgemussel, dwarf (Alasmidonta heterodon)

E Whale, finback (Balaenoptera physalus)

E Whale, humpback (Megaptera novaeangliae)

E Whale, right (Balaena glacialis [incl. Australis])

E Woodpecker, red-cockaded (Picoides borealis)

Plants – 14

Status Listing

T Joint-vetch, sensitive (Aeschynomene virginica)

T Amaranth, seabeach (Amaranthus pumilus)

E Rock-cress, shale barren (Arabis serotina)
4

T Birch, Virginia round-leaf (Betula uber)

E Bittercress, small-anthered (Cardamine micranthera)

E Coneflower, smooth (Echinacea laevigata)

T Sneezeweed, Virginia (Helenium virginicum)

T Pink, swamp (Helonias bullata)

E Mallow, Peter's Mountain (Iliamna corei)

T Pogonia, small whorled (Isotria medeoloides)

T Orchid, eastern prairie fringed (Platanthera leucophaea)

E Sumac, Michaux's (Rhus michauxii)

E Bulrush, Northeastern (Scirpus ancistrochaetus)

T Spiraea, Virginia (Spiraea virginiana)

District of Columbia – 3 listings

Animals – 3

Status Listing 

E Amphipod, Hay's Spring (Stygobromus hayi)

T Eagle, bald (lower 48 States) (Haliaeetus leucocephalus)

E Puma, eastern (Puma concolor couguar)

Plants – 0

Delaware – 19 listings

Animals – 15

Status Listing 

T Eagle, bald (Haliaeetus leucocephalus) – Lower 48 States

T Plover, piping (Charadrius melodus)

E Puma, eastern (Puma concolor couguar)

T Sea turtle, green (Chelonia mydas) – Except where endangered

E Sea turtle, hawksbill (Eretmochelys imbricata)

E Sea turtle, Kemp's ridley (Lepidochelys kempii)

E Sea turtle, leatherback (Dermochelys coriacea)

T Sea turtle, loggerhead (Caretta caretta)

E Squirrel, Delmarva Peninsula fox (Sciurus niger cinereus) – except Sussex

County, Delaware

XN Squirrel, Delmarva Peninsula fox [XN] (Sciurus niger cinereus)

E Sturgeon, shortnose (Acipenser brevirostrum)

T Turtle, bog (northern) (Clemmys muhlenbergii)

E Whale, finback (Balaenoptera physalus)

E Whale, humpback (Megaptera novaeangliae)

E Whale, right (Balaena glacialis)
5

Plants – 4

Status Listing 

T Pink, swamp (Helonias bullata)

T Pogonia, small whorled (Isotria medeoloides)

E Dropwort, Canby's (Oxypolis canbyi)

T Beaked-rush, Knieskern's (Rhynchospora knieskernii)

T Sea turtle, green (Chelonia mydas) – Except where endangered

E Sea turtle, hawksbill (Eretmochelys imbricata)

E Sea turtle, Kemp's ridley (Lepidochelys kempii)

E Sea turtle, leatherback (Dermochelys coriacea)

T Sea turtle, loggerhead (Caretta caretta)

E Whale, finback (Balaenoptera physalus)

E Whale, humpback (Megaptera novaeangliae)

E Whale, right (Balaena glacialis)

E Sturgeon, shortnose (Acipenser brevirostrum)