Conservation Units of Managed Fish, 

Threatened or Endangered Species, and 

Marine Mammals 

Report of a Workshop: February 14-16, 2006 

Silver Spring, Maryland 

Steering Committee: 

 Thomas C. Eagle (Chair) 

 Steven X. Cadrin 

 Megan E. Caldwell 

 Richard D. Methot 

 Marta F. Nammack 

U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

NOAA Technical Memorandum NMFS-OPR-37 

January 2008 

Conservation Units of Managed Fish, Threatened or Endangered Species, 

and Marine Mammals 

Report of a Workshop: February 14-16, 2006, Silver Spring, Maryland 

Steering Committee: 

Thomas C. Eagle (Chair) 

 Office of Protected Resources 

 Silver Spring, MD 

Steven X. Cadrin 

 Northeast Fisheries Science Center 

 Cooperative Marine Education and Research 

 New Bedford, MA 

Megan E. Caldwell 

 Office of Sustainable Fisheries 

 Silver Spring, MD 

 Current Affiliation: 

Atlantic States Marine Fisheries Commission 

Washington, D.C. 

Richard D. Methot 

 Office of Science and Technology 

 Seattle, WA 

Marta F. Nammack 

 Office of Protected Resources 

 Silver Spring, MD 

NOAA Technical Memorandum 

NMFS-OPR-37 

January 2008 

United States Department of Commerce 

 Carlos Gutierrez, Secretary 

National Oceanic and Atmospheric Administration 

 Vice Admiral Conrad C. Lautenbacher, Jr., USN (Ret.) 

 Under Secretary of Commerce for Oceans and Atmosphere 

National Marine Fisheries Service 

 James W. Balsiger, Acting Assistant Administrator for Fisheries 

iii 

Executive Summary 

The National Marine Fisheries Service (NMFS) is responsible for the conservation of 

living marine resources and their habitats with primary authority from three Federal 

statutes: the Magnuson-Stevens Fishery Conservation and Management Act (MSA), the 

Endangered Species Act (ESA), and the Marine Mammal Protection Act (MMPA). The 

MSA governs the exploitation of fish stocks for the maximum net benefit of the Nation, 

while preventing overfishing and rebuilding overfished stocks of fish to biomass levels 

capable of producing Maximum Sustainable Yield (MSY). The ESA governs the taking 

of species that have an elevated risk of extinction to ensure that effects of human activity 

are restricted to levels that would allow recovery of the species to the point it is no longer 

threatened or endangered. The MMPA governs the taking of marine mammals so that the 

total of such taking is sustainable, that is, it would allow populations of marine mammals 

to recover to or to be maintained within their Optimum Sustainable Populations (OSP). 

Meeting the different objectives mandated by each law requires potentially different 

definition of biological stocks and management units. 

NMFS convened a workshop of scientists, managers, and policy advisors to discuss 

issues related to conservation units, exchange information about the biological basis for 

stock structure, learn about case studies in which particular aspects of population 

structure are important, discuss strengths and weaknesses of NMFS’ identification of 

conservation units under the three statutes, and to recommend alternative approaches or 

revisions for identifying conservation units under the three statutes. Presentations and 

discussions at the workshop provided a basis to address two pressing questions for the 

agency: 

(1) Why are our conservation units different under MSA, ESA, and MMPA? 

(2) Is there a biological paradigm that may be used to explain differences noted in 

conservation units? 

Much, but not all, of the answer to the first question can be found in the objectives of 

these laws. A major motivating factor for the ESA was a desire to preserve genetic 

variability, between and within species. Accordingly, conservation units under the ESA 

should be substantially reproductively isolated from one another to be listed under this 

act. On the other hand, objectives of the MMPA include keeping populations or stocks of 

animals above their Optimum Sustainable Populations OSP levels. The MSA allows for 

management units that may contain multiple species as members of a complex, but the 

concept of demographically independent stocks within a species is commonly used to 

determine the status of fishery resources. Thus, demographic independence is an 

appropriate basis for identifying conservation units (distinguishing among populations or 

stocks) for the MSA and MMPA. 
iv 

A low amount of exchange among groups for breeding may be sufficient to prevent 

development of important genetic differences; however, these groups may remain 

demographically independent from one another. Therefore, it is generally expected that 

conservation units identified on the basis of reproductive isolation would be larger than 

those identified on the basis of demographic independence. Thus, discrete groups under 

the DPS policy would generally be larger than discrete groups identified for management 

under the MSA or MMPA. Furthermore, marine mammal biology includes internal 

fertilization, live birth, parental care, and maintenance of family groups; these features 

act as barriers to mixing among groups and help produce fine-scale population structure. 

Demographic Independent Populations (DIP) represent a paradigm that may be used to 

explain differences in conservation units identified under the ESA versus the MSA or 

MMPA. A single DIP would be an appropriate conservation unit of managed fish or 

marine mammals due to the demographic nature of the objectives of the MSA and 

MMPA. However, although DIPs are discrete from one another demographically, they 

may be genetically similar. Therefore, a discrete group under the DPS policy formulated 

for implementation of the ESA may contain individuals from two or more DIPs. 

Participants at the workshop agreed that guidance used to identify conservation units 

under the three statutes is generally acceptable and has worked well for a number of 

years. Despite this general acceptance, discussions at the workshop revealed a number of 

places where each set of guidance could be improved and noted two specific challenges 

for identifying conservation units common under all three statutes: (1) seasonal mixing 

of individuals from various stocks and (2) clines or continuously-distributed species. The 

steering committee recommends that NMFS, along with appropriate partner agencies or 

organizations, revise the statute-specific guidance to incorporate necessary 

improvements.
v 

Table of Contents 

Executive Summary...........................................................................................................iii

Introduction......................................................................................................................... 1 

Guidance from the Leadership Council .......................................................................... 2 

Presentations ....................................................................................................................... 4 

Biology of Population Structure ..................................................................................... 4 

What Is a Population? ................................................................................................. 5 

The Biology of Marine Population Structure.............................................................. 7 

Management of Biological Stocks under the MSFCMA, ESA, and MMPA ............. 9 

Legal Requirements and Guidance ............................................................................... 11 

Determining Management Units Pursuant to the Magnuson-Stevens Act ............... 11 

ESA Management Units ........................................................................................... 12 

MMPA Management Units....................................................................................... 13 

Current Guidelines for Identifying Conservation Units................................................ 14 

Endangered Species Act: Species, Subspecies, and DPSs........................................ 14 

Marine Mammal Stock Identity Guidelines............................................................ 156 

Guidelines for Identifying Conservation Units in the 

Fishery Conservation and Management Act............................................................. 18 

Case Studies.................................................................................................................. 21 

Groundfish Stocks in Alaska .................................................................................... 21 

Stock Structure and Management Units for West Coast Groundfish ....................... 23 

Stock Identification of New England Groundfish .................................................... 25 

Atlantic Bluefin Tuna: Swim Anywhere They Want, Wanted Everywhere They 

Swim ......................................................................................................................... 28

Management Units for Sedentary Stocks: The Atlantic Sea Scallop Example ....... 30 

Case Study: Petition to Reclassify Two "Subpopulations" of the Loggerhead Turtle 

(Caretta caretta) as Distinct Population Segments .................................................. 32 

Humpback Whale: Gulf of Maine Stock Definition................................................ 34 

Pacific Salmon .......................................................................................................... 38 

Delineation of an ESA Distinct Population Segment Incorporating Cherry Point 

Pacific Herring.......................................................................................................... 41 

Distinct Population Segments of North American Green Sturgeon ......................... 44 

Harbor Porpoise, Pacific Coast Stocks and Harbor Seals in Alaska......................... 46 

Defining Stock Structure of Coastal Bottlenose Dolphins, Tursiops truncatus, along 

the Atlantic Coast of the U.S.: A Multidisciplinary Approach................................. 48 

Killer Whales ............................................................................................................ 50 

Discussion Sessions .......................................................................................................... 52

Statute-specific Discussions.......................................................................................... 52 

Magnuson-Stevens Act Group.................................................................................. 52 

Endangered Species Act Group ................................................................................ 53 

Marine Mammal Protection Act Group .................................................................... 57 

Blended Discussions ..................................................................................................... 59 

Conclusions and Recommendations ................................................................................. 65 

Magnuson-Stevens Act ................................................................................................. 67 
vi 

Endangered Species Act ............................................................................................... 67 

Marine Mammal Protection Act ................................................................................... 68 

Literature Cited ................................................................................................................. 70 

Appendices........................................................................................................................ 75 

Appendix 1. Workshop Agenda.................................................................................... 76 

Appendix 2. Workshop Participants ............................................................................. 82 

Appendix 3a. Excerpts from MSA and supporting documents related to stock 

identification of managed fish. ................................................................................. 83 

Appendix 3b. Definition of “species” from the ESA and the joint DPS policy ....... 86 

Appendix 3c. Definition of population stock from the MMPA and the population 

identity segment of NMFS’ guidelines for assessing marine mammal stocks. ........ 98 
1 

Introduction 

Natural populations are seldom homogeneous and typically consist of intra-specific 

groups. Individuals within these groups may move or migrate to other groups. As 

exchange between groups is diminished, structuring occurs, and this structuring may affect 

the management or conservation of the groups. These groups are usually recognized and 

conserved as separate populations. Different degrees of inter-group exchange of 

individuals occur within species, resulting in sub-specific structuring. Such structuring is 

recognized in the ecological and conservation literature as subspecies, populations, or 

other such groups. An important question, therefore, arises for conservation agencies 

regarding how little exchange (or how much separation) is necessary of individuals among 

groups to result in recognizing these groups as separate conservation units. The answer to 

this question depends in large part upon the purposes or goals of conservation programs. 

The National Marine Fisheries Service (NMFS) is responsible for the conservation and 

stewardship of living marine resources and their habitats with primary authority from three 

Federal statutes: the Magnuson-Stevens Fishery Conservation and Management Act 

(MSA), the Endangered Species Act (ESA), and the Marine Mammal Protection Act 

(MMPA). The MSA governs the exploitation of fish stocks for the maximum net benefit 

of the Nation, while preventing overfishing and rebuilding, as necessary, stocks to biomass 

levels capable of producing Maximum Sustainable Yield (MSY). The ESA governs the 

taking of species that have an elevated risk of extinction to ensure that effects of human 

activity is restricted to levels that would allow recovery of the species to the point it is no 

longer threatened or endangered. The MMPA governs the taking of marine mammals so 

that the total of such taking is sustainable, that is, it would allow populations of marine 

mammals to recover to or to be maintained within their Optimum Sustainable Populations 

(OSP). Meeting the different objectives mandated by each law requires potentially 

different definition of intra-specific groups. These differences may be difficult to explain 

to many of the agency’s constituents and may be confusing for NMFS staff and managers. 

To alleviate confusion related to the identification of conservation or management units 

under the three statutes, NMFS convened a workshop of scientists, managers, and policy 

advisors to discuss issues related to management units, exchange information about the 

biological basis for stock structure, learn about case studies in which particular aspects of 

population structure are important, discuss strengths and weaknesses of NMFS’ 

identification of conservation units under the three statutes, and to recommend alternative 

approaches or revisions for identifying conservation units under the three statutes. Three 

major questions may represent the major underlying issues for the agency: 

1. What conservation units make sense for NMFS to fulfill its stewardship 

responsibilities? 

2. Can we draw on similarities and differences in our three major acts to 

describe different perceptions in identifying conservation units? 
2 

3. What, if any, are the practical limitations in identifying more conservation 

units within a species? 

The workshop consisted of the following sessions: 

• Introduction of problems associated with identifying management units from the 

perspective of NMFS’ Leadership Council 

• The biology of population structure 

• The legal frameworks for conservation under the MSA, ESA, and MMPA 

• Approaches used to identify conservation units under the three statutes 

• Case studies of the implementation of conservation programs for conservation 

units under the three statutes 

• Breakout sessions to discuss 

o Strengths and weaknesses of identifying conservation units under each 

statute 

o Similarities and differences among the three statutes regarding conservation 

objectives and identifying conservation units 

This report includes a summary of the introductory remarks describing the problem; 

abstracts of the presentations on population biology, legal frameworks, existing guidance 

for identifying conservation units, and case studies; summaries of the breakout sessions; 

and conclusions and recommendations from the steering committee. The steering 

committee recognized that the discussions at the workshop could indicate the need for 

change to established policies for identifying conservation units. The scope of this 

workshop was limited, however, because responsibilities under the MSA, ESA and 

MMPA are shared with other organizations (Regional Fishery Management Councils, U.S. 

Fish and Wildlife Service, and Marine Mammal Commission). Accordingly, changes to 

policies for identifying conservation units were not addressed in this workshop. Rather, 

this workshop identified strengths and weaknesses of the approaches used under each 

statute to allow statute-specific guidance to be reviewed and, as needed, changed in 

partnership with the other affected agencies. 

Guidance from the Leadership Council 

Dr. William Fox, Director of the Southwest Fisheries Science Center, Dr. Douglas 

DeMaster, Director of the Alaska Fisheries Science Center, and James Lecky, Director of 

the Office of Protected Resources, presented aspects of the Leadership Council’s concerns 

related to the identification of conservation units. The major problem is that constituents 

often do not understand the bases upon which NMFS identifies conservation units and 

perceive that these units are identified inconsistently among the three major statutes. The 

Assistant Administrator often encounters such views from constituents and has no concise 

summary of NMFS’ policies for identifying conservation units. 

The primary question is, “Why are our conservation units different under MSA, ESA, and 

MMPA?” To some extent, this question arises because the objectives of the statutes are 

different; thus, conservation units under each statute may be different and designed to 
3 

meet the objectives of the specific statute. The purpose of the MSA is to provide 

maximum net benefit to the Nation by preventing overfishing, rebuilding overfished 

stocks, and ensuring optimal harvest of fish stocks. The ESA is designed to promote the 

recovery of threatened or endangered species and the habitats upon which these species 

depend. The MMPA protects all marine mammals, regardless of the status of the 

population stock to which they belong, with a major objective of maintaining each stock 

within its OSP, keeping in mind the carrying capacity of the environment. These 

differences in policies for identifying conservation units are confusing. Because the 

selection of a unit to conserve has cultural and economic implications, unexplained 

differences and their resulting confusion lead to a lack of understanding of our policies by 

constituencies, with particular sensitivities by regulated communities. 

Most members of the Leadership Council have experience and expertise in fishery 

management and are familiar with the identification of fishery stocks. They understand 

that the conservation units in fishery management assume some sort of genetic basis for 

dividing fish into stocks and use various measures (e.g., tagging, use of different spawning 

ground, exposure to different mortality rates, or other biological parameters) in identifying 

stocks. Many of our fish stocks, however, were identified long ago, before the widespread 

use of technologies now used in identifying conservation units (e.g., molecular genetics). 

In contrast, most senior managers are less experienced in the ESA and MMPA and see 

conflict in structure of conservation units defined under these laws. In particular, there is a 

perception that conservation units under these statutes are smaller than under the MSA, 

particularly for marine mammals; further, social structure within populations, combined 

with little genetic information, makes the identification of conservation units more 

complicated. Such perception and ongoing re-evaluations of marine mammal population 

stocks, which result in small conservation units, leads to a concern that population stocks 

could become too small for practical aspects of management. To explain the rationale 

behind different approaches under the three statutes, it would be helpful to find a common 

paradigm that may be used as a starting point for identifying conservation units under the 

different laws. 

The Leadership Council representatives noted that a clear, concise description of our 

guidance for identifying conservation units under the MSA, ESA, and MMPA would help 

agency officials explain the apparent differences perceived for managed fish, threatened 

and endangered species, and marine mammals. The description should be in the form of a 

“white paper” or “primer” that agency officials could distribute to interested constituents 

when questions arise. 
4 

Presentations

To provide a broad scope of information, which would serve as the basis for discussions 

later in the workshop, scientists and managers from various offices with NMFS were 

invited to make presentations to the workshop. Presentations were grouped into the 

following aggregations to ensure participants heard biological, legal, and policy 

perspectives on identifying conservation units and examples of the application of existing 

guidance to identifying conservation units under the three statutes: 

• Biology of Population Structure 

• Legal Requirements and Guidance 

• Current Guidelines for Identifying Conservation Units 

• Case Studies 

 

Biology of Population Structure

Presentations in this section described the biological basis for identifying populations, 

biological characteristics that result in population structure, and the consequences of 

alternatives for identifying conservation units or populations. 
5 

What Is a Population? 

Robin S. Waples 

Northwest Fisheries Science Center 

(much of this material is covered in more detail in Waples and Gaggiotti, 2006) 

Among the most important and vexing questions in marine conservation and management 

is, “How many stocks or populations of a given species are there?” No single 

scientifically “correct” answer exists for this question; instead, the answer depends on 

several factors that involve a combination of science and policy. First, it is important to 

clearly articulate the objectives one is trying to achieve because that can influence the way 

populations are defined. Examples of possible objectives include: 1) We want to maximize 

sustainable harvest; 2) We need to manage “stocks” or “populations” separately because 

of a legal mandate; 3) We want to minimize impacts on “weak” stocks. Second, it is 

important to articulate what a population is conceptually. Again, no single approach is 

“correct.” Two commonly used frameworks for considering populations are the 

ecological paradigm (which emphasizes demographic cohesion) and the evolutionary 

paradigm (which emphasizes reproductive cohesion). It is important to match the 

appropriate population paradigm with the management or conservation objectives. For 

example, with respect to Objective 3 above, we might want to minimize impacts on weak 

stocks for either (or both) of two reasons: 3A) Locally depleted stocks take a long time to 

rebuild; or 3B) Local extirpation might represent an irreversible loss of biodiversity. If we 

are primarily concerned with 3A, the ecological paradigm is more suitable because the key 

factor is the degree of demographic exchange among subunits. In contrast, if the primary 

concern is loss of biodiversity, the evolutionary paradigm is more appropriate. 

Given the central importance of the population/stock concept, one might expect to be able 

to find definitions of “population” that are objective and quantitative enough that 

independent researchers could apply them to a common problem and achieve the same 

results. In fact, however, a review of the literature indicates that few of the commonly 

used definitions of ‘population’ are operational in this sense; instead, they typically rely on 

qualitative descriptions such as “a group of organisms of the same species occupying a 

particular space at a particular time” (Krebs 1994). This illustrates the need for a third key 

step in defining populations: one must identify quantitative criteria for how different units 

must be before they are considered separate “populations.” Population differentiation 

occurs along a continuum, and no single point on the continuum captures all reasonable 

concepts of “population” (Figure 1). Choice of the quantitative criteria is necessarily 

somewhat arbitrary but can be made more objective by relating them directly to the 

management/conservation goals. It is important to realize that standard statistical tests 

generally evaluate the null hypothesis of a single, randomly mating population—a 

scenario that lies at one extreme end of the population differentiation continuum. 

Rejection of that hypothesis, therefore, does not directly address the issue as to whether 

the differences among units are large enough to warrant separate population status. 

Perhaps the best, published example of a quantitative population definition is that of a 

demographically independent population (DIP) in the Viable Salmonid Populations 
6 

Figure 1. The continuum of population differentiation. Each group of circles represents a 

group of subpopulations with varying degrees of connectivity (geographic overlap and/or 

migration). A) Complete independence. B) Modest connectivity. C) Substantial 

connectivity. D) Panmixia; “subpopulations” are completely congruent (Waples and 

Gaggiotti, 2006). 

(VSP) report (McElhany et al. 2000). The focus of that document is describing the 

characteristics of healthy salmon populations and Evolutionarily Significant Units (ESU), 

and DIPs are natural units upon which to base viability analyses. The VSP definition of a 

population is one in which demographic exchanges with other populations occur at a low 

enough level that they do not substantially affect extinction risk over a 100-year time 

frame. 

Many marine species are particularly challenging for stock/population identification 

because high levels of gene flow ensure that the genetic signal from population 

differentiation is weak, and various errors associated with estimating population genetic 

parameters that might normally be safely ignored assume a relatively greater importance. 

Insights into stock identification in marine species can best be obtained by using a 

combination of methods that provide information on both ecological and evolutionary time 

scales. Experimental design and data analysis and interpretation should be conducted in 

the context of detailed information on the ecology and life history of the species in 

question. 

A B CD

Isolation Panmixia

Divergence
7 

The Biology of Marine Population Structure 

Barbara Taylor 

Southwest Fisheries Science Center 

Population structure is the end product of complex biological processes whereby animals 

maximize their fitness to adapt to variation in their physical and biological environment. 

For even a single species the complex interaction of the changing biotic and abiotic 

environment results in complex population structure that evolves with time. Humpback 

whales illustrate this complexity by exhibiting very different structures in different ocean 

basins. The North Atlantic is primarily composed of a single breeding area with multiple 

feeding areas maintained by maternally learned migration patterns. As such, each feeding 

area is a DIP (demographically independent population) but would not qualify as a DPS 

(distinct population segment) because the heritable nuclear markers are mixed on an 

ocean-basin level. In contrast, the larger North Pacific has several breeding grounds and 

several feeding grounds. Some feeding grounds have individuals only from a single 

breeding ground, while other feeding grounds have individuals from multiple breeding 

grounds. Successful management of such a complex structure requires a deep 

understanding of management objectives.

Biological structure, from the population level to the species level, exists on a continuum, 

yet, management rules are simple and discrete. In simple terms, the objective of the 

MMPA is to maintain “population stocks” as functioning elements of their ecosystem, 

whereas the goal of the ESA is to maintain the evolutionary potential of the “species.” 

Clear quantitative objectives facilitate management that accounts for complex biology. 

Figure 2 illustrates a way to conceptualize one type of population structure that is common 

for coastal marine species. The “water bottles” represent groups of individuals with 

random mating within the group. These groups are connected to neighboring groups by 

dispersal. Human removals are symbolized by the spigots. If removals are small and 

evenly distributed across the range then detailed understanding of population structure is 

not needed (see A). However, if human caused removals are concentrated (see B) then the 

level of connectivity becomes important. The needed level of dispersal (external 

recruitment) depends on the specific management objectives, the pattern of human-caused 

removals and the ability of the groups to grow (internal recruitment). An example of 

quantitative management objectives needed to “solve” the problem in B would be: 1) 

maintain the range, and 2) no part of the range should be reduced to less than X% of 

historical numbers. 
8 

3

3

2

2

1

1

4

4

5

5

?

Estimate the flow between the Units

How much connectivity is enough? Is there a fixed level of dispersal that identifies a DIP?

The level of dispersal used to define “independent independent” is case specific

•Distribution of animals and exploitation

•Natural population growth rate

Figure 2. Conceptual model of population structure for coastal marine species. 
9 

Management of Biological Stocks under the MSFCMA, ESA, and MMPA 

Richard Methot 

Office of Science and Technology 

 The major legislative mandates for NOAA Fisheries: MMPA, ESA, and MSA 

provide guidance for addressing the conservation and management of biological stock 

units. For the MMPA and ESA, conservation of stock units, at some level of aggregation, 

is the paramount goal. The ESA is designed to prevent extinction and to recover stock 

units listed as threatened or endangered with extinction. The MMPA seeks healthy 

ecosystems, with each marine mammal stock as a functioning component of its ecosystem. 

While MMPA explicitly focuses attention on the finest discernable population scale in 

order to maintain its role in the local ecosystem, ESA focuses on broader taxonomic units: 

species, sub-species, or distinct population segments of a (sub)species. For MSA, the 

paramount goal is achievement of optimum benefits from the fishery while preventing 

overfishing, rebuilding depleted stocks and protecting the marine ecosystem; conservation 

of stock units is implicit and necessary to achieve these goals. MSA is not explicit about 

biological units. In practice, fishery management units range from multi-species 

complexes down to local aggregations of a species. Marine species exhibit structure along 

a continuum of scales of aggregation. As scientific methods improve our ability to discern 

biological units with finer degrees of distinction, the gap between management focused on 

protection of these fine units and management focused on protection of entire species 

grows. Such a difference is not irrational. Finer scale units are the scale that interacts with 

the local ecosystem, including human communities, on the time scale of generations. But 

units at this spatial scale may be ephemeral on the evolutionary time scale from the 

species’ perspective (Figure 3). Pro-active, preventative management actions may best be 

focused on the finest scales in order to protect all potential units. But when existing 

management measures have not been able to keep a species from the brink of extinction, it 

is rational to step back to a broader scale of aggregation. Good, science-based 

management on a fine scale is ideal, but fine scale management increases the data 

requirements and management costs, and limits flexibility for management and 

constituents to adapt to changing spatial patterns. Recognizing the continuum of spatial 

scales on which each species functions is fundamental to good management under all 3 

mandates. 
10 

Figure 3. Temporal and spatial domains and levels of biological organization relevant to 

the unit stock (from Secor 2005). 

Brood

School

Year-class

Contingent

Population

Meta-population

Sub-species

Species

107

106

105

Individual

104

103

102

10

Years of 

Coherence

Stock

Entity

Region of 

Coherence
11 

Legal Requirements and Guidance 

The purpose of this session was to summarize the general objectives for the MSA, ESA, 

and MMPA; explain references to, definitions of, and requirements for conservation or 

management units; and discuss how issues related to conservation units have been 

"clarified" by case law or congressional reports. 

Determining Management Units Pursuant to the Magnuson-Stevens Act 

Stacey Nathanson 

General Counsel for Fisheries 

The primary goal of the he Magnuson-Stevens Fishery Conservation and Management Act 

is to ensure sustainable and economically viable fisheries, and is focused on resource 

extraction rather than resource protection. The purpose of National Standard 3 is to induce 

a comprehensive approach to fishery management. The geographic scope of the fishery, 

for planning purposes, should cover the entire range of the stock(s) of fish, and not be 

overly constrained by political boundaries. Wherever practicable, an FMP should seek to 

manage interrelated stocks of fish. National Standard 3 states that “to the extent 

practicable, an individual stock of fish shall be managed as a unit throughout its range, and 

interrelated stocks of fish shall be managed as a unit or in close coordination” See 16 

U.S.C. 1851(a)(3). A “stock of fish” is “a species, subspecies, geographical grouping, or 

other category of fish capable of management as a unit” See 16 U.S.C. 1802(37). A 

“fishery” is “(A) one or more stocks of fish which can be treated as a unit for purposes of 

conservation and management and which are identified on the basis of geographical, 

scientific, technical, recreational, and economic characteristics; and (B) any fishing for 

such stocks” See 16 U.S.C. 1802(13). National Standard 3 promotes unity of management: 

cooperation and understanding among entities concerned with the fishery (e.g. Councils, 

States, Federal Government, international commissions, foreign nations) 

where management of a fishery involves multiple jurisdictions, coordination among the 

several entities should be sought in development of the FMP. The term “management 

unit” is defined in the National Standard 3 guidelines as a fishery or that portion of a 

fishery identified in an FMP as relevant to the FMP’s management objectives. There is no 

definition of species in the Magnuson-Stevens Act or its regulations. The Act is focused 

on flexibility and ease of management. However, tension exists between setting up 

management units for the fishery and the requirements to undertake research and 

conservation for the individual stocks.
12 

ESA Management Units 

Karl Gleaves 

General Counsel for Fisheries 

The Endangered Species Act states that the term “species” includes any subspecies of fish 

or wildlife or plants, and any distinct population segment of any vertebrate fish or wildlife 

which interbreeds when mature [Section 3 (16) T]. Legislative history indicates an 

intention to protect populations. The interpretation by NMFS was defined in the 1991 

NMFS Pacific salmon Evolutionarily Significant Unit (ESU) policy: the stock must satisfy 

two criteria to constitute an ESU: 1) it must be substantially reproductively isolated, and 2) 

it must represent an important component of the evolutionary legacy of the species. The 

1996 Joint FWS-NMFS Distinct Population Segment (DPS) policy is that two elements 

are considered in a decision regarding the status of a possible DPS as endangered or 

threatened: 1) discreteness of the population segment in relation to the remainder of the 

species to which it belongs, and 2) the significance of the population segment to the 

species to which it belongs. Future issues are defining significant portion of range, 

management units or DPS’s in the context of recovery and dealing with special subunits 

such as hatchery stock or hybrids. 
13 

MMPA Management Units 

Karl Gleaves 

General Counsel for Fisheries 

 

The Marine Mammal Protection Act defines the term “population stock” or “stock” as a 

group of marine mammals of the same species or smaller taxa in common spatial 

arrangement, that interbreed when mature [Section 3 (11)]. The findings and declaration 

emphasize populations: “The Congress finds that – (1) certain species and population 

stocks of marine mammals are, or may be, in danger of extinction or depletion as a result 

of man’s activities; (2) such species and population stocks should not be permitted to 

diminish beyond the point at which they cease to be a significant functioning element in 

the ecosystem in which they are a part... (3) there is inadequate knowledge of the ecology 

and population dynamics of such marine mammals... (Section 2). The Legislative history 

shows that “population stock” involves a new concept, permitting and requiring the 

Secretaries to discriminate between different groups of animals distinguishable from other 

populations of the same species [HR 10420 (1971) House Merchant Marine and Fisheries 

Committee Report]. The Alaskan polar bear, for example, is clearly a population stock 

within the general worldwide species classification of polar bears. A “population stock” or 

“stock” refers to a group of marine mammals of the same species that interbreed when 

mature [S 2871 (1972) Senate Commerce Committee Report]. This concept permits a 

discrimination between different groups of animals distinguishable from other populations 

of the same species. 

 
14 

Current Guidelines for Identifying Conservation Units 

For this session, presenters were asked to describe existing guidelines for identifying 

conservation units under the three statutes, with particular reference to the following: 

• Identify the intersection of biological principles (population structure) with 

statutory requirements; 

• Describe the development of technical guidelines and criteria; and 

• Discuss challenges in applying (or developing) policies 

Endangered Species Act: Species, Subspecies, and DPSs 

Marta Nammack 

Office of Protected Resources 

The ESA allows us to list a species, subspecies, or a DPS of a vertebrate species as 

threatened or endangered. We have two policies for defining DPSs: a NMFS one for 

Pacific salmon (November 1991), another one with the FWS for all other vertebrate 

species (February 1996). These policies are consistent with each other. Both include a 2-

step process: 1) reproductive isolation, or “discreteness;” and 2) importance to the 

evolutionary legacy of the species, or “significance.” The only real difference is that the 

joint policy allows us to use international boundaries to satisfy the “discreteness” criterion 

when management mechanisms or status of the species differs in the two countries. Robin 

Waples developed the approach for defining “distinct population segments” for Pacific 

salmon, using the term “evolutionarily significant unit” (ESU). The ESA purpose of 

preventing extinction and its goal of preserving genetic diversity guided his approach, as 

did congressional direction to use the provision sparingly. Out of 201 stocks of Pacific 

salmon identified by Nehlsen et al. (2001), NMFS has identified 52 ESUs and listed 26 of 

them as threatened or endangered. In addition to these 26 ESUs, we listed 10 DPSs 

(including 4 populations of marine turtle with FWS) as threatened or endangered, and 

FWS has listed 45 DPSs. Listing a DPS does not preclude us from managing for 

population substructure; we can do this through section 7 consultations and recovery 

planning. I describe a few examples, including Atlantic salmon, of how the policies have 

been implemented and review some of the challenges facing us in this area. 

Although most rivers in Maine historically contained populations of Atlantic salmon, only 

a portion of these rivers were included in the range of the Gulf of Maine DPS (see Figure 

4). Genetic data, life history data (including straying rates), and the international boundary 

were used to support discreteness between these populations and those in Canada. Because 

loss of this group of populations would result in a major gap in the range of the species, 

we determined that it met the DPS policy’s “significance” criterion. The State of Maine 

challenged the listing, claiming that there were no wild salmon left, and, therefore, there 

was no DPS to list. A National Academy of Sciences report confirmed that salmon in the 

Gulf of Maine were discrete and significant. Recently, further genetic studies by Tim King 
15 

of the U.S. Geological Service confirmed our DPS determination, and our decision was 

also upheld in court. We are currently considering whether to include a few additional 

populations in this DPS. 

 

 

Figure 4. Historic range of Atlantic salmon in Maine and range of the Gulf of Maine DPS 

(rivers shown in green). 
16 

Marine Mammal Stock Identity Guidelines 

Thomas C. Eagle 

Office of Protected Resources 

The term, "population stock" or "stock" is the fundamental conservation unit under the 

MMPA and is defined as "a group of marine mammals of the same species or smaller taxa 

in a common spatial arrangement, that interbreed when mature." The MMPA, however, 

does not provide additional information to clarify the definition of population stock. The 

congressional reports accompanying the MMPA in 1972 note that it is a new concept but 

provide little additional information. The House (House of Representatives, Report 92-

707, December 4, 1971) stated that Alaskan polar bears were clearly a population stock 

within the worldwide species classification for polar bears. Ironically, the FWS identifies 

two stocks of polar bears in Alaska both of which move beyond the US Exclusive 

Economic Zone. 

To consider the meaning of population stock, one can consider two "eras" under the 

MMPA, Pre- and Post-1994. Prior to 1994, population identity was not often used outside 

of determinations whether a stock was depleted or not. The first two stocks designated as 

depleted were bowhead whales and Hawaiian monk seals. Both of these were designated 

as depleted throughout the range of the species due to the species listing as Endangered 

under the ESA. For northern fur seals and bottlenose dolphins, NMFS identified only part 

of the US range of the species as a stock that was depleted (Pribilof Islands stock of fur 

seals and the Atlantic coastal migratory stock of bottlenose dolphins) distinguishing them 

from other individuals in other areas (fur seals breeding on San Miguel Island and 

bottlenose dolphins inhabiting bays, sounds, and estuaries along the Atlantic coast. 

Similarly, certain aggregations of spinner and spotted dolphins in the Eastern Tropical 

Pacific Ocean were designated as depleted, distinguishing them from other aggregations of 

these dolphins in the Pacific Ocean. 

The Post-1994 era of the MMPA is marked primarily by the requirement to prepare stock 

assessment reports for all stocks of marine mammals that occur in waters under U.S. 

jurisdiction. These reports contain information necessary to support a data-intensive, 

stock-specific regime to govern interactions between marine mammals and commercial 

fishing operations. The MMPA Amendments of 1994 required initial draft stock 

assessment reports to be prepared within 90 days of enactment. Therefore, NMFS had to 

act quickly to establish guidelines for preparing the reports, including guidance to identify 

stocks of marine mammals. 

The original draft guidelines were prepared as the result of a workshop held in La Jolla, 

CA, in June 1994. The draft guidelines were made available for public review and 

comment prior to final guidelines. The guidelines were subsequently reviewed and revised 

in workshops in 1997 and 2003. After public review and comment, each of the draft 

revisions was made final in 1997 or 2005, respectively. 
17 

Because the statutory definition of population stock was not clear, NMFS reviewed other 

parts of the MMPA and its legislative history for guidance and found helpful statements in 

the purposes and policies of the act, especially in noting that population stocks should not 

be permitted to diminish below the point at which they cease to be a significant 

functioning element of the ecosystem of which they are a part. From this indirect guidance 

and the definition of population stock, NMFS used demographic independence as a 

primary determinant of stock identity. 

The guidelines note that ideally, a stock would be a management unit that identifies a 

demographically isolated biological population. The guidelines, however, refer to a 

pragmatic realization that identified stocks may fall short of this ideal due to a lack of 

evidence or for other reasons. Additional guidance for identifying marine mammal stocks 

notes that morphological or genetic difference in animals from different geographic 

regions indicates reproductive isolation, and reproductive isolation is proof of 

demographic isolations. Evidence that may be used to identify stocks include distribution 

and movements, differences in population trends, morphology, life history, genetics, 

contaminant or isotope loads, parasite loads, and oceanographic habitat. The guidelines 

conclude that separate management is appropriate when such differences are noted. 

Failure to detect differences among groups of marine mammals in the types of evidence 

described above does not necessarily mean that separate stocks are not appropriate due to 

sample size and statistical power. In particular, the genetic models are sensitive to very 

small levels of migration among groups. 

A major goal of identifying stocks under the guidelines is to avoid potential for localized 

depletion where marine mammals are subject to human-caused mortality and serious 

injury. This goal is consistent with the concept of OSP and maintaining marine mammal 

stocks as functioning elements of their ecosystem, as noted in the purposes and policies of 

the MMPA. Challenges in the application or interpretation of the guidelines include the 

following: lack of information, seasonal or periodic mixing of individuals from different 

stocks (e.g., assigning mortality or abundance to specific aggregations), identifying stock 

boundaries of continuously distributed species, political influence due to socio-economic 

considerations, and commitment to constituent processes (e.g., co-management) that move 

more slowly than the compilation of biological information. 
18 

Guidelines for Identifying Conservation Units Under the 

Magnuson/Stevens Fishery Conservation and Management Act 

Steve Cadrin 

Northeast Fisheries Science Center 

The MSA and associated National Standard 3 guidelines include some direct guidance on 

identifying conservation units for U.S. fishery management. More precise guidelines on 

stock identification are implied by the conservation and management mandates of the Act. 

In order to effectively meet the requirements of the Act, conservation units should be selfsustaining groups of individuals, for which intrinsic population parameters (e.g., growth, 

recruitment, natural mortality and fishing mortality) are the most important factors 

determining fishery production, while extrinsic factors (e.g., migration, larval transport) 

are considered to be negligible. 

National Standard 3 states, “to the extent practicable, an individual stock of fish shall be 

managed as a unit throughout its range, and interrelated stocks of fish shall be managed 

as a unit or in close coordination.” The term ‘stock of fish’ means “a species, subspecies, 

geographical grouping, or other category of fish capable of management as a unit.” This 

definition of ‘stock of fish’ may appear circular, but a more meaningful and useful 

interpretation is that ‘capable of management as a unit’ involves all of the implicit 

requirements associated with National Standard 1: “Conservation and management 

measures shall prevent overfishing while achieving on a continuing basis, the optimal 

yield from each fishery for the United States fishing industry.” 

National Standard 1 mandates that fishery management is based on a MSY strategy. 

‘Overfishing’ is defined in the Act as “a rate or level of fishing mortality that jeopardizes 

the capacity of a fishery to produce maximum sustainable yield on a continuing basis.” 

‘Optimal yield’ is defined as : “maximum sustainable yield from the fishery, as reduced by 

any relevant economic, social, or ecological factor; and in the case of an overfished 

fishery, provides for rebuilding to a level consistent with producing maximum sustainable 

yield...” Estimation of MSY and associated reference points for status determination 

requires the identification of groups within a species that have independent population 

dynamics, on an ecological time scale (i.e., years to decades). Furthermore, the Act 

requires that fishery management plans shall “specify a time period for ending overfishing 

and rebuilding the fishery that shall... not exceed ten years...” This implicitly specifies 

the ecological time scale of reproductive isolation and medium-term population dynamics 

that pertain to stock identification for fishery management, as compared to evolutionary 

time scales (i.e., millennia) typically required for genetic changes and adaptation. 

The opening phrase of National Standard 3, “to the extent practicable” allows for practical 

compromises from ideal stock identification that are typical in fisheries science and 

management. For fisheries that harvest mixed stocks or the same or even different species, 

determining stock composition of the catch is often difficult or impossible, and the stock 

complex is monitored and managed as a unit stock. On the other extreme, geographic 

portions of a stock may be difficult to monitor or manage, and a subset of a single self-
19 

sustaining resource may be considered a unit stock for status determination and 

management (Figure 5). National Standard 1 guidelines confirm this allowance: “...status 

determination criteria should generally be specified in terms of the level of stock 

aggregation for which the best scientific information is available.” 

National Standard 3 guidelines state that “the geographic scope of the fishery, for planning 

purposes, should cover the entire range of the stock(s) of fish, and not be overly 

constrained by political boundaries.” This guidance on international management of 

transboundary stocks is consistent with the practical need to monitor and manage selfsustaining resources as a unit. National Standard 3 guidelines also specify ‘management 

units’ for fishery management plans, which are practical subdivisions based on a variety of 

biological and socioeconomic factors, but do not offer more specific guidance on stock 

identification. 

These direct and indirect guidelines are entirely consistent with current conventions in 

fishery science related to stock identification. The discipline has developed to be 

interdisciplinary, considering various information on genetics and life history to attain 

accurate delineation of stocks. Considering the mandate of National Standard 2, 

“conservation and management measures shall be based upon the best scientific 

information available,” conservation units for fishery management should apply state-ofthe-art technologies and advancements in stock identification to accurately and reliably 

manage the fishery and conserve the resource. 
20 

 

Figure 5. Fishery conservation units expressed as a hierarchy of variation and structure. 

Species Complex

Species

Stock Complex

Genetic Stock

Phenotypic Stock

Harvest Stock

Species

Genetic Stock Genetic Stock

Phenotypic Stock

Harvest Stock

Species Complex

Species

Stock Complex

Genetic Stock

Phenotypic Stock

Harvest Stock

Species

Genetic Stock Genetic Stock

Phenotypic Stock

Harvest Stock
21 

Case Studies 

The final group of presentations involved the description of examples where conservation 

units have been identified under NMFS' policy guidelines for such identification. 

Presenters were asked to address the following points in their case studies: 

• Summarize the population's structure 

• Identify the intersection of biological principles with statutory requirements 

• How has the individual act’s policy guidance been applied? 

• What was the basis for the decision made to identify the management unit? 

• Describe how stock ID implementation has helped meet agency missions 

(successes) 

• Describe challenges or impediments to implementing (or developing) policies 

(failures) 

• What has not been successful to this point? 

Groundfish Stocks in Alaska 

Grant Thompson 

Alaska Fisheries Science Center 

Two general areas (Figure 6) are covered by fishery management plans (FMPs) in Alaska: 

the Bering Sea/Aleutian Islands (BSAI) and the Gulf of Alaska (GOA). The factors by 

which management units may be defined are FMP (BSAI or GOA), region (BS, AI, or 

GOA), area (e.g., Western, Central, or Eastern GOA), management category (e.g., target 

species, prohibited species, forage species), and species or species complex. However, 

stock assessments are not always nested within the above management units. For example, 

BS/AI/GOA sablefish and W/C/E GOA Pacific ocean perch have single assessments, but 

separate catch limits for individual regions or areas. Some issues are: determining the 

basis for combining species or splitting complexes, protecting small stocks within 

complexes, mismatches between management area boundaries and stock ranges, difficult 

species identification in the field, and recognizing new taxonomy. 
22 

Figure 6. Areas included in the Bering Sea/Aleutian Islands and Gulf of Alaska Fishery 

Management Units. 
23 

Stock Structure and Management Units for West Coast Groundfish 

Richard Methot 

Office of Science and Technology/Northwest Fisheries Science Center 

Many species of groundfish harvested off the coasts of California, Oregon and 

Washington tend to have relatively sedentary behavior as adults and broad spatial 

distributions extending through much of the continental shelf of the North Pacific. A 

slowly growing body of genetic stock structure data tends to find some significant, 

although not large, differences across large spatial scales such as southern California to 

Puget Sound or west coast to the Aleutian Islands. Genetic separation on a spatial scale 

that would be within the CA-OR-WA region is not common and tends to occur for some 

nearshore rockfish and near faunal breaks like major rocky headlands. Although genetic 

data do not indicate a multiplicity of separate small stocks along the coast, there still may 

be only limited mixing of larvae, juveniles and adults along the coast. Most of the 

demographic analyses (stock assessments) conducted on west coast groundfish have 

treated the entire west coast as a unit demographic stock. A few have separated the coast 

into northern and southern sections. Although several of these stocks have distributions 

that span the US-Canada border, nearly all assessments have truncated at the border due to 

discontinuities in data and the lack of a full framework for coordination of management. 

Truncation at the border may not cause bias in the demographic analyses if cross-border 

movement is very low, but if movement is that slow then greater consideration should be 

given to structure within the west coast zone. With only slow rates of mixing, there is a 

risk of localized depletion if the fishery does not freely conform to the stock’s spatial 

distribution and there is a risk of erroneous assessment results if trends and patterns 

observed in only one area are incorrectly asserted to represent trends in the entire 

coastwide stock. An example of finer scale geographic patterning is shown for canary 

rockfish (Figure 7. Arguably, there are 6-8 canary rockfish aggregations along the coast 

with unknown degrees of demographic connectivity. Although more high-resolution 

genetic evidence would help discern the boundaries of these aggregations, there seems to 

be sufficient evidence to warrant an investigation of finer scale demographic analyses and 

an analysis of the risks of misplaced or missing assessment boundaries. 
24 

Figure 7. Geographic variation in size of canary rockfish 

100 150 200 250 300 350 400 450 500 550 600 650

 <=38

 38-38.6

38.6-39.8 (BodegaBayFt.Bragg)

 39.8-41

 41-42

42-42.75

 42.75-43

 43-43.1 (Coos Bay)

 43.1-44

 44-45

 45-46.75

 46.75-47.4 (Gray's Harbor)

 47.4-48

 48-48.9

48.9-49.15 (Barkley Sound)

49.15+

Size (mm)

Canary Rockfish Size-by-Latitude
25 

Stock Identification of New England Groundfish 

Steve Cadrin 

Northeast Fisheries Science Center 

New England groundfish species are typically managed as discrete stocks based on 

multidisciplinary information that indicates fishery resources within geographic areas that 

have similar life history dynamics (e.g., growth, maturity, recruitment) and limited 

movement with adjacent, conspecific resources. Stock definitions and boundaries are 

occasionally reconsidered when new information is available and revised when the new 

definition will improve fisheries science and management. The recent revision of 

yellowtail flounder stock definitions is a typical example. 

An interdisciplinary study of yellowtail stocks off the northeast coast of the USA that 

evaluated geographic patterns of abundance, geographic variation in growth and maturity, 

larval transport, morphometry, and genetics suggested that yellowtail flounder comprise 

three separate management stocks despite genetic homogeneity. Two harvest stocks of 

yellowtail flounder have significantly different patterns of abundance and biomass over 

time, with a boundary on southwest Georges Bank. Geographic patterns of size and 

proportion mature at age indicate two phenotypic stocks of yellowtail flounder, with a 

boundary on northern Georges Bank. Therefore, southern New England yellowtail form a 

separate harvest stock than Georges Bank yellowtail, and Cape Cod yellowtail are a 

separate phenotypic stock than those on Georges Bank or off southern New England. 

However, population dynamics of the Cape Cod-Gulf of Maine stock are sensitive to 

movements of fish from adjacent yellowtail stocks. In recognition of this, a tagging study 

was initiated in collaboration with New England fishermen and fishery scientists. To date, 

over 35,000 yellowtail from the Gulf of Maine to the Mid Atlantic Bight have been tagged 

using conventional disc tags and data-storage tags. Preliminary results indicate frequent 

movements within stock areas, and less frequent movements among stocks (Figure 8). 

Data-storage tags indicate distinct off-bottom behavior, typically in evening hours, lasting 

an average of about four hours. The frequent off-bottom movements and occasional 

movements to different depths strongly suggest that yellowtail flounder can move between 

fishing grounds or stock areas using mid-water currents. Therefore, movements across 

current stock boundaries (e.g., shallow shoals or deep channels) may occur more 

frequently than previously thought. The movement information will be considered in the 

next benchmark stock assessment of yellowtail flounder resources. 

A review of the basis of New England groundfish stock definitions shows that a similar 

approach is used for all species, but the amount of information available varies by species: 

• Atlantic cod are managed as two stocks (Gulf of Maine and Georges Bank) based 

on meristics, spawning seasons, growth rates, maturity, observed movements, 

parasites, and distribution of eggs and larvae. New information on Atlantic cod 

stocks from recent tagging and genetic studies will be considered in the next 

benchmark stock assessment. 
26 

• Haddock are managed as two stocks (Gulf of Maine and Georges Bank) based on 

meristics, ichthyoplankton distribution, growth rates, age at maturity, observed 

movements and parasites. 

• Winter flounder are managed as three stocks (Gulf of Maine, Georges Bank, and 

southern New England-Mid Atlantic) based on meristics, growth rates, age at 

maturity, observed movements and distribution. 

• Silver hake are managed as two stocks (northern and southern) based on genetics, 

morphometrics, growth, tagging, spawning seasons, distribution of life stages, and 

traditional fishing areas. 

• Pollock are managed as a single stock (Georges Bank/Gulf of Maine) based on 

genetics, meristics, morphometrics, growth, maturity, distribution of life stages, 

and tagging. 

• White hake are managed as a single stock (Georges Bank/Gulf of Maine) based on 

meristics, morphometrics, tagging, spawning season, growth and distribution of 

larvae and adults. 

• Acadian redfish are managed as a single stock (Gulf of Maine/Georges Bank) 

based on taxonomic studies, meristics, morphometrics, growth, maturity, parasites 

and larval distribution. 

• American plaice are managed as a single stock (Gulf of Maine/Georges Bank) 

based on growth, spawning seasons and distribution of eggs and adults. 

• Witch flounder are managed as a single stock from the Gulf of Maine to the Mid 

Atlantic based on growth, distribution and larval period. 

• Red hake are managed as two stocks (northern and southern) based on meristics, 

demographics and distribution. 

• Windowpane flounder are managed as two stocks (Gulf of Maine/Georges Bank; 

Southern New England/Mid-Atlantic) based on spawning seasons and growth. 

• Atlantic halibut is managed as a single stock in the Gulf of Maine despite extensive 

movement to other areas in the Northwest Atlantic. 

• Ocean pout and offshore hake have little information on stock structure and are 

managed as single stocks in U.S. waters. 

The Northeast Fisheries Science Center continues to conduct research on stock 

identification, and stock structure is reviewed through regular benchmark stock 

assessments. 
27 

Figure 8. Releases (circles) and recaptures (triangles) of tagged yellowtail 

flounder and the three U.S. management areas. 
28 

Atlantic Bluefin Tuna: Swim Anywhere They Want, 

Wanted Everywhere They Swim 

Clay E. Porch 

Southeast Fisheries Science Center 

Atlantic bluefin tuna Thunnus thynnus are among the largest and fastest of bony fishes, 

weighing up to 700 kg and able to swim at over 90 km h-1. Their endothermic physiology 

allows them to maintain a relatively stable body temperature even in waters as cold as 3oC. 

This combination of size, speed and thermoregulation enables individuals to range widely 

throughout the Atlantic basin, from the warm shallows of the Caribbean Sea to the frigid 

waters off Norway. 

Atlantic bluefin tuna have long been prized as food fish, particularly in the vicinity of the 

Mediterranean Sea, where a substantial fishery has existed for more than 4,000 years 

(Roman records attest to catching thousands of tons). The fishery for bluefin in the 

western Atlantic dates back only to the early 1900’s, when bluefin were occasionally taken 

by harpoons and traps, but were regarded mostly as a nuisance. The advent of Japanese 

longliners in the late 1950s and U.S. and European purse seiners during the 1960s resulted 

in a large increase in bluefin landings throughout the Atlantic, but perhaps the single most 

important development in the fishery was the burgeoning sashimi market in Japan. The 

high demand and even higher prices (one 200-kg specimen recently sold for almost 

$174,000) made bluefin so valuable that fishermen could afford to target them even at 

relatively low densities. Currently it is believed that the total landings of bluefin tuna 

exceed 50,000 MT and are not sustainable. 

The high demand for bluefin tuna coupled with the fact that they routinely swim through 

multiple jurisdictions (including the high seas) makes them rather difficult to manage. The 

need for International coordination was formally recognized in 1966 with the signing of 

the International Convention for the Conservation of Atlantic Tunas (ICCAT), the stated 

goal of which is “maintaining the populations of tuna and tuna-like fishes at levels which 

will permit maximum sustainable catch.” Currently, ICCAT manages bluefin tuna on the 

premise that there are two primary stocks, one which spawns in the Gulf of Mexico and 

another that spawns in the Mediterranean Sea. This premise helps the agency mission by 

averting the possibility that declines in the smaller western stock will go unnoticed or 

simply not be acted upon. 

The major challenges facing management under the two-stock premise include (1) 

defining the boundary that best delineates the eastern and western management areas (and 

stocks); (2) quantifying the nature and degree of intermixing across that boundary; (3) 

incomplete data, particularly for the eastern stock; and (4) different management schemes 

applied to each stock with different, perhaps confused, goals. The poor quality of the catch 

and size statistics for the eastern stock is particularly vexing as it precludes effective 

modeling of the effect of mixing between the two stocks. If substantial westward mixing 

exists, then the uncertainty in the east will confound estimates for the west (i.e., the status 

of the western stock may be inestimable by current methods). The different management 
29 

schemes also pose a problem. Enforcement in the eastern management zone (eastern 

Atlantic and Mediterranean Sea) is widely seen as rather lax in comparison to the west. 

Catches are believed to exceed the imposed TAC and, until recently, size limits were often 

ignored. This has led to a perception that no matter how much fishing pressure is reduced 

in the western management zone, the western stock will remain overfished owing to their 

frequent forays into the eastern management area. One could also argue that there has been 

some confusion in terms of the basic goal; whether to maintain high catches in each 

management area or to maintain high catches of each stock. The former can perhaps be 

achieved by maintaining a healthy eastern stock, whereas the latter presupposes that 

maintaining population diversity matters. 

Recent advances in electronic tagging, genetics, and otolith microconstituent analyses, 

coupled with satellite imagery and the enhanced scale of ongoing oceanographic 

measurements, promise to help unveil many of the mysteries relating to the interaction 

between eastern and western bluefin tuna. To date, the results have tended to support the 

two-stock premise used by ICCAT, however the nature and degree of mixing remains 

somewhat unclear. 
30 

Management Units for Sedentary Stocks: 

The Atlantic Sea Scallop Example

Dvora Hart 

Northeast Fisheries Science Center 

Fishery stocks are typically idealized as well-mixed, closed populations. The "well-mixed" 

assumption implies that all (adult) individuals are subject to a similar environment and, 

thus, have similar life history characteristics and fishing mortality risks. These attributes 

are rarely correct in those stocks where adults are sedentary or sessile. Sedentary animals 

are strongly influenced by their local environment. As a result, life history attributes such 

as growth rates and length-weight relationships can vary strongly within a stock. For 

example, the growth rate of the Atlantic sea scallop (Placopecten magellanicus) depends 

on depth, so that reference points for deep water sea scallops may be different than those 

in shallow water. Fishing effort can also vary greatly spatially, as it is influenced by 

factors such as resource abundance, distance to port, and spatial management measures 

(e.g., fishery closures). In mobile stocks, individuals can move among areas with different 

fishing mortality rates, and thus may be approximately subject to the spatially averaged 

fishing mortality. By contrast, fishing mortality risks can vary greatly in a sedentary stock, 

with individuals in popular fishing grounds being subject to much higher fishing mortality 

than those in lightly fished or closed areas. 

For these reasons, sedentary stocks are often subject to localized over- and under-fishing, 

even when the spatially averaged fishing mortality meets the whole-stock target. Localized 

variation in fishing mortality can reduce yield per recruit compared to that which would be 

expected if fishing mortality was uniform (Figure 9). Depending on larval transport 

patterns, localized overfishing may also induce recruitment failure “downstream” of 

overfished areas. Whole-stock target reference points that may be required under the 

current national standards can not prevent localized overfishing. In some cases, where a 

substantial proportion of the stock is not fished either due to management measures (as is 

the case with sea scallops) or because of toxicity issues (as with ocean quahogs), meeting 

the whole-stock fishing mortality target necessarily implies localized overfishing in the 

fished areas. 

Area management is typically required for proper management of sedentary stocks. For 

example, the Canadian Bay of Fundy sea scallop stock is divided into a number of 

“scallop production areas” (SPAs) based on depth and the fishing fleet that traditionally 

has exploited the area. Each SPA can be assigned its own target reference points and 

fishing quota, thereby obtaining near-optimum yield from each area. Rotational fishing, as 

used in the U.S. sea scallop fishery, is another way of alleviating the effects of spatial 

variability on yield. 
31 

Figure 9. Effect of various levels of fishing mortality on yields of Atlantic sea scallops. 

Fishing mortality

F1 FMAX F2 c F3 F4 (F3+F4)/2

Yield-per-recruit
32 

Case Study: Petition to Reclassify Two "Subpopulations" of the 

Loggerhead Turtle (Caretta caretta) as Distinct Population Segments 

Barbara Schroeder 

Office of Protected Resources 

The loggerhead turtle (Caretta caretta) was listed as threatened throughout its global 

range in 1978. The species is found circumglobally, primarily inhabiting temperate and 

subtropical benthic and pelagic habitats. Nesting occurs primarily on subtropical and 

temperate mainland and island beaches. Analyses of mtDNA show that adult females 

exhibit natal homing (returning to nesting beaches where they were hatched). Juveniles, 

adult males, and non-nesting females from different nesting assemblages regularly mix at 

foraging grounds. Analyses of nDNA indicate that males provide an avenue of gene flow 

among nesting assemblages. 

The southeast United States provides nesting habitat for one of the largest, globally 

significant nesting assemblages, with nesting primarily occurring from North Carolina 

through the panhandle of Florida. Four "subpopulations" have been identified within this 

nesting assemblage, based on mtDNA analyses. Two of these subpopulations, the 

"northern nesting unit" and the "Florida panhandle nesting unit" (Figure 10) were the 

subject of a 2002 listing petition. The petition requested that NMFS and FWS (sea turtles 

are jointly listed) reclassify the northern and Florida panhandle nesting units as DPSs and 

list them both as endangered. 

NMFS and FWS issued a 90-day finding indicating that the petition presented substantial 

scientific information indicating that the petitioned action may be warranted. The Services 

then jointly conducted a formal review under the DPS policy, with the first step focused 

on the question of discreteness. As required by the DPS policy, discreteness may be 

determined under one or more criteria. A summary of our evaluation under each of these 

criteria follows: 

Delimited by international governmental boundaries 

• Petitioned 'units' did not meet this criterion. 

Markedly separated from other populations of the same taxon by physical, physiological, 

ecological , or behavioral factors. 

• Genetic factors, based on mtDNA and nDNA findings differed. The mtDNA 

analyses supported discreteness among the nesting units (indicative of natal 

homing) however, there were differences among analyses with regard to 

specific findings of genetic independence among the nesting units. Increased 

sampling at additional nesting beaches resulted in a more complex genetic 

picture with somewhat conflicting results. Preliminary nDNA analyses showed 

no substantial subdivisions across the nesting units suggesting that males breed 

with females from other nesting units, including their own. 
33 

• Several physiological and ecological factors were examined as possible 

indicators of marked separation including the annual variability in nesting 

within and between nesting assemblages, hatchling sex ratios among nesting 

assemblages, genetic composition of non-nesting distribution of individuals 

from the four nesting assemblages, the genetic composition of adult females on 

foraging grounds, and nesting female body size among the nesting 

assemblages. 

While the lines of evidence examined indicated the identified nesting assemblages were 

discrete to some degree, the Services determined that the separation was not highly rigid 

and the assemblages were not markedly separated. Despite finding that the petitioned 

action was not warranted (i.e., the northern and Florida panhandle nesting assemblages 

were not discrete and did not qualify for reclassification as DPSs), the Services did find 

that these nesting assemblages are critical components of the overall southeast United 

States nesting aggregation. Each nesting assemblage is interdependent for the overall 

species survival and recovery. The Recovery Team for the U.S. Atlantic Populations of the 

Loggerhead is revising the current recovery plan and is considering the various nesting 

assemblages as recovery units. 

Figure 10. Location of nesting subpopulations of loggerhead sea turtles in the 

southeastern United States. 
34 

Humpback Whale: Gulf of Maine Stock Definition 

Philip Clapham1

 and Richard Pace2

Northeast Fisheries Science Center 

In the western North Atlantic, humpback whales feed during spring, summer and fall 

over a range which encompasses the eastern coast of the United States (including the 

Gulf of Maine), the Gulf of St. Lawrence, Newfoundland/Labrador, and western 

Greenland (Katona and Beard 1990). Other North Atlantic feeding grounds occur off 

Iceland and northern Norway, including off Bear Island and Jan Mayen (Christensen et 

al. 1992; Palsbøll et al. 1997). These six regions represent relatively discrete 

subpopulations, fidelity to which is determined matrilineally (Clapham and Mayo 1987). 

Genetic analysis of mitochondrial DNA (mtDNA) has indicated that this fidelity has 

persisted over an evolutionary timescale in at least the Icelandic and Norwegian feeding 

grounds (Palsbøll et al. 1995; Larsen et al. 1996). 

Previously, the North Atlantic humpback whale population was treated as a single stock 

for management purposes (Waring et al. 1999). Indeed, earlier genetic analyses (Palsbøll 

et al. 1995), based upon relatively small sample sizes, had failed to discriminate among 

the four western North Atlantic feeding areas. However, genetic analyses often reflect a 

timescale of thousands of years, well beyond those commonly used by managers. 

Accordingly, the decision was recently made to reclassify the Gulf of Maine as a separate 

feeding stock; this was based upon the strong fidelity by individual whales to this region, 

and the attendant assumption that, were this subpopulation wiped out, repopulation by 

immigration from adjacent areas would not occur on any reasonable management 

timescale. This reclassification has subsequently been supported by new genetic analysis 

based upon a much larger collection of samples than those utilized by Palsbøll et al.

(1995). These analyses have found significant differences in mtDNA haplotype 

frequencies of the four western feeding areas, including the Gulf of Maine (Palsbøll et al.

2001). During the recent Comprehensive Assessment of North Atlantic humpback whales, 

the International Whaling Commission acknowledged the evidence for treating the Gulf of 

Maine as a separate stock for the purpose of management (IWC 2002). 

During the summers of 1998 and 1999, the Northeast Fisheries Science Center conducted 

surveys for humpback whales on the Scotian Shelf. The objective of these surveys was to 

establish the occurrence and population identity of the animals found in this region, which 

lies between the well-studied populations of the Gulf of Maine and Newfoundland. 

Photographs from both surveys have now been compared to both the overall North 

Atlantic Humpback Whale Catalogue and a large regional catalogue from the Gulf of 

Maine (maintained by the College of the Atlantic and the Center for Coastal Studies, 

respectively); this work is summarized in Clapham et al. (2003). The match rate between 

the Scotian Shelf and the Gulf of Maine was 27% (14 of 52 Scotian Shelf individuals from 

both years). Comparable rates of exchange were obtained from the southern (26%, n=10 of 

 

1 Currently at the Alaska Fisheries Science Center 2 Presented the paper 
35 

36 whales) and northern (27%, n=4 of 15 whales) ends of the Scotian Shelf, despite the 

additional distance of nearly 100 nautical miles (one whale was observed in both areas). In 

contrast, all (36 of 36) humpback whales identified by the same NMFS surveys elsewhere 

in the Gulf of Maine (including Georges Bank, southwestern Nova Scotia and the Bay of 

Fundy) had been previously observed in the Gulf of Maine region. The sighting histories 

of the 14 Scotian Shelf whales matched to the Gulf of Maine suggested that many of them 

were transient through the latter area. There were no matches between the Scotian Shelf 

and any North Atlantic feeding ground, except the Gulf of Maine; however, instructive 

comparisons are compromised by the often low sampling effort in other regions in recent 

years. Overall, while it is not possible to define the Gulf of Maine population by drawing a 

strict geographical boundary, it appears that the effective range of many members of this 

stock does not extend onto the Scotian Shelf. Further work on the Scotian Shelf was 

conducted in August 2002 and August 2003; this sampling extended further north and east 

as far as the Laurentian Channel, and the results are expected to further clarify the issue of 

stock identity from this region. The very low match rate between the two sampled years 

(only one animal was resighted in the region in both 1998 and 1999) suggests that the 

Scotian Shelf is host to a larger population of humpback whales than was previously 

thought. However, preliminary analysis of photographs collected in 2002 and 2003 

revealed a number of inter-annual matches; it is not yet clear whether a suitably precise 

abundance estimate can be calculated from these data. 

In winter, whales from all feeding areas (including the Gulf of Maine) mate and calve 

primarily in the West Indies, where spatial and genetic mixing among subpopulations 

occurs (Clapham et al. 1993; Katona and Beard 1990; Palsbøll et al. 1997; Stevick et al.

1998). A few whales of unknown northern origin migrate to the Cape Verde Islands 

(Reiner et al., 1996). In the West Indies, the majority of whales are found in the waters of 

the Dominican Republic, notably on Silver Bank, on Navidad Bank, and in Samana Bay 

(Balcomb and Nichols 1982; Whitehead and Moore 1982; Mattila et al. 1989, 1994). 

Humpback whales are also found at much lower densities throughout the remainder of the 

Antillean arc, from Puerto Rico to the coast of Venezuela (Winn et al. 1975; Levenson and 

Leapley 1978; Price 1985; Mattila and Clapham 1989). 

It is apparent that not all whales migrate to the West Indies every winter, and that 

significant numbers of animals are found in mid- and high-latitude regions at this time 

(Clapham et al. 1993; Swingle et al. 1993). An increased number of sightings of 

humpback whales in the vicinity of the Chesapeake and Delaware Bays occurred in 1992 

(Swingle et al. 1993). Wiley et al. (1995) reported 38 humpback whale strandings which 

occurred during 1985-1992 in the U.S. mid-Atlantic and southeastern states. Humpback 

whale strandings increased, particularly along the Virginia and North Carolina coasts, and 

most stranded animals were sexually immature; in addition, the small size of many of 

these whales strongly suggested that they had only recently separated from their mothers. 

Wiley et al. (1995) concluded that these areas are becoming an increasingly important 

habitat for juvenile humpback whales and that anthropogenic factors may negatively 

impact whales in this area. There have also been a number of wintertime humpback 

sightings in coastal waters of the southeastern U.S. (NMFS unpublished data; New 

England Aquarium unpublished data; Florida DEP unpublished data). Whether the 
36 

increased sightings represent a distributional change, or are simply due to an increase in 

sighting effort and/or whale abundance, is presently unknown. 

A key question with regard to humpback whales off the southeastern and mid-Atlantic 

states is their population identity. This topic was recently investigated using fluke 

photographs of living and dead whales observed in the region (Barco et al. 2002). In this 

study, photographs of 40 whales (live or dead) were of sufficient quality to be compared to 

catalogues from the Gulf of Maine (the closest feeding ground) and other areas in the 

North Atlantic. Of 21 live whales, 9 (42.9%) matched to the Gulf of Maine, 4 (19.0%) to 

Newfoundland and 1 (4.8%) to the Gulf of St Lawrence. Of 19 dead humpbacks, 6 

(31.6%) were known Gulf of Maine whales. Although the population composition of the 

mid-Atlantic is apparently dominated by Gulf of Maine whales, lack of recent 

photographic effort in Newfoundland makes it likely that the observed match rates underrepresent the true presence of Canadian whales in the region. Barco et al. (2002) suggested 

that the mid-Atlantic region primarily represents a supplemental winter feeding ground 

that is used by humpbacks for more than one purpose. 

Feeding is the principal activity of humpback whales in New England waters, and their 

distribution in this region has been largely correlated to prey species and abundance, 

although behavior and bottom topography are factors in foraging strategy (Payne et al.

1986, 1990). Humpback whales are frequently piscivorus when in these waters, feeding on 

herring (Clupea harengus), sand lance (Ammodytes spp.), and other small fishes. In the 

northern Gulf of Maine, euphausiids are also frequently taken (Paquet et al. 1997). 

Commercial depletion of herring and mackerel led to an increase in sand lance in the 

southwestern Gulf of Maine in the mid 1970's with a concurrent decrease in humpback 

whale abundance in the northern Gulf of Maine. Humpback whales were densest over the 

sandy shoals in the southwestern Gulf of Maine favored by the sand lance during much of 

the late 1970's and early 1980's, and humpback distribution appeared to have shifted to 

this area (Payne et al. 1986). An apparent reversal began in the mid 1980's, and herring 

and mackerel increased as sand lance again decreased (Fogarty et al. 1991). Humpback 

whale abundance in the northern Gulf of Maine increased dramatically during 1992-1993, 

along with a major influx of herring (P. Stevick, pers. comm.). Humpback whales were 

few in nearshore Massachusetts waters in the 1992-1993 summer seasons. They were 

more abundant in the offshore waters of Cultivator Shoal and the Northeast Peak on 

Georges Bank, and on Jeffreys Ledge; these latter areas are more traditional locations of 

herring occurrence. In 1996 and 1997, sand lance and, thus, humpback whales were once 

again abundant in the Stellwagen Bank area. However, unlike previous cycles, where an 

increase in sand lance corresponded to a decrease in herring, herring remained relatively 

abundant in the northern Gulf of Maine, and humpbacks correspondingly continued to 

occupy this portion of the habitat, where they also fed on euphausiids (unpublished data, 

Center for Coastal Studies and College of the Atlantic). 

In early 1992, a major research initiative known as the Years of the North Atlantic 

Humpback (YONAH) (Smith et al. 1999) was initiated. This project was a large-scale, 

intensive study of humpback whales throughout almost their entire North Atlantic range, 

from the West Indies to the Arctic. During two primary years of field work, photographs 
37 

for individual identification and biopsy samples for genetic analysis were collected from 

summer feeding areas and from the breeding grounds in the West Indies. Additional 

samples were collected from certain areas in other years. Results from analyses of this 

ocean basin-wide study have helped elucidate much of the population structure pertaining 

to North Atlantic humpbacks. Abundant data collected at multiple geographic scales 

highlight the differences in establishing conservation management units to satisfy ESA 

versus MMPA. On the one hand, NA humpbacks are unequivocally panmictic among 

nearly all the major feeding areas. However, high feeding area fidelity together with our 

lack of knowledge relative to potential recolonization rates to vacant habitats suggests that 

the feeding area scale is more in keeping with the spirit of MMPA.

Figure 11. Nucleotide diversity within feeding aggregations of humpback whales in the 

Atlantic Ocean. 

0.000

0.005

0.010

0.015

0.020

0.025

0.030

Ba rents S ea

Iceland

West G reenland

Labrador

Newfoundla nd

Gulf of St. Lawrenc e

Gulf of Ma ine

We st Indies

0.000

0.005

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Ba rents S ea

Iceland

West G reenland

Labrador

Newfoundla nd

Gulf of St. Lawrenc e

Gulf of Ma ine

We st Indies
38 

Pacific Salmon 

Robin S. Waples 

Northwest Fisheries Science Center 

NMFS has ESA jurisdiction for the five species of Pacific salmon that occur in North 

America (Chinook, coho, sockeye, chum, and pink), as well as for steelhead, the 

anadromous form of rainbow trout. When the first petitions for ESA listing of Pacific 

Northwest salmon were filed in 1990, they invoked the provision in the ESA (Section 

3(15)) that allows listing not only of taxonomic species and subspecies, but also DPSs of 

vertebrates such as salmon. At that time, neither of the agencies responsible for 

implementing the ESA (FWS and NMFS) had developed formal guidance for how to 

interpret the DPS provision in the ESA. A joint workshop was held with FWS in 1990, 

with the objective of developing an overall framework for DPS considerations by both 

agencies. It was expected that the NMFS policy on salmon would be consistent with this 

overall policy but provide more specific guidance for salmon. However, the joint policy 

soon stalled within FWS, while the clock continued to tick on the one-year deadline for 

response to the salmon petitions. Because of the pressing need for guidance on how to 

consider the DPS question for salmon, and because of the unusual biological attributes of 

these species, NMFS concluded that it needed to develop a DPS policy for Pacific salmon. 

To address this need, Waples (1991) developed a framework that stipulated that a salmon 

population (or group of salmon populations) would be considered a DPS if it represents an 

ESU of the taxonomic species. According to this framework, a population unit must 

satisfy two criteria to be considered an ESU: 1) reproductive isolation, and 2) 

evolutionary significance. These criteria capture two common meanings of the word 

‘distinct’: “separate, or apart from” (reproductive isolation); and “unique, or distinctive” 

(evolutionary significance). Isolation does not have to be absolute; it only has to be strong 

enough to allow evolutionarily important differences to accrue in different units. The 

“significance” criterion is met if the population unit contributes substantially to 

ecological/genetic diversity of the species as a whole—that is, to its evolutionary legacy. 

Waples (1995) defined the evolutionary legacy as “genetic variability that is the product of 

past evolutionary events and that represents the reservoir upon which future evolutionary 

potential [of the species] depends.” 

NMFS adopted Waples’ ESU approach for salmon as a formal policy in 1991 (FR 56, 

58612, 20 November 1991). After dealing with the initial petitions, NMFS proactively 

initiated a series of comprehensive status reviews (FR 59, 46808, 12 September 1994) and 

used the policy framework to identify ESUs in all seven species of Pacific salmon from 

Washington, Idaho, Oregon, California, and parts of southern British Columbia 

(Weitkamp et al., 1995; Hard et al., 1996; Busby et al., 1996; Gustafson et al., 1997; 

Johnson et al., 1997, 1999; Myers et al., 1998). Reviewing a broad geographic range 

provided a context for interpreting local patterns of variation, and applying the same 

approach across seven species provided opportunities to learn from congruent patterns of 

relationships, as well as species-specific ones. A great deal of molecular genetic data are 

available for Pacific salmon, and these data, together with information from tagging 

studies and inferences about natural barriers, were the primary factors used to assess 
39 

reproductive isolation. Traits that are evolutionarily significant must have a genetic basis 

and be adaptive or at least potentially adaptive, so life history variation was carefully 

evaluated for the second ESU criterion. However, since most life history traits can be 

affected by environmental as well as genetic factors, ecological features of the habitat (as a 

proxy for different selective regimes) were also considered important. Molecular genetic 

data are generally thought to reflect neutral (non-selective) differences and thus were 

considered relevant to the second criterion only if the differences were substantial enough 

to lead to the presumption that adaptive differences had developed. 

Pacific salmon have a complex population structure and most species exhibit several 

hierarchical levels of diversity between the entire species on one hand and a local breeding 

population on the other. For example, in Oncorhynchus mykiss (steelhead/rainbow trout), 

eight separate hierarchical levels have been identified on the Oregon Coast, each of which 

potentially represents a biologically suitable unit for the focus of conservation units 

(Waples 2006). NMSF has defined ESUs of Pacific salmon at a scale intermediate to these 

two extremes, with the result that each ESU typically contains 20-30 or so of what most 

people would agree are separate populations or stocks. In contrast, it appears that most 

other published ESU frameworks would be more likely to identify units at either the local 

population or the species level (Waples 2006). 

NMFS has identified over 50 ESUs in the 6 species of anadromous Pacific salmonids, and 

about half of these are currently listed as threatened or endangered “species” under the 

ESA. One of the first steps in formal ESA recovery planning for salmon is to identify DIPs 

within ESUs. These populations are the logical units for evaluating viability, which is 

done using the Viable Salmonid Populations framework described by McElhany et al. 

(2000). 

Almost all listed salmon ESUs have hatchery fish associated with them. NMFS evaluated 

the ESU status of each hatchery population using the same criteria described above and 

determined many to be part of the listed ESUs. However, most of these hatchery 

populations were not listed, because doing so would not provide any conservation benefit 

but would create more regulatory burden for everyone. In 2001, a court ruling (Alsea 

Valley Alliance v. Evans, 161 F. Supp. 2d 1154, D. Oreg. 2001) held that this approach is 

not permissible because the smallest unit that can be listed under the ESA is a distinct 

population segment, and NMFS had listed only part of most salmon DPSs. As a 

consequence, NMFS revised its hatchery listing policy (70FR 37204; 28 June 2005) and 

the Biological Review Team (BRT) updated its assessments of the status of all listed 

salmon ESUs (Good et al. 2005). 
40 

Figure 12. Genetic stock identification of juvenile chinook salmon (D. Teel, NMFS, 

unpublished data). 
41 

Delineation of an ESA Distinct Population Segment 

Incorporating Cherry Point Pacific Herring 

Richard G. Gustafson 

Northwest Fisheries Science Center 

Pacific herring that spawn at Cherry Point, near the USA-Canada border, were examined 

for possible listing under the ESA as a DPS. Although Cherry Point Pacific herring 

spawner biomass has more than doubled since 2000, the population biomass has declined 

by 87% since 1973. In 2004, this decline led organizations to submit two petitions to 

NOAA Fisheries to list the Cherry Point stock of Pacific herring as a DPS under the ESA. 

NOAA Fisheries determined that the second petition presented substantial information to 

suggest that listing may be warranted. A previous Pacific herring status review, completed 

in 2001, was initiated in response to a 1999 petition to list all Pacific herring in Puget 

Sound as a DPS. The 2001 status review concluded that Pacific herring stocks in Puget 

Sound do not constitute a DPS and identified a Georgia Basin Pacific herring DPS 

consisting of inshore stocks from Puget Sound (including Cherry Point) and the Strait of 

Georgia. 

In 2004-05, a newly formed Pacific herring BRT examined the DPS question for Cherry 

Point Pacific herring and concluded that it is a “discrete” population under the provisions 

of the joint agency DPS policy; however, there was no support on the BRT for a finding 

that Cherry Point Pacific herring were “significant” to the taxon of Pacific herring as a 

whole, under the provisions of the DPS policy. The BRT identified multiple characteristics 

that distinguish the Cherry Point population as discrete from other local herring 

populations, including: locally unique spawn timing; an unusual, relatively exposed 

spawning location; discrete microsatellite DNA allele frequencies; and physiological 

factors such as unusual growth rate characteristics for the locality and differential parasite 

incidence, otolith microchemistry, and accumulation of toxic contaminants that were 

indicative of disparate rearing conditions compared to Pacific herring in Puget Sound 

proper. These discrete population differences were contrasted with data from other Pacific 

herring, both regionally and throughout the biological species’ range across the North 

Pacific Ocean, in order to evaluate the “significance” of the Cherry Point population to the 

taxon as a whole. Significance criteria articulated in the DPS policy that were identified as 

pertinent to the individual Cherry Point situation included the population’s persistence in 

an ecological setting that is unusual or unique for the taxon, the population’s marked 

differentiation from other populations of the taxon in its genetic characteristics, and other 

information that might bear on biological and ecological importance to the taxon as a 

whole. Evidence that supported the BRT’s conclusion that the discrete Cherry Point 

herring population was not “significant” included the observation that other Pacific herring 

stocks with unusual spawn timing for their area was not exceptional and that a number of 

other Pacific herring stocks also spawn on fairly exposed coastlines of inshore waters in 

the Pacific Northwest. The BRT interpreted the microsatellite genetic data as evidence that 

some Pacific herring sampling sites were somewhat demographically isolated from each 

other, but concluded that this level of divergence could not be characterized as differing 
42 

“markedly from other populations of the species in its genetic characteristics.” In general, 

the genetic studies suggested that Pacific herring are characterized by high levels of gene 

flow among populations across fairly large geographic areas, consistent with the results of 

extensive physical tagging studies, which also indicated that widespread straying can 

occur among spawning localities. 

The BRT concluded that Cherry Point Pacific herring were a component subpopulation of 

the Georgia Basin Pacific herring DPS, as described in the previous 2001 ESA status 

review. As currently defined, the Georgia Basin Pacific herring DPS encompasses 

spawning locations of Pacific herring in all the marine waters of Puget Sound, the Strait of 

Georgia, and eastern Juan de Fuca Strait in both the U.S. and Canada. In coming to this 

decision the BRT noted that the ecological discreteness of the Georgia Basin (the inshore 

waters of Puget Sound and the Strait of Georgia) and concordance of age composition of 

Pacific herring among the Strait of Georgia and Puget Sound locations provided support 

for this decision. 

Finally, the BRT noted that available information (genetics, life history, and tagging 

studies) suggests that population structure of Pacific herring roughly conforms to the 

“mixed structure” concept of a metapopulation, in which local subpopulations are linked 

demographically by at least episodic migration, extinction and recolonization of local 

subpopulations are common over ecological time frames, and some populations, such as 

Cherry Point, are relatively more distinctive, based on spawn timing, growth rate, 

contaminant profiles, and genetic differences. These differences are not of a magnitude 

that suggests long-term evolutionary divergence, but it is possible that demographic 

linkages between Cherry Point and other subpopulations in the DPS are weak enough that 

they are largely demographically independent on ecological time scales. 
43 

Figure 13. Spawning times of Pacific herring. 

0

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44 

Distinct Population Segments of North American Green Sturgeon 

Steve Lindley 

Southwest Fisheries Science Center 

In June 2001 NMFS received a petition to list North American Green Sturgeon (Acipenser 

medirostris) as a threatened or endangered species under the ESA. Green sturgeon are 

anadromous and are thought to return to their natal river for spawning. Fidelity to natal 

breeding sites can generate biologically important structure within species. The petition 

noted that stock structure in this species is not well described, and there may be more than 

one DPS within this species. NMFS convened a Biological Review Team (BRT) to review 

and interpret the best available information on the species to (1) recommend whether there 

was one or more DPSs within the species and (2) describe the risk of extinction for listable 

entities identified in the DPS analysis. The BRT reviewed information on population 

genetics (microsatellite DNA) and movements and breeding-site fidelity (from tagging 

studies). The genetics information indicates that there are at least two distinct groups of 

green sturgeon within the species. Allele frequencies in the Klamath River were very 

similar to those in the Rogue River, and significantly different from those in San Pablo 

Bay. However, these two groupings were significantly different from one another (Israel et 

al. 2004). 

Tagging studies (Figure 14) suggested little movement among breeding sites, but 

extensive mixing of populations in some non-natal habitats. 

Figure 14. Movements of North American green sturgeon along the west coast of the 

North America. Arrows indicate movement from site of tagging to another area; green 

pentagons are spawning rivers, white ovals are non-natal rivers, light blue ovals are 

locations in the Pacific Ocean, and blue-grey rectangles are large estuaries. 

Sturgeon have strong homing tendencies, which lead to high spawning site fidelity. Thus, 

isolation provides another argument supporting two DPSs of green sturgeon. A graphical 

representation of breeding site rivers (Figure 15) shows the Sacramento River is well 

separated from the more northern rivers; however, the northern rivers (Rogue, Klamath, 

and Eel) are relatively close together. 
45 

Figure 15. Graphical representation of breeding site rivers for North American green 

sturgeon (distances among rivers are km). 

If green sturgeon dispersal differences are large (>370 km) then the graphical analysis 

suggests that there would be only one breeding population. Dispersal distances of less than 

about 100 km would indicate four different breeding populations. 

The BRT concluded that the best available scientific evidence indicated there were at least 

two discrete groupings within the species, based on neutral genetic maskers, limited 

migration among spawning sites, the distances among the spawning areas, and that each of 

these discrete units is biologically significant to the species. NMFS concluded that there 

were two DPSs of green sturgeon; the Northern DPS included breeding groups in north of 

the Eel River, and the Southern DPS included green sturgeon breeding in the Sacramento 

River system. 
46 

Harbor Porpoise, Pacific Coast Stocks and Harbor Seals in Alaska 

Barbara Taylor, Greg O’Corry-Crowe, Karen Martien, and Susan Chivers 

Southwest Fisheries Science Center 

Identifying the intersection of biological principles with statutory requirements is 

necessary for stock definition. Species with “discrete” biology fit more easily with 

“discrete” management definitions, but continuous distributions are most common for 

marine species and present a difficult case for successful management. We present two 

cases of continuous distributions: harbor porpoise and harbor seals. Both range roughly 

from California to Japan in all coastal waters with no clear gaps in their distribution. Both 

have tagging data indicating home ranges that are small relative to their large range within 

the North Pacific Ocean basin so a hypothesis of panmixia is biologically highly 

implausible. Nevertheless, it is likely that a stock boundary drawn anywhere within the 

range will have individuals that regularly cross back and forth. 

Harbor porpoises are continuously distributed with non-uniform density, are nonmigratory, have small group size, but exhibit differences in pollutant ratios, habitats and 

genetics. An expanded genetic study using both nuDNA and mtDNA revealed more 

structure. As information has increased on harbor porpoise off of California, Oregon and 

Washington the stock boundaries have been refined by the agency with the support of the 

Scientific Review Group (SRG) without controversy. The SRGs were created in the 1992 

revisions to the MMPA to review the science produced and used by the agency to 

implement the MMPA. 

Harbor seals are also continuously distributed with non-uniform distribution, are mostly 

non-migratory, and exhibit clinal differences in coat color, skull morphology, pupping 

timing, and geographic differences in trends in abundance, habitat and haul-out substrate. 

The 12 defined management units generally agree with trends in abundance and 

movement (see Figure 16). Revising stock structure in Alaska has been complicated by 

declines (past and on-going) and user groups that could be affected by changes, such as 

Alaskan natives that subsistent hunt the seals and fisheries that kill seals as bycatch. No 

revisions have been made to the original three stock boundaries (dashed lines in Figure 16) 

despite multiple lines of evidence supporting additional stock structure within each of the 

defined stocks. These case studies illustrate that whenever possible stock structure should 

be researched before management issues arise. 
47 

Figure 16. Genetic strata consistent with demographic independence (black circles), areas 

surveyed for trends in abundance (colored circles) and current stock boundaries for 

Alaskan harbor seals. 

Increasing: 

Stable: 

Decreasing:
48 

Defining Stock Structure of Coastal Bottlenose Dolphins, Tursiops truncatus,

along the Atlantic Coast of the U.S.: A Multidisciplinary Approach

Aleta A. Hohn, Patricia E. Rosel, and Larry J. Hansen 

Southeast Fisheries Science Center 

Bottlenose dolphins, Tursiops truncatus, are continuously distributed in coastal waters 

from New York through Florida and are found in multiple habitat types, including coastal 

and inshore-estuarine areas. The original stock assessment for this region, implemented in 

1994, delineated a single coastal migratory stock. However, alternative hypotheses about 

stock structure exist- including multiple migratory populations, the presence of resident 

estuarine populations, or a combination of these hypotheses. The MMPA requires that 

assessments of abundance and human-caused mortality be stock specific. Therefore, 

evaluating these possible stock structure hypotheses is a critical component of the stock 

assessment for coastal bottlenose dolphins in the Atlantic. A multidisciplinary research 

approach was initiated and included photo-identification, genetics, stable isotope ratios 

and telemetry methodologies. Comparison of seasonal mixing among coastal animals in 

various locations and determining whether estuarine stocks exist and how much, if any, 

mixing occurs between coastal and estuarine animals at the same latitude and among 

estuarine populations at different latitudes were all necessary. Genetic information 

provided evidence of population structure for coastal bottlenose dolphins. Significant 

differences in isotope ratios showed promise for distinguishing between animals that 

inhabit estuarine versus coastal waters. Tagging data provided further support to reject the 

null hypothesis of a single coastal migratory stock. In conclusion, the single stock 

hypothesis was rejected. Instead, the population structure of coastal bottlenose dolphins is 

quite complex and a minimum of five populations are currently delineated on the basis of 

gene frequencies, supported by photo-identification and telemetry. A seasonal component 

to stock structure adds additional complexity and results in mixed stocks in some areas 

and times and further work is needed to tease apart this complicated population structure. 
49 

 

Figure 17. Seasonal ranges of provisional coastal bottlenose dolphin management units 

along the Atlantic coast as defined in the 2005 Stock Assessment Report. 

Reassessment of Stock Structure and New Management Units for 

Bottlenose Dolphins along the Atlantic Coast of the U.S.

FL

GA

SC

NC

VA

NJ Northern 

migratory 

management unit

Northern North Carolina 

management unit

SUMMER 

DISTRIBUTION

WINTER 

DISTRIBUTION

Northern migratory and 

northern NC units

Southern NC unit

Northern Florida unit

Georgia unit

South Carolina unit

Central Florida unit

Southern NC unit

No large-scale 

seasonal 

movements yet 

identified

Reassessment of Stock Structure and New Management Units for 

Bottlenose Dolphins along the Atlantic Coast of the U.S.

FL

GA

SC

NC

VA

NJ Northern 

migratory 

management unit

Northern North Carolina 

management unit

SUMMER 

DISTRIBUTION

WINTER 

DISTRIBUTION

Northern migratory and 

northern NC units

Southern NC unit

Northern Florida unit

Georgia unit

South Carolina unit

Central Florida unit

Southern NC unit

No large-scale 

seasonal 

movements yet 

identified

FL

GA

SC

NC

VA

NJ

FL

GA

SC

NC

VA

NJ Northern 

migratory 

management unit

Northern North Carolina 

management unit

SUMMER 

DISTRIBUTION

WINTER 

DISTRIBUTION

Northern migratory and 

northern NC units

Southern NC unit

Northern Florida unit

Georgia unit

South Carolina unit

Central Florida unit

Southern NC unit

No large-scale 

seasonal 

movements yet 

identified
50 

Killer Whales 

Paul Wade 

Alaska Fisheries Science Center 

Killer whales (Orcinus orca) are top level predators inhabiting all oceans of the world. 

Within the North Pacific Ocean, three forms or ecotypes of killer whales are recognized 

(Transient - mammal eaters; Resident – fish eaters, and Offshore). Differences among 

these forms and within residents and transients have been investigated using several lines 

of evidence, including genetics (mitochondrial and nuclear DNA), morphology (dorsal fin 

and saddle patch [Figure 18]), behavior (movements and associations, diet, acoustics, etc.), 

and chemistry (fatty acids and polychlorinated biphenyls). 

Figure 18. Examples of dorsal fins and saddle patches of resident, transient and offshore 

killer whales. 

Figure 19. Hierarchical population structure in resident killer whales. The outer ellipses 

depict sub-populations (each has been recognized as a population stock under the 

MMPA), the inner ellipses clans, the larger circles pods, and the smaller circles 

matrilines. NR, SAR, and SR refer to the northern resident, southern Alaskan resident, and 

southern resident subpopulations, respectively. 
51 

Resident forms of killer whales have been well-studied and demonstrate fine-scaled 

population structure (Figure 19). NMFS received a petition to list Southern Resident killer 

whales under the ESA. A BRT convened to advise NMFS noted that Southern Resident 

killer whales are discrete from other groups of killer whales and are likely to be a DPS 

only if Northern Pacific Residents are the taxon of reference in the analysis for 

significance. NMFS determined that the global species was the reference taxon and did not 

list Southern Resident killer whales as a species under the ESA. That determination was 

overturned in court, which noted that NMFS could not accept the single species as the best 

available information because it was wrong. In 2004, the BRT was reconvened and 

recommended that Southern Resident killer whales should be recognized as a DPS, with 

evidence for its significance including their occupation of a unique ecological setting, their 

loss would result in a significant gap in the range of North Pacific Residents, and they 

differ markedly from other North Pacific residents in their genetic characteristics. 

Under the MMPA, NMFS recognizes eight stocks of killer whales in the Eastern North 

Pacific Ocean. These include three resident stocks (Alaska Resident, Northern Resident, 

and Southern Resident), three transient stocks (Gulf of Alaska/Aleutian Islands/Bering Sea 

Transient, AT1 Transient, and West Coast Transient), one offshore stock, and a Hawaii 

stock. 

 
52 

Discussion Sessions

Workshop participants held a large-group discussion about conservation units and 

meaning of various terms under the statutes, especially the ESA. These discussions 

included a participant’s view of management units under the ESA indicating that 

management involves a wide range of units from entire species to individual. Following 

this discussion, workshop participants agreed that the ESA applies to various levels of 

organization below the DPS level; however, the guidance from NMFS leadership 

suggested emphasis on aggregations or groups of individuals that could be listed under the 

ESA. Accordingly, remaining discussion on conservation units under the ESA workshop 

participants agreed that the purpose of the workshop, with respect to the ESA, was limited 

to species, sub-species, or DPS. 

Workshop participants then divided into breakout groups to discuss two topics. In the first 

session, three groups were identified, based upon the statutory program (MSA, ESA, or 

MMPA). Although many individuals conducted program activities on more than one 

statute (with a blending of ESA and MMPA more likely than MSA with one of the other 

two statutes), participants were asked to select the program in which they had done most 

of their work. Each working group was to assess how well guidelines for identifying 

conservation units supported NMFS' mission under the statute. 

In the second session, participants were divided again into three groups to discuss the 

workshop objective to understand how activities under one statute could inform decisions 

related to the structure of conservation units of another program. In this session, 

participants were to discuss linkages or common themes under the statutes and how 

identification of conservation units under the primary statutes contributed to NMFS' 

ecosystem approach to management. 

Statute-specific Discussions

In this session, participants were divided by their statute (MSA, ESA, or MMPA) of 

expertise or most experience. The three groups were asked to address three questions: 

1. Do the guidelines meet the requirements of the Act? 

2. Do the guidelines go far enough? 

3. Is the language in the guidelines clear enough? 

Magnuson-Stevens Act Group 

Three questions were posed to the breakout group: 

1. Do guidelines meet requirements of the act? 

a. The breakout group felt that the guidelines adequately address the “unity of 

management” requirement in NS3, particularly in the context of 

interjurisdictional resources. 
53 

b. However, guidance on stock identification that should be considered in the 

implementation of other requirements of the Act (e.g., National Standard 1) 

is not met by the guidelines. 

2. Do they go far enough? 

a. The group agreed that more guidance is needed to promote consistency and 

application of “the best scientific information available” for stock 

identification. For example, the term ‘stock’ is not defined in the 

guidelines. The term ‘management unit’ is not in the Act and only adds 

confusion to definitions of ‘fishery’ and ‘stock.’ 

3. Is the language clear enough? 

a. There was consensus in the group that the guidelines were not clear 

enough, particularly with respect to confusion about the use of ‘fishery,’ 

‘stock,’ and ‘management unit.’ 

b. The group proposed that: 

i. A FMP unit should include a collection of fisheries and stocks that 

benefit from closely coordinated management. 

ii. The ‘management units’ section of NS3 guidelines should be 

replaced with a section on “stocks and coordinated management” 

that promotes close coordination of all fisheries that harvest the 

same stocks, even those crossing regional or international 

management boundaries. 

iii. The terms fishery and stock are used interchangeably all too often. 

Guidance should be provided to clarify the distinction between the 

two terms: 

1. The term ‘stock’ should be defined as a conservation unit for 

which MSY and status determination can be appropriately 

determined. 

2. The term ‘fishery’ should be defined as the activity of 

fishing for a stock (or stocks) for which OY is determined. 

The group felt that these definitions will also improve clarity 

of NS1 guidelines. 

iv. Clarify the apparent contradiction of managing a stock “throughout 

its range” and defining a stock as a “geographical grouping.” 

v. Guidance is needed for management of mixed-stock fisheries to 

avoid local depletion, while maintaining a consistent definition of 

the term ‘stock.’ 

Relevant portions the Act and Guidelines are excerpted in Appendix 3a. 

Endangered Species Act Group 

After quickly deciding to tackle the differences between “significant portion of its range” 

and “distinct population segments” another day, this group spent most of its time 

discussing the meaning of “discreteness” in the joint NMFS/ FWS Policy on the 

Recognition of Distinct Vertebrate Population Segments under the ESA (DPS policy). 
54 

Does “discreteness” as described in the DPS policy equate to “reproductive isolation” as 

described in the NMFS Policy on the Definition of Species for Pacific Salmon under the 

ESA (ESU policy)? 

Background on the development of the DPS policy

Marta Nammack provided background on how the DPS policy was developed. She said 

that John Fay of FWS developed a draft based partially on previous FWS attempts to 

develop policy. Nammack and Fay worked together to address issues raised by both 

agencies. Nammack coordinated reviews with the NMFS regions and science centers, and 

NMFS’ input focused on the desire to make this policy consistent with the ESU policy. 

During these discussions, it was clear that the first criterion of the draft DPS policy, 

“discreteness,” was intended to have the same meaning as the first criterion of the ESU 

policy, “substantial reproductive isolation.” And the second criterion, “significance to the 

taxon,” was intended to have the same meaning as the second criterion of the ESU policy, 

“important to the evolutionary legacy of the species.” The only difference is that a second 

factor can be considered to satisfy the first criterion in the DPS policy: delimitation by 

international governmental boundaries within which differences in control of exploitation, 

management of habitat, conservation status, or regulatory mechanisms exist. Nammack 

noted that managers may choose to satisfy the “discreteness” criterion under the 

international governmental boundary factor, but based on her many years of experience 

working on the DPS policy and listing actions, substantial reproductive isolation is 

necessary for satisfying the first factor of the “discreteness” criterion (i.e., “markedly 

separated”). 

“Discreteness” requires “substantial reproductive isolation”

The first factor of the “discreteness” criterion is: “It is markedly separated from other 

populations of the same taxon as a consequence of physical, physiological, ecological, or 

behavioral factors. Quantitative measures of genetic or morphological discontinuity may 

provide evidence of this separation.” The fact that the “markedly separated” language is 

followed with “as a consequence of physical, physiological, ecological, or behavioral 

factors” supports the view that “markedly separated” equates to “substantially 

reproductively isolated.” Physical, physiological, ecological, and behavioral factors are all 

considered mechanisms that lead to reproductive isolation. If two animals cannot breed 

because of physical distance, this can lead to reproductive isolation. Animals can also 

diverge physiologically enough so that, even if they are located in the same place: 1) they 

cannot interbreed; 2) their gametes will be infertile; 3) their zygotes will not develop; or 4) 

their embryos will abort. Animals that occupy different ecological niches are, in effect, 

reproductively isolated from each other. And if animals do not choose to mate with each 

other because of behavioral factors (e.g., not attracted to each other), then they will not 

reproduce successfully. 

The ESA’s purpose of preventing extinction or irreplaceable loss means that genetic 

diversity needs to be preserved. This is the rationale for requiring a certain degree of 

reproductive isolation between populations before they can be recognized as DPSs. 
55 

Rationale for interest in alternate interpretation

This group had numerous participants who believed that populations do not have to be 

reproductively isolated in order to satisfy the “discreteness” criterion. This issue arose 

principally because some felt that we could protect some populations more easily if we 

could identify them as separate DPSs that could be listed separately under the ESA. The 

rationale was that providing the flexibility to list populations separately, even if they are 

not substantially reproductively isolated, would make sense for certain species (i.e., 

humpback whales, loggerheads). Others explained that these populations could be 

protected through other mechanisms, such as the section 7 consultation process and 

recovery units identified under a recovery plan, even if the populations are not listed 

separately. Those who supported greater flexibility argued that it would be easier to delist 

a population of a species of marine mammal than the entire species. However, others 

noted that only populations that are genetically independent should be listed or delisted as 

units. Otherwise, problems with sink/source dynamics could occur. 

The group began discussing factors other than reproductive isolation that could be 

considered for satisfying “discreteness.” Most members of the group believed that there 

may be other “sufficient conditions” for satisfying the discreteness criterion. Some stated 

that perhaps we could equate “discreteness” or “markedly separated” to DIPs by looking at 

taxonomy, geography, genetics, ecology, and demographics. 

Work group on other “sufficient conditions” for satisfying “discreteness” criterion

Because of the interest among participants, a work group of this group met several times 

by conference call (after this workshop) to discuss whether substantial reproductive 

isolation was necessary to satisfy the “discreteness” criterion of the DPS policy. A 

summation of the work group’s discussions is attached. The majority of the work group 

agreed that reproductive isolation is not a necessary criterion for “discreteness,” stating 

that: (1) the DPS policy is clear in its intent that marked separation as a consequence of 

physical, physiological, ecological, or behavioral factors can fulfill the “discreteness” 

criterion in either the absence or presence of reproductive isolation;3

 and (2) the provision 

 

3

 Nammack disagrees and notes that the DPS policy is not clear in its intent that marked 

separation as a consequence of physical, physiological, ecological, or behavioral factors 

can fulfill the “discreteness” criterion in either the absence or presence of reproductive 

isolation. As discussed earlier, because of the “as a consequence” language, substantial 

reproductive isolation is necessary before the “discreteness” criterion can be satisfied 

(except for the international governmental boundary factor, which is a special case). 

Post-workshop discussions with FWS staff indicate that FWS still considers “discreteness” 

to mean “substantial reproductive isolation.” In fact, there is some discussion at FWS of 

the possibility of revising the DPS policy to require more genetic differentiation between 

populations before they can be considered DPSs. To date, both agencies have required 

populations to be substantially reproductively isolated from each other before qualifying 
56 

regarding international governmental boundaries clearly establishes that reproductive 

isolation is not a requisite condition for “discreteness.” Instead of developing other 

“sufficient conditions” that might satisfy the “discreteness” criterion, as initially charged, 

the work group members agreed that the language in the DPS policy already provides 

adequate guidance and flexibility for delineating DPSs. While the majority of the work 

group believed that the DPS policy does not require population “discreteness” to coincide 

with independent risks of extinction, others in the work group disagreed, stating that a 

listed organism should be an independent entity (i.e., not dependent on input from other 

members of the same species outside of the population for long-term viability). This latter 

argument is supported by the fact that independence is necessary in order to manage the 

recovery (as well as the other legal mandates outlined in sections 4, 6, 7, 9, and 10 of the 

ESA) of these taxa. 

Significance criterion of the DPS policy

The group then moved on to a discussion of the “significance” criterion of the DPS policy. 

What does it mean to have a “significant gap in the range” of a species, and would the fact 

that the loss of a particular discrete population would result in a significant gap in the 

range of a species be important enough to support a separate DPS? This factor under 

“significance” seems to be overused. We have supported identification of a DPS in the 

northern or southern extreme of a species’ range by stating that its loss would represent a 

significant gap in the range of a species. 

Also, how should “time” play into how significant or discrete a population is? Some 

believe that evolutionary timeframes of separation are appropriate for assessing whether 

discrete populations are significant to the taxon. Others believe that the time required for 

separation can be much shorter (e.g., a hydropower dam that has separated populations for 

100 years). In general, we have tried to think in terms of evolutionary timeframes, as we 

do when applying the ESU policy to Pacific salmon. 

Other issues

The “sparingly” language in a 1979 House Report was discussed, and it was noted that 

Congress urged the two agencies to use the “distinct population segment” provision 

sparingly. Congress didn’t want to see it abused, using the squirrels in a city park as an 

example of a “distinct population segment” that could be identified if the provision was 

used less than sparingly. Some participants argued that this was further rationale for 

interpreting the “discreteness” criterion to mean “substantial reproductive isolation.” 

 

as “discrete” populations, with the exception of the instances in which the international 

governmental boundary factor of the “discreteness” criterion has been invoked. The DPS 

policy is a joint FWS/NMFS policy, and it is good practice to interpret the same policy in 

the same way in both agencies. 
57 

It was noted that the “significance” criterion of the DPS policy is assessed in relation to 

the taxon to which the population belongs, and this can be a taxonomic species or 

subspecies. 

Regarding the definition of subspecies, it was noted that there is no good definition. 

Subspecies are identified and named, but there is no accepted set of criteria for 

determining whether a population or group of populations can qualify as a subspecies. 

Given this, it is a good idea to provide the rationale used to delineate a subspecies that 

isn’t already recognized formally in the scientific community. 

It was pointed out that flexibility considerations are not good rationale for changing the 

interpretation of a policy that has been clear, consistent, and defended against legal 

challenges in the past. 

Some discussion attempted to differentiate among DPSs, DIPs, population stocks, and 

recovery units. This was discussed further by the full group of participants. 

 

Marine Mammal Protection Act Group 

Three questions were posed to breakout groups: 

1. Do the guidelines meet requirements of the act?

Participants expressed strong concurrence that the existing guidelines for 

identifying population stocks of marine mammals met the requirements of the act. 

The guidelines have been a part of a larger set of guidelines for preparing marine 

mammal stock assessment reports for more than 10 years, with their initiation 

following the MMPA Amendments of 1994. Although the guidelines have been 

reviewed and modified twice (1997 and 2003), with emphasis in each review on 

stock identity, the modifications have been minor. The modifications resulting 

from these reviews clarified particular aspects of identifying population stocks of 

marine mammals and have not been a substantial change in the way stocks are 

identified. 

2. Do the guidelines go far enough?

Participants felt the guidelines adequately addressed the considerations that must 

be given to a variety of biological information (or lack thereof) to identify stocks 

of marine mammals in a manner consistent with the purposes and policies of the 

MMPA. 
58 

3. Is the language in the guidelines clear enough?

Although the group felt that generally the marine mammal stock identity guidelines were 

clear, there were a few places where additional clarification would be warranted. These 

areas are as follows: 

• Some managers and constituents have expressed concern that additional 

information generally leads to identification of increasingly smaller aggregations 

of marine mammals as stocks. Such smaller groups would make it increasingly 

difficult to correctly assign abundance and mortality to the appropriate stock, 

particularly when individuals from neighboring aggregations overlap in 

distribution. The group stated a goal for the stock identity guidelines, which is to 

define stocks well enough that abundance/mortality can be assigned correctly. 

• When does identified statistical significance not mean separate biological stocks 

(e.g., bowhead whales)? The stock identity guidelines state that many different 

types of information can be used to identify stocks and that differences in this 

information indicate reproductive isolation, which, in turn, is proof of demographic 

isolation among different aggregations. Thus, when [statistical] differences are 

found in measures for these groups, separate management is appropriate. The 

group felt in general this guidance should continue to apply; however, they noted 

an exception where recent genetic analyses of bowhead whales indicate differences 

from older samples available from specimen archives. These differences were the 

result of the recent samples being collected from a much-reduced population 

(following over-exploitation of bowhead whales in commercial whaling 

operations), and these differences do not indicate additional stock structuring in the 

Western Arctic stock of bowhead whales. Therefore, additional clarification in the 

stock identity guidelines would be appropriate to advise that exceptions may be 

found for certain situations where statistical differences between samples do not 

necessarily indicate biological difference between aggregations. 

• The existing guidelines note that our goal in identifying stocks of marine mammals 

is to identify demographically isolated (or independent) aggregations as separate 

stocks. The guidelines state, "Demographic isolation means that the population 

dynamics of the affected group is more a consequence of births and deaths within 

the group (internal dynamics) rather than immigration or emigration (external 

dynamics). Thus, the exchange of individuals between population stocks is not 

great enough to prevent the depletion of one of the populations as a result of 

increased mortality or lower birth rates." 

The choice for demographic isolation as the major criterion for identifying marine 

mammal stocks was based in large part upon the purposes and policies of the 

MMPA, which state that marine mammal stocks should not diminish beyond the 

point at which they cease to be significant functioning elements in the ecosystems 

in which they are a part. The MMPA's definition for population stock states that 

stocks are groups of marine mammals in common spatial arrangement that 
59 

interbreed when mature. In some cases, such as where large whales form feeding 

aggregations based upon matrilines and breeding areas include interbreeding 

individuals from more than one feeding aggregation, these two concepts could be 

confused. Because the statutory definition of population is more important in a 

legal sense than inferences from purposes and policies statements, the guidelines 

should be modified to indicate that "demographic independence" is consistent with 

the statutory definition of population stock. 

• The MMPA requires that stock assessment reports describe the geographic range 

of the affected stock, including any seasonal or temporal variation in such range. 

The geographic ranges of stocks are usually depicted by maps, with the ranges for 

various stocks delineated by lines on the map. In most cases, the ranges of different 

population stocks of the same species of marine mammal overlap at least 

seasonally. Such overlap is especially true in continuously distributed species, 

where individuals from one stock may be found at almost anytime within the range 

of the adjacent stock. The group indicated that the guidelines should be revised to 

indicate that any line drawn on a map should not be interpreted as a fail-safe 

separator between adjacent stocks of marine mammals. Rather, such lines indicate 

the general range of the affected stock of marine mammals, and a few individuals 

from adjacent stocks may cross the line at times. 

• There was a mixed reaction in the group to a statement that the guidelines define or 

describe "demographic isolation" too loosely. The majority of members of the 

group were satisfied with descriptions of this term in the guidelines, and a minority 

said further clarification would be appropriate. Rather than try to come to 

consensus on this issue, the group recommended that this suggestion be included in 

a future effort to revise the guidelines. If the results of that discussion indicated 

clarification to "demographic isolation" was necessary, this future effort should 

suggest the appropriate changes. 

Blended Discussions

A second set of breakout discussions consisted of blended expertise in small groups 

describing common themes among the statutes related to the use or identification of 

conservation units. These discussions identified linkages among the various Acts and 

support our identifying ways in which decisions under one statue would inform or be 

helpful in one or more of the others. Although there were separate presentations from three 

different groups, these presentations contained substantial overlap due to the objective of 

identifying common themes. Therefore, the results of these discussions are presented as a 

single summary. 

Workshop participants noted that the MSA and MMPA have many similarities in goals 

despite the focus of the MSA on yield from stocks of fish and managing the Nation’s 

fisheries and that of the MMPA on protection and recovery of marine mammal stocks. 

Among the key concepts in managing fish stocks are MSY, which has been defined in 
60 

regulations as the largest long-term average catch or yield that can be taken from a stock 

or stock complex under prevailing ecological and environmental conditions (50 CFR 

600.310(c)(1)), and OY, which is defined with respect to yield from a fishery as the 

amount of fish that will provide the greatest net benefit to the Nation. The basis for OY for 

a fishery is the MSY of affected fish stocks, reduced by relevant economic, social, or 

ecological factors. Under the MSA, the first of the National Standards for developing 

Fishery Management Plans is to prevent over-fishing and achieve, on a continuing basis, 

the OY from each fishery for the U.S. fishing industry (50 CFR 600.310(f)(1)). As 

directed by National Standard 1, FMPs must provide for rebuilding overfished stocks to 

their MSY stock size, the abundance or biomass that provides maximum net annual 

production) within certain periods of time. 

Unlike the MSA, the MMPA protects individual animals, regardless of their status, by 

prohibiting the take (which includes the killing, injuring, or harassing, or attempting to 

kill, injure, or harass marine mammals). The MMPA contains many exceptions to this 

general moratorium on taking marine mammals, and most of these exceptions require a 

determination that authorized taking be consistent with the policies and purposes of the 

MMPA, which include maintaining stocks of marine mammals as functioning elements of 

their ecosystems and encouraging each stock not to diminish below its OSP, the lower 

limit of which is the maximum net productivity level (MNPL), the abundance or biomass 

that provides maximum net annual production. 

Despite the different focuses of the two statutes (MSA on yield or catch and MMPA on 

protection and recovery), fundamental objectives of the statutes are similar, which is to 

maintain the affected populations at levels at or above the abundance or biomass providing 

maximum net annual production. 

Participants noted and discussed the similarities between MSY stock size and MNPL and 

between the fishing mortality rate (or catch) that would result in the MSY stock size 

(Fmsy) and the per capita rate of increase that results in maximum net annual production 

(Rmnpl or 1⁄2 Rmax). Participants concluded that demographic considerations are of 

primary importance in identifying conservation units for implementing both of these acts 

to ensure that catch or taking did not reduce the population size below stated limits. 

The ESA, on the other hand, is designed to prevent the extinction of species, which 

includes sub-species and DPSs, thereby, preserving genetic diversity. NMFS earlier noted 

that a review of the legislative history of the ESA indicated a major motivating factor for 

the act was the desire to preserve genetic variability, between and within species (56 FR 

58612, November 20, 1991). Accordingly, identifying conservation units (that could be 

listed as threatened or endangered) required both demographic and reproductive 

considerations. 

The considerations of demographic independence and reproductive isolation under the 

three major statutes are summarized in Table 1. As noted in Table 1, conservation units in 

each of the three statutes require a consideration of discreteness. Intra-specific groups 

must be demographically independent from other aggregations to be considered as 
61 

conservation units under each of the three statutes. Although there may be consideration of 

the extent of reproductive isolation in identifying fish stocks under MSA and population 

stocks under the MMPA (e.g., stock-recruit relationships), the conservation 

Table 1. A summary of organizing concepts in identifying conservation units and identified 

discreteness and significance as key terms in the statutes, and several characteristics 

could be attributed to each of these terms. 

Decision Criterion MSA 

Stock 

MMPA

Stock 

ESA 

ESU 

ESA 

DPS 

ESA 

Recovery unit4

1. Discreteness 

a. demographically 

independent 

X X X X X? 

 b. reproductively isolated 

 i. ecological time X X X? X 

 ii. evolutionary time X X? 

 c. Political boundaries 

2. a. Significance X 

 b. Evolutionary Legacy X 

goals of these statutes are focused primarily on demographic considerations; therefore, 

reproductive isolation on an ecological time scale can be of secondary importance in 

identifying discrete conservation units. Under the ESA, however, with its major goal of 

preserving genetic diversity within and between species, a consideration of the degree of 

reproductive isolation is a major factor in identifying discrete units. Furthermore, the DPS 

policy requires a consideration of discreteness as well as a consideration of the 

significance or importance of the discrete unit to the species or sub-species to which it 

belongs. 

Workshop participants agreed that DIPs seemed to be a unifying concept in identifying 

management or conservation units under the three statutes. For purposes of the MSA or 

MMPA, demographic independence was equated with "discreteness" so that aggregations 

of individuals that are demographically independent of one another should be managed 

separately because their population dynamics would be independent of each other. 

Under the ESA, demographic independence alone is insufficient to identify discrete units. 

Accordingly, DIPs could be aggregated (Figure 20) into larger units that are substantially, 

but not completely reproductively isolated from other groups of conspecifics. If these 

discrete units are significant or important to the species or subspecies as a whole, then the 

resulting aggregations of DIPs would be considered a DPS. 

 

4 Workshop participants originally included recovery units in their discussions; however, 

the group later agreed that ESA conservation units should be limited to "listable" entities 

(species, sub-species, or DPSs) for purposes of this workshop. Therefore, there was no 

additional discussion of recovery units. 
62 

Figure 20. An illustration of combining groups of individuals (circles) into DIPs (shaded 

circles) and the further aggregation of DIPs into reproductively isolated units for 

consideration as a DPS. 

Workshop participants also noted that correctly identifying conservation units under each 

of the three statutes was critical to an informed ecosystem approach to management. 

Furthermore, each of the statutes had ecosystem considerations embodied within its text. 

The MSA incorporates protecting the ecosystem as an integral part of the definition of OY 

(MSA section 3(28)), which is one of the fundamental concepts of that law. In addition, 

MSA section 3(29)(b) requires that MSY be reduced by economic, social, or ecological 

factors in defining Optimum Yield. ESA section 2(b) states a purpose of the act is to 

"...provide a means whereby the ecosystems upon which endangered species and 

threatened species depend may be conserved...". MMPA section 2(6) states the act's 

primary objective as maintaining the health and stability of marine ecosystems and notes 

that population stocks of marine mammals should not be permitted to diminish beyond the 

point at which they cease to be a significant functioning element in the ecosystem of 

which they are a part. Accordingly, each of these laws contains ecosystem considerations, 

and the identification of conservation units under each of them should be consistent with 

NOAA’s ecosystem approach to management. Therefore, delineation of conservation units 

should consider conventional boundaries of Large Marine Ecosystems (Sherman and 

Alexander 1986). 

DPS 
63 

Workshop participants discussed Secor's pyramid (Secor 2005) as a model to illustrate 

various aggregations, individuals, DIPs, DPSs, Subspecies, and Species. These discussions 

related the aggregations to time (years of coherence) and action (listing vs. management or 

recovery) under the three statutes. Workshop participants agreed that an illustration such 

as Figure 21 is a useful and concise summary of the relationship between stock units and 

management under the three statutes. 

Figure 21. Conservation units of the MMPA, MSA and ESA depicted as a continuum of 

time of coherence within groups (adapted from Secor 2005). 

Under the MMPA the major focus of conservation is at the population stock level with 

important protections being applied at the level of individuals marine mammals (depicted 

by a solid arrow in Figure 21). The MMPA also considers, but at a less extent, species and 

sub-species of marine mammals (depicted by a dashed arrow in Fig. 2). The MSA gives 

primary conservation focus at the stock level, which may be identified by a DIP. The ESA 

is more complicated with its definition of species (that could be listed as threatened or 

endangered) as a biological species, subspecies, or DPS. Although the ESA and MMPA 

provide protections for individuals, such protections were not within the scope of the 

workshop. 

In closing, workshop participants identified two areas that will present difficulties in 

identifying conservation units under all three statutes. 
64 

• How to identify mixed stocks. This problem can also be termed as correctly 

assigning mortality or abundance to the correct stock in areas where individuals 

from more than one biological population may be found. 

• Clines. Individuals from well-separated areas may be reproductively or 

demographically isolated from one another, but boundaries between adjacent 

aggregations cannot be identified reliably. 
65 

Conclusions and Recommendations

The conclusions and recommendations in this report are those of the steering committee 

and were compiled following the conclusion of the workshop. 

As noted by the representatives of NMFS’ Leadership Council, the identification of 

conservation units for managed fish (MSA), threatened and endangered species (ESA), 

and marine mammals (MMPA) differs among the affected living resources. Such 

differences are confusing to some constituents, and a clear, concise explanation of these 

differences and the rationales for them would be helpful. The Leadership Council 

expressed the need for a common paradigm that can help NMFS guide the identification of 

conservation units under the three statutes. 

Waples and Gaggiotti (2006) described a conceptual framework for identifying 

populations. They recognized two different paradigms for a working definition of 

“population”: 

Ecological paradigm: A group of individuals of the same species that co-occur in 

space and time and have an opportunity to interact with each other. 

Evolutionary paradigm: A group of individuals of the same species living in close 

enough proximity that any member of the group can potentially mate with any 

other member. 

Conservation units under the MSA and MMPA, where it is important to identify groups 

that are demographically independent from one another, would likely be considered under 

the ecological paradigm, above. Under the ESA, where the potential loss of genetic 

variability within and between species is important, conservation units would more likely 

be identified as populations under the evolutionary paradigm. 

Earlier, Taylor and Dizon (1996) noted that conservation units under the ESA are framed 

predominantly by population genetics criteria. The MMPA, on the other hand, has more 

demographic-based objectives, such as OSP and maintaining stocks as functioning 

elements of their ecosystems. They also note that population structure may not be 

identified from a genetics (reproductive isolation) perspective because gene flow may be 

sufficiently high to homogenize populations genetically yet may be too low to alter 

demographics of the affected groups. That is, DIPs may not be distinguishable genetically 

due to a low but sufficient degree of interbreeding among them. Consequently, each 

reproductively isolated group contains one or more DIPs, which results in a DIP being the 

fundamental conservation unit under the MSA, ESA, and MMPA. 

In general, many people perceive that managed fish stocks are aggregated to the greatest 

degree, threatened and endangered species are intermediate, and marine mammal 

population stocks or stocks are subjected to the smallest aggregations identified for 

conservation. The steering committee notes that in some cases under the ESA (e.g., large 

whales and sea turtles) the entire taxonomic species was listed as threatened or 
66 

endangered; however, the workshop focused only on those situations where DPSs were 

identified for listing. 

One of the first major questions asked of workshop participants was whether the 

differences in identification of conservation units are simply artifacts of the different 

objectives of the Federal laws requiring conservation of living marine resources. To some 

extent, different objectives account for different degrees of separation under the three 

statutes. The protections of the ESA attempt to prevent the extinction of species; thus, they 

are designed to avoid the irreplaceable loss of genetic traits or adaptations. The MSA and 

MMPA provide a framework for managing the population dynamics of fish and marine 

mammals, respectively. Accordingly, conservation units (aggregations that may be 

identified for listing) under the ESA should be based primarily upon the degree of 

reproductive isolation and would contain one or more DIPs. Another factor that explains 

the tendency to identify relatively small stocks of marine mammals is the nature of marine 

mammal populations, which typically involve internal fertilization, live birth, parental 

care, and maintenance of family groups; these features act as barriers to mixing among 

groups and help produce fine-scale population structure. 

The MSA and MMPA, however, attempt to maintain discrete aggregations of fish and 

marine mammals within certain abundance or biomass limits, and a single DIP would be 

identified as a conservation unit under either of these statutes. Accordingly, DPSs would 

be expected to be larger than stocks of fish or marine mammals because the criterion for 

separation is more difficult to achieve. 

The MSA and MMPA apply active management to all stocks within their jurisdiction and 

might be considered as pro-active approaches to prevent problems from developing. Thus, 

it is logical that they seek to apply their management to the smallest reasonable units. On 

the other hand, the ESA is called into action only when some aspect of conventional 

management has not adequately protected the species. Accordingly it seems logical that 

protection under ESA scales back to a broader degree of stock aggregation (DPSs). 

Participants at the workshop generally agreed that the guidance used to identify 

conservation units under the three statutes is generally acceptable and has worked well for 

years. Despite the general acceptance, discussions at the workshop revealed a number of 

places each set of guidance could be improved. In particular, two challenges were noted 

for identifying conservation units under all three statutes: (1) mixing of individuals from 

various stocks seasonally and (2) clines or continuously-distributed species. The steering 

committee also recommends that each set of guidelines for identifying conservation units 

explicitly address transboundary circumstances, that is, where stocks, DPSs, or population 

stocks extend beyond the U.S. Exclusive Economic Zone where the affected living marine 

resources may be subject to exploitation or mortality that is not subject to conservation or 

regulatory mechanisms under the three statutes. 

In addition to these three areas in common among the statutes, there are a few statutespecific recommendations that would benefit the identification of conservation units. 

These statute-specific recommendations appear below. 
67 

Magnuson-Stevens Act

Although participants in the workshop generally agreed that the guidance in the MSA and 

National Standards met the requirements and objectives of the act, there is confusion 

among terms that are used almost interchangeably in fishery management. These terms are 

“stock”, “fishery”, and “management unit”. The steering committee agrees with the MSA 

breakout group in noting the need to distinguish more clearly between “stock” and 

“fishery”. Further, the term “management unit” within the National Standard 3 guidelines 

enables a wide diversity of bases for these units and does not provide a primary focus on 

demographically isolated units. 

Most stocks of fish had already been identified when the MSA was enacted in 1976. Since 

these stocks were identified, the technology for describing the biological basis of 

population structure has improved, and much new information has been collected, 

analyzed, and, at least partially, interpreted related to fish population structure. As NMFS 

and its fishery management partners begin to use more recent information to review fish 

stock structure and make necessary changes, clear and concise guidance for distinguishing 

among stocks of fish would benefit the process by promoting a more consistent national 

approach to fish stock identification. The steering committee recommends that such 

guidance be developed in the near future. The process for developing these guidelines 

would benefit by including marine mammal biologists to discuss the aspects of marine 

mammal stock identity guidelines that have worked well or not so well. 

Endangered Species Act

DPS policy guidance was developed jointly by NMFS and FWS. This policy has generally 

worked well, has been subjected to legal challenge and review, and was upheld by Federal 

court. 

 Is it necessary to have a significant degree of reproductive isolation to meet the 

discreteness test in the DPS policy? Discussion in the ESA breakout group indicated 

disagreement among biologists experienced in implementing programs under the ESA 

regarding the requirement for discrete groups to be reproductively isolated from one 

another. Part of that group noted that reproductive isolation was implicit in the 

discreteness criteria, and others maintained that other factors could result in marked 

separation between or among groups. NMFS’ ESU policy explicitly includes substantial 

reproductive isolation as one of its tests (56 CFR 58612, November 20, 1991), and the 

DPS policy (61 FR 4722, February 7, 1996) notes that NMFS and FWS consider the ESU 

policy to be consistent with the DPS policy. It follows, therefore, that substantial 

reproductive isolation is implicit in the discreteness test of the DPS policy. However, the 

steering committee notes that if such disagreement exists among experienced biologists, 

then the procedure must be confusing to a less-informed public. 

The discreteness test includes the term “markedly separated from other populations” and 

notes that quantitative evidence of genetic discontinuity may provide evidence of 
68 

discreteness. Similarly, the significance test includes “discrete population segment differs 

markedly from other populations of the species in its genetic characteristics.” The use of 

“markedly separated” in one test and “differs markedly”, particularly with respect to 

genetic analyses, is confusing. Accordingly, the steering committee recommends that 

NMFS and FWS review the wording of the DPS policy and revise it to reduce the 

potential for confusion and to explicitly address the role of reproductive isolation in the 

discreteness test. 

The DPS policy is strong and well-supported; however, it is incomplete as a tool for 

promoting consistency in the overall identification of “species” under the ESA. The term 

“species” includes species, sub-species and DPSs. As noted earlier in this document, the 

list of endangered species lumps two species of right whales in a single listing. Scientists 

may sometimes disagree as to whether a currently recognized species would be better 

described as two or more species, even upon examining the same information. 

Consequently, the naming of new species may be much slower than information is 

accumulated. However, in a recent case involving Southern Resident killer whales, the 

court held that NMFS must consider the best available scientific information regarding 

taxonomy even if taxonomists have not completed a formal change of the existing 

nomenclature. 

Marine Mammal Protection Act

The guidelines for assessing marine mammal stocks, including the stock identity 

provisions, were drafted initially in 1994 and revised twice (1997 and 2005). Each set of 

guidelines was evaluated by independent scientific review groups and by the public, 

including many academics and well-informed constituents. The steering committee notes 

that the two revisions made only minor modifications to the initial guidelines prepared in 

1994; therefore, the stock identity approach in these guidelines appear to have withstood 

the test of time. However, it is among marine mammals that smaller groupings of marine 

mammals have been identified as stocks as information has accumulated, leading to 

concern expressed from various constituent groups. Accordingly, the steering committee 

recommends that the guidelines for assessing marine mammal stocks be updated in a 

future revision to include a discussion of these concerns. 

The guidelines clearly support the use of DIPs as stocks of marine mammals. However, 

the MMPA defines stock to mean groups that interbreed when mature. Unfortunately, the 

MMPA does not indicate to what extent breeding should occur within the stock instead of 

among stocks. The guidelines should, therefore, include a rationale for recognizing DIPs 

as stocks in cases where males from one stock may breed with females from the same 

stocks and other stocks. 

Workshop participants reviewed aspects of population structure, requirements under three 

major Federal statutes, existing guidance for identifying conservation units under these 

statutes, and case studies describing various aspects of the implementation of the existing 

guidance. Based upon the discussions at the workshop, the steering committee concluded 

that DIPs form a rational basis for describing conservation units, which may vary under 
69 

the three statutes. Although the existing guidance under each statute is consistent with the 

law and its policies, each set of guidance could be improved. The steering committee, 

therefore, recommends that NMFS address the statute-specific guidance as described 

above. 
70 

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75 

Appendices

1. Workshop agenda 

2. Workshop participants 

3. Statutory Text, Existing Guidelines 

 a. MSA 

 b. ESA 

 c. MMPA 
76 

Appendix 1. Workshop Agenda

Management Units Workshop 

Primary objective: Review the identification of management (conservation) units, and 

guidelines by which units are identified, under the MSFCMA, MMPA, and ESA to 

determine if NMFS' current management units are appropriate for the conservation of 

resources under the appropriate statute and an ecosystem approach to management. If 

changes are needed in identifying management units or internal guidelines for identifying 

management units, recommend such changes to NMFS management. 

Expected product or outcomes from the workshop: Because this is a NMFS-only 

workshop, the expectations should end with identifying issues, how we have addressed 

them in the past, and alternatives (plus strengths and weaknesses) to address them in the 

future. When we want to get to specific resolutions or recommendations for resolutions, 

we may have to broaden participation to include people from outside NMFS, particularly 

for MMPA and ESA issues. The products would be (1) a report containing introductory 

material, summaries of all presentations (due by presenters before workshop), a summary 

of the discussion, and recommendations of the workshop, and (2) identifying a team to put 

the Methot white paper in final form for publication in an appropriate outlet. 

Workshop Details 

Duration: 2 1⁄2 to 3 days in length 

Location: SSMC2, Room 2358 

 1325 East West Highway 

 Silver Spring, MD 20910 

Dates: February 14-16, 2006 (Tues, Wed, Thurs) 

Target Audience: NMFS employees; resource managers and policy makers 

Lodging: 

A block of rooms has been reserved at the Courtyard (Marriott) in Silver Spring. 

Group name: NOAA Fisheries (Call by Jan 23 for the Group block) 

 Gov't Rate: $187/night 

Courtyard by Marriott (Downtown) 

8506 Fenton Street 

Silver Spring, MD 20910 

Phone: 301-589-4899 

 or Toll Free Reservations: 800-321-2211 

There is no budget for the workshop; therefore, participants' home office would 

have to support travel. 
77 

Day 1 - February 14, 2006 

Welcome and Introductions:

Workshop Moderator: Megan Caldwell, Office of Sustainable Fisheries 

8:30 Welcome – Jim Lecky, Office of Protected Resources 

8:40 Introductions – participants introduce themselves; describe their connection or 

interest in identifying management/conservation units 

8:55 Reiterate workshop objectives, structure and flow – Megan 

PRESENTATIONS

Session 1: The Biology of Population Structure and Associated Issues 

9:00-10:00 Biology of Population Structure 

• What is a Population? -- Robin Waples, Northwest Fisheries Science 

Center 

• Identifying Units to Conserve – Barbara Taylor, Southwest Fisheries 

Science Center 

• Management of Biological Stocks under the MSFCMA, ESA, and MMPA 

– Rick Methot (Office of Science and Technology) 

10:00 – 10:45 Session 2: Legal requirements and guidance related to identifying 

management units 

Session introduction: Megan 

Presentations will: 

• Summarize general objectives of each act (to help explain why 

implementation of stock ID decision may be different among the acts) 

• Explain references, definitions or requirements for management units in 

each act, and how this has been "clarified" by case law or congressional 

reports. 

MSFCMA -- Stacey Nathanson - General Counsel for Fisheries 

ESA – Karl Gleaves, General Counsel for Fisheries 

 

MMPA - Karl Gleaves 
78 

10:45-11:15 Break

11:15-12:00 Population Structure Issues as Discussed in the Leadership Council 

(Video link)

 Bill Fox – Southwest Fisheries Science Center 

 Doug DeMaster – Alaska Fisheries Science Center 

 12:00 – 12:45 Session 3: Current Guidelines for Identifying Conservation Units 

Presentations will: 

• Identify the intersection of biological principles (population structure) with 

statutory requirements 

• Describe the development of technical guidelines and criteria 

• Discuss challenges in applying (or developing) policies 

ESA – Species, Sub-species and DPS policy – Marta Nammack, Office of Protected 

Resources 

MMPA – Stock ID guidelines - Tom Eagle, Office of Protected Resources 

MSFCMA – Steve Cadrin – Northeast Fisheries Science Center 

Discussing the state of the art techniques for defining a management unit or 

a stock; the need to develop policy guidance for this issue, will discuss 

where international agreement (e.g., in ICES and NAFO ) are issues 

12:45 – 2:00 Lunch on your own 

Session 4: Case Studies 

 

Session introduction: Megan Caldwell 

Presentations will: 

• Summarize the population's structure 

• Identify the intersection of biological principles with statutory requirements 

• How has the individual act’s policy guidance been applied? 

• What was the basis for the decision made to identify the management unit? 

• Describe how stock ID implementation has helped meet agency missions 

(successes) 

• Describe challenges or impediments to implementing (or developing) policies 

(failures) 

• What has not been successful to this point? 
79 

2:00 Regional Groundfish (multidisciplinary approach) (1 hour total) 

 Alaska – Grant Thompson, Alaska Fisheries Science Center 

 Northwest – Rick Methot 

 Northeast – Steve Cadrin 

3:00-3:30 Break

3:30 Bluefin Tuna – Clay Porch, Southeast Fisheries Science Center (Video link), 

MSFCMA/Intl Agreements 

4:00 Scallops – Dvora Hart, Northeast Fisheries Science Center – via video) MSFCMA 

4:30 Atlantic loggerhead turtles – Barbara Schroeder, Office of Protected Resources – 

ESA 

5:00 Western North Atlantic Humpback Whales –. Richard Pace, Northeast Fisheries 

Science Center – ESA/MMPA 

5:30 Adjourn – Megan 

Day 2 – February 15, 2006 

8:30 Opening comments, brief plan for day – Megan Caldwell 

8:45 Pacific salmon – Robin Waples – ESA 

9:15 Cherry Point, WA, Herring - Rick Gustafson, Northwest Fisheries Science Center 

– ESA 

9:45 Green Sturgeon – Steve Lindley, Southwest Fisheries Science Center - ESA 

10:15 – 10:30 Break

10:30 Harbor Porpoise, Pacific Coast Stocks and Harbor Seals in Alaska – Barbara 

Taylor, Southwest Fisheries Science Center -- MMPA 

1100 Bottlenose Dolphins, Western N. Atlantic coastal stocks) – Aleta Hohn and Patty 

Rosel, Southeast Fisheries Science Center – MMPA 

11:30 Killer whales – Paul Wade, Alaska Fisheries Science Center – ESA/MMPA 

12:00 – 1:30 Lunch on your own 

DISCUSSION AND BREAKOUT 
80 

1:30-2:15 – Breakout 1 

2:15-3:00 – Plenary, report of breakouts and discussion 

3:00-3:15 Break

3:30 3:45 – Breakout 2 

3:45-4:30 – Plenary, report of breakouts and discussion 

4:30 – Overview of the day's discussion and adjourn – Megan 

Day 3 – February 16, 2006 

8:30 – Opening comments and brief plan for the day – Megan 

8:45-9:30 - Breakout 3 

9:30-10:15 – Plenary, report of breakout and discussion 

10:15-10:30 Break

10:30-11-15 - Breakout by statute interest for recommendations to prepare for afternoon 

discussion with senior managers 

1. Does the approach under the statute make sense for our stewardship responsibilities? 

2. What concerns do we have about this approach, and are revisions needed? 

3. Suggestions to resolve the concerns. 

11:15 – 12:00 – Plenary, report of breakout and discussion 

12:00 – 1:30 Lunch on your own 

1:30-?? Reconvene for discussions with senior managers, including 

recommendations from the morning breakout sessions and discussions 

Identify team to work with Rick Methot to complete white paper for publication and 

adjourn 

________________________ 

Breakout sessions (number of groups depends upon number of participants) 

Guiding Questions for Discussion: Each breakout group will be assigned several of 

these questions, and it may be good for at least some questions to have more than one 

breakout group address the question. 

1. What level of consistency should there be in identifying stocks (at least discrete 

management units) under the 3 statutes, or should different policies and purposes of the 
81 

three laws allow very different approaches in identifying management units under each 

statute? (This question is, in part, based on the different interpretations for Atlantic 

humpback whales and loggerhead turtles, where NMFS recognized the Gulf of Maine 

feeding aggregation as a separate population stock of Atl humpbacks but the Northern and 

Southern Florida sub-populations of loggerheads failed the discreteness test under the DPS 

policy for the ESA) 

2. What are the biological and socio-economic consequences of large vs. small 

conservation units (i.e., what are the trade-offs for lumping and splitting)? 

3. Sometimes a subregion of a stock is designated as a management unit (managed fish 

example, West. N. Atl coastal bottlenose dolphins, ESA example) to provide temporal or 

spatial control for mortality. Should the management units be reported as if they were 

separate stocks? 

4. Sometimes an assessment boundary is drawn along a political boundary that clearly is 

not a biological stock boundary. Do we get reliable results by assessing a portion of a 

stock's range? Can we deal with transboundary issues more effectively? 

5. When a large management unit contains highly structured aggregations (even mixed 

stocks), it seems necessary to align the assessment (demographic analysis) boundaries 

with new information on stock boundaries. Is it always necessary to create finer-scale 

management boundaries? 

6. Do we have taxonomic inconsistencies (or discrimination) in stock structure 

(particularly under the ESA)? E.g., salmon and killer whales. In other words, do we lump 

more for fish than for marine mammals? 

7. Ephemeral vs evolutionary separation. (Question getting to our jobs under the MMPA 

and MSA vs the ESA) This could also get to the question of just how separated 

aggregations should be from one another before we recognize them as a separate stock. 

8. Do we need a written set of guidelines for identifying stocks under the MSA 

comparable to the DPS policy under the ESA and the SAR guidelines under the MMPA? 

Plenary sessions: 

Report of breakout results and discussion among all participants. 

Workshop Products: 

NOAA Technical Memorandum with biological background, recommendations, and 

rationale. 

Identification of authors and steps to produce the “white paper” or “primer” for outreach 

and education related to identifying conservation units. 
82 

Appendix 2. Workshop Participants (M-Moderator, P-Presenter ,S-Steering Committee) 

Douglas DeMaster (by video conference) Alaska Fisheries Science Center P 

Grant Thompson Alaska Fisheries Science Center P 

Paul Wade Alaska Fisheries Science Center P 

Corey Niles Ecosystem Goal Team 

Steve Cadrin Northeast Fisheries Science Center P,S 

Trish Clay Northeast Fisheries Science Center 

Dvora Hart (by video conference) Northeast Fisheries Science Center P 

Phil Logan Northeast Fisheries Science Center 

Richard Pace Northeast Fisheries Science Center P 

Kim Damon-Randall Northeast Region 

David Gouveia Northeast Region 

Richard Gustafson Northwest Fisheries Science Center P 

Robin Waples Northwest Fisheries Science Center P 

Donna Darm Northwest Region 

Scott Rumsey Northwest Region 

Christopher Rogers Office of International Affairs 

Melissa Andersen Office of Protected Resources 

Thomas Eagle Office of Protected Resources P,S 

Craig Johnson Office of Protected Resources 

Patricia Lawson Office of Protected Resources 

James Lecky Office of Protected Resources 

Katherine McFadden Office of Protected Resources 

Marta Nammack Office of Protected Resources P,S 

Michael Payne Office of Protected Resources 

Susan Pultz Office of Protected Resources 

Cheryl Ryder Office of Protected Resources 

Barbara Schroeder Office of Protected Resources P 

Richard Methot Office of Science and Technology P,S 

Megan Caldwell Office of Sustainable Fisheries M,S 

Debra Lambert Office of Sustainable Fisheries 

Mark Millikin Office of Sustainable Fisheries 

Karl Gleaves Office of the General Counsel for Fisheries P 

Stacey Nathanson Office of the General Counsel for Fisheries P 

Melissa Snover Pacific Islands Fisheries Science Center 

Sheryan Epperly Southeast Fisheries Science Center 

Aleta Hohn Southeast Fisheries Science Center P 

Clay Porch (by video conference) Southeast Fisheries Science Center P 

Patricia Rosel Southeast Fisheries Science Center P 

Kyle Baker Southeast Region 

John McGovern Southeast Region 

William Fox (by video conference) Southwest Fisheries Science Center P 

Steve Lindley Southwest Fisheries Science Center P 

Barbara Taylor Southwest Fisheries Science Center P 

Christina Fahy Southwest Region 
83 

Appendix 3a. Excerpts from MSA and supporting documents related to stock 

identification of managed fish.

Magnuson-Stevens Fishery Conservation and Management Act 

• National Standard 1: “Conservation and management measures shall prevent 

overfishing while achieving on a continuing basis, the optimal yield from each 

fishery for the United States fishing industry.”

• National Standard 2: “Conservation and management measures shall be based 

upon the best scientific information available.” 

• National Standard 3: “To the extent practicable, an individual stock of fish shall be 

managed as a unit throughout its range, and interrelated stocks of fish shall be 

managed as a unit or in close coordination.”

• Stock of fish: “a species, subspecies, geographical grouping, or other category of 

fish capable of management as a unit.”

• Overfishing: “a rate or level of fishing mortality that jeopardizes the capacity of a 

fishery to produce maximum sustainable yield on a continuing basis.”

• Optimal yield: “maximum sustainable yield from the fishery, as reduced by any 

relevant economic, social, or ecological factor; and in the case of an overfished 

fishery, provides for rebuilding to a level consistent with producing maximum 

sustainable yield...”

• Fishery: “one or more stocks of fish which can be treated as a unit for purposes of 

conservation and management and which are identified on the basis of 

geographical, scientific, technical, recreational, and economic characteristics; and 

any fishing for such stocks.”

• Rebuilding Overfished Fisheries – fishery management plans shall “specify a time 

period for ending overfishing and rebuilding the fishery that shall... not exceed ten 

years...” 

National Standard 1 Guidelines

• Mixed-stock fisheries: “In the case of a mixed-stock fishery, MSY should be 

specified on a stock-by-stock basis. However, where MSY cannot be specified for 

each stock, then MSY may be specified on the basis of one or more species as an 

indicator for the mixed stock as a whole or for the fishery as a whole.” 

• Overfishing ‘stocks:’ “To overfish means to fish at a rate or level that jeopardizes 

the capacity of a stock or stock complex to produce MSY on a continuing basis.” 

• “Overfishing occurs whenever a stock or stock complex is subjected to rate or 

level of fishing mortality that jeopardizes the capacity of a stock or stock complex 

to produce MSY on a continuing basis.” 

National Standard 3 Guidelines: 

§600.320 National Standard 3—Management Units. 

(a) Standard 3. To the extent practicable, an individual stock of fish shall 

be managed as a unit throughout its range, and interrelated stocks of fish 

shall be managed as a unit or in close coordination. 
84 

(b) General. The purpose of this standard is to induce a comprehensive 

approach to fishery management. The geographic scope of the fishery, for 

planning purposes, should cover the entire range of the stocks(s) of fish, 

and not be overly constrained by political boundaries. Wherever 

practicable, an FMP should seek to manage interrelated stocks of fish. 

(c) Unity of management. Cooperation and understanding among entities 

concerned with the fishery (e.g., Councils, states, Federal Government, 

international commissions, foreign nations) are vital to effective 

management. Where management of a fishery involves multiple 

jurisdictions, coordination among the several entities should be sought in 

the development of an FMP. Where a range overlaps Council areas, one 

FMP to cover the entire range is preferred. The Secretary designates which 

Council(s) will prepare the FMP, under section 304(f) of the MagnusonStevens Act. 

(d) Management unit. The term “management unit” means a fishery or that 

portion of a fishery identified in an FMP as relevant to the FMP's 

management objectives. 

(1) Basis. The choice of a management unit depends on the focus of the 

FMP's objectives, and may be organized around biological, geographic, 

economic, technical, social, or ecological perspectives. For example: 

(i) Biological—could be based on a stock(s) throughout its range. 

(ii) Geographic—could be an area. 

(iii) Economic—could be based on a fishery supplying specific product 

forms. 

(iv) Technical—could be based on a fishery utilizing a specific gear type or 

similar fishing practices. 

(v) Social—could be based on fishermen as the unifying element, such as 

when the fishermen pursue different species in a regular pattern throughout 

the year. 

(vi) Ecological—could be based on species that are associated in the 

ecosystem or are dependent on a particular habitat. 

(2) Conservation and management measures. FMPs should include 

conservation and management measures for that part of the management 

unit within U.S. waters, although the Secretary can ordinarily implement 

them only within the EEZ. The measures need not be identical for each 

geographic area within the management unit, if the FMP justifies the 
85 

differences. A management unit may contain, in addition to regulated 

species, stocks of fish for which there is not enough information available 

to specify MSY and OY or to establish management measures, so that data 

on these species may be collected under the FMP. 

(e) Analysis. To document that an FMP is as comprehensive as practicable, 

it should include discussions of the following: 

(1) The range and distribution of the stocks, as well as the patterns of 

fishing effort and harvest. 

(2) Alternative management units and reasons for selecting a particular 

one. A less-than-comprehensive management unit may be justified if, for 

example, complementary management exits or is planned for a separate 

geographic area or for a distinct use of the stocks, or if the unmanaged 

portion of the resource is immaterial to proper management. 

(3) Management activities and habitat programs of adjacent states and 

their effects on the FMP's objectives and management measures. Where 

state action is necessary to implement measures within state waters to 

achieve FMP objectives, the FMP should identify what state action is 

necessary, discuss the consequences of state inaction or contrary action, 

and make appropriate recommendations. The FMP should also discuss the 

impact that Federal regulations will have on state management activities. 

(4) Management activities of other countries having an impact on the 

fishery, and how the FMP's management measures are designed to take 

into account these impacts. International boundaries may be dealt with in 

several ways. For example: 

(i) By limiting the management unit's scope to that portion of the stock 

found in U.S. waters; 

(ii) By estimating MSY for the entire stock and then basing the 

determination of OY for the U.S. fishery on the portion of the stock within 

U.S. waters; or 

(iii) By referring to treaties or cooperative agreements. 

[61 FR 32540, June 24, 1996, as amended at 63 FR 24234, May 1, 1998] 
86 

Appendix 3b. Definition of “species” from the ESA and the joint DPS policy 

ESA definition of species, section 3(15):

The term "species" includes any subspecies of fish or wildlife or plants, and any distinct 

population segment of any species or vertebrate fish or wildlife which interbreeds when 

mature.

DPS policy (text version of the act retrieved from GPO Acces)s:

Federal Register: February 7, 1996 (Volume 61, Number 26)] 

[Notices ] 

[Page 4721-4725] 

From the Federal Register Online via GPO Access [wais.access.gpo.gov] 

[DOCID:fr07fe96-107] 

[[Page 4721]] 

_______________________________________________________________________ 

Part IV 

Department of the Interior 

Fish and Wildlife Service 

Department of Commerce 

National Oceanic and Atmospheric Administration 

_______________________________________________________________________ 

Policy Regarding the Recognition of Distinct Vertebrate Population; 

Notice 

[[Page 4722]] 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

 

Policy Regarding the Recognition of Distinct Vertebrate 

Population Segments Under the Endangered Species Act 

AGENCIES: Fish and Wildlife Service, Interior; National Marine 

Fisheries Service, NOAA, Commerce. 

ACTION: Notice of policy. 

----------------------------------------------------------------------- 

SUMMARY: The Fish and Wildlife Service and the National Marine 

Fisheries Service (Services) have adopted a policy to clarify their 

interpretation of the phrase ``distinct population segment of any 

species of vertebrate fish or wildlife'' for the purposes of listing, 
87 

delisting, and reclassifying species under the Endangered Species Act 

of 1973, as amended (16 U.S.C. 1531 et. seq.) (Act). 

ADDRESSES: The complete record pertaining to this action is available 

for inspection, by appointment, during normal business hours at the 

Division of Endangered Species, U.S. Fish and Wildlife Service, in Room 

452, Arlington Square Building, 4401 North Fairfax Drive, Arlington, 

Virginia. 

FOR FURTHER INFORMATION CONTACT: E. LaVerne Smith, Chief, Division of 

Endangered Species, U.S. Fish and Wildlife Service at the above address 

(703/358-2171), or Russell Bellmer, Chief, Endangered Species Division, 

National Marine Fisheries Service, 1335 East-West Highway, Silver 

Spring, Maryland 20910 (301/713-1401). 

SUPPLEMENTARY INFORMATION: 

Background 

 The Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et. 

seq.). (Act) requires the Secretary of the Interior or the Secretary of 

Commerce (depending on jurisdiction) to determine whether species are 

endangered or threatened. In defining ``species,'' the Act as 

originally passed included, ``* * * any subspecies of fish or wildlife 

or plants and any other group of fish or wildlife of the same species 

or smaller taxa in common spatial arrangement that interbreed when 

mature.'' In 1978, the Act was amended so that the definition read ``* 

* * any subspecies of fish or wildlife or plants, and any distinct 

population segment of any species of vertebrate fish or wildlife which 

interbreeds when mature.'' This change restricted application of this 

portion of the definition to vertebrates. The authority to list a 

``species'' as endangered or threatened is thus not restricted to 

species as recognized in formal taxonomic terms, but extends to 

subspecies, and for vertebrate taxa, to distinct population segments 

(DPS's). 

 Because the Secretary must ``* * * determine whether any species is 

an endangered species or a threatened species'' (section 4(a)(1)), it 

is important that the term ``distinct population segment'' be 

interpreted in a clear and consistent fashion. Furthermore, Congress 

has instructed the Secretary to exercise this authority with regard to 

DPS's ``* * * sparingly and only when the biological evidence indicates 

that such action is warranted.'' (Senate Report 151, 96th Congress, 1st 

Session). The Services have used this authority relatively rarely; of 

over 300 native vertebrate species listed under the Act, only about 30 

are given separate status as DPS's. 

 It is important in light of the Act's requirement to use the best 
88 

available scientific information in determining the status of species 

that this interpretation follows sound biological principles. Any 

interpretation adopted should also be aimed at carrying out the 

purposes of the Act (i.e., ``* * * to provide a means whereby the 

ecosystems upon which endangered species and threatened species depend 

may be conserved, to provide a program for the conservation of such 

endangered species and threatened species, and to take such steps as 

may be appropriate to achieve the purposes of the treaties and 

conventions set forth in subsection (a) of this section'' (section 

2(b)). 

 Available scientific information provides little specific 

enlightenment in interpreting the phrase ``distinct population 

segment.'' This term is not commonly used in scientific discourse, 

although ``population'' is an important term in a variety of contexts. 

For instance, a population may be circumscribed by a set of 

experimental conditions, or it may approximate an ideal natural group 

of organisms with approximately equal breeding opportunities among its 

members, or it may refer to a loosely bounded, regionally distributed 

collection of organisms. In all cases, the organisms in a population 

are members of a single species or lesser taxon. 

 The National Marine Fisheries Service (NMFS) has developed a Policy 

on the Definition of Species under the Endangered Species Act (56 FR 

58612-58618; November 20, 1991). The policy applies only to species of 

salmonids native to the Pacific. Under this policy, a stock of Pacific 

salmon is considered a DPS if it represents an evolutionarily 

significant unit (ESU) of a biological species. A stock must satisfy 

two criteria to be considered an ESU: 

 (1) It must be substantially reproductively isolated from other 

conspecific population units; and 

 (2) It must represent an important component in the evolutionary 

legacy of the species. 

 This document adopts an interpretation of the term ``distinct 

population segment'' for the purposes of listing, delisting, and 

reclassifying vertebrates by the U.S. Fish and Wildlife Service (FWS) 

and NMFS. The Services believe that the NMFS policy, as described 

above, on Pacific salmon is consistent with the policy outlined in this 

notice. The NMFS policy is a detailed extension of this joint policy. 

Consequently, NMFS will continue to exercise its policy with respect to 

Pacific salmonids 

 The Services' draft policy on this subject was published on 

December 21, 1994 (59 FR 65885) and public comment was invited. After 

review of comments and further consideration, the Services adopt the 

policy as issued in draft form. 
89 

Summary of Comments and Recommendations 

 The Services received 31 letters from individuals and organizations 

commenting on the draft policy. In addition, since publication of the 

draft policy, the National Academy of Sciences, National Research 

Council (NRC), has published a report titled ``Science and the 

Endangered Species Act,'' prepared by a committee appointed by the 

Academy at the request of several members of Congress. This report in 

part examines the definition of ``species'' under the Act, and endorses 

the recognition of scientifically identified evolutionary units for 

conservation purposes. It discusses the recognition of DPS's in terms 

of ``distinctiveness,'' which is consistent with the concept of 

``discreteness'' as presented in the draft policy except that it would 

not recognize an international political boundary to delimit a DPS. The 

committee noted that: ``Although there can be good policy reasons for 

such delineations, there are not sound scientific reasons to delineate 

species only in accordance with political boundaries.'' The Services 

agree that the inclusion of international boundaries in determining 

whether a population segment is discrete is sometimes undertaken as a 

matter of policy rather than science. Although the committee 

[[Page 4723]] 

expressed the belief that application of a distinctiveness test 

(analogous to the standard of discreteness in the policy) would 

adequately carry out the congressional instruction that the authority 

to address DPS's be exercised sparingly, the Services continue to 

believe that a judgement regarding the significance of any unit found 

to be discrete is necessary to comply with congressional intent. 

 Respondents presented a wide range of opinion regarding the 

recognition of DPS's. Some argued that the draft policy would be too 

restrictive and make it difficult or impossible to protect important 

elements of biodiversity; others maintained that the draft was not 

restrictive enough and would allow the Services to extend protection to 

entities never intended to be eligible for protection under the Act. A 

few respondents questioned the need for any policy framework and 

advocated case-by-case determinations of the eligibility of entities 

for listing under the DPS provision. The Services continue to believe 

that the Act will be best administered if there is a general policy 

framework governing the recognition of DPS's that can be disseminated 

and understood by the affected public. 

 Several respondents questioned the relationship of the draft policy 

to the NMFS policy regarding salmonids. The Services believe that the 

NMFS policy for salmonids is consistent with the general policy 

outlined in this notice, although the salmonid policy is formulated 

specifically to address the biology of this group. Several respondents 

also questioned the use of qualifying words such as ``significant'' or 
90 

``markedly'' in the policy. The Services intended these words to have 

their commonly understood senses. At the time any distinct population 

is recognized or not recognized the reasons for which it is believed to 

satisfy or not satisfy the conditions of the policy will be fully 

explained. 

 Several respondents maintained that a policy of this nature 

required adoption under rulemaking procedures of the Administrative 

Procedure Act. The Services disagree, and continue to regard the policy 

as non-regulatory in nature. Specific recommendations advanced by 

respondents are paraphrased and responded to below. 

Only Full Species are Genetically Distinct From one Another, and 

Listing Should Only be Extended to These Genetically Distinct Entities. 

 Restricting listings to full taxonomic species would render the 

Act's definition of species, which explicitly includes subspecies and 

DPS's of vertebrates, superfluous. Clearly, the Act is intended to 

authorize listing of some entities that are not accorded the taxonomic 

rank of species, and the Services are obliged to interpret this 

authority in a clear and reasonable manner. 

The Services Should Focus on Genetic Distinctness in Recognizing a 

Distinct Population Segment. Conversely, Some Respondents Believed 

There Should be No Requirement That a DPS be Genetically Differentiated 

or Recognizable for it to be Protected Under the Act 

 There appears to be a diversity of understanding regarding the 

purposes of the Act, with some individuals viewing it as directed 

almost exclusively toward the conservation of unique genetic resources 

while other individuals emphasize its stated intention of conserving 

ecosystems. This diversity of viewpoints is reflected in comments 

addressing the role to be played by genetic information in the draft 

policy. The Services understand the Act to support interrelated goals 

of conserving genetic resources and maintaining natural systems and 

biodiversity over a representative portion of their historic 

occurrence. The draft policy was intended to recognize both these 

intentions, but without focusing on either to the exclusion of the 

other. Thus, evidence of genetic distinctness or of the presence of 

genetically determined traits may be important in recognizing some 

DPS's, but the draft policy was not intended to always specifically 

require this kind of evidence in order for a DPS to be recognized. The 

ESU policy of NMFS also does not require genetic data before an ESU can 

be identified. Thus in determining whether the test for discreteness 

has been met under the policy, the Services allow but do not require 

genetic evidence to be used. At least one respondent evidently 

understood the draft policy to require that genetic distinctness be 
91 

demonstrated before a DPS could be recognized, and criticized the draft 

on that basis. As explained above, this was never intended. 

The Elements Describing Reasons for Considering a Population Segment 

Significant Should be Laid Out Comprehensively, Rather Than Presented 

as an Open-Ended Set of Examples as in the Draft Policy 

 The Services appreciate the need to make a policy on this subject 

as complete and comprehensive as possible, but continue to believe that 

it is not possible to describe in advance all the potential attributes 

that could be considered to support a conclusion that a particular 

population segment is ``significant'' in terms of the policy. When a 

distinct population is accepted or rejected for review pursuant to a 

petition or proposed for listing or delisting, the Services intend to 

explain in detail why it is considered to satisfy both the discreteness 

and significance tests of the policy. 

In Assessing the Significance of a Potential Distinct Population 

Segment, the Services Should Focus on its Importance to the Status of 

the Species to Which it Belongs. Alternatively, the Services Should 

Emphasize the Importance of a Potential DPS to the Environment in Which 

it Occurs 

 Despite its orientation toward conservation of ecosystems, the 

Services do not believe the Act provides authority to recognize a 

potential DPS as significant on the basis of the importance of its role 

in the ecosystem in which it occurs. In addition, it may be assumed 

that most, if not all, populations play roles of some significance in 

the environments to which they are native, so that this importance 

might not afford a meaningful way to differentiate among populations. 

On the other hand, populations commonly differ in their importance to 

the overall welfare of the species they represent, and it is this 

importance that the policy attempts to reflect in the consideration of 

significance. 

International Boundaries are not Appropriate in Determining That a 

Population is Discrete in the Draft Policy; Political Boundaries Other 

Than Those Between Nations may be Appropriate in Some Cases to Delimit 

DPS's 

 The Services recognize that the use of international boundaries as 

a measure of discreteness may introduce an artificial and nonbiological element to the recognition of DPS's. Nevertheless, it 

appears to be reasonable for national legislation, which has its 

principal effects on a national scale, to recognize units delimited by 

international boundaries when these coincide with differences in the 
92 

management, status, or exploitation of a species. Recognition of 

international boundaries in this way is also consistent with practice 

under the Convention on International Trade in Endangered Species of 

Wild Fauna and Flora, which is implemented in the United States by the 

Act. Recognition of other political boundaries, such as State lines 

within the United States, would appear to lead to the recognition of 

[[Page 4724]] 

entities that are primarily of conservation interest at the State and 

local level, and inappropriate as a focus for a national program. The 

Services recognize, as suggested in some comments, that infra-national 

political boundaries offer opportunities to provide incentives for the 

favorable management of species if they were used as a basis for 

recognizing discrete entities for delisting or for exclusion from a 

listing. Particularly when applied to the delisting or reclassification 

of a relatively widespread species for which a recovery program is 

being successfully carried out in some States, recognition of State 

boundaries would offer attractive possibilities. Nevertheless, the Act 

provides no basis for applying different standards for delisting than 

those adopted for listing. If the Services do not consider entities for 

listing that are not primarily of conservation interest at a national 

level, they must also refrain from delisting or reclassifying units at 

this level. 

Complete Reproductive Isolation Should be Required as a Prerequisite to 

the Recognition of a Distinct Population Segment 

 The Services do not consider it appropriate to require absolute 

reproductive isolation as a prerequisite to recognizing a distinct 

population segment. This would be an impracticably stringent standard, 

and one that would not be satisfied even by some recognized species 

that are known to sustain a low frequency of interbreeding with related 

species. 

 The Services Should Emphasize Congress' Instruction to use Their 

Authority to Dddress DPS's ``Sparingly'' 

 The Services believe that application of the policy framework 

announced in this document will lead to consistent and sparing exercise 

of the authority to address DPS's, in accord with congressional 

instruction. 

The Occurrence of a Population Segment in an Unusual Setting Should not 

be Used as Evidence for its Significance 

 The Services continue to believe that occurrence in an unusual 

ecological setting is potentially an indication that a population 

segment represents a significant resource of the kind sought to be 
93 

conserved by the Act. In any actual case of a DPS recognized in part on 

this basis, the Services will describe in detail the nature of this 

significance when accepting a petition or proposing a rule. 

The Authority to Address DPS's Should be Extended to Plant and 

Invertebrate Species 

 The Services recognize the inconsistency of allowing only 

vertebrate species to be addressed at the level of DPS's, and the 

findings of the NRC committee also noted that such recognition would be 

appropriate for other species. Nevertheless, the Act is perfectly clear 

and unambiguous in limiting this authority. This policy acknowledges 

the specific limitations imposed by the Act on the definition of 

``species.'' 

The Services Should Stress Uniqueness and Irreplaceability of 

Ecological Functions in Recognizing DPS's 

 The Services consider the Act to be directed at maintenance of 

species and populations as elements of natural diversity. Consequently, 

the principal significance to be considered in a potential DPS will be 

the significance to the taxon to which it belongs. The respondent 

appears to be recommending that the Services consider the significance 

of a potential DPS to the community or ecosystem in which it occurs and 

the likelihood of another species filling its niche if it should be 

extirpated from a particular portion of its range. These are important 

considerations in general for the maintenance of healthy ecosystems, 

and they often coincide with conservation programs supported by the 

Act. Nevertheless, the Act is not intended to establish a comprehensive 

biodiversity conservation program, and it would be improper for the 

Services to recognize a potential DPS as significant and afford it the 

Act's substantive protections solely or primarily on these grounds. 

Congress did not Intend to Require That DPS's be Discrete. In a Similar 

Vein, Congress did not Require That a Potential DPS be Significant to 

be Considered Under the Act 

 With regard to the discreteness standard, the Services believe that 

logic demands a distinct population recognized under the Act be 

circumscribed in some way that distinguishes it from other 

representatives of its species. The standard established for 

discreteness is simply an attempt to allow an entity given DPS status 

under the Act to be adequately defined and described. If some level of 

discreteness were not required, it is difficult to imagine how the Act 

could be effectively administered or enforced. At the same time, the 

standard adopted does not require absolute separation of a DPS from 
94 

other members of its species, because this can rarely be demonstrated 

in nature for any population of organisms. The standard adopted is 

believed to allow entities recognized under the Act to be identified 

without requiring an unreasonably rigid test for distinctness. The 

requirement that a DPS be significant is intended to carry out the 

expressed congressional intent that this authority be exercised 

sparingly as well as to concentrate conservation efforts undertaken 

under the Act on avoiding important losses of genetic diversity. 

A Population Should Only be Required to be Discrete or Significant, but 

not Both, to be Recognized as a Distinct Population Segment 

 The measures of discreteness and significance serve decidedly 

different purposes in the policy, as explained above. The Services 

believe that both are necessary for a policy that is workable and that 

carries out congressional intent. The interests of conserving genetic 

diversity would not be well served by efforts directed at either welldefined but insignificant units or entities believed to be significant 

but around which boundaries cannot be recognized. 

Requiring That a DPS be Discrete Effectively Prevents the Loss of Such 

a Segment From Resulting in a Gap in the Distribution of a Species. 

Essentially, if Distinct Populations are Entirely Separate, the Loss of 

One Has Little Significance to the Others 

 If the standard for discreteness were very rigid or absolute, this 

could very well be true. However, the standard adopted allows for some 

limited interchange among population segments considered to be 

discrete, so that loss of an interstitial population could well have 

consequences for gene flow and demographic stability of a species as a 

whole. On the other hand, not only population segments whose loss would 

produce a gap in the range of a species can be recognized as 

significant, so that a nearly or completely isolated population segment 

could well be judged significant on other grounds and recognized as a 

distinct population segment. 

The Services Lack Authority to Address DPS's of Subspecies 

 The Services maintain that the authority to address DPS's extends 

to species in which subspecies are recognized, since anything included 

in the taxon of lower rank is also included in the higher ranking 

taxon. 
95 

[[Page 4725]] 

 The following principles will guide the Services' listing, 

delisting and reclassification of DPS's of vertebrate species. Any 

proposed or final rule affecting status determination for a DPS would 

clearly analyze the action in light of these guiding principles. 

Policy 

 Three elements are considered in a decision regarding the status of 

a possible DPS as endangered or threatened under the Act. These are 

applied similarly for addition to the lists of endangered and 

threatened wildlife and plants, reclassification, and removal from the 

lists: 

 1. Discreteness of the population segment in relation to the 

remainder of the species to which it belongs; 

 2. The significance of the population segment to the species to 

which it belongs; and 

 3. The population segment's conservation status in relation to the 

Act's standards for listing (i.e., is the population segment, when 

treated as if it were a species, endangered or threatened?). 

 Discreteness: A population segment of a vertebrate species may be 

considered discrete if it satisfies either one of the following 

conditions: 

 1. It is markedly separated from other populations of the same 

taxon as a consequence of physical, physiological, ecological, or 

behavioral factors. Quantitative measures of genetic or morphological 

discontinuity may provide evidence of this separation. 

 2. It is delimited by international governmental boundaries within 

which differences in control of exploitation, management of habitat, 

conservation status, or regulatory mechanisms exist that are 

significant in light of section 4(a)(1)(D) of the Act. 

 Significance: If a population segment is considered discrete under 

one or more of the above conditions, its biological and ecological 

significance will then be considered in light of Congressional guidance 

(see Senate Report 151, 96th Congress, 1st Session) that the authority 

to list DPS's be used `` * * * sparingly'' while encouraging the 

conservation of genetic diversity. In carrying out this examination, 

the Services will consider available scientific evidence of the 

discrete population segment's importance to the taxon to which it 

belongs. This consideration may include, but is not limited to, the 

following: 

 1. Persistence of the discrete population segment in an ecological 

setting unusual or unique for the taxon, 

 2. Evidence that loss of the discrete population segment would 

result in a significant gap in the range of a taxon, 
96 

 3. Evidence that the discrete population segment represents the 

only surviving natural occurrence of a taxon that may be more abundant 

elsewhere as an introduced population outside its historic range, or 

 4. Evidence that the discrete population segment differs markedly 

from other populations of the species in its genetic characteristics. 

 Because precise circumstances are likely to vary considerably from 

case to case, it is not possible to describe prospectively all the 

classes of information that might bear on the biological and ecological 

importance of a discrete population segment. 

 Status: If a population segment is discrete and significant (i.e., 

it is a distinct population segment) its evaluation for endangered or 

threatened status will be based on the Act's definitions of those terms 

and a review of the factors enumerated in section 4(a). It may be 

appropriate to assign different classifications to different DPS's of 

the same vertebrate taxon. 

Relationship to Other Activities 

 The Fish and Wildlife Service's Listing and Recovery Priority 

Guidelines (48 FR 43098; September 21, 1983) generally afford DPS's the 

same consideration as subspecies, but when a subspecies and a DPS have 

the same numerical priority, the subspecies receives higher priority 

for listing. The Services will continue to generally accord subspecies 

higher priority than DPS's. 

 Any DPS of a vertebrate taxon that was listed prior to 

implementation of this policy will be reevaluated on a case-by-case 

basis as recommendations are made to change the listing status for that 

distinct population segment. The appropriate application of the policy 

will also be considered in the 5-year reviews of the status of listed 

species required by section 4(c)(2) of the Act. 

Effects of Policy 

 This guides the evaluation of distinct vertebrate population 

segments for the purposes of listing, delisting, and reclassifying 

under the Act. The only direct effect of the policy is to accept or 

reject population segments for these purposes. More uniform treatment 

of DPS's will allow the Services, various other government agencies, 

private individuals and organizations, and other interested or 

concerned parties to better judge and concentrate their efforts toward 

the conservation of biological resources at risk of extinction. 

 Listing, delisting, or reclassifying distinct vertebrate population 

segments may allow the Services to protect and conserve species and the 

ecosystems upon which they depend before large-scale decline occurs 

that would necessitate listing a species or subspecies throughout its 

entire range. This may allow protection and recovery of declining 
97 

organisms in a more timely and less costly manner, and on a smaller 

scale than the more costly and extensive efforts that might be needed 

to recover an entire species or subspecies. The Services' ability to 

address local issues (without the need to list, recover, and consult 

rangewide) will result in a more effective program. 

 Author/Editor: The editors of this policy are Dr. John J. Fay of 

the Fish and Wildlife Service's Division of Endangered Species, 452 

ARLSQ, Washington, DC 20240 (703/358-2105) and Marta Nammack of the 

National Marine Fisheries Service's Endangered Species Division, 

1335 East-West Highway, Silver Spring, Maryland 20910 (301/713- 

2322). 

 Authority: The authority for this action is the Endangered 

Species Act of 1973, as amended (16 U.S.C. 1531 et seq.). 

 Dated: February 1, 1996. 

John G. Rogers, 

Acting Director, Fish and Wildlife Service. 

 Dated: February 1, 1996. 

Nancy Foster, 

Deputy Assistant Administrator for Fisheries, National Marine Fisheries 

Service. 

[FR Doc. 96-2639 Filed 2-6-96; 8:45 am] 

BILLING CODE 3510-22-P 
98 

Appendix 3c. Definition of population stock from the MMPA and the population 

identity segment of NMFS’ guidelines for assessing marine mammal stocks. 

MMPA definition (Section 3(11)):

The term “population stock” or “stock” means a group of marine mammals of the same 

species or smaller taxa in common spatial arrangement, that interbreed when mature. 

Excerpt from NMFS’ guidelines for assessing marine mammal stocks. This document is 

available at: http://www.nmfs.noaa.gov/pr/sars/

“Population stock” is the fundamental unit of legally-mandated conservation. The MMPA 

defines population stock as “a group of marine mammals of the same species or smaller 

taxa in a common spatial arrangement, that interbreed when mature.” To fully interpret 

this definition, it is necessary to consider the objectives of the MMPA. In Sec. 2 (Findings 

and Declaration of Policy) of the MMPA it is stated that “...species and populations stocks 

of marine mammals...should not be permitted to diminish beyond the point at which they 

cease to be a significant functioning element in the ecosystem of which they are a part, 

and, consistent with this major objective, they should not be permitted to diminish below 

their optimum sustainable population.” Further on in Sec. 2, it states “...the primary 

objective of their management should be to maintain the health and stability of the marine 

ecosystem. Whenever consistent with this primary objective, it should be the goal to obtain 

an optimum sustainable population keeping in mind the carrying capacity of the habitat.” 

Therefore, stocks must be identified in a manner that 

is consistent with these goals. For the purposes of management under the MMPA, a stock 

is recognized as being a management unit that identifies a demographically isolated 

biological population. It is recognized that in practice, identified stocks may fall short of 

this ideal because of a lack of information, or for other reasons. 

Many types of information can be used to identify stocks of a species: e.g., distribution and 

movements, population trends, morphological differences, differences in life history, 

genetic differences, contaminants and natural isotope loads, parasite differences, and 

oceanographic habitat differences. Different population responses (e.g., different trends in 

abundance) between geographic regions is also an indicator of stock structure, as 

populations with different trends are not strongly linked demographically. When different 

types of evidence are available to identify stock structure, the report must discuss 

inferences made from the different types of evidence and how these inferences were 

integrated to identify the stock. 

Evidence of morphological or genetic differences in animals from different geographic 

regions indicates that these populations are reproductively isolated. Reproductive 

isolation is proof of demographic isolation, and, thus, separate management is 

appropriate when such differences are found. Demographic isolation means that the 

population dynamics of the affected group is more a consequence of births and deaths 

within the group (internal dynamics) rather than immigration or emigration (external 

dynamics). Thus, the exchange of individuals between population stocks is not great 
99 

enough to prevent the depletion of one of the populations as a result of increased mortality 

or lower birth rates. 

Failure to detect differences, however, does not mean that populations are not 

demographically or reproductively isolated. Dispersal rates, though sufficiently high to 

homogenize morphological or genetic differences detectable between putative populations, 

may still be insufficient to deliver enough recruits from an unexploited population (source) 

to an adjacent exploited population (sink) so that the latter remains a functioning element 

of its ecosystem. Insufficient dispersal between populations where one bears the brunt of 

exploitation coupled with their inappropriate pooling for management could easily result 

in failure to meet MMPA objectives. For example, it is common to have human-caused 

mortality restricted to a portion of a species’ range. Such concentrated mortality (if of a 

large magnitude) could lead to population fragmentation, a reduction in range, or even 

the loss of undetected populations, and would only be mitigated by high immigration rates 

from adjacent areas. 

Therefore, careful consideration needs to be given to how stocks are identified. In 

particular, where mortality is greater than a PBR calculated from the abundance just 

within the oceanographic region where the human-caused mortality occurs, serious 

consideration should be given to identifying an appropriate management unit in this 

region. In the absence of adequate information on stock structure and fisheries mortality, 

a species’ range within an ocean should be divided into stocks that represent defensible 

management units. Examples of such management units include distinct oceanographic 

regions, semi-isolated habitat areas, and areas of higher density of the species that are 

separated by relatively lower density areas. Such areas have often been found to represent 

true biological stocks where sufficient information is available. In cases where there are 

large geographic areas from which data on stock structure of marine mammals are 

lacking, stock structure from other parts of the species’ range may be used to draw 

inferences as to the likely geographic size of stocks. There is no intent to identify stocks 

that are clearly too small to represent demographically isolated biological populations, 

but it is noted that for some species genetic and other biological information has 

confirmed the likely existence of stocks of relatively small spatial scale, such as within 

Puget Sound, WA, the Gulf of Maine, or Cook Inlet, AK. 

In trans-boundary situations where a stock's range spans international boundaries or the 

boundary of the U.S. Exclusive Economic Zone (EEZ), the best approach is to establish an 

international management agreement for the species. In the interim, if a stock is migratory 

and it is reasonable to do so, the fraction of time in U.S. waters should be noted, and the 

PBR for U.S. fisheries should be apportioned from the total PBR based on this fraction. In 

a non-migratory situation, the PBR for U.S. fisheries should be calculated based on the 

abundance estimate of the stock residing in U.S. waters. For situations where a species 

with a broad pelagic distribution which extends into international waters experiences 

mortalities within the U.S. EEZ, PBR calculations should be based on the abundance in 

the EEZ. If there is evidence for movement of individuals between the EEZ and offshore 

pelagic areas and there are estimates of mortality from US and other sources throughout 
100 

the stock’s range, then PBR calculations may be based upon a range-wide abundance 

estimate for the stock. 

Prospective Stocks 

When information becomes available that appears to justify a different stock structure or 

stock boundaries, it may be desirable to include the new structure or boundaries as 

“prospective stocks” within the existing report. The descriptions of prospective stocks 

would include a description of the evidence for the new stocks, calculations of the 

prospective PBR for each new stock, and estimates of human-caused mortality and serious 

injury, by source. The notice of availability of draft reports with prospective stocks would 

include a request for public comment and additional scientific information specifically 

addressing the prospective stock structure. Prospective stocks would be expected to 

become separate stocks in a timely manner unless additional evidence were produced to 

contradict the prospective stock structure. Summary information for prospective stocks 

should be included in the standard table in the SARs that summarizes Nmin, Rmax, etc. for 

each stock.