Report of the Workshop on 

Assessing the Population Viability of 

Endangered Marine Mammals 

in U.S. Waters

13–15 September 2005 

Savannah, Georgia

Prepared by the Marine Mammal Commission 

2007 

This is one of five reports prepared in response to a directive from Congress to the 

 Marine Mammal Commission to assess the cost-effectiveness of protection programs for the 

most endangered marine mammals in U.S. waters 

 

iii 

TABLE OF CONTENTS 

List of Tables ..................................................................................................................... iv 

Executive Summary.............................................................................................................v 

I. Introduction..............................................................................................................1 

II. Biological Viability..................................................................................................1 

III. Population Viability Analysis..................................................................................5 

IV. Viability of the Most Endangered Marine Mammals ..............................................6 

 Extinctions and recoveries .......................................................................................6 

 Assessment of biological viability...........................................................................7 

V. Improving Listing Decisions..................................................................................10 

 Quantifying the listing process ..............................................................................10 

 A theoretical decision tree for listing under the Endangered Species Act.............10 

VI. Improving Other Management Decisions..............................................................11 

VII. Acknowledgments..................................................................................................12 

VIII. Literature Cited ......................................................................................................12 

Appendix I. Examples of Existing Marine Mammal Population Models......................19 

North Atlantic Right Whales .....................................................................19 

Southern Resident Killer Whales...............................................................20 

Cook Inlet Beluga Whales .........................................................................21 

 Florida Manatees........................................................................................22 

Hawaiian Monk Seals ................................................................................24 

Steller Sea Lions — Western Stock...........................................................25 

Steller Sea Lions — Eastern Stock ............................................................26 

California Sea Otters..................................................................................27 

Appendix II. Workshop Attendees..................................................................................29 

Appendix III. Workshop Agenda .....................................................................................30 
LIST OF TABLES 

Table 1. Summary of the biological status of 22 marine mammal species and stocks 

currently listed as endangered or threatened under the Endangered Species Act or 

designated as depleted under the Marine Mammal Protection Act .............................15 

Table 2. Examples of wild populations that have recovered from extremely low 

 population sizes............................................................................................................16

Table 3. A theoretical decision tree and analytical recommendations for listings 

under the Endangered Species Act ..............................................................................18 

 

iv 
 

v 

EXECUTIVE SUMMARY 

Congress, in its 2004 Omnibus Appropriations Act, directed the Marine Mammal 

Commission to “review the biological viability of the most endangered marine mammal 

populations and make recommendations regarding the cost-effectiveness of current 

protection programs.” As part of its response to the directive, the Commission convened a 

workshop to examine the state of science regarding population viability analysis (PVA) for 

marine mammal populations. The workshop was held 13–15 September 2005 in Savannah, 

Georgia. Its goals were to (1) review estimates of the viability of the most endangered 

marine mammals, (2) review the status of ongoing modeling efforts, particularly PVA, for 

endangered marine mammals, and (3) develop recommendations to improve listing and 

management decisions based on explicit consideration and improved estimation of 

population extinction risk. 

The workshop focused on the 22 marine mammal taxa occurring in U.S. waters and either 

listed as threatened or endangered under the Endangered Species Act or designated as 

depleted under the Marine Mammal Protection Act. Participants agreed that, with two or 

possibly three exceptions, all those taxa—with appropriate management—appear to have 

the potential for persisting into the future. The first exception is the Caribbean monk seal, 

which has not been observed and documented since 1952 and is presumed to be extinct. 

The second is the AT1 stock of killer whales, which numbers fewer than 10 individuals, 

has not produced a single surviving calf for more than 20 years, and is highly unlikely to 

persist beyond the lifetimes of existing individuals. The possible third exception is the 

eastern population of North Pacific right whales, which has been a matter of concern 

based largely on the rarity of sightings, lack of information on the population, and its 

history of commercial exploitation. That concern has been tempered somewhat by recent 

evidence of successful reproduction (observations of cow-calf pairs). In addition to these 

obvious exceptions, the stock structure of many marine mammal species is poorly known, 

and participants noted that some additional stocks, yet to be identified, may be unlikely to 

persist into the future. For the taxa that were considered to be potentially viable, the 

available published analyses at the time of the workshop were not sufficient for a 

systematic and consistent quantification of their respective viabilities. The workshop 

identified methodological issues that need to be addressed to allow meaningful quantitative 

comparisons among viability estimates. 

Participants reviewed the current state of PVA for marine mammals and other wildlife. 

For candidate species or species that are already listed, the growing trend is to use PVA to 

support listing and management decisions. PVA provides a mechanism for integrating all 

relevant data into a quantitative assessment to produce an estimate of extinction risk over a 

defined period of time. Such analyses are more objective than the qualitative listing 

approaches used to date, more amenable to explicit inclusion of all relevant data, more 

transparent with respect to assumptions and uncertainties, more easily standardized, and 

more conducive to the kind of structured decision-making that is needed to improve listing 

and management of endangered, threatened, and depleted taxa. 
 

vi 

Participants also highlighted several common impediments to quantitative analyses for 

many marine mammal taxa. These include poor understanding of stock structure, 

insufficient biological data for recognized taxa, insufficient data for characterizing potential 

relationships between specific threats or management actions and population responses, 

and difficulty in predicting future threats and management actions that may affect their risk 

of extinction. Further, participants expressed a need for caution when using commercially 

available analytical software without proper documentation and without an understanding 

of the structure, function, and assumptions incorporated into the software. 

Participants generally agreed with the findings of the Quantitative Working Group 

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

(DeMaster et al. 2004) to develop quantitative criteria for listing decisions. Among other 

things, those findings included the need for (1) performance testing of models used in the 

listing process to determine the likelihood of correct vs. incorrect decisions, given the life 

histories of species involved and uncertainties in the data or analytical results, and (2) clear 

links between policy decisions and quantitative models, particularly with regard to 

interpreting the uncertainty reflected in model results. 

Finally, participants in the Savannah workshop considered and expressed support for a 

proposed decision tree incorporating simple PVAs to assess the status of poorly known 

taxa and guide listing decisions. The decision tree would use available data on the species 

of interest; default values where data are lacking; a structured, standardized, and simple 

analytical framework; and explicit guidelines for interpreting results. With appropriate 

development, the decision tree might be used to structure listing decisions in much the 

same manner as the potential biological removal concept is used to identify strategic stocks 

in the management of marine mammal/fishery interactions under the Marine Mammal 

Protection Act. 
 

1 

I. INTRODUCTION 

In its 2004 Omnibus Appropriations Act, Congress directed the Marine Mammal Commission to 

“review the biological viability of the most endangered marine mammal populations and make 

recommendations regarding the cost-effectiveness of current protection programs.” In response 

to the directive, the Commission reviewed systems for classifying species (Lowry et al. 2007), 

reviewed current protection programs (Weber and Laist 2007), conducted a case study of the 

North Atlantic right whale recovery program to examine the issue of cost-effectiveness in depth 

(Reeves et al. 2007), and held a workshop on the state and utility of population viability analysis 

(PVA) in the management of marine mammal populations. 

The population viability workshop was held 13–15 September 2005 in Savannah, Georgia. Its 

goals were to (1) review estimates of the viability of the most endangered marine mammals, (2) 

review the status of ongoing modeling efforts, particularly PVAs, for endangered marine 

mammals, and (3) develop recommendations to improve listing and management decisions based 

on explicit consideration and improved estimation of extinction risk. This report summarizes the 

discussions and findings of the workshop. 

II. BIOLOGICAL VIABILITY 

For the purposes of this report, we define biological viability (or simply viability) to mean the 

potential to persist far into the future with appropriate management of human-related threats. 

Although species are often characterized as either viable or not viable (implying a high or low 

potential for such persistence), there is a meaningful intermediate area between these two 

extremes. The transition from viable to not viable has been the subject of extensive research 

aimed at identifying the “minimum viable population.” This term was based on the idea that a 

declining population would reach a predictable point at which factors driving it toward extinction 

would dominate and recovery would be impossible or highly unlikely. This concept has been 

largely abandoned in the face of a growing body of contrary, empirical data illustrating that 

viability is generally a function of multiple natural and anthropogenic influences, the transition 

from viable to nonviable is dependant on species and circumstances, and a threshold for such 

transition that can be applied generally across taxa is not readily and reliably predicted. 

Practically speaking, the viability of marine mammal taxa can be categorized as follows: 

• Taxa that are extinct. These are taxa that have zero potential of persisting, as exemplified 

by the Steller’s sea cow. 

• Taxa that are almost certain to become extinct in the near future. The persistence of such 

taxa is highly improbable and there is little or no hope that they will continue to persist or 

can be saved, irrespective of human efforts. The AT1 stock of killer whales appears to 

fall into this category. 
 

2 

 

• Taxa with the potential to persist far into the future, but that may require the extra 

protections provided for threatened or endangered species on an ongoing basis. The 

Hawaiian monk seal may be one such species. 

• Taxa with the potential to recover fully but that require extra protections until they have 

done so. Most listed species fit this category. 

• Taxa that have recovered. The eastern North Pacific population of gray whales is the best 

example of this category. 

The primary distinguishing elements of these categories are (1) a taxon’s inherent potential for 

recovery and persistence, and (2) its dependence on human intervention (e.g., management 

actions and policy decisions) to address threats. These two elements are becoming more 

entwined as the effects of human activities become more nearly ubiquitous (e.g., climate change) 

and the boundary between anthropogenic and natural risk factors becomes less distinguishable 

(e.g., climate change). As a rule, scientists conducting PVAs have not made this distinction but 

rather have estimated population viability as a function of the list of known risk factors, both 

natural and anthropogenic, that may influence a population’s persistence. The primary outcome 

of a PVA is a measure of the population’s probability of extinction over a set period1

 based on 

the projected effects of such risk factors. Thus, a PVA is an approach to risk analysis that 

attempts to predict the probability of extinction based on available data. Except in rare situations 

that are usually apparent even without modeling, its results generally do not provide definitive 

answers as to when a species is no longer viable. For example, results of a PVA indicating that a 

population is declining toward extinction may be due to anthropogenic factors unrelated to its 

intrinsic ability to reproduce and grow. If those factors can be identified and addressed by 

effective management action, the population’s decline could be reversed to allow recovery. Thus, 

a predicted declining trend may simply underscore the urgent need for management attention. A 

review of the taxa considered in this report indicates that they have all been influenced in a 

significant manner by human activities. 

Factors affecting population viability generally fall into three categories. The first includes 

features of the population itself (e.g., abundance, age/sex structure, distribution, life history 

characteristics such as reproductive and survival rates). The viability of a marine mammal 

population may be a particular concern if, for example, it contains only a limited number of 

reproductive females (for example, the AT1 stock of killer whales includes only two or three 

females of reproductive age). The second category includes factors that are a function of the 

population’s environment or ecology (e.g., availability of prey, abundance of predators, exposure 

to disease, variation in the physical parameters of the environment). Small populations 

1

 PVAs often indicate the risk that a population will reach some specific, small number other than zero, called a “quasiextinction” threshold. Such thresholds are generally based on the assumption that extinction is virtually certain at or below the 

chosen level. They are required for demographic models that describe animal abundance using real numbers (rather than integers)

that may approach zero exponentially but never actually reach that level. Quasi-extinction thresholds are often used when 

modeling marine mammal populations because actual extinction may be delayed beyond the time period modeled, even for 

rapidly declining populations, if individual animals are relatively long-lived. Some authors have interpreted the quasi-extinction 

threshold to represent the lip of an extinction vortex (an interaction of risk factors creating adverse feedback loops that hasten a 

population toward extinction), but this interpretation is often difficult to demonstrate and justify. 
 

3 

 

occupying limited areas may be especially vulnerable to catastrophes. For example, Florida 

manatees, which tend to have clustered distributions in shallow waters, are vulnerable to toxic 

effects of periodic red tides. The third category includes factors that are a function of human 

activities (e.g., habitat destruction, competition for prey, disturbance, contaminants). Human 

activities, particularly exploitation, likely played a decisive role in the extinction of the Steller 

sea cow, Caribbean monk seal, Japanese sea lion, and North Atlantic gray whale, and have 

placed many other marine mammal taxa at risk of extinction (e.g., right whales). 

Small populations also are especially vulnerable to the following sources of variability (also 

called stochasticity). 

Genetic Variability—Two major concerns for small populations are (1) whether they contain 

sufficient genetic diversity to persist in the face of changing environmental conditions, and (2) 

whether mating between a limited number of breeding individuals will lead to the expression of 

deleterious genes affecting reproduction or survival (hence, population growth rate) because of 

inbreeding or genetic drift (i.e., random fluctuations in gene frequency). Although the former 

concern is often related to a species’ ability to adapt to change over long periods of time (i.e., 

evolutionary time frame), the rapid pace of climate change illustrates that this concern also is 

relevant to short-term changes (i.e., ecological time frame). As a general rule, genetic diversity 

decreases with decreasing population size. Smaller populations are therefore less likely to 

contain sufficient genetic variation to persist in the face of selection imposed by significant 

environmental change. With regard to inbreeding, matings in small populations are more likely 

to be between related individuals, which increases the probability that deleterious recessive 

genes will be expressed in their offspring. The probability of such events also is influenced by 

the species’ mating pattern. For example, inbreeding effects are more likely in polygamous than 

in monogamous species. Even in the absence of inbreeding, genetic drift in small populations can 

result in the expression of genetic defects. The effects of genetic drift and inbreeding depression 

may not be expressed for several to many generations, with the time frame depending on 

population size, the initial genetic diversity, the frequency of deleterious genes, and the 

reproductive strategy. Thus, their adverse consequences are more likely to manifest themselves 

in populations that are held at low abundance for long periods of time or that are repeatedly 

reduced to small size. 

Demographic Variability—Demographic variability is the result of random variations in 

biological processes or parameters, such as survival, reproduction, or sex ratio at birth. If the fate 

of each individual in a population is subject to the same probability, the resulting variation will 

be a function of population size. That is, as the size of a population shrinks, the likelihood that it 

will deviate from the expected norm for that process or parameter will increase. For example, if 

the expected sex ratio at birth is 50 percent females and 50 percent males, a substantial deviation 

from that sex ratio is more likely to occur in a small population than in a larger one2

. For 

depleted marine mammal populations, having more females generally is beneficial because of 

their role in reproduction, whereas a relative increase in males generally is detrimental. The 

2

 Similarly, significant deviation from the expected 50:50 heads to tails ratio is more likely to occur if you flip a coin a few times 

versus many times. 
 

4 

actual consequences of such deviations depend on the population’s composition and social 

structure, including its reproductive strategy, but they become more likely to affect the long-term 

persistence of a population as its abundance declines. 

Environmental Variability—Environmental variability can alter population demographics by 

changing prey abundance, weather or oceanographic conditions, or abundances of predators. All 

individuals in a population may be affected, whether the population is large or small. Populations 

that occupy large areas may be exposed to a range of environmental conditions and thus may 

experience a degree of buffering from poor conditions in portions of the range. Small 

populations are more likely to occupy smaller areas where environmental conditions tend to be 

more homogeneous and, therefore, such populations may be more vulnerable to unfavorable 

circumstances. Metapopulations (collections of related subpopulations) may be buffered against 

such circumstances if animals are dispersed among subpopulations experiencing different 

environmental conditions. 

Catastrophic Variability—Catastrophic variability has been considered by some to be an 

extreme form of environmental variability and by others to be a separate type of risk factor 

because its nature and spatial-temporal patterns (e.g., hurricanes, tsunamis) are inconsistent with 

those of environmental variability. Here too, the problem for small populations is that all or some 

large percentage of the individuals in the population may be exposed to the effects of the same 

catastrophic event if their distribution is limited relative to the distribution of the event. 

Metapopulation structure and broad distribution enhance resilience to catastrophic variation. 

Allee Effects—Population parameters also vary as a function of animal density. As the number of 

individuals in a population declines, the potential for population growth may increase because of 

reduced competition for prey, habitat, or other resources. However, at very low levels, 

populations also may experience accelerating declines in reproductive or survival rates due to socalled Allee effects. For example, if animals are sparsely distributed, adult females may be 

unable to find mating partners. Similarly, strategies for foraging, predator avoidance, and rearing 

young may be impaired in very small populations if those behaviors depend on the cooperation 

or participation of multiple individuals. Allee effects and other risk factors may combine either 

additively or synergistically to create cumulative effects that, ultimately, determine the 

population’s risk of extinction. Such interactions may create negative feedback loops that hasten 

decline toward extinction, a phenomenon referred to as an extinction vortex. 

Population Structure—Finally, assessment of the risk factors discussed here is confounded by 

insufficient information on population (or stock) structure. The conservation and management 

frameworks established by the Endangered Species Act, the Marine Mammal Protection Act, and 

related statutes are predicated on scientists being able to identify appropriate units to conserve. 

As indicated earlier, stock structure is poorly understood for many marine mammal species 

despite recent progress using molecular genetics techniques. The failure to recognize distinct 
 

5 

 

population segments3 or population stocks increases risk if, for any number of reasons, some are 

more vulnerable than others to the above-described risk factors and they are managed in a 

manner that does not recognize and adjust for that vulnerability. The identification and 

characterization of population structure are essential for accurate assessment of population 

viability. Therefore, this subject warrants continued scientific investigation. 

III. POPULATION VIABILITY ANALYSIS 

To support and improve listing and management decisions for taxa that are either candidate 

species or are already listed as endangered or threatened, the growing trend is toward more 

structured, objective decision-making using the best available quantitative tools to determine risk 

of extinction. All of the early marine mammal listings involved species that were reduced to low 

levels by human exploitation (usually commercial hunting) and ineffective or non-existent 

management. Those listing decisions required expert judgment and a degree of qualitative 

assessment. Even the best information available at that time was subject to important limitations. 

Abundance, for example, is clearly an important consideration with regard to the risk of 

extinction. However, it has subsequently become clear that abundance is only one indicator of 

extinction risk, and an imperfect one at that. Some small populations may have a low probability 

of extinction because of favorable environmental conditions and an absence of significant 

threats, whereas some large populations may have a high probability of extinction because of 

poor environmental conditions and significant threats. As noted above, the risk of extinction also 

is a function of a potentially wide range of factors, including those related to the taxon itself, its 

environment, and the threats posed by human activities. 

PVAs provide a means for integrating many kinds of information to produce robust indicators of 

extinction risk. Such analyses vary in form as a function of the population under consideration, 

its life history traits, the nature and amount of data available on its biology and population 

dynamics, the nature and amount of data available on factors that may affect its risk of extinction 

(e.g., threats), and the modeler’s technical (i.e., mathematical) preferences. When feasible, such 

analyses incorporate the types of variation described earlier, usually by representing variables as 

distributions of possible values and running multiple analyses drawing randomly from those 

values to estimate the range of possible outcomes and their probability. The results can be used 

for a number of purposes, including informing listing processes under the Endangered Species 

Act and Marine Mammal Protection Act, evaluating the effects of past management actions, and 

predicting the effects of proposed actions. 

At the workshop, participants discussed existing PVA models or similar quantitative analyses for 

California sea otters, Cook Inlet beluga whales, Florida manatees, Hawaiian monk seals, North 

3

 In 1996 the National Marine Fisheries Service and the Fish and Wildlife Service finalized a policy statement interpreting the 

Endangered Species Act term “distinct population segment” to mean a population that is (1) discrete from the remainder of the 

species (e.g., markedly separate), (2) significant to the species (e.g., its loss could cause a major gap in the range or includes 

unique genetic characteristics), and (3) threatened or endangered based on the Act’s five listing factors. Use of the term in this 

report is intended to be consistent with that interpretation. 
 

6 

 

Atlantic right whales, southern resident killer whales, and the eastern and western stocks of 

Steller sea lions (Appendix 1). Several of the models had been used to inform listing decisions, 

but the others were not used for that purpose because they were created after listing had already 

occurred. These latter models were created for other purposes and varied in their objectives, 

model parameters, and complexity. In all cases the models were constrained to varying degrees 

by limited information pertaining to biology (e.g., reproductive and survival rates), cause-andeffect relationships between specific threats or management actions and population responses, 

and factors likely to determine the nature and extent of future threats. Given limitations in 

available data, scientists developing each of the models were required to make certain 

simplifying assumptions (e.g., homogeneity in vital rates over space or time, relevant risk 

factors). As is generally the case in science, the assumptions warrant further consideration and 

testing. However, an important characteristic of these models (and of PVA models in general) is 

that all such assumptions are made explicit, and therefore the potential implications of erroneous 

assumptions can be directly evaluated using sensitivity analyses. Moreover, as new information 

becomes available, the data used in the models can be updated, the model processes refined, and 

the validity of simplifying assumptions re-evaluated, all of which will result in more robust and 

reliable model results. Thus, PVA is an evolving process, open to review and subject to 

improvement as new information and insights become available. 

IV. VIABILITY OF THE MOST ENDANGERED MARINE MAMMALS

To assess the biological viability of the most endangered marine mammals, the workshop 

focused on the 22 species and stocks occurring in U.S. waters and listed as endangered or 

threatened under the Endangered Species Act or designated as depleted under the Marine 

Mammal Protection Act (Table 1). Some other marine mammal species (e.g., the Yangtze River 

dolphin or baiji4

) may be equally or more endangered but were not discussed in detail at the 

workshop or included in this report because they do not occur in U.S. waters or have not been 

listed. A wide variety of taxa, including marine mammals and other species, either have been 

rendered extinct or have been brought near to extinction before rebounding. Those cases also 

provide useful insights regarding the question of species viability. 

Extinctions and recoveries 

Human activities have caused the extinction of at least four marine mammal taxa. The northern 

(Steller’s) sea cow inhabited kelp-forested coastlines of the Bering Sea until the second half of 

the 18th century, when it was driven extinct by commercial seal and sea otter hunters who 

hunted sea cows for food (Stejneger 1887, Forsten and Youngman 1982). The last reliable 

sighting of a Caribbean (West Indian) monk seal was in 1952 (Kenyon 1977); this species also 

was a victim of uncontrolled hunting, disturbance, and habitat destruction. The Japanese sea lion 

was last sighted and documented in 1951 and is listed as extinct by IUCN–The World 

4

 During the preparation of this report, an international team of marine mammal scientists conducted an extensive survey of the 

Yangtze River and failed to detect a single baiji. 
 

7 

Conservation Union (IUCN). It was exploited for various purposes and persecuted because it was 

perceived as a competitor of fisheries. The North Atlantic population of gray whales vanished by 

the 18th century, and whaling almost certainly was a contributing, if not decisive, factor in its 

demise. 

A number of other marine mammal taxa have been brought near to extinction and then 

recovered, at least partially, following protection from the main threat, which almost always has 

been deliberate exploitation (Table 2). Many populations of fur seals (Arctocephalus spp.), 

elephant seals (Mirounga spp.), sea otters, and baleen whales were harvested to the point where 

hunting for them was no longer profitable. In a few cases (e.g., Guadalupe fur seal), numbers 

were so low that a species or population was considered extinct, only to be discovered again and 

to recover under protection. These examples (and examples from other taxonomic groups, Table 

2) demonstrate the potential resilience and viability of wild species and populations, even when 

reduced to low population size. 

Assessment of biological viability 

PVAs have not been completed for most of the 22 taxa considered at the workshop because of 

insufficient information or lack of a standard for conducting such analyses on data-poor species. 

The general opinion of workshop participants was that all but 2 or possibly 3 of the 22 listed 

marine mammal taxa are potentially viable if human-related threats are effectively managed. The 

Caribbean monk seal probably is extinct, and the AT1 stock of killer whales does not appear to 

be biologically viable, regardless of recovery efforts. The viability of the eastern population of 

North Pacific right whales has been a matter of concern based on its history of exploitation, 

rarity of sightings, and lack of biological information on the population. 

The discussion of viability for the remaining taxa was based primarily on PVAs or a combination 

of expert opinion and varying amounts of quantitative information. Of the eight taxa for which 

quantitative biological analyses had been conducted, three (Florida manatee, eastern population 

of Steller sea lions, and southern sea otter) have experienced positive growth in recent years, 

although growth rates have been difficult to characterize (Florida manatee) or slower than 

expected (southern sea otter, eastern population of Steller sea lions). Thus, each of these three 

taxa is reasonably considered biologically viable although the persistence of at least two of them 

likely will continue to depend on rigorous, effective management of known threats (i.e., disease, 

contaminants, and fisheries for the southern sea otter and boat strikes and loss of warm-water 

refuges for the Florida manatee). 

The Hawaiian monk seal is now declining at about 4 to 5 percent per year, and its total 

population size in 2005 was estimated at 1,250 to 1,300. The species consists of seven 

reproductively isolated subpopulations including one in the main Hawaiian Islands and six in the 

remote Northwestern Hawaiian Islands. The subpopulations are subject to a range of threats 

(e.g., reduced prey availability, entanglement, shark predation, male aggression, disease). 

Although monk seals benefit from a robust research program that helps direct a growing 
 

8 

management effort and although some sweeping protection and conservation measures have 

been implemented recently, the species clearly is at risk of extinction. Rigorous, effective 

management of human-related threats is essential to its conservation. The species has persisted 

for 12 to 15 million years in approximately the same geographic range, and there is no reason to 

believe that it cannot continue to persist far into the future as long as human-related threats are 

managed effectively. 

The western population of Steller sea lions has declined by about 80 percent in the past three 

decades, and much of the decline has yet to be explained. Contributing causes may include 

natural changes in environmental conditions leading to a reduction in prey, predation by killer 

whales that lost a preferred prey source because of commercial whaling, deliberate or incidental 

killing in connection with fisheries, and competition for prey with large-scale commercial fishing 

that rapidly expanded in the region in the 1960s and early 1970s. The most recent abundance 

estimate is about 38,000 animals, and recent counts suggest that the population may have 

stabilized. Although there is still cause for concern regarding the future of this population and 

much remains to be learned about the importance of various risk factors, there is no basis for 

concluding that the population is incapable of persisting if human-related threats are managed 

effectively. 

The number of North Atlantic right whales was reduced by commercial whaling prior to the 

1940s and currently numbers about 300 to 350 whales. This population’s estimated rate of 

increase was positive in the 1980s but apparently declined in the 1990s due to mortality from 

ship strikes and entanglement in fishing gear. The population appears capable of maintaining a 

positive population growth rate if human-related threats are controlled, and therefore it appears 

to be viable. 

The southern resident stock of killer whales occurring each summer in the Puget Sound area has 

been subject to a range of human-related threats. A relatively large portion of the population was 

captured in the 1960s and early 1970s to supply animal-display facilities. Prior to that, the 

animals were subject to unregulated shooting and harassment (Hoyt 1981). In recent years, the 

stock has been subject to three primary threats: loss of prey (primarily chinook salmon) 

secondary to loss of salmon habitat and fishing, exposure to contaminants, and noise and 

disturbance due to watercraft traffic, including whale-watching vessels. Abundance of the stock 

under pristine conditions is unknown although it is likely to have been in the low hundreds. 

Although the elevated risk of extinction for this stock is a matter of significant concern, there is 

no basis for concluding that its low numbers and recent decline are due to an inherent lack of 

biological viability, particularly in view of the multiple human-related threats to which the stock 

is exposed. 

Abundance of the Cook Inlet beluga whale was reduced sharply in the 1990s by Alaska Native 

subsistence harvests. The harvest was restricted in the late 1990s, but trend analysis of 

abundance estimates from 1994 through 2006 indicates a statistically significant decline. 

Research is urgently needed to identify the causes for continued decline after the harvest was 
 

9 

brought under control. A number of natural and anthropogenic factors could be contributing to 

the continued decline. There is no basis for concluding that the population has lost the potential 

to recover, but it is clear that its recovery potential is eroding rapidly and the population is in 

great need of rigorous, effective management to identify and address the factors perpetuating the 

decline. 

PVAs have not been conducted or were not discussed at the workshop for the remaining 12 taxa 

considered. The bowhead whale, fin whale, humpback whale, sperm whale, mid-Atlantic stock 

of bottlenose dolphins, Guadalupe fur seal, northern fur seal, and southwest Alaska stock of 

northern sea otters all are either known to be increasing or number at least 10,000 animals, and 

there is no basis for concluding that any of them has lost the potential to recover and persist. 

Blue and sei whale population structure and abundance are not well known. The National Marine 

Fisheries Service recognizes eastern and western North Pacific blue whale stocks and a North 

Atlantic stock. The eastern North Pacific stock, the only one for which an abundance estimate is 

available, consists of about 3,000 animals and may be increasing. It is therefore reasonably 

considered to be viable. The status of the other two blue whale stocks that occur in U.S. waters is 

not known, although the general sense of workshop participants was that they are capable of 

persisting if human threats are effectively managed. There are no current, reliable estimates of 

sei whale abundance in the North Pacific and North Atlantic Oceans. The sei whale estimate of 

>133 in Table 1 represents a combined minimum estimate for the eastern North Pacific and 

Hawaii stocks, but likely it is strongly and negatively biased. Better estimates of sei whale 

abundance are clearly needed and will provide a better basis for judging the viability of sei whale 

stocks. The Antillean subspecies of West Indian manatee occurred historically over a relatively 

large range in coastal areas of Central and South America and around islands in the Caribbean 

Sea. Manatees are now rare in the U.S. Virgin Islands, and the most recent (1994) count in 

Puerto Rico suggested a minimum of 86 animals. As the Antillean manatee is threatened in U.S. 

waters mainly by boat strikes and entanglement in fishing nets, the primary recovery challenge 

appears to be controlling those human-related threats. Any further decline in numbers would 

erode the potential for recovery of the manatee populations in Puerto Rico and the Virgin 

Islands. Outside U.S. waters, deliberate killing also poses a significant risk and undermines the 

potential for recovery. Finally, the viability of the eastern population of North Pacific right 

whales is a significant concern. Since the mid-1990s only 23 individuals have been identified, 

including three cow-calf pairs. It is unlikely that the identified animals represent the entire 

population, but it also seems unlikely that there are a great many more than that number. 

Whether 23—or even 25 to 50—individuals would be sufficient for recovery is unclear. 

However, populations of other mammal species have recovered from such low numbers (e.g., 

northern elephant seals, southern sea otters) so there is a basis for hoping that this population is 

still capable of recovery. 
 

10 

V. IMPROVING LISTING DECISIONS

Two efforts to improve listing decisions were discussed at the workshop, one undertaken by the 

National Marine Fisheries Service and the Fish and Wildlife Service, and one proposed by Dr. 

Daniel Goodman. Those efforts are summarized briefly below. 

Quantifying the listing process 

In 2004 the National Marine Fisheries Service and Fish and Wildlife Service convened a 

Quantitative Working Group to evaluate listing decisions under the Endangered Species Act and 

develop procedures that would be “more transparent, consistent, and scientifically and legally 

defensible.” The working group identified several conceptual models for listing purposes, all of 

which are directly or indirectly related to risk of extinction (DeMaster et al. 2004). 

The working group noted that implementation of these approaches would require explicit policy 

input. Specifically, policy guidance must be provided regarding the degree to which errors in the 

listing process are acceptable if they result in over-protection (i.e., listing species that, in fact, are 

not endangered or likely to become so in the foreseeable future) versus under-protection (i.e., 

failing to list species that, in fact, are endangered or likely to become so). The extent to which 

the process should be precautionary (i.e., favor over-protection) also would require specification. 

In many cases, the Fish and Wildlife Service and National Marine Fisheries Service must make 

listing decisions for species with very limited information on either population status or threats. 

The working group recommended that in those cases quantitative proxies, or “alternative 

decision metrics,” be developed (e.g., a 95 percent decline in abundance could serve as a proxy 

for an unacceptable probability of extinction). Both listing standards and proxies should be tested 

to determine the likelihood of correct versus incorrect listing decisions, given the life history of a 

species and uncertainty in the data or analytical results. The working group has initiated such 

performance testing for a suite of potential listing standards and proxies. An additional option 

recommended for consideration by the working group is a threshold approach similar to that used 

by a number of other organizations including IUCN in its Red List of Threatened Species, parties 

to the Convention on International Trade in Endangered Species of Wild Fauna and Flora for 

listing species on its appendices, and the Committee on the Status of Endangered Wildlife in 

Canada for listing species under the Canadian Species at Risk Act. 

A theoretical decision tree for listing under the Endangered Species Act 

Participants at the Commission’s PVA workshop also considered a theoretical decision-making 

framework for listing decisions proposed by Dr. Goodman. The framework was developed to 

simplify and standardize listing decisions using quantitative tools and criteria, better document 

the decision-making process, provide default assessment methods for data-poor taxa, and guide 

the use of limited resources to develop more reliable assessments. The suggested framework is 

designed to classify “at-risk” populations into four categories based on their population dynamics 
 

11 

and then use category-specific quantitative modeling approaches to assess a population’s 

viability and determine whether the population should be listed based on defined decision rules. 

The four suggested categories are (1) populations that are too small, (2) populations that are 

nearly too small, (3) populations that are large but declining, and (4) populations that are large 

but have volatile population dynamics (Table 3). For each category, standards would be 

established for classifying species as threatened or endangered. 

Several technical and scientific issues would have to be addressed before such a framework 

could be used. The framework would have to include options for taxa with known threats but 

little or no population data. Also, the term “too small” would have to be defined, and quantitative 

assessment methods for each category would need to be developed and tested. Those methods 

would require some flexibility to take into account different life history types (e.g., long-lived 

versus short-lived species or species with low versus high reproductive rates). Although some atrisk marine mammals may fit less cleanly than others into these four categories, an explicit 

decision tree framework with specific categories and corresponding quantitative assessments 

would enhance the objectivity and consistency of the listing process for data-poor taxa. For that 

reason, workshop participants favored the development of such a framework. With appropriate 

development, the decision tree might help structure listing decisions in much the same manner as 

the potential biological removal concept has structured the management of incidental take of 

marine mammals in commercial fisheries under the Marine Mammal Protection Act. 

VI. IMPROVING OTHER MANAGEMENT DECISIONS

In addition to listing decisions under the Endangered Species Act, decisions regarding a range of 

marine mammal management actions are based on qualitative assessments of limited quantitative 

data on population status, trends, and threats. The underlying analyses often are not explicit with 

regard to assumptions and uncertainties, and therefore they can seem subjective and arbitrary. 

This problem can be addressed, at least in part, by making the decision-making process more 

explicit, objective, and quantitative. For example, when deciding among management actions, 

quantitative models can be used to analyze or predict their alternative effects, thereby informing 

the decision-making process. Such models also can provide a mechanism to evaluate the 

significance of assumptions and uncertainty inevitably associated with management decisions. In 

addition, they may help identify factors likely to affect population recovery and help characterize 

the nature and significance of the likely effects. All of these benefits—if communicated 

effectively between scientists and managers—would result in a more structured and 

comprehensive process for making management decisions. 

Recently both the Fish and Wildlife Service and the National Marine Fisheries Service have 

increased their use of explicit, quantitative models to inform management decisions. In part, this 

increase is related to requirements for “objective, measurable” recovery criteria in recovery plans 

prepared under the Endangered Species Act. Quantitative models can be and have been used to 

assess relative risks from various threats and relative benefits of alternative management 
 

12 

strategies in the recovery planning process. They also have been used in section 7 consultations 

under the Endangered Species Act to assess the effects of incidental takes of individuals from 

species or populations listed as endangered or threatened. 

Many PVA analyses have been conducted using VORTEX (Bob Lacy, Department of 

Conservation Biology, Chicago Zoological Society) or other standardized software. Although 

such software can be very useful for heuristic purposes (e.g., exploring the dynamics of different 

populations and the effects of different management actions), workshop participants expressed 

concern that it may be used without adequate understanding of the actual structure, function, and 

assumptions incorporated into the software model. Such uninformed use may result in 

misunderstanding of population status and risk of extinction. Although participants did not 

necessarily suggest that complex models should be created from first principles for each analysis, 

they did suggest that analyses using standardized software should be conducted with a thorough 

understanding of their limitations and assumptions. All the case studies presented at the 

workshop and reviewed here were customized models specifically tailored to the circumstances 

of the population and the nature of the available data. 

VII. ACKNOWLEDGMENTS 

The Marine Mammal Commission thanks all those who participated in, or provided support for, 

the workshop. The Commission is especially grateful to the presenters and panel members who 

led many of the discussions. A steering committee of experts directed the Commission’s 

response to the Congressional directive, including this workshop. Its members were David 

Cottingham, Deborah Crouse, Daniel Goodman, Lloyd Lowry, Linda Manning, Randall Reeves, 

Michael Simpkins, and Phil Williams. David Laist managed various components of the 

Commission’s response, and Michael Simpkins and Timothy Ragen collaborated on preparation 

of the workshop report. SRA International, particularly Linda Manning and Regan Maund, 

provided expert assistance in planning and facilitating the workshop and also helped with 

drafting of this report. Elizabeth Taylor, a 2005 Knauss Sea Grant Fellow at the Commission, 

also contributed substantially in organizing the workshop and drafting early versions of this 

report. Jeff Benoit from SRA International and Suzanne Montgomery provided editorial 

assistance for later revisions. Katherine Ralls helped with the development of Table 2. 

VIII. LITERATURE CITED 

Baker, S. C., and P. J. Clapham. 2004. Modeling the past and future of whales and whaling. 

Trends in Ecology and Evolution 19(7):365–371.

Bartholomew, G. A., and C. L. Hubbs. 1960. Population growth and seasonal movements of the 

northern elephant seal, Mirounga angustirostris. Mammalia 24:313–324. 
 

13 

Canadian Wildlife Service and U.S. Fish and Wildlife Service (CWS and FWS). 2005. Draft 

international recovery plan for the whooping crane. Recovery of Nationally Endangered 

Wildlife (RENEW), Ottawa, and U.S. Fish and Wildlife Service, Albuquerque, NM. 

DeMaster, D., R. Angliss, J. Cochrane, P. Mace, R. Merrick, M. Miller, S. Rumsey, B. Taylor, 

G. Thompson, and R. Waples. 2004. Recommendations to NOAA Fisheries: ESA listing 

criteria by the Quantitative Working Group, 10 June 2004. U.S. Dep. Commerce, NOAA 

Tech. Memo. NMFS-F/SPO-67. 

Forsten, A., and P. M. Youngman. 1982. Hydrodamalis gigas. Mammalian Species. No. 165. 

American Society of Mammalogists. 3 pp. 

Gallo, J. P. 1994. Factors affecting the population status of Guadalupe fur seal, Arctocephalus 

townsendi (Merriam, 1897), at Isla de Guadalupe, Baja California, Mexico. Ph.D. Thesis, 

University of California, Santa Cruz. 

Hoyt, E. 1981. Orca the whale called killer. Firefly Books, Ltd. Altona, Manitoba, Canada. 291 

pp. 

Hubbs, C. L. 1956. Back from oblivion, Guadalupe fur seal: still a living species. Pacific 

Discovery 9(6):14–21. 

Hubbs, C. L., and K. S. Norris. 1971. Original teeming abundance, supposed extinction, and 

survival of the Juan Fernández fur seal. Antarctic Research Series 18:35–51. 

Kenyon, K. W. 1977. Caribbean monk seal extinct. Journal of Mammalogy 58(1):97–98. 

Lowry, L., D. Laist, and E. Taylor. 2007. Endangered, threatened, and depleted marine mammals 

in U.S. waters: a review of species classification systems and listed species. Marine 

Mammal Commission, Bethesda, MD. 

McCullough, D. R., J. K. Fischer, and J. D. Ballou. 1996. From bottleneck to metapopulation: 

recovery of the Tule elk in California. Pages 375–403 in Metapopulations and Wildlife 

Conservation (D. R. McCullough, ed.). Island Press. 

National Park Service (NPS). 1998. Tule elk, the return of a species. Point Reyes National 

Seashore, CA. 

New Zealand Department of Conservation (NZ DOC). 2001. Black robin recovery plan, 2001–

2011. Department of Conservation, Wellington, New Zealand. 

Pucek, Z. 2004. Status survey and conservation action plan, European bison. IUCN–The World 

Conservation Union. 

Reeves, R. R., A. Read, D. Boness, L. Lowry, and S. K. Katona. 2007. Report of the North 

Atlantic right whale program review, 13–17 March 2006, Woods Hole, Massachusetts. 

Marine Mammal Commission. Bethesda, MD. 

Riedman, M. L., and J. A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology, and 

natural history. Biological Report 14. U.S. Fish and Wildlife Service, Department of the 

Interior. Washington, D.C. 126 pp. 

Soule, M. E. 1986. Conservation Biology, the Science of Scarcity and Diversity. Sinauer 

Associates, Inc. Sunderland, MA. 

Stejneger, L. 1887. How the great northern sea-cow (Rytina) became exterminated. American 

Naturalist 21:1047–1054. 

Stewart, B. S., P. K. Yochem, H. R. Huber, R. L. DeLong, R. J. Jameson, W. J. Sydeman, S. G. 

Allen, and B. J. LeBoeuf. 1994. History and present status of the northern elephant seal 
 

14 

population. Pages 29–48 In (B. J. LeBoeuf and R. M. Laws, eds.) Elephant Seals: 

Population Ecology, Behaviour and Physiology. University of California Press, Berkeley. 

Wakefield, S., J. Knowles, W. Zimmermann, and M. van Dierendonck. 2003. Status and action 

plan for the Przewalski’s horse (Equus ferus przewalskii). Pages 82–92 in Status Survey 

and Conservation Action Plan, Equids: zebras, asses, and horses (P. D. Moehlman, ed.). 

IUCN–The World Conservation Union. 

Weber, M. L., and D. W. Laist. 2007. The status of protection programs for endangered, 

threatened, and depleted marine mammals in U.S. waters. Marine Mammal Commission, 

Bethesda, MD. 
 

15 

Table 1. Summary of the biological status of 22 marine mammal species and stocks currently 

listed as endangered or threatened under the Endangered Species Act or designated as 

depleted under the Marine Mammal Protection Act (from Lowry et al. 2007). Question 

marks indicate apparent population trends that have not been confirmed. 

Taxon 

Current 

population size 

Current 

population trend 

Population size 

relative to historical 

level 

Endangered species 

West Indian manatee, Florida >3,300 Increasing? Unknown 

West Indian manatee, Antillean Unknown Declining? Reduced? 

Caribbean monk seal 0 N/A Extinct 

Hawaiian monk seal 1,252 Declining 4.9 

percent a year 

Reduced 60 percent 

from 1958 

Steller sea lion, western population 38,513 Stable Reduced 81 percent 

from the 1970s 

Blue whale1 >2,994 Increasing? Reduced 

Bowhead whale, western Arctic 

population 10,545 Increasing 3.4 percent a year 

Reduced 54 percent 

from the 1800s 

Fin whale >11,970 Unknown Reduced 

Humpback whale >6,692 Increasing Reduced 

North Atlantic right whale 299 Declining? Reduced 

North Pacific right whale, eastern 

population >23 Unknown Reduced 

Sei whale2 >133 Unknown Reduced 

Sperm whale3 >14,468 Unknown Reduced 

Killer whale, southern resident 

population 84 Unknown Reduced 

Threatened species 

Southern sea otter 2,825 Increasing Reduced 

Northern sea otter, southwest 

Alaska population 41,865 Declining Reduced 55 to 67 percent from 1976 

Guadalupe fur seal 7,408 Increasing Reduced 

Steller sea lion, eastern population 44,996 Increasing Unknown 

Depleted (only) species 

Northern fur seal, eastern 

population 688,028 Declining Reduced 65 percent from the 1950s 

Beluga whale, Cook Inlet 

population 278 Declining? Reduced 57 percent from 1994 

Bottlenose dolphin, mid-Atlantic 

coastal population 33,000 Unknown Reduced 

Killer whale, AT1 group 8 Declining Reduced 64 percent 

from 1988 

1

Data are not available for the North Atlantic and western North Pacific stocks. 

2

Data are not available for the Nova Scotia stock. 

3

Data are not available for the North Pacific stock. 
 

16 

Table 2. Examples of wild populations that have recovered from extremely low population sizes, 

with (*) or without the assistance of captive/assisted breeding programs; (+) indicates 

that additional animals survive in captivity. 

Species, stock, or population 

Estimate of minimum 

population size 

(approximate date) 

Estimate of 

current wild 

population size 

Source(s) of 

information 

Marine mammals 

Northern elephant seal 

(Mirounga angustirostris) 

20–100 

(1890) >175,000 

Bartholomew and 

Hubbs 1960, Stewart et 

al. 1994 

Southern sea otter 

(Enhydra lutris nereis) 

50 

(1938) >2,500 Riedman and Estes 1990 

Guadalupe fur seal5

(Arctocephalus townsendi) 

70–75 

(1955) >7,000 Hubbs 1956, Gallo 1994 

Southern right whale 

(Eubalaena australis) 

<300 

(1920) >7500 Baker and Clapham 

2004 

Juan Fernandez fur seal 

(Arctocephalus philippii) 

700–750 

(1970) >12,000 Hubbs and Norris 1971, 

UNEP6

Terrestrial mammals 

Black-footed ferret* 

(Mustela nigripes) 

18 

(1987) 650+ Black-footed ferret 

recovery team7

Tule elk 

(Cervus elaphus nannodes) 

28 

(1895) 3,200 McCullough et al. 

1996, NPS 1998 

Przewalski horse* 

(Equus ferus przewalskii) 

31 

(1945) 175+ Wakefield et al. 2003 

European bison* 

(Bison bonasus)

54 

(1918) 1700+ Pucek 2004 

Golden lion tamarin* 

(Leontopithecus rosalia) 

<200 

(1970s) 1,500+ Smithsonian Natl. 

Zoological Park8

Birds 

Mauritius kestrel* 

(Falco punctatus) 

4 

(1974) 800–1,000 Birdlife International9

Chatham island black robin* 

(Petroica traversi) 

5 – one breeding pair 

(1979) 250 NZ DOC 200110

 

5

 Considered extinct in the 1930s and early 1940s 6

 United Nations Environment Programme; http://www.unep-wcmc.org/species/data/species_sheets/juanfern.htm 7

 http://www.blackfootedferret.org/ 

8

 http://nationalzoo.si.edu/ConservationAndScience/EndangeredSpecies/GLTProgram/default.cfm 9

 http://www.birdlife.org/datazone/index.html 

10 also see: http://www.doc.govt.nz/Conservation/001~Plants-and-Animals/001~Native-Animals/Black-Robin.asp 
 

17 

Table 2, continued. 

Species, stock, or population 

Estimate of minimum 

population size 

(approximate date) 

Estimate of 

current wild 

population size 

Source(s) of 

information 

Whooping crane* 

(Grus americana) 

21 

(1944) >300+ CWS and FWS 2005 

California condor* 

(Gymnogyps californianus)

25–35 

(1979) 127+ California Dept. of Fish and Game11

Seychelles warbler 

(Acrocephalus sechellensis) 

50 

(1965) >2,000 Birdlife International5

Guam rail* 

(Gallirallus owstoni) 

100 

(1983) 400+ Smithsonian Natl. 

Zoological Park12

 

11 http://www.dfg.ca.gov/hcpb/species/t_e_spp/tebird/condor.shtml 12 http://nationalzoo.si.edu/Support/AdoptSpecies/AnimalInfo/Guamrail/default.cfm 
 

18 

Table 3. A theoretical decision tree and analytical recommendations for listings under the 

Endangered Species Act 

Decision Tree Categories PVA Model Recommendation 

Populations that are too 

small 

When a species or population is already known to be too small 

(through obvious proxy measures), then no PVA is necessary; 

the population should be listed. 

Populations that are nearly 

too small 

When a population is nearly too small, the important question is 

whether the population is likely to become too small. In that 

case, a simple PVA model could be designed to test whether the 

current or foreseeable population trend is, or is likely to be, 

negative. 

Populations that are large, 

but declining 

When a population is large but declining, the important question 

is whether the population could decline too much. In that case, a 

population viability model could be designed to test whether the 

current or foreseeable trend is likely to cause the population to 

become too small. The model would need to be slightly more 

complex because it must evaluate the possibility that the 

population decline could halt before the population became too 

small. 

Populations that are large, 

but have volatile 

population dynamics 

When a population is large but volatile (highly variable), the 

important question is whether the volatility in population 

dynamics is large enough to cause the population to become too 

small. For populations with a high degree of variability, a model 

could be designed to test whether the population could reach a 

critical threshold size as a result of random fluctuations. Such 

models must accurately represent the variability in various 

population parameters. 
 

19 

APPENDIX I 

Examples of Existing Marine Mammal Population Models

North Atlantic Right Whales (Presented by Hal Caswell, Woods Hole Oceanographic 

Institution) 

Background and purpose: The North Atlantic right whale is the least abundant species of large 

whale in the world. It occurs primarily along the East Coast of the United States and Canada. It 

was reduced to levels approaching extinction by centuries of commercial whaling and is listed as 

endangered under the Endangered Species Act. Current abundance is about 300 to 350 whales. 

Entanglement in fishing gear and collisions with ships are the major factors impeding recovery. 

A model was developed to estimate the population’s reproductive, survival, and population 

growth rates; predict extinction risks; and evaluate hypotheses about factors influencing 

population trends, including potential effects of variable oceanographic conditions. 

Approach: The matrix population model is based on biologically defined life history stages. It 

incorporates environmental and demographic variability by using observed variations in vital 

rates over the past 20 years. Parameters (e.g., stage-specific reproductive and survival rates) are 

estimated using mark-recapture methods (Caswell 2001, Fujiwara and Caswell 2002, Caswell 

and Fujiwara 2004). The estimation procedure automatically incorporates effects of uncertainty 

in the data and provides confidence intervals around parameter estimates. 

Data: The model uses data from 1980 through 1998 on age, sex, and reproduction for individual 

whales documented in a photo-identification catalog of the population. The catalog is believed to 

include at least some records for most of the individuals in the population, although the number 

of resighting records varies greatly among individual whales. The data are subjected to a multistage mark-recapture analysis to estimate parameters under a variety of statistical hypotheses that 

consider variation over time and the effects of environmental variables. Information-theoretic 

criteria are used to select the statistical hypotheses that are most highly supported by the 

available data. 

Results: The analysis suggests that the population was increasing at about 4 percent per year in 

the early 1980s, but that the growth rate declined until it became negative in the mid-1990s. The 

decline appears to be due to a declining trend in birth rates and survival of mothers and calves 

between 1980 and 1998. The rate of decline has varied with the North Atlantic Oscillation, 

suggesting that the population’s dynamics are affected by changing atmospheric and 

oceanographic conditions. By the late 1990s the estimated population growth rate was below 

replacement level, indicating that the population would not persist without mitigation of human 

impacts. As for all marine mammals, population growth is most sensitive to the survival of 

mature females. All other things equal, a reduction of human-related mortality by two adult 

females per year could return the population growth rate to replacement level. Further reduction 

would allow recovery, albeit at a slow rate. 
 

20 

Recent publications using the model: 

Caswell, H., M. Fujiwara, and S. Brault. 1999. Declining survival probability threatens the North 

Atlantic right whale. Proceedings of the National Academy of Science 96:3308–3313. 

Fugiwara, M., and H. Caswell. 2001. Demography of the North Atlantic right whale. Nature 

414:537–541. 

Caswell, H., and M. Fujiwara. 2004. Beyond survival estimation: mark-recapture, matrix 

population models, and population dynamics. Animal Biodiversity and Conservation 

27:471–488. 

Kraus, S. D., M. W. Brown, H. Caswell, C. W. Clark, M. Fujiwara, P. K. Hamilton, R. D. 

Kenney, A. R. Knowlton, S. Landry, C. A. Mayo, W. A. McLellan, M. J. Moore, D. P. 

Nowacek, D. A. Pabst, A. J. Read, and R. M. Rolland. 2005. North Atlantic right whales 

in crisis. Science 309:561–562. 

Caswell, H. 2006. Applications of Markov chains in demography. Pages 319–334 in (A. N. 

Langville and W. J. Stewart, eds.) MAM2006: Markov Anniversary Meeting. Boson 

Books, Raleigh, NC, USA. 

Caswell, H. 2007. Sensitivity analysis of transient population dynamics. Ecology Letters 10:1–

15. 

Southern Resident Killer Whales (Presented by Paul Wade, National Marine Mammal 

Laboratory, National Marine Fisheries Service) 

Background and purpose: Southern resident killer whales comprise three distinct pods, identified 

as J, K, and L pods, that occur principally in Washington’s Puget Sound and southern British 

Columbia, Canada. Historically, the population may have included more than 200 individuals. In 

the mid-1960s the stock was thought to number at least 100 animals, but it then declined sharply 

in the late 1960s and early 1970s as a result of live captures for aquaria. By 1995 abundance had 

recovered to 98 animals. Since then, the stock first declined to 81 animals in 2001 and then 

increased to 88 animals in 2004. The declining trend seems to have been driven primarily by 

changes in the largest pod, L pod. The recent increase, however, has been driven primarily by an 

increase in J and K pods. Pod-specific trends are important because males rarely mate with 

females from their own pod (and resident killer whales in the North Pacific mate only within 

their ecotype). As a result, the reproductive success of a resident pod is determined not only by 

the fecundity of the females within that pod but also by the availability of fertile males from 

other resident pods. Three potential factors may be impeding recovery of southern resident killer 

whales: high contaminant loads; declines in available prey, particularly salmon; and disturbance 

by whale-watching ventures and other vessel activity. The purpose of this model was to estimate 

extinction risks for southern resident killer whales as part of a status review to inform decisionmakers regarding listing of the stock as threatened or endangered under the Endangered Species 

Act. 
 

21 

Approach: The analysis used a sex-, age- and pod-structured model that allowed for (1) 

demographic variability, (2) environmental variability, (3) potential catastrophes, (4) Allee 

effects, and (5) variation in carrying capacity. Variation in survival rates was based on observed 

rates over the past 30 years, with an apparent 6-year cycle. Allee effects were imposed using 

social constraints on reproduction: females in a pod could not become pregnant unless another 

pod included an adult male. Carrying capacity was allowed to vary with values ranging from 100 

to 400 animals. 

Data: Demographic parameters for the model were estimated using censuses of southern resident 

killer whales conducted annually since 1974. Parameters included age and sex composition, 

survival, fecundity, and reproduction of each of the population’s three pods. Initial parameters 

and ranges for environmental variability, catastrophes, and carrying capacity were based on a 

literature review and expert judgment. The model was initialized with the known 2003 age, sex, 

and pod composition and was projected into the future for 100, 200, and 300 years. Because 

survival rates varied throughout the 29-year census record, the model was run using survival 

estimates from three subsets of the data: the most recent 10 years (with the lowest survival rates), 

the most recent 14 years, and all 29 years. 

Results: Scenarios using survival estimates from the preceding 29 years of data resulted in 0.1 to 

3 percent likelihood of extinction in 100 years and 2 to 42 percent in 300 years. Scenarios using 

survival estimates from the most recent 10 years resulted in 1 to 19 percent likelihood of 

extinction in 100 years and 68 to 94 percent in 300 years. Survival rates in all three pods 

followed a similar pattern; the largest pod, which occurs farthest from shore, was the most 

severely affected by changes in survival. In addition, changes were evident in all age and sex 

classes, but old males appeared to be most affected. The results suggest that the patterns in 

survival may be caused by environmental factors (e.g., changes in prey availability through 

time). Results of the analysis supported a 2006 decision to list southern resident killer whales as 

endangered. 

Recent publications using the model: 

Krahn, M. M., M. J. Ford, W. F. Perrin, P. R. Wade, R. P. Angliss, M. B. Hanson, B. L. Taylor, 

G. M. Ylitalo, M. E. Dahlheim, J. E. Stein, and R. S. Waples. 2004. Status review of 

Southern Resident killer whales (Orcinus orca) under the Endangered Species Act. U.S. 

Dept. of Commerce, NOAA Tech. Memo. NMFS-NWFSC-62. 73 pp. 

Cook Inlet Beluga Whales (Presented by Daniel Goodman, Montana State University) 

Background and purpose: Data from National Marine Fisheries Service aerial surveys indicate 

that the Cook Inlet beluga whale stock declined from an estimated 653 individuals in 1994 to 347 

in 1998, and then declined at a lower rate to 278 in 2005. The decline from 1994 to 1998 was due 

primarily to subsistence harvesting by Alaska Natives. After the harvest was brought under 
 

22 

management control in 1998 (only three whales were harvested between 1999 and 2004), the 

stock was expected to recover at a rate of 2 to 6 percent annually. Its failure to recover suggests 

that other factors also are affecting this stock. Its summer range contracted concurrently with the 

decline, and beluga whales now are rarely seen in offshore waters or the lower reaches of the 

inlet. Because their remaining habitat is near Anchorage, the largest urban area in Alaska, the 

whales are exposed to a range of human activities. An analysis was conducted to characterize the 

trend to date and project whether the population is likely to decline further. 

Approach: The analysis fits an exponential population growth model to past survey estimates 

and produces a distribution of possible growth rates, including negative values consistent with a 

decline. The distribution of growth rates is then used to predict the trend in the near future. The 

model does not include the effects of subsistence harvest (which may be negligible at present) or 

environmental variability. 

Data: The analysis used annual abundance estimates (and variances of those estimates) from 

aerial surveys conducted between 1994 and 2004. 

Results: The results suggest that even without environmental variation and harvests, the 

likelihood of continuing decline is 45 percent.13 The National Marine Fisheries Service currently 

is reviewing a petition to list the Cook Inlet beluga whale stock as endangered under the 

Endangered Species Act. 

Recent publications using the model: 

Lowry, L., G. O’Corry-Crowe, and D. Goodman. 2006. Delphinapterus leucas (Cook Inlet 

population). In 2006 IUCN Red List of Threatened Species. IUCN–The World 

Conservation Union. 

Florida Manatees (Presented by Michael Runge, Patuxent Wildlife Research Center, U.S. 

Geological Survey) 

Background and purpose: The West Indian manatee, listed as endangered under the Endangered 

Species Act, is comprised of Antillean and Florida subspecies. The Florida subspecies occurs in 

rivers and coastal waters of the southeastern United States. Because of their limited tolerance for 

cold temperatures, most Florida manatees winter near warm-water discharges from natural 

springs or power plant outfalls located in the southern two-thirds of the Florida peninsula. The 

anticipated loss of discharge sites as a result of power plant closures represents a long-term threat 

that would reduce available habitat and lower the effective environmental carrying capacity for 

manatees. At present, the largest source of direct human-related manatee mortality—and 

 

13 A more recent analysis using the same model and data from 1994 to 2006 suggests an 81 percent probability that the 

population is declining (i.e., the growth rate is negative). 
 

23 

probably the most significant factor impeding population recovery—is collisions with boats. 

Watercraft-related deaths typically account for a quarter to a third of all manatee deaths annually. 

Since 1985 population models have been used to assess trends in manatee abundance. More 

recently, modeling objectives have focused on evaluation of negative and positive effects of 

specific threats and management actions. At the Savannah workshop, the model’s utility for 

predicting population trends and estimating the effects of changes in carrying capacity were 

described. The model will be used to inform reclassification decisions under the Endangered 

Species Act and Florida state statutes. 

Approach: The model projects population trends based on reproduction and survival 

probabilities for each of several life history stages, such as calves, juveniles, adult males, and 

adult females. The model accounts for variability in demographic parameters and the largely 

independent dynamics of four relatively discrete manatee subpopulations in Florida. The model 

incorporates catastrophes (e.g., red tide bloom, disease epidemic), density dependence, and 

changes in habitat availability (e.g., availability of winter warm-water refuges). Additional 

factors can and will be added to address specific questions that arise, such as the effects of 

specific management actions, hurricanes, and climate change. 

Data: Extensive data were used to develop model parameters (e.g., survival rates, reproductive 

rates, carrying capacity), including 10 to 25 years (depending on subpopulation) of photoidentification mark-recapture data on more than 1,000 animals. Estimates for model parameters 

such as carrying capacity and density dependence were based on the advice of an expert panel. 

Results: The model has been used to estimate population trends for each of four regional 

subpopulations in Florida. When based on data from the last 10 years, the model indicates that 

manatees are increasing in three regions: the northwest (growth rate [λ] = 1.037), upper St. Johns 

River (λ = 1.062), and Atlantic (λ = 1.010). Manatees in the southwest region appear to be 

declining (λ = 0.989), based on the most recent 10 years of data. Further analysis suggests that 

management actions should focus on increasing adult survival rates and that improved 

monitoring of those rates would reduce the overall uncertainty in model results. 

Recent publications using the model: 

Runge, M. C. 2003. A model for assessing incidental take of manatees due to watercraft-related 

activities. In U.S. Fish and Wildlife Service Environmental Impact Statement: 

Rulemaking for the incidental take of small number of Florida manatees (Trichechus 

manatus latirostris) resulting from government programs related to watercraft access and 

watercraft operation in the state of Florida, Appendix I (March 2003) U.S. Fish and 

Wildlife Service. Jacksonville, FL. 

Runge, M. C., C. A. Langtimm, and W. L. Kendall. 2004. A stage-based model of manatee 

population dynamics. Marine Mammal Science 20:361–385. 
 

24 

Haubold, E. M., C. Deutch, and C. Fonnesbeck. 2006. Final biological status review of the 

Florida manatee, Trichechus manatus latirostris. Florida Wildlife Research Institute, 

Florida Fish and Wildlife Conservation Commission. St. Petersburg, FL. 

Hawaiian Monk Seals (Presented by Albert Harting, Harting Biological Consulting) 

Background and purpose: The Hawaiian monk seal is the most endangered seal in U.S. waters. 

Hawaiian monk seals occur almost entirely in the Hawaiian archipelago, where about 90 percent 

of all animals live on and around the remote Northwestern Hawaiian Islands. The majority of 

pups are born at six relatively discrete breeding subpopulations located at French Frigate Shoals, 

Laysan Island, Lisianski Island, Pearl and Hermes Reef, Midway Atoll, and Kure Atoll. Since 

the late 1950s when Hawaiian monk seals were first studied, beach counts at these six major 

pupping colonies have declined by more than 60 percent. The total population is currently 

estimated to number fewer than 1,300 animals and is declining at a rate of about 4 to 5 percent 

per year. 

Threats to monk seal recovery include both human-related and natural factors that have varied 

over time and by colony. The human-related factors include disturbance and displacement of 

hauled-out seals by people and animals, entanglement in derelict fishing gear, depletion of prey 

resources by commercial fishing, interactions with recreational and commercial fishing gear, and 

oil spills. Natural factors include shark predation; naturally occurring biotoxins; disease; 

aggressive behavior by some adult male seals toward pups, juveniles, and adult females; the 

effects of oceanographic changes on prey resources; and the loss of pupping beaches to erosion. 

In general, the small, isolated nature of the Northwestern Hawaiian Islands makes their local 

ecosystems exceedingly vulnerable to both natural and human impacts. 

A metapopulation model was developed to predict population abundance over relatively short 

time horizons (5 to 20 years), assess the sensitivity of the population to natural or managementinduced perturbations, and perform long-range projections for risk assessments and population 

viability analyses. 

Approach: The metapopulation model represents the species as a group of spatially distinct and 

largely independent breeding subpopulations. The primary events during each simulation year 

are births and deaths, both of which could be affected by simulated catastrophes. The simulation 

also can include specific natural perturbations (e.g., adult male aggression and shark predation), 

migration between subpopulations, and management actions (e.g., captive rearing or 

translocation of pups and removal of aggressive adult males). Density-dependent regulation of 

reproductive and survival rates also can be incorporated in simulations. 

Data: The model uses the life history and demographic data collected through an intensive 

program of cohort tagging and replicate seasonal counts of each subpopulation. These efforts, 

conducted since the early 1980s, provide detailed data for estimating age-specific survival and 
 

25 

reproductive rates, current age/sex structure, inter-site movement rates, and the effects of specific 

natural perturbations (e.g., shark predation rates). 

Results: This model has been used for analyzing the impact of shark predation on monk seal 

recovery at French Frigate Shoals, conducting National Environmental Policy Act assessments, 

analyzing potential impacts of an epizootic outbreak in the Northwestern Hawaiian Islands, and 

assessing the likely benefits from proposed management interventions. Further development of 

this model will include linking the model to oceanographic data, analyzing historical data for 

evidence of density-dependent regulation to refine the density-dependence formulation now used 

in the model, and adding the main Hawaiian Islands monk seal subpopulation to the model. 

Due primarily to poor juvenile survival rates, long-term projections using survival rates derived 

from observations in recent years (2001–2005) indicate a decline at all subpopulations except 

Laysan Island, with French Frigate Shoals declining most precipitously. Projections utilizing 

survival rates (and variances) from all data years (1985–2005) again predict a marked decline at 

French Frigate Shoals, with a gradual decline at Kure Atoll (remaining subpopulations stable or 

increasing). 

Recent publications using the model: 

Harting, A. L. 2002. Stochastic simulation model for the Hawaiian monk seal. Ph.D. thesis, 

Montana State University, Bozeman. 328 pp. 

National Marine Fisheries Service. 2006. Draft recovery plan for the Hawaiian monk seal, 

Monachus schauinslandi. National Marine Fisheries Service. Silver Spring, MD. 148 pp. 

Steller Sea Lions — Western Stock (Presented by Daniel Goodman, Montana State 

University) 

Background and purpose: Over the past three or four decades, Steller sea lions have declined 

precipitously throughout portions of their range, and the species was listed as threatened under 

the Endangered Species Act in 1990. In 1997 the species was determined to consist of at least 

two distinct population segments. The western population segment, occurring from the central 

Gulf of Alaska and westward, was listed as endangered, while the eastern segment, occurring 

from California through Southeast Alaska, remained listed as threatened. The decline of the 

western stock slowed during the 1990s, and since 2000 its abundance may have stabilized. The 

cause or causes of decline have been a matter of extensive debate and controversy. Leading 

hypotheses include nutritional stress as a result of competition with commercial fisheries and/or 

shifting environmental conditions, and predation by killer whales. The marked changes observed 

in western Steller sea lion abundance in recent decades suggest that the population may face 

significant extinction risks even at relatively high abundance. A population viability analysis was 

undertaken to estimate the population’s extinction risk. 
 

26 

Approach: The PVA for western Steller sea lions simulated a random population growth regime 

based on observed, unexplained variation over recent decades, with the assumption that such 

variation would continue into the future. The results were summarized in terms of probability of 

extinction over time and were used to inform efforts by the Steller Sea Lion Recovery Team to 

develop recovery criteria (National Marine Fisheries Service 2006). 

Data: Available data consist of 45 years of episodic census figures. Additional information on 

environmental variation also was used in the model. 

Results: The analysis concluded that in the next 100 years the population has a 37 percent chance 

of declining to an effective population size of 1,000 animals, which equates to a total population 

size of 4,743 animals. 

Recent publications using the model: 

National Marine Fisheries Service. 2006. Draft Revised Recovery Plan for the Steller sea lion 

(Eumetopias jubatus). National Marine Fisheries Service, Silver Spring, MD. 

Steller Sea Lions — Eastern Stock (Presented by Daniel Goodman, Montana State 

University) 

Background and purpose: The eastern stock of Steller sea lions, a distinct population segment 

from California through Southeast Alaska, has increased steadily in size since the 1980s. It is 

recovering from human-caused mortality from the late 1800s to the 1970s. A population growth 

model was developed to determine whether the population is still growing. 

Approach: The analysis fits an exponential growth model to past survey estimates to produce a 

distribution of possible growth rates. The distribution indicates the likelihood of continued 

increase. The residuals of the growth model are random and relatively small, suggesting that 

neither external factors (e.g., environmental variation) nor density dependence is altering the 

population dynamics appreciably, and those factors need not be incorporated into the model. 

Data: The available data were drawn from annual censuses conducted from 1976 to 2002. 

Results: The exponential growth model fits the population data well and indicates that the 

population is still growing. 

Recent publications using the model: 

National Marine Fisheries Service. 2006. Draft Revised Recovery Plan for the Steller sea lion 

(Eumetopias jubatus). National Marine Fisheries Service, Silver Spring, MD. 
 

27 

California Sea Otters (Presented by Martin Tinker, Dept. of Ecology and Evolutionary 

Biology, University of California, Santa Cruz) 

Background and purpose: Over-exploitation for the fur trade in the 18th and 19th centuries 

brought sea otters in the North Pacific to near-extinction by the early 1900s. When commercial 

harvesting was banned by an international treaty in 1911, only a small remnant population of 

what is now recognized as the southern sea otter subspecies survived in California along the 

coast between Monterey and Big Sur. Recovery of the subspecies after 1911 was extraordinarily 

slow, and in 1977 the U.S. Fish and Wildlife Service listed the subspecies as threatened under 

the Endangered Species Act. In the late 1980s a translocation program was implemented to 

establish southern sea otters at San Nicolas Island off southern California and thereby provide 

another colony that could serve as a source for recovery efforts if the still-small mainland 

population were to be affected by a large catastrophe, such as an oil spill. At the same time, the 

Service established a management zone south of Point Conception where sea otters were to be 

excluded to prevent a southward expansion of the sea otter range and thereby protect commercial 

shellfish fisheries in southern California. 

Recent surveys indicate that the population is increasing but still at a slower rate than expected. 

The population also has been expanding its range northward as well as southward into the 

management zone. In the late 1990s the number of otters in the management zone increased, and 

efforts to remove them were limited and largely unsuccessful. In addition, the translocated 

population failed to increase as expected and currently numbers just a few tens of animals. As a 

result, the Fish and Wildlife Service is considering steps to declare the translocation program a 

failure and to allow the mainland population to continue its expansion southward. 

A population model was developed at the request of the Fish and Wildlife Service to project the 

rate of population recovery and range expansion over time. It provides a general framework for 

evaluating management options and conservation strategies for the southern sea otter. 

Approach: The model is stage-based and incorporates spatial structure, movement rates, and 

demographic information. The model begins by estimating survival rates by location and time for 

each age/sex class (stage). The survival rates are then combined with stage-specific dispersal 

kernels to parameterize a multi-state matrix model for the entire population (structured by spatial 

region and allowing for inter-regional movements), which utilizes stage-structured difference 

equations to predict annual rates of range expansion into unoccupied habitat. Uncertainty is 

explicitly incorporated by using Monte Carlo simulations that allow all parameters to vary within 

the full range of previously observed values, and simulations include variance due to 

measurement and process error. 

Data: The model uses survey data from the past 20 years (including total counts and counts of 

mature animals and dependent pups), age-at-death data from beach-cast carcasses, and radio 

telemetry data from free-ranging sea otters. From these data sources, estimates are derived (using 

maximum likelihood methods) for stage-specific reproduction, survival, and annual individual 
 

28 

movement distances for identified age and sex components of regional subpopulations, as well as 

associated variance estimates for each parameter. 

Results: Survival rates vary regionally, with lowest survival in the north and highest in the south. 

Female survival decreased in the mid-1990s. Sea otters are expanding their range southward at a 

rate of about 6 km/year. 

Recent publications using the model: 

Tinker, M. T., D. F. Doak, J. A. Estes, B. B. Hatfield, M. M. Staedler, and L. Bodkin James. 

2006. Incorporating diverse data and realistic complexity into demographic estimation 

procedures for sea otters. Ecological Applications 16:2293–2312. 

Tinker, M. T., J. A. Estes, K. Ralls, T. M. Williams, D. Jessup, and D. P. Costa. 2006. Population 

Dynamics and Biology of the California Sea Otter (Enhydra lutris nereis) at the Southern 

End of its Range. MMS OCS Study 2006–2007. Coastal Research Center, Marine 

Science Institute, University of California, Santa Barbara, California. MMS Cooperative 

Agreement Number 14-35-0001-31063. 

U.S. Fish and Wildlife Service. 2005. Draft Supplemental Environmental Impact Statement on 

the Translocation of Southern Sea Otters. Ventura, California. 242 pp + appendices. 
 

29 

APPENDIX II 

Workshop Attendees

Presenters 

Hal Caswell Wood Hole Oceanographic Institution 

Jean Cochrane U.S. Fish and Wildlife Service 

Deborah Crouse Endangered Species Office, U.S. Fish and Wildlife Service 

Daniel Goodman Montana State University, Bozeman 

Albert Harting Harting Biological Consulting 

Lloyd Lowry Marine Mammal Commission, Committee of Scientific Advisors 

Marta Nammack National Marine Fisheries Service 

Michael Runge Patuxent Wildlife Research Center, U.S. Geological Survey, 

Barbara Taylor Southwest Fisheries Science Center, National Marine Fisheries Service 

Martin (Tim) Tinker Dept. of Ecology and Evolutionary Biology, University of California, Santa 

Cruz 

Paul Wade National Marine Mammal Laboratory, National Marine Fisheries Service 

Michael Weber Consultant 

Attendees 

Steven Beissinger University of California, Berkeley 

Daryl Boness Marine Mammal Commission, Committee of Scientific Advisors 

Douglas Burn U.S. Fish and Wildlife Service 

Therese Conant National Marine Fisheries Service, Office of Protected Resources 

Paul Dayton Scripps Institution of Oceanography, University of California, San Diego 

Daniel Doak Dept. of Ecology and Evolutionary Biology, University of California, Santa 

Cruz 

Thomas Eagle National Marine Fisheries Service 

David Gouveia National Marine Fisheries Service 

Dawn Jennings U.S. Fish and Wildlife Service 

Craig Johnson National Marine Fisheries Service 

Rosa Meehan U.S. Fish and Wildlife Service 

Katherine Ralls Smithsonian National Zoological Park, Conservation & Research Center 

Randall Reeves Okapi Wildlife Associates 

Gregory Silber National Marine Fisheries Service 

Robert Small Alaska Department of Fish and Game 

James Valade U.S. Fish and Wildlife Service 

Marine Mammal Commission and SRA Staff 

David Cottingham Marine Mammal Commission 

David Laist Marine Mammal Commission 

Linda Manning SRA International 

Regan Maund SRA International 

Timothy Ragen Marine Mammal Commission 

Michael Simpkins Marine Mammal Commission 

Elizabeth Taylor Marine Mammal Commission 
 

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APPENDIX III 

Workshop Agenda

Workshop Objectives 

• Review efforts to use PVA and other types of population models for endangered, 

threatened and depleted marine mammals occurring substantially in U.S. waters; 

• Evaluate the extent to which PVA or other types of models can be relied upon for 

determining population status and predicting population trends for ESA classification 

listing decisions; and 

• Evaluate the ability of PVA or other types of models to improve the decision-making 

process with regard to developing and selecting potential management actions other than 

ESA classification listing decisions. 

________________________________________________________________________ 

Day One Review existing efforts to use PVA and other types of population models for 

endangered, threatened and depleted marine mammals 

8:30 – 9:00 Opening Remarks, Introductions, and Agenda Review (David Cottingham) 

9:00 – 10:30 Current Approaches to the Assessment and Management of Listed Species 

under U.S. Law 

• Overview of U.S. Fish and Wildlife Decision-making Processes from Listing through 

Delisting — Current Approaches (Deborah Crouse) 

• Overview of National Marine Fisheries Service Decision-making Processes from Listing 

through Delisting — Current Approaches (Marta Nammack) 

• Cases of U.S. Fish and Wildlife Service Use of Decision-Making Tools Including PVA 

(Jean Cochrane) 

• Current Tools and New Approaches at the National Marine Fisheries Service (Barbara 

Taylor and Paul Wade 

10:30 – 10:45 Break 

10:45 – 5:00 Reviewing Existing Marine Mammal Population Models 

• Florida Manatees (Mike Runge) 

• Hawaiian Monk Seals (Albert Harting) 

• North Atlantic Right Whales (Hal Caswell) 

• Southern Resident Killer Whales (Paul Wade) 

• California Sea Otters (Tim Tinker) 

• Steller Sea Lions and Cook Inlet Beluga Whales (Daniel Goodman) 
 

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Day Two Evaluate the extent to which PVA or other types of models can be relied upon 

for determining population status and predicting population trends for ESA 

classification listing decisions 

8:30 – 9:00 Opening Remarks/Agenda Review 

9:00 – 9:45 Overview of Available Information on the Status of Listed Marine Mammals 

 (Lloyd Lowry) 

9:45 – 10:00 Break 

10:00 – 12:30 Panel Session IA: What steps could or should be taken to better use or develop 

PVA models or other types of models to improve ESA classification decisions for 

“data rich” species? 

12:30 – 2:00 Lunch break 

2:00 – 5:00 Panel Session IB: What steps could or should be taken to better use or develop 

PVA models or other types of models to improve ESA classification decisions for 

“data poor” species? 

5:00 - 5:30 Closing Remarks 

Day Three Evaluate the ability of PVA methods to improve decision-making processes for 

developing and selecting potential management actions other than ESA 

classification decisions 

8:30 – 9:30 Overview of the Status of Protection Programs for Listed Marine Mammals 

(Michael Weber) 

9:30 – 11:00 Panel Session II – What steps could or should be taken to develop or improve 

population models for use in making routine/operational management decisions 

for the endangered, threatened, and depleted species?

 

11:00 – 11:15 Break 

11:15 – 1:00 Panel Session II, continued 

1:00 – 2:00 Closing Remarks and Next Steps