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Journal of Mammalogy, 82(3):641–651, 2001
PREDATION AND COMPETITION: THE IMPACT OF FISHERIES ON
MARINE-MAMMAL POPULATIONS OVER THE NEXT ONE
HUNDRED YEARS
DOUGLAS P. DEMASTER,* CHARLES W. FOWLER, SIMONA L. PERRY,
AND
MICHAEL F. RICHLEN
National Marine Mammal Laboratory, Alaska Fisheries Science Center,
National Marine Fisheries Service, 7600 Sand Point Way NE,
Seattle, WA 98115 (DPD, CWF)
School of Marine Affairs and Department of Zoology, University of Washington,
Seattle, WA 98115 (SLP, MFR)
We discuss the potential for commercial fisheries to adversely impact $1 population of
marine mammal by the end of the 21st century. To a large degree, patterns over the last
50 years regarding human population growth, success and failure in marine-fisheries management, and life history and status information on marine mammals are the basis for 6
predictions. First, annual worldwide landings of fish and shellfish by the end of the 21st
century will be less than 80 million tons. Second, virtually all of the predictions regarding
species composition and energy flow within a marine community, based on models developed to date with incomplete information on species abundance, food habits, genetic effects
of fishing, and variability of predator food habits, will prove wrong on a decadal or longer
time scale. Third, the most common type of competitive interaction between marine mammals and commercial fisheries will be that in which commercial fisheries adversely affect
a marine-mammal population by depleting localized food resources without necessarily
overfishing the target species of fish (or shellfish). Because of this, the number of extant
populations and species richness of marine mammals will be reduced by the end of the
21st century, and coastal populations and species will be affected more negatively than
will noncoastal species. Fifth, predator control programs designed to reduce local populations of marine mammals will be common without changes in existing forms of fishery
management. Finally, protein from marine mammals will become a more important component of the human diet than it currently is.
Key words:
commercial fishery, competition, marine mammals, predation
. . . animals living in the water, especially the sea waters, are protected from
the destruction of their species by Man.
Their multiplication is so rapid and their
means of evading pursuit or traps are so
great that there is no likelihood of his
being able to destroy the entire species
of any of these animals.
Lamarck (1809 cited in Roberts and
Hawkins 1999) may have been asked by
some well-intentioned symposium organizer, as we were, to make predictions about
resource management 100 years into the future. Lamarck was clearly wrong concerning this particular prediction over the next
100 years, and we now remark at his naı̈veté. There is no reason to think that scientists reviewing our predictions 100 years
hence will see any less humor in our assessments. Therefore, we have used this ex-
Jean Baptiste Lamarck
* Correspondent: [email protected]
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JOURNAL OF MAMMALOGY
ercise of predicting future events primarily
as a venue for our recommendations for the
next few generations of scientists and managers regarding the management of marine
mammal–fishery interactions.
Numerous lines of thought suggest that
commercial fisheries have the potential to
affect adversely $1 population of marine
mammal by the end of the 21st century.
Herein, we have dealt with biological (or
indirect) interactions, as opposed to direct
interactions (e.g., incidental mortality—
Beverton 1985). We also have chosen not
to address the interesting issue of whether
marine-mammal populations will adversely
affect $1 population of commercially important marine resources (i.e., finfish and
shellfish). To a large degree, we have used
patterns observed over the last 50 years regarding human population growth, success
and failures in marine-fisheries management, and life history and status information on marine mammals to develop predictions and recommendations regarding the
future status of mammals occupying marine
environments.
ENVIRONMENTAL CONTEXT
Human population growth.—Since the
industrial revolution, the human population
has increased from 1 billion to more than 6
billion people (United States Census Bureau, International Data Base, Washington,
D.C.). After 1950, the human population
continued to increase, although the rate of
increase has slowed (Fig. 1). Based on this
projection, the size of the human population
will stabilize in about 2070. By 2020, the
human population will likely exceed 8 billion, and it could be as large as 12 billion
by 2050. Sadly, the human species does not
seem to have the capacity to regulate its
own population size, other than by the regulatory mechanisms described by Malthus
(1798 cited in Dhamee 1996 at http://
landow.stg.brown.edu/victorian/economics/
malthus.html) in the 18th century (i.e., war,
famine, pestilence, and plague). Such regulatory mechanisms are not conducive to
Vol. 82, No. 3
FIG. 1.—Human population growth rates between 1950 and 2050 (United States Census Bureau, International Data Base).
humans avoiding the tragedy of the commons (Sandvik 1998), which does not bode
well for marine-mammal populations.
Currently, 50% of the world’s human
population lives #60 km from the coast,
and it is likely that this figure will increase
to 75% by 2020 (Intergovernmental Panel
on Climate Change, in litt.). Based on these
trends, coastal waters likely will become increasingly polluted over the next 100 years.
As reported by Roberts and Hawkins
(1999), 95% of marine-fish catches come
from the continental shelf regions. Therefore, a related prediction for the next century is that the amount and quality of fish
as a human food source will diminish. Implications of these trends for marine mammals will be discussed in the last section of
this paper.
Marine-fisheries management and marine mammals.—In the past 50 years, marine-fishery production has increased from
just ,20 million tons/year to 80–90 million
tons/year. However, the rate at which marine-fishery landings have been increasing
has dropped dramatically in recent years
from almost 10%/year to zero (Grainger
and Garcia 1996). In the Atlantic Ocean,
landings actually have decreased in absolute terms since about 1983, with no evidence that the decline in landings is slowing. In other areas (e.g., Mediterranean Sea
and Indian Ocean), landings continue to increase, although the rate of increase is declining. The National Research Council
August 2001
SPECIAL FEATURE—MARINE MAMMALS
(Anonymous 1999) estimated that about
74% of individual stocks of fish and shellfish have either been overfished (30%) or
are being fished at or near the maximum
long-term potential catch (44%).
Globally, 28% of fishery products in
1996 were used as protein supplements for
animal feed (Anonymous 1999), whereas
marine fisheries contributed roughly 14 kg
of food/person. If one includes current bycatch estimates with landings of target species, it is likely that humans remove about
100 million tons of biomass/year from the
world’s oceans. Some have argued that this
figure is likely equal to the total production
of ocean ecosystems and the ‘‘maximum
long-term potential catch of marine animals’’ (Anonymous 1999:3). Others suggest that it is well beyond what may be realistically sustainable (Fowler 1999a; Fowler and Perez 1999; Fowler et al. 1999).
Key lessons have been learned about
fisheries management as a result of the collapse of numerous fisheries worldwide in
the 1960s. Butterworth (1999:5) noted that
‘‘oversubscribed industries create undue
pressure to delay necessary catch reductions by advancing socio-economic arguments, with results that can take decades to
rectify. Fisheries management is gambling,
intelligently.’’ The international move to
‘‘limited entry fisheries’’ is a sign that fishery managers are learning how to manage
social ‘‘momentum’’ and limit fishing effort, at least in some fisheries. On the other
hand, Dayton et al. (1995) maintained that
fishery managers have a long way to go before their practices can be considered sustainable. That is, managers must take a
‘‘more balanced scientific approach that
considers both Type I (i.e., falsely rejecting
the null hypothesis) and Type II (falsely accepting the null hypothesis) errors and the
relative risks of various management alternatives, especially with regard to whether
other non-target components of the ecosystems deserve protection’’ (Dayton et al.
1995:224).
The proposition that the current level of
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human-related removals of marine fish and
shellfish is sustainable at the 100-year level
remains debatable. Many experts in the
field of marine fisheries have argued that
the current level of human-related removals
is not sustainable and that fishery managers
need to reduce overall fishing mortality
(Anonymous 1999). Fowler (1999a, 1999b)
has developed an approach in which fishery
‘‘management action could be guided by
frequency distributions of empirical examples of sustainability’’ (Fowler 1999b:25).
That is, managers could use the observed
harvest rate by marine predators on marine
prey to estimate maximum harvest rates
that are sustainable at ecosystem and biosphere levels, on a very long time scale
(i.e., an evolutionary time scale). Such an
approach, if implemented, would lead to a
dramatic reduction in worldwide fishery
landings on an annual basis.
Reducing catches is not the only topic
before managers, and implementing change
of any kind needs guidance. It is important
to identify appropriate management measures, the kinds of changes that are advisable, and then the extent of change that is
needed. Alternative fishery-management
approaches could be integrated into current
fishery practices and would be more sustainable than many of the current practices
or approaches (Table 1).
By the end of this century, the planet
likely will be inhabited by an additional 6–
10 billion people. If all existing food sources for humans contributed evenly to sustaining as many as 12–16 billion humans,
then fishery production would have to double or triple. If 100 million tons of annual
production is an optimistic estimate of all
that we can harvest sustainably with existing guilds of marine species, this will not
happen. It is more likely, given the presumed social and economic pressure associated with expanding human populations,
that marine ecosystems will continue to be
overexploited, which in the long run will
provide less protein for the human population, rather than more. At the same time,
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JOURNAL OF MAMMALOGY
Vol. 82, No. 3
TABLE 1.—Summary of recommendations to fishery managers reported in a special issue of Ecological Applications (1998:8, supplement).
Management practice
Reference
Establish marine reserves
Use performance measures based on annual and decadal time scales
Target equilibrium population to 0.75K and use tax incentives to promote
0.75K target
Establish ‘‘spawn at least once’’ policy
Establish areas closed to all fishing
Expand use of alternative fisheries management systems, including: individual transferable quotas, community development quotas, and transferable fishing privileges
Expand use of individual transferable quotas
Improve efforts to design marine reserves and improve marine-fisheries
management
many populations of marine mammals protected from direct exploitation will increase
in abundance as they recover from having
been overharvested in the past century.
Therefore, by the end of the 21st century,
annual worldwide landings of fish and
shellfish likely will be ,100 million tons.
Severe political and social pressure from
some segments of the fishing community
will cause the purposeful removal (or at
least reduction in density) of other top predators (e.g., marine mammals and seabirds)
from the marine ecosystem as a way to
solve the problem of an imbalance between
worldwide demand for fishery products and
production of marine ecosystems available
for human consumption. This pressure will
be justified by the argument that such removals will leave a greater fraction of annual net production for human consumption. This prediction is based on observations that calls for culling top-level predators to enhance commercial fisheries have
already been heard, and historically, this
has been a common management strategy
in terrestrial settings.
STATUS
OF
MARINE-MAMMAL POPULATIONS
There are 124 extant species of pinnipeds, cetaceans, and sirenians (Rice 1998).
At a minimum, adequate information about
the ecological status of their populations
should include data on population structure
Lauck et al. (1998)
Steele (1998)
Roughgarden (1998)
Meyers and Mertz (1998)
Fogarty and Murawski (1998)
Fujita et al. (1998)
Dewees (1998)
Allison et al. (1998)
within each species and population size. To
fully understand the role of marine mammals in the marine environment, information on distribution, abundance, trends in
abundance, and current population level relative to carrying capacity (or, lacking information on carrying capacity, relative to
population levels before recent human disturbances) is required. This information is
not available for most species. Further, to
evaluate the potential for competition between commercial fisheries and marine
mammals, one also needs to know age- (or
size-) specific information on energy needs
and food habits. The available information
on energy needs and food habits of marine
mammals is incomplete. So how do we proceed with this evaluation?
Several authors have ventured boldly
where few others have dared to go (Anderson and Ursin 1977; Green 1977; Innis et
al. 1981). For example, Trites et al. (1997)
addressed the issue of competition between
fisheries and marine mammals for prey and
primary production in the Pacific Ocean.
Thereafter, an international scientific organization concerned with the North Pacific
ecosystem created a working group that
produced a report on abundance and seasonal distribution of marine mammals and
seabirds by subregion of the Pacific. Tamura and Ohsumi (1999) estimated total
food consumption by cetaceans in the
August 2001
SPECIAL FEATURE—MARINE MAMMALS
oceans. Because of complex ecosystem interactions that are not well studied or well
understood, the uncertainty associated with
estimates of marine-mammal abundance
and food habits, and the logistical difficulty
and expense of collecting this information,
predictions from these models remain untested with empirical data (J. W. Young, in
litt.). Therefore, it is unknown if it is possible to adequately model marine ecosystems and thus produce reliable predictions
about how reducing the biomass of 1 species will affect the biomass of another species. Furthermore, for these very reasons,
virtually all of projections based on models
developed to date with incomplete information likely will prove wrong on a decadal
or longer time scale (other than the most
general predictions, such as fish species are
the largest consumer of fish species in any
marine ecosystem). To a large extent, this
is why Fowler (1999a, 1999b) has recommended using nature’s ‘‘Monte Carlo’’ experiment as a better viewing port into the
inner workings of complex systems such as
marine ecosystems.
It is beyond the scope of this paper to
summarize the status of all marine-mammal
populations. Recent summaries by Read
and Wade (1999) on the status of marine
mammals in waters off the United States,
Perry et al. (1999) on the status of 6 species
of endangered large whales, Clapham et al.
(1999) on the status of large whales, and
Gerber et al. (2000) on recent trends in
managing endangered populations of large
whales are recommended. However, 1 generalization from these works and others
(e.g., Best 1993) is that we know substantially more about marine-mammal species
that inhabit coastal waters (e.g., gray whale,
Eschrichtius robustus; most pinniped species; marine otters; sirenians; polar bear,
Ursus maritimus), than we do about pelagic
species (fin whale, Balaenoptera physalus;
sei whale, Balaenoptera borealis; minke
whale, Balaenoptera acutorostrata; all
beaked whales, Ziphius, Berardius, Tasmacetus, Indopacetus, Hyperoodon, and
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Mesoplodon; sperm whale, Physeter macrocephalus; ribbon seal, Histriophoca fasciata). For example, out of 153 marinemammal stocks in United States waters, we
have trend data for 26% and abundance
data for 66% (Read and Wade 1999). However, by taxon, we have trend data for 10%
and abundance data for 60% of odontocete
stocks, whereas we have trend data for 74%
and abundance data for 96% of pinniped
stocks (Read and Wade 1999). Presumably
this reflects the dependence of pinnipeds on
pupping and hauling out on land (or ice),
which makes them logistically easier to
study than odontocetes, many of which are
pelagic throughout their lives.
In addition, more populations of marine
mammals are either stable or increasing
than decreasing (at least for those populations where data exist). For example, for
populations where trend data are available
(Read and Wade 1999), 27 populations are
increasing, 5 are decreasing, and 7 are stable. Also, Best (1983) reported that for 12
populations of large whales where trend
data are available, 10 are increasing in
numbers. This does not mean that management of marine mammals has been successful across all taxa (Clapham et al.
1999); however, it does suggest that many
populations of marine mammals have recovered to some extent from overexploitation in the 19th and 20th centuries and will
continue to increase well into the next century.
Of greatest concern in trying to predict
the degree to which commercial fisheries
will adversely impact marine-mammal populations in the 21st century is the lack of
information on pelagic species of marine
predators in general, including nonmammalian species (e.g., squid) but particularly
pelagic species of cetaceans. At present no
credible population estimates or trends in
abundance exist for any population of
sperm whale. The same is true for the complex of beaked whale (Ziphius, Berardius,
Tasmacetus, Indopacetus, Hyperoodon, and
Mesoplodon) species. Consequently, it is
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JOURNAL OF MAMMALOGY
not possible to reliably predict current biomass of prey needed to sustain these populations. Further, it is not possible to test if
the food habits of recovering populations of
large whales have changed over time because most of the food-habits information
available for large whales was collected as
part of commercial whaling operations before the moratorium on commercial whaling established in 1985–1986.
By the end of the 21st century, it is likely
that at least crude time series of abundance
estimates will exist for virtually all populations of marine mammals. This bold statement is predicated on recent advances in
remote survey technology (visible- and invisible-wavelength technology and acoustic
technology) and the growing interest of the
general public in developed countries in
supporting research on, and the protection
of, marine mammals. It is not obvious that
the same can be said for many of the other
marine predators that are not of commercial
value. Further, it is not at all clear if human
society in the near future will value marine
science sufficiently to fund necessary research to collect the information needed to
make reliable predictions about human impacts on marine ecosystems (E. L. Miles, in
litt.).
COMPETITION BETWEEN COMMERCIAL
FISHERIES AND MARINE-MAMMAL
POPULATIONS
Beverton’s (1985:4) broad overview of
the different types of interactive systems
between commercial fisheries and marine
mammals formed the basis of our analysis.
Beverton (1985:4) noted ‘‘the conflict of interests arising from the interactions (real or
supposed) between marine mammals and
fisheries has, indeed, become something of
a cause celebré in recent years.’’ That certainly has not changed in the last 15 years
and likely will not change in the next 100
years. Also, as noted by Beverton (1985:4)
‘‘the world into which these mammal populations are recovering is not the same as it
Vol. 82, No. 3
FIG. 2.—Conceptual model of the interactions
in the Steller sea lion–groundfish fishery.
was when they were at their height decades
ago.’’
Although Beverton (1985) described 6
types of interactions, for simplicity, we only
summarize 3 types that are most important
to our predictions and recommendations.
Existing data are inadequate to show beyond reasonable doubt that proposed interactions are the primary mechanism driving
the system in each case; therefore, the marine mammal–fishery interactions presented
below are intended to represent an underlying process rather than a classification of
a particular interaction. It is also likely that
other anthropogenic forces (e.g., global climate change) and nonanthropogenic forces
(e.g., Pacific decadal oscillation) are important in determining the long-term state of
marine ecosystems. The degree to which
multiple factors influence the resulting species composition of marine communities remains an important question.
Steller sea lion and the groundfish fishery
of the North Pacific.—In this type of interaction (Fig. 2), the commercial fishery is
not overfished as defined in current approaches to management. However, the
fishery causes a significant reduction in biomass of the target species relative to an unfished condition and causes localized depletions of key prey species that result in a
reduction in the foraging efficiency of the
August 2001
SPECIAL FEATURE—MARINE MAMMALS
marine-mammal predator. This type of interaction likely will be the most important
of the 3 in the future, and it primarily will
affect smaller marine mammals, such as
marine otters and pinnipeds. We make these
projections because, in this type of interaction, many such fisheries are being wellmanaged as judged by the current definition
of overfishing, and we expect many if not
most fisheries in developed countries will
adopt these practices in the future. Further,
distributions of most commercial fisheries
are coastal, as are distributions of most populations of marine otters and pinnipeds. The
reason we believe that small species of marine mammals will be most involved in this
type of interaction is because they are the
ones that must balance energy needs, including those of their young, on a relatively
short time scale (i.e., days), and in a relatively small area, compared with the situation for other marine-mammal species, such
as whales. If the scale of the localized depletion caused by a fishery is on the same
scale as the foraging area of the marine
mammal, then commercial fishing likely
will affect adversely the marine-mammal
population with which it competes.
Harp seal and cod fishery of the North
Atlantic.—In this type of interaction (Fig.
3), the fishery has overharvested the target
species as a whole, or a widely distributed
subpopulation, and caused it to become severely depleted. Because of its former commercial value, a management need exists
for the stock to recover as quickly as possible. However, when the target species of
fish also is an important prey species for a
marine-mammal population, the fishing
community often puts pressure on managers
to minimize predation pressure by reducing
the predator population (even though the
actual cause of the decline may not be related to predation pressure by the marine
mammal). This interaction generally is associated with marine-mammal populations
that have broad food habits, such that the
collapse of the commercial target species
does not cause a similar collapse in the ma-
647
FIG. 3.—Conceptual model of the interactions
in the harp seal–cod fishery.
rine-mammal population. Interactions of
this type also figure heavily in the minds of
many when the marine-mammal population
is large (e.g., western North Atlantic population of harp seal), even if the marinemammal species preys on the target species
to only a minor extent. Nonetheless, even a
low level of predation by a large marinemammal population could adversely affect
the recovery of the fish species of interest.
A similar form of interaction has been proposed to describe the interaction between
populations of California sea lions (Zallophus californianus) and harbor seals (Pagophilus groenlandicus) that prey on endangered runs of salmonids and between
sea otters (Enhydra lutris) and certain species of shellfish along the west coast of
North America. This interaction will be
common if fishery managers allow widespread overfishing. Further, it will occur
when anthropogenic (e.g., pollution) and
natural factors result in severe population
declines in commercially important species
of fish and shellfish.
Hawaiian monk seal and commercial
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JOURNAL OF MAMMALOGY
FIG. 4.—Conceptual model of the interactions
in the Hawaiian monk seal–lobster fishery.
lobster fisheries in the North Pacific.—Unlike the previously described type of interaction, the marine-mammal population (or
$1 age or sex class in the population) in
this scenario (Fig. 4) is dependent on the
health of the target fish species. Therefore,
the collapse of the target species results in
the collapse of the marine-mammal population or retards its recovery, making extirpation more likely. In this situation, the
commercially harvested species typically
has a much greater reproductive potential
than does the marine-mammal population.
Consequently, recovery potential for the
commercially important fish species far exceeds that of the marine-mammal population. In such situations, extirpation of the
marine mammal is much more likely than
that of the species of commercial interest.
OVERVIEW
We have made 3 general predictions regarding competition between marine mammals and commercial fisheries over the next
100 years. First, in the 21st century, annual
worldwide landings of fish and shellfish
will remain #80–90 million tons. Because
of the imbalance between worldwide de-
Vol. 82, No. 3
mand for fishery products and production
of marine ecosystems available for human
consumption, severe pressure will exist to
remove, or at least reduce the density of,
top predators (e.g., marine mammals and
seabirds) from the marine ecosystem to
leave a greater fraction of the annual net
production for human consumption. Second, virtually all current predictions regarding species composition and energy flow
within a marine community will prove
wrong on a decadal or longer time scale
because these predictions were based on
models that were developed with incomplete information on abundance of marine
mammals, energy needs, food habits, genetic effects of fishing (Law et al. 1993),
and life history and abundance of prey species. Third, the most common type of competitive interaction between marine mammals and commercial fisheries will be that
in which commercial fisheries adversely
impact a marine-mammal population by reducing the overall biomass of a target species and then prosecuting the fishery in
such a way that food resources of marine
mammals are locally depleted without necessarily overfishing the target species of
fish or shellfish. This type of interaction primarily will affect smaller marine mammals
that are coastal in distribution, such as sea
otters and pinnipeds.
It is unclear how human society will respond to the changes likely to occur in the
future. If commercial fisheries are managed
using current management practices, it is
likely that changes will occur in the species
composition of marine communities that are
more rapid and more severe than previously
observed. This is based on recent work
(Fowler 1999a, 1999b; Fowler and Perez
1999; Fowler et al. 1999) that suggests that
if humans remove biomass from marine
ecosystems at rates that are unprecedented
in nature, ecosystems that experienced degradation (Pauley et al. 1998) will eventually
collapse or change in an unpredictable manner with undesirable consequences. The literature on management science suggests
August 2001
SPECIAL FEATURE—MARINE MAMMALS
that harvest practices of humans have led
to instability in prey populations relative to
the stability in prey populations not used by
humans, which have survived the unavoidable filter imposed by natural selection
(Fowler 1999b; Fowler and Perez 1999).
Improvements in sustainability could be
achieved if the principle of maintaining system processes (Fig. 5) were applied within
the normal range of natural variation (Fowler and Perez 1999; Fowler et al. 1999). In
all cases, human harvest rates far exceed
nonhuman harvest rates. As recommended
by Fowler (1999a, 1999b) and Fowler et al.
(1999), information about the variation in
consumption rates among other predatory
species could be used to guide fisheries to
achieve harvest levels that are within the
usual range of natural variation. Such a
practice likely would minimize the disruptive influence of fisheries on community
structure in the marine environment.
Although changes in the composition of
the marine community due to short- and
long-term changes in environmental regime
have been a persistent feature throughout
the evolution of this planet, the speed with
which these communities change when exposed simultaneously to natural and anthropogenic factors likely will cause localized
extirpations and species-level extinctions at
an unprecedented rate in the future. In part,
this will be due to the mechanism described
by Estes (1979), where long-lived species,
such as marine mammals, have not evolved
life-history mechanisms to adapt to sudden
and major changes in their environment.
Because changes may coincide with periods
of time where harvest levels of marine
products will fall well below the current
level of 80–90 million tons, local societies
may turn to predator control to minimize
nutritional and economic stresses suffered
by their members. Unless major changes
are made, the current recovery of marinemammal populations will be replaced by
regular periods in which conventional
forms of management will exercise predator
control. The impact of managing marine
649
FIG. 5.—Frequency distributions for the amount of
prey consumed at various levels of predation in the
Bering Sea (adapted from Fowler and Perez 1999). a)
Consumption of pollock (log10 tons per year) by 6 species of marine mammals compared with commercial
takes by fisheries. b) Consumption of finfish by 20
species of marine mammals, and by commercial fisheries. c) Total removal of biomass in this ecosystem
by 20 species of marine mammals in contrast to humans (fisheries). d) Consumption of biomass for the
entire marine environment comparing that for 55 species of marine mammals with the total take by fisheries. e) Expansion of the comparison of (d) to the
level of the biosphere to compare biomass consumption by the 55 species of marine mammals with the
ingestion of biomass by the entire human population.
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JOURNAL OF MAMMALOGY
mammals at levels well below their carrying capacities likely will lead to high levels
of local extirpation and species-level extinctions. This likely will occur to species
that occupy coastal habitats.
Perhaps it is best to conclude with a succinct list of predictions regarding the future
status of marine mammals. We apologize to
those offended by predictions that are largely unacceptable by today’s standards, but
we submit that today’s standards will not
matter 100 years from now. We predict that
considerably fewer extant populations and
species of marine mammals will exist by
the end of the 21st century than now, and
that coastal populations and species will be
impacted proportionally harder than noncoastal species; that predator-control programs designed to reduce or eliminate local
populations of marine mammals will be
common without changes in existing forms
of fishery management; that protein from
marine mammals will be a more important
component of the human diet than it currently is; and that harvest levels of marine
resources will be less than the current 80–
90 million tons/year. If fishery managers
adopt management strategies that are sustainable at spatial scales that encompass entire ecosystems and time scales that approach the century mark, our predictions
will be less likely to occur. If ecosystemfriendly management regimes are not
adopted, the degree to which ecosystem
health will diminish relative to the current
standard will be severe. That is, the rate and
number of species-level extinctions for all
marine species, not just marine mammals,
will continue to increase, the marine environment increasingly will become degraded, and our ability to use marine resources
to feed ourselves will be compromised severely.
ACKNOWLEDGMENTS
We thank P. K. Anderson for arranging the
symposium on how marine mammals will fare
over the next 100 years. The symposium was
successful because of his hard work and dili-
Vol. 82, No. 3
gence, as well as the fact that all of the speakers
took their assignments seriously and presented
interesting and compelling talks. We also thank
the American Society of Mammalogy for sponsoring the symposium as part of their annual
meetings. Finally, we thank P. K. Anderson, T.
Klinger, L. Mazzuca, and M. Smolen for their
review of early drafts; their comments improved
the text considerably.
LITERATURE CITED
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Special Feature Editor was Michael R. Willig.