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Marine Reserves as a Tool for Ecosystem-Based Management: The
Potential Importance of Megafauna
Source: BioScience, 54(1) : 27-39
Published By: American Institute of Biological Sciences
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Marine Reserves as a Tool for
Ecosystem-Based Management:
The Potential Importance of
Marine predators attract significant attention in ocean conservation planning and are therefore often used politically to promote reserve designation. We discuss whether their ecology and life history can help provide a rigorous ecological foundation for marine reserve design. In general, we
find that reserves can benefit marine megafauna, and that megafauna can help establish target areas and boundaries for ecosystem reserves. However, the spatial nature of the interplay between potential threats and predator life histories requires careful consideration for the establishment of
effective reserves. Modeling tools such as demographic sensitivity analysis will aid in establishing protection for different life stages and distributional ranges. The need for pelagic marine reserves is becoming increasingly apparent, and it is in this venue that marine predators may be most
effectively used as indicator species of underlying prey distribution and ecosystem processes.
Keywords: marine predators, conservation, marine reserves, indicator species, modeling
The seas are by no means dead, but they are
unquestionably less alive than they were when
humanity discovered them.
—Leatherwood and Reeves (1983)
he state of the global oceans is rapidly deteriorating,
with dire consequences for marine species (Jackson et al.
2001). Historically, most conservation efforts have focused on
terrestrial systems, but it is becoming increasingly apparent
that conservation efforts are urgently required for the oceans
as well (Myers et al. 1997, Casey and Myers 1998). Recently,
significant attention has been given to the establishment of
marine reserves (Boersma and Parrish 1999, Mangel 2000),
with most of the focus of research directed at economically
valuable (i.e., mid–trophic level) species (Rowley 1994). Some
of the lessons learned from these reserves have now been
widely accepted (e.g., bigger is better, and dispersal matters;
NCEAS 2001). However, one of the most interesting questions
to emerge from the initial exploration of marine reserve design theory is the significance of life-history characteristics.
Here we review issues concerning the ecology of higher
predators and their relevance for the design and selection of
marine reserves.
The grouping of higher marine predators describes ocean
megafauna, including a variety of taxa: cetaceans, pinnipeds,
sea otters, polar bears, seabirds, sharks, cephalopods, and
predatory fish. Our primary expertise is in marine mammal
ecology, and so most of our review focuses on the ecology and
conservation of this group. Nevertheless, many aspects of
these species’ ecology, life history, and demography apply to
other marine predators as well, allowing us to propose certain generalities that apply to all marine predators. There is
currently a trend toward the advocation and establishment of
marine sanctuaries based on their marine megafauna, and particularly their mammal or bird fauna (table 1). However,
systematic theory on how to select, design, and monitor these
reserves is lacking, and their efficacy in protecting marine
predators is not clear. We discuss two issues here: (1) the
potential for marine reserves to protect marine predators, and
(2) the question of whether these species can serve as ecological
indicators, demonstrating where and how to target and
design marine reserves. This article is loosely based on
Sascha K. Hooker (e-mail: is a Royal Society
Dorothy Hodgkin Research Fellow in the Sea Mammal Research Unit at the
University of St. Andrews, Fife, KY16 9LB, Scotland. She studies marine
mammal foraging behavior, its relationship with the surrounding oceanographic
environment, and the implications for marine conservation. Leah R. Gerber
is an assistant professor in the School of Life Sciences at Arizona State
University, Tempe, AZ 85287. She works on developing approaches to connect
scientific uncertainty to decisionmaking in endangered species recovery,
marine reserve design, and disease and conservation. © 2004 American
Institute of Biological Sciences.
January 2004 / Vol. 54 No. 1 • BioScience 27
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Table 1. Examples of marine conservation areas established on the basis of their marine mammal and marine bird fauna.
Country/region Type of reserve
Whale sanctuary,
International Whaling Commission
European candidate special
area of conservation
International sanctuary for
Mediterranean cetaceans
Europe (France,
Monaco, and
National park
Marine national park
Conservation park
Marine park
New Zealand
Marine mammal sanctuary
Biosphere reserve
Whale sanctuary (marine
provincial park)
Ecological reserve
National humpback whale
Marine national park
Pilot marine protected area
Special reservation (US
Department of the Treasury)
Fish cultural and forest
reserve (Forest Reserves Act)
Año Nuevo State Park
National marine sanctuaries
National marine sanctuary
United States
United States
United States
United States
United States
Geographic area
Faunal basis for establishment
Southern Ocean
Baleen whales and sperm whale (for
recovery from historical human exploitation)
Bottlenose dolphin
Moray Firth, United Kingdom
Ligurian Sea, Mediterranean
Wadden Sea, Germany
Great Australian Bight, southern
Seal Bay, Kangaroo Island,
South Australia
Macquarie Island, Subantarctic
Fin, sperm, Cuvier’s beaked, and long-finned
pilot whales; Risso’s, striped, bottlenose,
and short-beaked common dolphins
Harbor porpoise
Southern right whale, Australian sea lion
(breeding colonies)
Australian sea lion, New Zealand fur seal
Subantarctic fur seals, Antarctic tern, fairy
prion, grey and blue petrels, and blackbrowed and wandering albatrosses (foraging
Hector’s dolphin
Southern right whale
Banks Peninsula, South Island
Upper Gulf of California
Golfo San Jose,
Peninsula Valdes
Lobos Island
Silver Bank
South American sea lion and fur seal
Humpback whale
Saguenay–St. Lawrence, Quebec
The Gully, eastern Canada
Pribiloff Islands (St. Paul and
St. George)
Afognak Island, Alaska
Beluga whale
Northern bottlenose whale
Northern fur seal (regulating commercial
Seals, walrus, and sea otters
Año Nuevo, California
Channel Islands, California
Hawaiian Islands
Northern elephant seals
Several marine mammal and bird species
Humpback whale
Source: Reeves 2000.
discussion generated by a symposium that we hosted at the
annual meeting of the Society for Conservation Biology in
2001, which focused on case studies and modeling approaches
in the design of marine reserves for marine megafauna.
Marine reserves
To date, conservation work has generally employed a triage
approach: Species receive protection only after it has been
demonstrated that there is a pressing need for such protection. Many of the conservation efforts around the world,
therefore, focus on threatened or rare species (Soulé and
Orians 2001). This focus has driven much of the legislation
on conservation, which often lists species as a mechanism to
initiate efforts to protect them (see, e.g., the Endangered
Species Act and the Marine Mammal Protection Act in the
United States). However, there has been an increasing emphasis
on the need to use ecosystems, communities, and assemblages, rather than single species, as the basis for conservation.
Reserves have the potential to take this type of holistic approach (rather than traditional single-species recovery models), providing protection both to the species of concern and
to the entire ecosystem.
However, applying models developed for terrestrial systems
to the marine environment is not straightforward. Terrestrial
and marine systems are quite different ecologically in terms
of spatial structure, scale, and trophic structure (Soulé and Orians 2001). The difficulty of placing boundaries around ecosystems is exacerbated in the marine environment, where borders are dynamic and fluid. The pelagic marine environment
is vast in scale, and marine reserve areas consequently often
need to be larger than their terrestrial equivalents. There are
also differences between basic ecological structures in marine
and terrestrial environments, most notably dynamism and
connectedness (Link 2002). The spatial discreteness of terrestrial ecosystems, which allows straightforward identification of habitats to protect, is not evident in the majority of
oceanic ecosystems, which may be transient in space and
Most conservation initiatives are driven by economic opportunities and constraints. In terrestrial settings, the hunting and, more recently, tourism industries have often spurred
conservation initiatives; in the marine environment, the majority of economic pressure has come from failing fisheries.
Thus, most work on marine conservation issues, and recently most evaluation of marine reserves, has been concerned with fishery recovery (NRC 2001). A recent review of
models pertaining to marine reserves (Gerber et al. 2003)
showed that none explicitly addressed reserves for top
28 BioScience • January 2004 / Vol. 54 No. 1
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predators, few included explicit movement, and there was little focus on
extinction risk or multispecies interactions.
In spite of the lack of a solid theoretical foundation, large ocean
megafauna—marine mammals and
birds—are often used to direct conservation efforts (table 1, figure 1). Yet
these initiatives often have little ecological basis and are driven by public
affection toward charismatic species.
That said, marine mammals are relatively vulnerable to extinction. Of the
approximately 120 currently recognized marine mammal species, 4
species or significant populations have
gone extinct, 11 are thought to be in
imminent peril of extinction, 17 are
thought to be of significant concern
with respect to extinction, and 8 were
once thought to be at risk of extinction
but are now recovering (table 2; VanBlaricom et al. 2000).
Definitions and goals
We define a marine protected area as
a geographic area designated for protection. This may include a broad area
with limited management restrictions
(e.g., prohibiting some activities such
as seismic exploration) but may also
encompass smaller “marine reserve
areas”—zones designated as closed to
extraction (NRC 2001). In this article, we focus on the degree to which the
spatial nature of marine protected
areas can promote recovery and en- Figure 1. (a) Bottlenose whales in the Gully, eastern Canada. The Gully has been
hance protection from the threats that designated a pilot marine protected area, largely because of the northern bottlenose
marine predators face. The question of whales found there. These whales often spend periods of time resting at the surface
whether marine reserves will provide between foraging dives. Threats to these and other cetaceans in this region include
protection and will prohibit the activi- ship strikes, noise pollution from exploitation and exploration, and interactions with
ties that threaten these predators longline fisheries. Photograph: Hal Whitehead laboratory. (b) Humpback whales in
or their ecosystems is a key issue. A Hawaii. The Hawaiian Islands Humpback Whale National Marine Sanctuary was
major criticism of marine reserves gen- established to protect breeding humpback whales. In general, threats are low in this
erally, and particularly several of those area, although a growing whale-watching industry and acoustic testing nearby may
established for marine mammals, is be causes for concern. Photograph: Robin W. Baird.
that they represent “paper parks” that
provide a false sense of conservation achievement (Duffus and
harvested fish or invertebrate populations to help support
Dearden 1995). This criticism stems from the lack of regulafisheries outside the reserve. The ranking of these goals will
tion and policing or wardening for such reserves or sanctudepend on the societal and economic pressures for a given
aries (Hooker et al. 1999).
region. Here, for the most part, we focus on the impact of
The goals of establishing a marine protected area are sevreserves on higher predators, although we also consider
eral: conservation of biodiversity (minimizing extinction
multispecies and multipurpose reserves in terms of whether
risk), ecosystem protection, reestablishment of ecosystem
fishery enhancement is possible in conjunction with conserintegrity, and enhancement of the size and productivity of
vation of higher predators.
January 2004 / Vol. 54 No. 1 • BioScience 29
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Table 2. Marine mammal species, subspecies, and populations that are extinct, at risk of extinction, or recovering from
near-extinct status.
Species (population)
Latin name
Extinct (4)
Steller’s sea cow
Caribbean monk seal
Japanese sea lion
Gray whale (North Atlantic)
Hydrodamalis gigas
Monachus tropicalis
Zalophus japonicus
Eschrichtius robustus
In imminent peril of extinction (11)
Indian river dolphin (Indus river)
Mediterranean monk seal
Gray whale (western North Pacific)
Right whale (eastern North Pacific)
Right whale (North Atlantic)
Bowhead whale (Davis Strait, Hudson Bay,
Spitsbergen, Barents Sea, and Sea of Okhotsk)
Beluga whale (Gulf of Alaska)
Beluga whale (Gulf of St. Lawrence)
Ringed seal (Lake Saimaa)
Lipotes vexillifer
Phocoena sinus
Platanista gangetica
Monachus monachus
Eschrichtius robustus
Balaena glacialis
Balaena glacialis
Balaena mysticetus
Of significant concern (17)
Blue whale
Hawaiian monk seal
Ringed seal (Baltic Sea)
Ringed seal (Lake Ladoga)
Harbor seal (western North Pacific)
Steller’s sea lion (western North Pacific)
Australian sea lion
Hooker’s sea lion
Guadalupe fur seal
Juan Fernandez fur seal
Walrus (Atlantic)
Walrus (Laptev Sea)
Amazonian manatee
West African manatee
West Indian manatee
Sea otter (California)
Marine otter
Balaenoptera musculus
Monachus schauinslandi
Pusa hispida botnica
Pusa hispida ladogensis
Phoca vitulina stejnegeri
Eumetopias jubatus
Neophoca cinerea
Phocarctos hookeri
Arctocephalus townsendi
Arctocephalus philippii
Odobenus rosmarus rosmarus
Odobenus rosmarus laptevi
Trichechus inunguis
Trichechus senegalensis
Trichechus manatus
Enhydra lutris nereis
Lutra felina
Once thought to be faced with
extinction but now recovering (8)
Bowhead whale (western Arctic)
Humpback whale
Gray whale (eastern North Pacific)
Northern elephant seal
Galapagos fur seal
Subantarctic fur seal
Antarctic fur seal
Sea otter (North Pacific and Russian coastal waters)
Balaena mysticetus
Megaptera novaeangliae
Eschrichtius robustus
Mirounga angustirostris
Arctocephalus galapagoensis
Arctocephalus tropicalis
Arctocephalus gazella
Enhydra lutris kenyoni
Delphinapterus leucas
Delphinapterus leucas
Pusa hispida saimensis
Source: VanBlaricom et al. 2000.
Marine predators and marine reserves
Threats to marine predators may take several forms (box 1,
figure 2; Richardson et al. 1995, Simmonds and Hutchinson
1996, Coe and Rogers 1997). Physical threats may include
strikes from ships or entanglement by fisheries, often leading
to the death of individual animals. Acoustic or environmental impacts may be more insidious. Seismic exploration, military exercises, shipping, or drilling may have far-reaching
acoustic impacts that cause species to leave an area, to become
temporarily unable to forage, or even to sustain physical
damage. Similarly, pollution, dumping, and oil spills may
increase the risk of extinction by increasing mortality. Ingestion
of plastic debris, oil contamination, and pollutants may have
an incremental effect on animals throughout their lives,
ultimately resulting in immunosuppression or reproductive
failure. Potentially irreparable ecosystem changes caused
by competition for resources may radically alter ecosystem
structure, resulting in dramatic shifts in population demographics (e.g., the Southern Ocean; May 1979), and habitat
disturbance or destruction can result in spatial shifts to
distribution or migration routes due to loss of cultural
memory. Many of these threats may be mitigated by spatial
In protecting a specific population, the optimal protected
area would encompass that population’s year-round distribution (Reeves 2000). However, for many marine predators, the
year-round distribution of a population may span entire
ocean basins. The question therefore becomes whether limited spatial protection in specific parts of a species’ range is
worthwhile. In some cases, when only a portion of a wideranging predator population may use a protected area, there
may be the potential for recolonization of overexploited
30 BioScience • January 2004 / Vol. 54 No. 1
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Box 1. Threats to higher predators
and to the ecosystem
Direct threats
Direct threats are those that cause mortality of top predators.
Fishery bycatch. Several seabird and cetacean species are
killed in fisheries around the world. The establishment of
reserves can mitigate these population-level impacts and
reduce exposure at an individual level.
Direct killing. In some places, seabird, cetacean, and pinniped
species are still the focus of directed hunts.
Ship strikes. In certain areas there are increased risks of ship
strikes. For instance, in the Bay of Fundy, in the northeastern
United States, ship traffic en route to Boston presents a large
threat to northern right whales.
Indirect threats
Rather than causing immediate death, these insidious threats
may cause accumulating harm over longer time scales.
Overexploitation of lower trophic levels. By removing lower
trophic levels from the food chain, nutritional stress may be
imposed on upper t …
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