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AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS
Aquatic Conser6
:
Mar.Freshw.Ecosyst.10: 437–458 (2000)
VIEWPOINT
Marine protected areas and ocean basin management
K. DAVID HYRENBACH
a,
*, KARIN A. FORNEY
b
and PAUL K. DAYTON
a
a
Scripps Institution of Oceanography,La Jolla,California,USA
b
Southwest Fisheries Science Center,National Marine Fisheries Ser6ice,Monterey,California,USA
ABSTRACT
1. All reserve designs must be guided by an understanding of natural history and habitat
variability.
2. Differences in scale and predictability set aside highly dynamic pelagic systems from terrestrial
and nearshore ecosystems, where wildlife reserves were first implemented. Yet, as in static systems,
many pelagic species use predictable habitats to breed and forage. Marine protected areas (MPAs)
could be designed to protect these foraging and breeding aggregations.
3. Understanding the physical mechanisms that influence the formation and persistence of these
aggregations is essential in order to define and implement pelagic protected areas. We classify
pelagic habitats according to their dynamics and predictability into three categories: static,
persistent and ephemeral features.
4. While traditional designs are effective in static habitats, many important pelagic habitats are
neither fixed nor predictable. Thus, pelagic protected areas will require dynamic boundaries and
extensive buffers.
5. In addition, the protection of far-ranging pelagic vertebrates will require dynamic MPAs
defined by the extent and location of large-scale oceanographic features.
6. Recent technological advances and our ability to implement large-scale conservation actions
will facilitate the implementation of pelagic protected areas.
7. The establishment of pelagic MPAs should include enforcement, research and monitoring
programmes to evaluate design effectiveness.
8. Ultimately, society will need a holistic management scheme for entire ocean basins. Such
overarching management will rely on many innovative tools, including the judicious use of pelagic
MPAs.
Copyright © 2000 John Wiley & Sons, Ltd.
KEY WORDS
: fronts; highly migratory species; marine protected area (MPA); migration routes; ocean basin
conservation; pelagic conservation; seamounts
INTRODUCTION
Once viewed as the ultimate wilderness, it is increasingly apparent that the oceans have been heavily
affected by human activities. The most serious impacts result from the diverse perturbations of fishing,
including the consumption of 25– 35% of the primary production from upwelling and temperate
continental shelves, the virtual removal of the top of coastal and pelagic food webs, the gross depletion
* Correspondence to: K. David Hyrenbach, Scripps Institution of Oceanography, La Jolla, CA 92093-0208, USA. E-mail:
khyrenba@coast.ucsd.edu
Copyright © 2000 John Wiley & Sons, Ltd. Received 19 April 2000
Accepted 15 August 2000
K.D. HYRENBACH
ET AL.
438
of target stocks, and the massive wastage of bycatch (Alverson et al., 1994; Dayton et al., 1995; Pauly and
Christiensen, 1995; Pauly et al., 1998).
Jean Baptiste Lamarck and Thomas Huxley considered marine organisms immune to extinction because
they were so plentiful and productive. This notion reflects the widespread belief of the 18th and 19th
centuries that inexhaustible ocean resources would never be depleted by human activities. In recent years,
however, the mounting number of extinctions and local extirpations suggests that the risk of extinction in
marine systems is greater than we have assumed (Brander, 1981; Carlton, 1993; Casey and Myers, 1998).
Currently, threatened pelagic species include invertebrates, teleosts, elasmobranchs, marine turtles,
seabirds, pinnipeds and cetaceans (Safina, 1995; Croxall and Gales, 1997; Roberts and Hawkins, 1999).
In the face of continued habitat degradation and mounting fishing pressure, this list is certain to increase
in the future.
One of the most pragmatic approaches to ocean conservation is to establish marine protected areas
(hereafter referred to as MPAs). Because the term MPA has been applied to many different concepts, we
use the expression in the generic sense to include a variety of management tactics. MPAs have been widely
proposed to protect estuarine and coastal systems, fisheries resources, critical habitats of endangered
species and parks for public enjoyment (Ray, 1976; Agardy, 1994; Murray et al., 1999). Often, the result
is a complicated patchwork of coastal sanctuaries, ecological reserves, refuges, national marine sanctuaries
and marine parks designed to meet disparate objectives and subject to different regulations. In California,
for example, 103 MPAs with 12 different denominations had been established by 1997 (McArdle, 1997).
While most discussions of MPAs have focused on nearshore habitats, such as intertidal communities
and coral reefs, protected areas have rarely been considered in pelagic conservation. Throughout this
paper, ‘pelagic’ refers to species, processes and ecosystems that occur in the water-column and are not
attached to the substrate. However, pelagic and benthic systems are coupled, and many water-column
properties arise from the interactions of currents with features of the sea floor. Our use of the term
‘pelagic’ does not involve political considerations, merely function and structure. Thus, ‘pelagic’ species
inhabit continental shelves, 200-mile Economic Exclusive Zones, and the ‘high seas’ beyond national
boundaries.
MPAs have not been used in pelagic conservation due to the open and dynamic nature of the high seas,
which inhibit MPA design and enforcement (Robinson, 1992; De Fontaubert et al., 1996; Boersma and
Parrish, 1999). Traditionally, pelagic systems are managed with single-species approaches, and
conservation relies on the improvement of regulations (e.g. quota enforcement and size restrictions) and
the modification of fishing gear (e.g. pingers and tori lines). Many of these regulations are dependent
upon accurate scientific knowledge of the life history, migratory patterns and influence of environmental
variability on population dynamics of the target species. Such information is difficult to obtain, and is
rarely available for commercially unimportant species (e.g. bycatch). The failure of single-species
management is exemplified by the overfished status of fish stocks worldwide, and by the pervasive
ecosystem-level impacts of bycatch (Dayton et al., 1995; Pauly et al., 1998).
This paper is designed to stimulate discussion and research on the implementation of pelagic protected
areas. We believe that the conservation of far-ranging pelagic species, both targeted and killed incidentally
by fishing, represents the most pressing problem; hence, we focus our review on the conservation of the
large vertebrates (fish, birds, turtles and mammals). Here, we highlight those habitat features that might
be used to identify and implement MPAs to protect these far-ranging species. We hope to build on the
paper by Mills and Carlton (1998), with full understanding that meaningful conservation efforts can only
succeed with the support of an international consensus based on an appreciation of oceanographic and
biological processes.
We hope the world community will respond to this growing crisis with the innovative integrated
management of entire ocean basins. Such management might be modelled after other successful
international agreements, such as the Convention for the Conservation of Antarctic Marine Living
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Resources (CCAMLR) or the International Whaling Commission (IWC). These agreements are far
beyond the scope of this paper. Our intention is to argue that in principle large-scale reserves can be
applied to the highly dynamic marine habitat, and can offer important tools for such ocean basin
management.
GENERAL CONSIDERATION OF PELAGIC SYSTEMS
For all systems, reserve designs must relate to both the ecology (e.g. habitats, ambits and migrations) and
the life history (e.g. mode of reproduction, ontogenetic habitat changes and social system) of the relevant
species, as well as the inherent variability of their habitats (e.g. disturbances, oceanographic regimes and
climatic change) (Ray and McCormick-Ray, 1993; Russ and Alcala, 1998; Boersma and Parrish, 1999).
Pelagic systems are inherently different from terrestrial landscapes where wildlife reserves were first
implemented. Terrestrial and marine ecosystems differ in the ecological constraints shaping life, in the
processes responsible for pattern, and in the dominant scales of physical and biological variability (Smith,
1978; Steele, 1985). The distributions of pelagic species are largely dictated by the intricacies of water flow,
and by the coupling of physical and biological processes that promote the growth and retention of
planktonic populations (Haury et al., 1978; Steele, 1978; McGowan and Walker, 1985). These, in turn, are
mediated by physical forcing dominated by large scales of time and space, between seasons and decades
and tens to thousands of kilometres (meso to mega scales; Stommel, 1963; Smith, 1978; Denman, 1994).
The dynamic nature of pelagic systems and the prevalence of variability over large scales blur the linkages
between physical and biological processes, spreading biotic interactions over spatial scales that greatly
exceed those prevalent in terrestrial systems (Vinogradov, 1981; Steele, 1985; Jaquet et al., 1996).
In spite of these intrinsic differences, some design issues and objectives of pelagic protected areas are
similar to those in nearshore and terrestrial systems. Similarities exist where properties of pelagic systems
derive from physical features that are geographically fixed or predictable, and when the objective is to
protect a static habitat (e.g. seamounts, mangroves or salt marshes), or a relatively sedentary species (e.g.
orange roughy, Hoplostethus atlanticus). Conversely, important differences arise from the unique, dynamic
properties of many pelagic systems. In particular, the issues of scale and predictability, which in turn drive
the extreme mobility exhibited by many pelagic species, will require new approaches and concepts before
effective pelagic MPAs can be implemented.
The simplest scenario involves protecting sedentary species or well-defined, geographically fixed habitats
with static protected areas (Agardy, 1994; Boersma and Parrish, 1999; Probert, 1999). However, even in
terrestrial systems, static protected areas have failed in cases where threatened species were highly-mobile
or migratory, because impacts outside of the protected areas were not mitigated or adequately understood
(Robbins et al., 1989; Boersma and Parrish, 1999). In pelagic systems, where many species range over
thousands of kilometres, and where migration routes are dynamic and poorly understood, the conservation
of highly-mobile and migratory species remains a most serious challenge.
The emperor penguin (Aptenodytes forsteri ) exemplifies the challenges posed by the conservation of
highly migratory pelagic species (Figure 1). After dispersing from their colonies, adult emperor penguins
remain within the Ross Sea. On the other hand, fledglings venture north of the 60th parallel, the boundary
defined by the Antarctic Treaty to protect Antarctic living resources (Kooyman et al., 1996). Pelagic species
forage far from their breeding areas and do not respect arbitrary boundaries imposed by managers.
Moreover, many pelagic predators, including pinnipeds, penguins, sharks and albatrosses, have complex
foraging strategies involving the segregation of different genders and age classes at sea (Strasburg, 1958;
Prince et al., 1992; Steward and DeLong, 1995; Kooyman et al., 1996). Thus, rigid designs based on politics
or convenience will likely lead to ineffective protected areas. Conversely, the boundaries of effective pelagic
MPAs will have to be guided by an understanding of natural history and habitat variability.
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Figure 1. An understanding of natural history is vital to delineate effective pelagic protected areas. Fledging emperor penguins
(hatched lines) disperse north of 60°S, the boundary defined by the Antarctic Treaty to protect them (December–March,
1995–1996). Redrawn from Kooyman et al. (1996).
The discussion of pelagic MPAs below includes both geographically restricted regions, which can be
important feeding or breeding grounds for marine predators, and larger oceanographic features at the
scale of entire ocean basins. This distinction is important because networks of isolated MPAs can protect
species in a given time and place, but most pelagic predators are far-ranging. Thus, effective pelagic
conservation will require consideration and protection of entire migration routes.
APPLYING MPA CONCEPTS TO PELAGIC SYSTEMS
Pelagic systems represent a vast and featureless landscape to our untrained eyes. Nevertheless, pelagic
species are not distributed randomly. Instead, their patchy distributions are influenced by patterns of
productivity and prey abundance, which are, in turn, driven by physical forcing at multiple scales (Haury
et al., 1978; Hunt and Schneider, 1987; Denman, 1994).
The transition from weekly-moving planktonic to actively-moving nektonic organisms introduces
additional MPA design complications because behaviour becomes an increasingly important determinant
of species distributions (Weber et al., 1986; Hunt and Schneider, 1987). Physical processes drive the timing
and magnitude of primary production (Holligan, 1981; Owen, 1981; LeFevre, 1986), and influence the
distribution of planktonic organisms (Haury et al., 1978; Wolanski and Hamner, 1988; Franks, 1992).
Conversely, large and mobile pelagic vertebrates are often decoupled from the underlying physical
structure because they can regulate their position with respect to the water flow (Denman, 1994;
Schneider, 1994). The distributions of marine predators and their prey may also be decoupled at small
spatial scales as a result of predator avoidance behaviour (e.g. Logerwell and Heargreaves, 1996), the
existence of prey refuges (e.g. Rose and Leggett, 1990), the inability of predators to profitably exploit
small patches (e.g. Piatt, 1990), and the failure to detect (e.g. Logerwell et al., 1998) and to aggregate at
small and ephemeral prey patches (e.g. Obst, 1985).
Yet, in spite of the potential decoupling between physical processes and nekton dispersion, there is
strong evidence that physical forcing does influence the distribution of pelagic vertebrates at multiple
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scales. Over ocean basins (thousands of kilometres), the ranges of nektonic species frequently mirror
large-scale oceanographic domains and current systems known to influence primary productivity and
plankton biogeography (Sund et al., 1981; Ballance et al., 1997; Brodeur et al., 1999). At finer scales (tens
to hundreds of kilometres), nekton distributions are likely mediated by the dispersion and availability of
prey (Hunt and Schneider, 1987; Rose and Leggett, 1990; Hunt et al., 1999). Cetaceans, seabirds and large
predatory fish exploit predictable regions of enhanced productivity and prey aggregation associated with
bathymetric gradients, water mass boundaries and upwelling plumes (Sund et al., 1981; Fiedler et al.,
1998; Hunt et al., 1998).
Knowledge of the dynamics and the scales of the processes responsible for the formation of these
important habitat features is essential to define and implement pelagic protected areas. In particular, the
degree to which habitat features reoccur, the amount of time they persist, and how much their location
and extent vary in time and space will determine the feasibility of pelagic MPAs. We have classified
habitat features into three categories according to their predictability and dynamics: static bathymetric,
persistent hydrographic and ephemeral hydrographic features. These represent progressively more difficult
systems for the implementation of MPAs. For these three types of habitat features, we describe the scales
of the relevant physical forcing functions, provide evidence of their biological effects, and discuss possible
management options to define and implement MPAs. We direct the readers to the extensive reviews by
Owen (1981), Robinson (1983), Boehlert and Genin (1987), Roden (1987), Schneider (1991), Olson et al.
(1994), and Hunt et al. (1999) for a more thorough discussion of physical– biological interactions in
marine systems.
Static bathymetric features
Many pelagic predators aggregate at static bathymetric features, such as reefs, shelf breaks, submarine
canyons, seamounts and in the lee (downstream) of islands. Irregularities of the sea floor often alter water
flow above them, enhance mixing, and promote upwelling of nutrient-rich waters. In turn, increased
turbulence and water-column mixing promote localized production and the aggregation of planktonic
prey at secondary convergence zones, persistent eddies and fronts (Thompson and Wolanski, 1984;
Simpson and Tett, 1986; Wolanski and Hamner, 1988). In addition to promoting and retaining elevated
localized production, bathymetric features can also enhance foraging opportunities for predators by
concentrating and making prey accessible. For instance, turbulent flow over banks and along passes often
drives zooplankton into surface waters and concentrates vertically migrating organisms into subsurface
patches, which are readily exploited by near-surface predators (Simard et al., 1986; Hunt et al., 1998,
1999).
Shelf breaks and submarine canyons also constitute important foraging habitats for pelagic vertebrates,
including seabirds, pinnipeds, cetaceans, salmon and swordfish. These marine predators exploit elevated
primary production and high standing stocks of zooplankton, fish and squid in the vicinity of shelf breaks
(Fournier et al., 1979; Simard et al., 1986; Springer et al., 1996). Two mechanisms have been invoked to
explain prey aggregations at shelf breaks: first, high primary production stimulates the localized
production of higher trophic levels; and second, shelf break fronts aggregate prey produced elsewhere
(Schneider, 1991; Springer et al., 1996). In addition, there is evidence that shallow shelves and ledges
adjacent to deep-water areas trap vertically-migrating zooplankton in shallow waters, where it is accessible
to diving predators (Schoenherr, 1991; Hunt et al., 1996; Fiedler et al., 1998).
Even though most examples of bathymetric physical forcing originate from coastal waters (Doty and
Oguri, 1956; Hunt et al., 1998), there is mounting evidence that similar mechanisms are at play in offshore
systems. Obstacles such as islands and guyots interact with ocean currents and promote water-column
mixing, which in turn stimulates primary production. In addition, eddies and stationary vortices, called
Taylor columns, stimulate primary production in the vicinity of guyots by bringing cold, nutrient-rich
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water closer to the surface (Boehlert and Genin, 1987; Roden, 1987; Comeau et al., 1995). The closed
circulation associated with these features likely retains the enhanced local production in the vicinity of
seamounts (Uda and Ishino, 1958; Boehlert and Genin, 1987). In turn, much of this localized production
is transferred to resident predators, such as euphausiids and rockfishes (Genin et al., 1988; Haury et al.,
1995; Koslow, 1997), which in turn support dense aggregations of mobile predators, including seabirds,
tuna and marine mammals (Sund et al., 1981; Ensor and Shaughnessy, 1990; Haney et al., 1995).
In summary, seamounts represent areas of high production and important foraging grounds of
predictable prey aggregation. In addition, the ecological significance of seamounts is underscored by
evidence that, oftentimes, they constitute the mating and spawning areas of far-ranging pelagic species.
For example, despite its vast range, pelagic armorhead (Pentaceros wheeleri ) spawning in the north Pacific
is restricted to seamounts along the southern Emperor– northern Hawaiian Ridge between 29° and 35°
latitude north (Boehlert and Sasaki, 1988). Similarly, there is evidence that far-ranging species, such as the
scalloped hammerhead (Sphyrna lewini ), aggregate in the vicinity of seamounts (Klimley, 1993).
Predictable mating aggregations of wide-ranging pelagic species are susceptible to destructive pulse
fisheries, which frequently also heavily damage slow-growing resident fish and invertebrate communities
(Dayton et al., 1995; Koslow, 1997; Koslow and Gowlett-Holmes, 1998).
Persistent hydrographic features
Persistent hydrographic features, such as currents and frontal systems, represent some of the best known
oceanographic patterns (Franklin, 1786; Sverdrup et al., 1942; Favourite et al., 1976). Fronts have long
been recognized as regions of elevated biological activity in continental shelves, where seabirds, marine
mammals and tunas aggregate to exploit prey concentrations supported by elevated production and
retention at convergences (Laurs et al., 1984; Briggs et al., 1988; Hunt et al., 1996). Similarly, oceanic
fronts and water mass boundaries are important features of the circulation, biogeography and ecology of
the world’s oceans (Sverdrup et al., 1942; Fager and McGowan, 1963; Laurs and Lynn, 1991).
In pelagic systems, changes in the types and abundances of marine organisms often occur at persistent
fronts, where waters of different temperature and salinity meet (Sund et al., 1981; Gould and Piatt, 1993;
Brodeur et al., 1999). Moreover, persistent hydrographic features constitute important foraging areas of
predictable primary production and prey aggregation (Ogi, 1984; Laurs and Lynn, 1991; Gong et al.,
1993). The high predictability and the persistence of oceanic fronts make them ideal signposts and
highways, delineating the migratory routes of pelagic species in otherwise featureless landscapes (Olson
and Podesta, 1987; Yoder et al., 1994; Morreale et al., 1996; Table 1).
Table 1. Spatial predictability of the frontal regions defining the transition zone in the subarctic North Pacific
Feature predictabilityOceanographic survey
Years Front MeanLatitude SpatialLongitude ReferencesMonths
variability(range) latitude(range)
1981–1986 SFZ 43°N 50 km39°– 48°N Roden (1991)170°E July
150 kmSFZ Roden (1991)43°N1981–198639°– 48°N 175.5°E July
42.5°– 45°N2.5° latitude Ignell et al. (1995)38.5°– 47.5°N 175.5°E July 1978–1991 SFZ
Yatsu et al. (1993)2° latitude43°– 45°NSFZ1984–199035°– 47°N 155°E–145°W May–
December
SAB 38.5°– 42°N 3.5° latitude38.5°– 47.5°N 175.5°E July Ignell et al. (1995)1978–1991
1984–1990 SAB 40°– 42°N35°– 47°N 155°E–145°W May– 2° latitude Yatsu et al. (1993)
December
The subarctic frontal zone (SFZ) separates subarctic proper and transition zone waters, and the subarctic boundary (SAB) separates
transition zone and subtropical waters.
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In the North Pacific, a narrow (40°– 44°N) region of strong temperature and salinity gradients, termed
the Transition Domain, is of particular biological importance (Fager and McGowan, 1963; Lynn, 1986;
Roden, 1991). The fronts delineating the extent of this oceanographic domain delimit the ranges of
subarctic and subtropical species, and influence the distribution of far-ranging fish, seabirds and marine
mammals (Laurs and Lynn, 1991; McKinnell and Waddell, 1993; Ignell et al., 1995). These frontal zones
contain the highest standing stocks of micronekton (small squids, small fishes and crustaceans) in the
North Pacific during the boreal spring and summer (Aron, 1962; Shimazaki, 1986; Pearcy, 1991). The
total fish and squid biomass caught at standardized drifnet sampling stations tripled from 100– 300 kg in
subtropical and subarctic waters, north and south of the Transition Domain, to 300– 1200 kg within the
waters of the Transition Domain (Shimazaki, 1986). These predictable prey aggregations are, in turn,
exploited by a variety of far-ranging predators which migrate into subarctic waters seasonally (Mishima,
1981; Ogi, 1984; Yatsu et al., 1993).
Nevertheless, the significance of the Transition Domain goes beyond the abundance and diversity of its
fauna. This region represents a vital foraging habitat and migratory route for many species, including
valuable fisheries resources (salmonids and albacore tuna Thunnus alalunga), and vulnerable non-target
species (albatrosses, shearwaters, sharks and turtles) (Table 2). Moreover, many cosmopolitan squid, fish,
mammals, birds and the endangered loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea)
turtles migrate across the Transition Domain following the North Pacific current (Laurs and Lynn, 1991;
Weatherall et al., 1993; Springer et al., 1999).
Perhaps the most significant ecological role of the Transition Domain is as a breeding and nursery
ground for far-ranging organisms. Many pelagic species, such as squids and sharks, segregate according
to age and sex, with the larger and more fecund individuals venturing farther north into the colder, more
productive subarctic Pacific (Strasburg, 1958; Mishima, 1981; Sinclair, 1991; Murata and Hayase, 1993).
For instance, blue shark (Prionace glauca) catches north of 40°N consist exclusively of large females,
whereas younger individuals of both genders are caught in waters to the south (Strasburg, 1958).
Similarly, neon flying squid (Ommastrephes bartrami ) seasonal migration patterns differ between genders
and across body size, with the larger females ranging farther north (Sinclair, 1991).
The Transition Domain also represents a nursery for the juveniles of far-ranging species during their
first years at sea. For instance, the summer migration route of albacore tuna between the spawning areas
in the western Pacific and North America runs through the Transition Domain (Laurs and Lynn, 1991).
Juveniles between 1– 4 years of age were incidentally taken in squid drifnets as they migrated through the
Transition Domain (Bartoo et al., 1993; Yatsu et al., 1993). Similarly, Gould and Piatt (1993) reported
that 79 and 88% of all sooty (Puffinus griseus) and short-tailed (P.tenuirostris) shearwaters recovered
from gillnets during the 1980s were immature birds commuting to the Bering Sea and the subarctic North
Pacific. Similar age composition data for tufted (Lunda cirrhata) and horned (Fratercula corniculata)
puffins suggest that the Transition Domain represents an important wintering area for seabirds breeding
in the North Pacific (Gould et al., 1982). In addition, analyses of bycatch and telemetry data have
revealed that this region is a nursery for juvenile northern fur seals (Callorhinus ursinus) from the Asian
and Pribilof stocks (Baba et al., 1993; Buckland et al., 1993; Yatsu et al., 1993).
Oceanic fronts, like the ones defining the North Pacific Transition Domain, support high densities of
marine predators and their prey (Aron, 1962; Ogi, 1984; Pearcy, 1991; Springer et al., 1999). Fishing
fleets, too, are attracted to these frontal zones, owing to improved fishing conditions (Gong et al., 1993;
Murata and Hayase, 1993). Thus, relatively small geographic areas often concentrate much of the pelagic
fishing effort and associated ecological impacts, such as tar and plastic pollution, bycatch, and ghost
fishing by lost and abandoned gear (Dahlberg and Day, 1985; Galt, 1985; Bartoo et al., 1993). The
ecological significance of oceanic frontal features and their susceptibility to intense fishing activities and
habitat degradation underscore the need to establish pelagic MPAs.
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Table 2. Habitats of selected North Pacific pelagic vertebrates during summer (June–September)
Core habitat SSTWater masses/Domains ReferencesSpecies Range SST
(°C) (°C)
Chinook salmon McKinnell and Waddell (1993), Yatsu et al. (1993)SAW 7–10 Subarctic boundary
McKinnell and Waddell (1993), Yatsu et al. (1993)Chum salmon Subarctic boundary2.5–11SAW
McKinnell and Waddell (1993), Yatsu et al. (1993)Coho salmon SAW 7–12 Subarctic boundary
Pink salmon McKinnell and Waddell (1993), Yatsu et al. (1993)SAW 3–11 Subarctic boundary
McKinnell and Waddell (1993), Yatsu et al. (1993)2.5–9SAW Subarctic boundarySockeye salmon
Miyashita (1993), Yatsu et al. (1993)Dall’s porpoise SAW/SFZ/TRD B17 Transition domain
Transition domain Baba et al. (1993), Buckland et al. (1993)Northern fur seal SAW/SFZ/TRD B17
Transition domain McKinnell and Waddell (1993), Yatsu et al. (1993)Eight-armed squid SAW/SFZ/TRD 8–15
Ogi (1984), Gould and Piatt (1993)Sooty shearwater Subarctic boundaryB19SAW/SFZ/TRD/STR
(12–10)
Transition domain Gould and Piatt (1993), Springer et al. (1999)SAW/SFZ/TRD/STR 11–20Laysan albatross
Black-footed albatross SAW/SFZ/TRD/STR 7–20 Transition domain Gould and Piatt (1993), Springer et al. (1999)
Pacific saury SAW/SFZ/TRD/STR 7–20 Subarctic boundary Ogi (1984), Yatsu et al. (1993)
(10.5–12.5)
Strasburg (1958), Nakano et al. (1985)SAW/SFZ/TRD/STR 8–20 Transition domainBlue shark
(11–16)
McKinnell and Waddell (1993), Yatsu et al. (1993)Transition domain6–15SAW/SFZ/TRD/STRBoreal chub-hook squid
Salmon shark McKinnell and Waddell (1993), Yatsu et al. (1993)SAW/SFZ/TRD 4–11 Transition domain
Pacific white-sided dolphin SFZ/TRD/STR 11–18 Transition domain Buckland et al. (1993), Miyashita (1993)
Gong et al. (1993), Yatsu et al. (1993)Neon flying squid Subtropical frontSFZ/TRD/STR 10–20
(18–20)
SAW/TRD/STR Weatherall et al. (1993), Yatsu et al. (1993)12–20,Leatherback turtle
15–18
Northern right whale dolphin TRD/STR 12–18 Transition domain Buckland et al. (1993), Miyashita (1993)
Laurs and Lynn (1991), Kimura et al. (1997)TRD/STRAlbacore tuna 14–20 Transition domain
(11–16)
Range describes surface temperature (SST) conditions inhabited by the various species within subtropical–subarctic waters.
Core habitat refers to the narrower range of sea surface temperature and to the hydrographic features where fisheries catches and sightings are concentrated.
SAW: subarctic water mass; SFZ: subarctic frontal zone; TRD: transition domain; STR: subtropical water mass.
OCEAN BASIN MANAGEMENT 445
Ephemeral hydrographic features
A network of isolated pelagic protected areas could protect species associated with predictable bathymetric
and hydrographic features. However, other ecologically important marine environments are neither fixed
in space nor persistent. A variety of physical forcing mechanisms, including upwelling, eddies and filaments
generate ephemeral fronts responsible for enhanced production and convergence (Franks, 1992; Larson et
al., 1994; Olson et al., 1994). Unlike the persistent features described above, ephemeral hydrographic features
are defined by short-lived gradients in water properties. These features vanish once they mix with the
surrounding waters. However, highly-mobile pelagic species find and exploit ephemeral fronts while they
persist (Laurs et al., 1977; Briggs et al., 1988). Fishermen also understand the significance of these features,
which, despite their small extent and short duration, support high catches of valuable species, including
tunas, salmonids and billfishes (Laurs et al., 1984; Ignell and Murphy, 1993; Podesta et al., 1993). The need
to protect ephemeral hydrographic features is underscored by evidence that these restricted areas represent
important habitats of enhanced biological activity, as well as rich fishing grounds, where fisheries catches
and bycatch are often concentrated (Uda and Ishino, 1958; Podesta et al., 1993).
Upwelling forcing is one of the best-understood processes responsible for transient gradients in water
properties. Upwelling replenishes surface nutrients and enhances primary production by vertically
transporting cool, nutrient-rich water to the surface. Upwelling is temporally predictable and occurs
seasonally in response to favourable wind conditions. Throughout the season of favourable winds, upwelling
episodes can persist from days to weeks (Traganza et al., 1981; Wing et al., 1995). Plumes of
recently-upwelled water may extend for tens of kilometres across the shelf and for hundreds of kilometres
in the along-shore direction (Mooers and Robinson, 1984; Briggs et al., 1988). Strong gradients in physical
and biological properties separate the cool, salty, nutrient-rich upwelling plumes from warmer, fresher,
nutrient-poor waters offshore. A variety of pelagic predators, including seabirds, marine mammals and
tunas, feed on the neuston, zooplankton and larval fish aggregated at the convergence zones and fronts
that delineate upwelling plumes (Laurs et al., 1977; Briggs et al., 1988; Larson et al., 1994).
The interaction of upwelled water with the dominant flow gives rise to ephemeral fronts and eddies disjunct
from upwelling centres. For example, off the west coast of North America, large volumes of upwelled water
are transported offshore by high-speed jets of cool and productive water. These filaments are thin and
elongated features, in the order of 50 km wide and up to several hundreds of kilometres long, which intrude
into warmer and nutrient-poor offshore waters. The resulting temperature and ocean colour fronts frequently
persist for a few weeks (Traganza et al., 1981; Mooers and Robinson, 1984; Strub et al., 1991). Pelagic
predators find and exploit these ephemeral and highly dynamic features before they disintegrate. Off central
California, for instance, albacore aggregate along the edge of warm-water filaments intruding into the cooler
coastal water, and in the vicinity of cold-water jets advecting offshore (Laurs et al., 1984).
Short-lived fronts are also created along the edges of eddies. These are highly dynamic and ephemeral
features formed as a result of flow instabilities along current edges and bathymetric obstacles (Royer, 1978;
Owen, 1980, 1981). The dynamic nature and the persistence of eddies make them important habitat features
capable of enhancing and retaining primary and secondary production (The Ring Group, 1981; Backus
and Craddock, 1982; Olson and Backus, 1985). Eddies are large, conspicuous, and long-lived hydrographic
features, with diameters in the order of tens to hundreds of kilometres, and lifespans of up to several months
(Owen, 1980, 1981; Robinson, 1983). Their rotation (vorticity) creates secondary flow features, including
high-speed peripheral jets, areas of upwelling and downwelling, and convergence zones. Cold-core
(anticyclonic) eddies are characterized by the doming of isopycnals and upwelling of nutrient-rich waters
at the centre, and by downwelling and retention along the periphery (Schmidtz and Vastano, 1976; Owen,
1981). Upwelling within cold-core rings supports enhanced primary production, which is, in turn, exploited
by a variety of predators, including seabirds and fish (The Ring Group, 1981; Yoder et al., 1981; Haney,
1986). Conversely, the aggregation of marine predators and their prey within warm-core (cyclonic) eddies
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is mediated by convergence and downwelling at their core (Schmidtz and Vastano, 1975; Olson and
Backus, 1985; Griffin, 1999). Overall, the significance of eddies as habitat features is underscored by
evidence that regions where permanent (Costa Rica Dome, Blackburn et al., 1970; Fiedler et al., 1991),
and transient (Oyashio– Kuroshio confluence, Uda and Ishino, 1958; Ignell and Murphy, 1993) eddies
predictably occur are characterized by elevated primary production, high zooplankton biomass, and the
aggregation of pelagic fishes, seabirds and marine mammals.
In addition to coastal upwelling and eddies, wind forcing, deep convection and buoyancy fluxes can
create small-scale fronts and convergence zones (Weller, 1985; Olson et al., 1994). These features promote
patchiness by aggregating floating objects and weakly-swimming zooplankton (Alldredge, 1982; Hamner
and Schneider, 1986). Although the ecological significance of these ephemeral fronts is poorly understood,
they appear to constitute important nurseries and foraging habitats for many pelagic species, including sea
turtles and billfishes (Carr, 1987; Podesta et al., 1993).
DESIGN RECOMMENDATIONS FOR PELAGIC MPAS
MPAs could conceivably be designed to protect important breeding and foraging grounds associated with
three generic types of pelagic habitats: bathymetrically static, hydrographically persistent, and
hydrographically ephemeral features. Pelagic protected areas could adopt the ‘core– buffer’ zonation
model devised for biosphere reserves, whereby a patchwork of ‘core’, ‘buffer’ and ‘transition’ areas with
distinct functional roles and levels of protection are integrated to achieve multiple research, conservation
and development goals (Batisse, 1982, 1993; Ray and McCormick-Ray, 1993). Pelagic MPAs based on the
‘core– buffer’ model have already been implemented to protect benthic communities and species
inhabiting bathymetrically-defined static habitats (Koslow and Gowlett-Holmes, 1998; Hooker et al.,
1999). However, the increasingly dynamic and unpredictable nature of hydrographic features will require
more complicated MPA designs.
The simplest scenario entails static MPAs designed to protect geographically fixed and easily discernible
bathymetric features, defined by isobaths on a chart. For instance, a small-scale (40×40 km) MPA could
be designed to protect the diverse cetacean assemblage inhabiting the Gully, a submarine canyon in the
Nova Scotian shelf (Figure 2). A fully protected ‘core’ area delineated by the extent of the 200 m and 2000
m isobaths would exclude oil and gas exploitation, boat traffic and fishing. ‘Buffers’ surrounding the
‘core’ area could then be used to protect cetaceans from other ‘low-impact’ activities, such as noise
pollution from seismic exploration. This MPA would require year-round enforcement to protect the
resident northern bottlenose whale (Hyperoodon ampullatus) population and 11 other seasonally-occurring
cetaceans (Hooker et al., 1999).
Static protected areas cannot track the dynamic features that many pelagic predators exploit. Thus, one
of the most important design modifications necessary to implement effective pelagic MPAs is the use of
flexible boundaries, defined by the properties of the water-column. Predictable associations among
species’ distributions and easily measurable ocean properties, such as temperature and chlorophyll
concentrations, could be used to delineate potential areas of suitable habitat and likely concentration
(Smith et al., 1986; Ignell et al., 1995; Polovina et al., 2000).
Large-scale protected areas can be defined on the basis of water mass properties. Particularly, ocean
temperature is an ideal variable to delineate dynamic MPA boundaries because it determines, to a great
extent, the ranges of pelagic organisms, and it can be readily monitored at sea and remotely from space.
In addition, because oceanographers and fisheries biologists already define species ranges on the basis of
water temperature, the thermal preferences of many marine predators are already well known (Mikol,
1997; Table 2). Furthermore, fishing fleets already use commercially available analyses of oceanographic
conditions to pinpoint profitable fishing areas associated with eddies and frontal zones (Laurs et al., 1984;
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Figure 2. Example of a static MPA around the Gully, off Nova Scotia. The rigid design of the current ‘whale sanctuary’ contrasts
with a bathymetrically defined MPA concept based on a ‘core’ area delineated by the 200 m and 2000 m isobaths, and a surrounding
10 km ‘buffer’. Redrawn from Hooker et al. (1999).
Mikol, 1997). For example, the 15°C isotherm defines the southern range limit of North Pacific salmonids
(Ignell et al., 1995), while high catches of albacore tuna frequently occur in the vicinity of the 13.9°C
thermal front (Mikol, 1997).
The same simple temperature measurements that have been used to pinpoint profitable fishing areas in
the past (Laurs et al., 1984; Mikol, 1997), could help define pelagic protected areas in the future. For
example, an MPA designed to protect the albacore tuna migration route across the North Pacific
Transition Domain could exclude fishing from that species’ preferred range of water temperature
(11°– 16°C; Table 2). Similar regulations have already been used to manage high-seas fisheries in the
North Pacific. For instance, during the 1980s, the Japanese large-mesh and squid drifnet fisheries were
regulated using a system of seasonal area closures designed to mitigate salmonid bycatch and conflicts
between coastal and longline fisheries targeting tunas (Nagao et al., 1993; Nakano et al., 1993). These
regulations defined seasonal area closures based on an understanding of the habitat preferences and the
seasonal occurrence of threatened non-target species. For instance, to minimize salmonid bycatch, drifnet
fisheries were excluded from subarctic waters. This was achieved by restricting fishing effort to the south
of a latitudinal boundary, which followed the northward migration of the subarctic boundary and ranged
from 40°N (June and December) to 46°N (July) (Nagao et al., 1993; Nakano et al., 1993).
Yet, many pelagic predators exploit habitats that are neither defined by static nor temporally persistent
features. The protection of pelagic species that exploit ephemeral hydrographic features, such as eddies
and fronts, is inherently difficult because these are dynamic features defined by short-lived gradients in
water properties. Eddies, filaments and upwelling plumes drift away, embedded in the dominant flow, age
as the water properties change, and finally disappear when the property gradients defining them vanish.
Even though these are ephemeral features, they are relatively predictable in space (within tens to hundreds
of kilometres), and somewhat (at least seasonally) predictable in time. For example, along eastern
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boundary currents, upwelling plumes originate from specific sites, often anchored on coastal points and
capes (Traganza et al., 1981; Huyer, 1983; Strub et al., 1991). Jets and squirts also occur at predictable
localities offshore from upwelling centres (Traganza et al., 1981; Mooers and Robinson, 1984; Strub et al.,
1991). Similarly, regions of strong eddy activity are not uniformly distributed across ocean basins (Roden,
1987; Fu and Cheney, 1995). Eddies are repeatedly spun from meandering currents, forced by wind-driven
upwelling, and created downstream from islands, banks and guyots (Barkley, 1968; Bernstein et al., 1977;
Owen, 1980). Off California, for instance, semi-permanent eddies are commonplace downstream from the
Point Conception and the Point Sur upwelling centres (Huyer, 1983; Haury et al., 1986). In particular, the
southern California eddy (SCE) constitutes the most predictable mesoscale feature off California. This is
a large (\200 km diameter) and highly predictable cyclonic eddy, which occurs persistently off southern
California between July and January, and periodically between February and May (Wyllie, 1966; Owen,
1980; Figure 3). The fact that many of these ephemeral hydrographic features are somewhat predictable
in space, makes it possible to consider ‘core’ and ‘buffer’ approaches to the design of MPAs. In each case,
geographically fixed (e.g. seamount) and temporally persistent (e.g. water mass boundary) features could
be used to delineate ‘core’ areas defined by the average extent of potential habitats, while ‘buffers’ could
be defined by the variability about those mean conditions.
Extensive ‘buffers’ will be necessary to reconcile the dynamic water-column properties, and the diffuse
physical– biological interactions in pelagic systems with effective MPA designs. ‘Buffers’ surrounding areas
of ‘core’ habitat would help MPAs accommodate the physical mechanisms that decouple foraging
aggregations from the bathymetric and hydrographic features ultimately responsible for water-column
mixing and elevated production. For instance, the shedding of Taylor columns and the propagation of
trapped eddies likely decouple regions of elevated production and dense prey aggregations from seamounts
(Barkley, 1972; Royer, 1978; Cheney et al., 1980). There are also pragmatic reasons to utilize the ‘buffer’
concept. For example, conditions at the sea surface are often decoupled from the subsurface properties
influencing the distribution of pelagic organisms (Murata and Hayase, 1993; Brill, 1994). For instance, the
physical and biological signatures of fronts may extend up to several tens of kilometres from the location
of their surface expression (e.g. surface isotherms) (Owen, 1981; Franks, 1992). In addition, when predators
aggregate at frontal features, they form patches that often match the spatial scales of the front (e.g.
Rossby radius, Briggs et al., 1988; Schneider et al., 1990). In fact, even MPAs designed to protect
benthic communities and sedentary mating aggregations may benefit from ‘buffers’ around a
bathymetrically-defined ‘core’ habitat. ‘Buffers’ have been suggested to mitigate certain far-reaching
Figure 3. Average 10-year incidence of eddies off southern California (31° – 35° N) from the coast to 300 nautical miles offshore
(1949–1965). Eddies are characterized by type (cyclonic or anticyclonic) and by size (diameter). Data from Owen (1980).
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human activities, and to maintain the linkages between benthic communities and water-column processes
(Koslow and Gowlett-Holmes, 1998; Hooker et al., 1999; Probert, 1999).
The understanding of the water mass preferences of marine predators could be used to delineate potential
habitats suitable for protection. These areas could then be protected using dynamic MPAs based on the
seasonal or permanent closure of large regions (hundreds to thousands of squared kilometres). For instance,
off central California, MPAs designed to protect the cool upwelling plumes where cetaceans and seabirds
forage could restrict fishing activities to warm waters above a prescribed temperature threshold (Smith et
al., 1986; Briggs et al., 1988). Ultimately, MPA designs would be guided by an understanding of the physical
forcing mechanisms (e.g. upwelling favourable winds), and of natural history (e.g. seasonal occurrence off
California). Pragmatically, such regulations would be communicated to fishing fleets using simple
descriptions of the temporal (e.g. months) and spatial (e.g. temperature range) extent of the fishery closures.
The familiar problems of displaced effort and enforcement that complicate nearshore MPAs occur in
the pelagic realm as well. For example, shifting fishing activities into less productive areas may actually
increase the overall effort. Without reducing effort, any aerial restriction may merely intensify the impacts
outside of the MPA by shifting the fishing pressure into adjacent areas. Thus, managers should anticipate
the likely ecosystem-level consequences of pelagic MPAs before they are implemented. Narrowly-focused
single-species management plans may merely reduce the bycatch of a threatened or popular species at the
expense of other taxa. For instance, efforts to protect Eastern Pacific dolphins by setting tuna nets on logs
have increased shark bycatch (Hall, 1998). Similarly, setting long-lines at night to protect threatened
albatrosses has led to higher bycatch of nocturnal white-chinned petrels (Procellaria aequinoctialis)
(Weimerskirch et al., 1999).
Another obvious roadblock inhibiting the establishment of pelagic protected areas is the inability to
enforce dynamic MPA boundaries in the high seas. Enforcement actions could be based on the ability to
determine the location of fishing vessels equipped with transponders, and to survey real-time ocean
properties over large-scales using satellite remote sensing (Bernstein et al., 1977; Smith et al., 1986; Fu and
Cheney, 1995).
OCEAN BASIN MANAGEMENT
Ultimately, society will need a holistic management scheme for entire ocean basins. Such overarching
management will depend upon the use of many innovative tools, including the judicious implementation
of MPAs. Clearly there are no all-serving management techniques because the scaling is so variable. Steele
(1978) and Denman (1994) selected the dimensions of patches and the ambits of species as appropriate
spatio-temporal scales for the study of pelagic systems. Similarly, the scales of ocean management can be
defined by foraging/breeding aggregations, and the ranges of the vulnerable populations and species (Prince
et al., 1992; Ray and McCormick-Ray, 1993; Saunders and McFarlane, 1997). However, there is a great
deal of uncertainty in this approach because the ambits of pelagic organisms range in the order of tens,
hundreds and thousands of kilometres for plankton, small nektonic organisms (forage fish and squid) and
large nekton (seabirds, cetaceans and tunas), respectively (Haury et al., 1978; Steele, 1978; Hunt and
Schneider, 1987). Basin-wide MPAs might be required to protect far-ranging species, such as the wandering
albatross (Diomedea exulans), the sperm whale (Physeter macrocephalus) and the leatherback turtle.
Our inability to protect far-ranging species is particularly problematic in oceanic systems, where
highly-mobile vertebrates range across entire ocean basins (Eckert and Sarti, 1997; Spear and Ainley, 1999;
Weimerskirch et al., 1999). In spite of the recognition for the need to link isolated MPAs into networks
(Ogden, 1997; Ray, 1999), the design of protected oceanic corridors remains a daunting challenge because
migration routes are dynamic and often poorly understood (Laurs and Lynn, 1991; Resendiz et al., 1997;
Spear and Ainley, 1999). In fact, even when predictable migratory pathways do exist, it would be impossible
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to set aside movement corridors for all threatened species. This line of thought has led to the conclusion
that large MPAs should encompass a large proportion (50– 90%) of the total suitable habitat (Mills and
Carlton, 1998; Boersma and Parrish, 1999).
MPAs designed to protect specific foraging and mating grounds could mitigate certain forms of habitat
degradation (e.g. oil spills, noise pollution and changing disturbance regimes), and mortality (e.g. bycatch
and boat strikes). It is unlikely, however, that a network of isolated MPAs would grant far-ranging
species protection because impacts outside of the protected areas would not be properly mitigated
(Kooyman et al., 1996; Eckert and Sarti, 1997; Boersma and Parrish, 1999). Thus, the foraging ranges and
the migration routes of pelagic species are also relevant for the design of pelagic protected areas.
The ineffectiveness of isolated MPAs and our inability to protect vast networks of movement corridors
represent major roadblocks to pelagic conservation. Yet, since the ocean is the habitat of many highly
endangered pelagic vertebrates, conservation and management measures must seek solutions at
comparable large scales (Prince et al., 1992; Eckert and Sarti, 1997; Weimerskirch et al., 1999). In
particular, it is our contention that pelagic MPA designs must scale up the protection of isolated habitat
features and protect large-scale features of the global ocean.
An example of potential basin-wide management tactics for the North Pacific would focus on the
ecological importance of the North Pacific Transition Domain. The Transition Domain supports a rich
and diverse fauna, comprising cosmopolitan, subarctic and subtropical visitors, as well as endemic
transitional species (Fager and McGowan, 1963; McKinnell and Waddell, 1993; Yatsu et al., 1993). At
least 40 species of seabirds, 18 cetaceans, two pinnipeds, three sea turtles, five squids, four sharks and 24
bony fishes, including economically valuable salmonids and tunas, occur at some time of the year in the
Transition Domain (Brodeur et al., 1999; Springer et al., 1999; Table 2). A large-scale, dynamic MPA
delineated by the location of sea surface isotherms could be used to protect commercially valuable and
non-target pelagic species during their transpacific migration across the Transition Domain (Figure 4).
However, most of these species also migrate extensively throughout the basin, often following the
currents that form the North Pacific gyre (Morreale et al., 1996; Spear and Ainley, 1999; Polovina et al.,
2000). Protection within the North Pacific Transition Domain will be ineffective if these same species
Figure 4. Example of a dynamic, large-scale MPA defined by sea surface temperature isotherms delineating the North Pacific
Transition Domain (16°–11°C). Isotherms during July 1998 provide a static snapshot of otherwise dynamic frontal features. Arrows
indicate the flow of the North Pacific current and the likely migration route of albacore tuna across the basin. Trimmed 1° SST
monthly mean data courtesy of the Pacific Fisheries Environmental Laboratory (http://www.pfeg.noaa.gov/).
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experience significantly higher mortality during the remainder of their migratory cycles from displaced
fishing effort. Traditional corridors tend to be idiosyncratic for specific species, and in any case, are
impossible here. One solution might be a single protected area, in the form of a ring encompassing the
mid-section of the currents forming the North Pacific gyre, that might protect species throughout their
migratory ranges (Figure 5). In such a design, any given cross-section of the broad migratory routes will
have a ‘safe’ path through which at least some individuals can migrate unharmed.
Thus, dynamic MPAs could be designed to protect large hydrographic features of the global ocean. The
permanent fronts defining water mass boundaries and current systems constitute ideal features for the
design of large-scale pelagic MPAs due to their predictability (Table 1). In particular, the strong
concordance between nekton species assemblages and water-column properties provides an effective
foundation for the design of large-scale dynamic MPAs defined by water properties (Table 2).
The establishment of dynamic MPAs designed to protect pelagic migration routes in the North Pacific
would represent an ecosystem management approach to the conservation of both pelagic vertebrates and
fisheries resources. Such large-scale MPA concepts would address immediate conservation goals by
granting protection to breeding aggregations (e.g. neon flying squid), mature and fecund individuals (e.g.
blue sharks, leatherback turtles and salmonids), and juveniles (e.g. fur seals, shearwaters and albacore
tuna) of threatened and economically-important far-ranging species. In addition, longer-term conservation
goals would be addressed by protecting large-scale ocean features critical to many other pelagic species.
Thus, this multi-species approach would represent a proactive and precautionary conservation umbrella
designed to protect fisheries resources and pelagic vertebrates before they became endangered (Mangel et
al., 1996; Dayton, 1998).
We support the protection of substantial areas of ecologically important and persistent hydrographic
features, such as fronts, boundary currents and gyres, to ensure the long-term conservation of pelagic
species and fishery resources. Here, we have focused on the North Pacific Transition Domain. However,
similar design concepts could be applied to other equally important regions of the world’s ocean, such as
the Bering Sea green belt, the Costa Rica dome, the equatorial convergence, the Oyashio– Kuroshio
confluence, the Antarctic polar front, and the California current.
Figure 5. Schematic of a large-scale pelagic MPA encompassing the average location of the currents forming the North Pacific gyre.
Arrows indicate the direction of water flow around the basin, and the likely migration route of may far-ranging pelagic vertebrates.
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Technological roadblocks have inhibited implementation of large-scale conservation measures in the
world’s oceans. Recent advances (e.g. global positioning systems, large-scale monitoring of ocean
conditions using satellite remote sensing, remote detection and monitoring of vessels using acoustic and
satellite technologies) will facilitate the implementation, enforcement and evaluation of pelagic MPAs.
Similarly, the ability to implement conservation actions at the necessary large scales may open the door
to the design of large-scale pelagic protected areas (e.g. highly migratory and straddling stocks agreement
(Aqorau and Bergin, 1998); bycatch mitigation plans (FAO, 1997); international pelagic species
conservation plans (FAO, 1998); United Nations drifnet resolution (United Nations, 1991)).
Clearly, this approach relies on political will which is not yet apparent. However, it represents the safest
way to ensure the long-term conservation of pelagic vertebrates and fisheries resources, given the
constraints of (1) imperfect knowledge of the habitats of all threatened pelagic species, (2) limited ability
to establish MPAs specifically designed to protect every single threatened species, and (3) the realization
that the processes responsible for the aggregation of pelagic vertebrates at isolated features may change
in the future, particularly in light of changing global climate. Our basic objective is to demonstrate that,
despite the many large uncertainties regarding ocean processes, the scientific information is presently
available to implement sweeping environmental reform that can protect our oceanic heritage, if only
humanity can find the political willpower to proceed.
ACKNOWLEDGEMENTS
We gratefully thank Dee Boersma, Jeff Field, John Horne, George Hunt, Vivian Mendenhall, Ken Morgan and all
those who provided valuable references used in this review. Jay Barlow, John Baxter, Doug Bertram, Gerald
Kooyman, Richard Neal, Carleton Ray and Randy Reeves provided useful comments that greatly improved earlier
versions of this manuscript. Sascha Hooker graciously provided Figure 2.
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