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ICES Journal of
Marine Science
ICES Journal of Marine Science (2014), 71(8), 2281– 2292. doi:10.1093/icesjms/fst242
Contribution to the Special Issue: ‘Commemorating 100 years since Hjort’s 1914 treatise on
fluctuations in the great fisheries of northern Europe’
Food for Thought
Active opportunist species as potential diagnostic markers for
comparative tracking of complex marine ecosystem responses
to global trends
Andrew Bakun*
Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA
*Corresponding author: tel: +1 305 967 4711; fax: +1 305 421 4600; e-mail: [email protected]
Bakun, A. Active opportunist species as potential diagnostic markers for comparative tracking of complex marine ecosystem responses to global
trends. – ICES Journal of Marine Science, 71: 2281 – 2292.
Received 9 December 2013; accepted 26 December 2013; advance access publication 7 February 2014
.
As it becomes ever clearer that on longer time scales marine ecosystems function as non-linear “complex adaptive systems”, potential consequences of global change become obscured within a maze of multiple possibilities. This essay attempts to route one pathway to a
potentially more robust conceptual synthesis, employing the globally important example of anchovies and sardines as a model.
Expressly, the anchovy emerges as an efficient specialist of neritic origin. In contrast, the sardine’s oceanic-based adaptations equip it to
deal with intermittent episodes of poorly productive conditions and to take advantage of associated reduction in predation pressure
on early life stages of their offspring. Based on the overall synthesis, the nimble, wide-ranging, actively opportunistic sardine appears
notably well equipped to deal with climate-related disruptions and dislocations and even to profit from their adverse effects on predators
and competitors. Global-scale multispecies population synchronies in the 1970s to the mid-1980s suggest that a variety of different species
types might be flagged for investigation as perhaps embodying similar “active opportunist” attributes. If so, events and anecdotes might, as
global changes proceed, be viewed within a developing universal framework that could support increasingly effective transfers of experience
and predictive foresight across different species groups and regional ecosystems.
Keywords: climate change, earth systems models, global climate models, representative concentration pathways.
Introduction
In the century that has passed since Johan Hjort’s (1914) seminal
publication, much has been learned about the intricate linkages of
physical and biological mechanisms operating within the structures
of marine ecosystems. Even so, there has been precious little success
in applying that progress towards improving fisheries management
and marine conservation efforts, i.e. towards the “ultimate”-level
goals of long-term preservation of the traditional economic and esthetic benefits that have come to be expected to flow forth from the
world’s marine ecosystems. Perplexingly, our current understanding of the dynamics of these systems remains rife with puzzles and
paradoxes (e.g. Bakun, 2011, 2012), and actionably reliable prediction continues to evade us (Houde, 2008). This is much in contrast
to many other fields of modern science in which the spread of successful applications has been explosive.
Certainly, part of the problem must be that we humans are not
marine organisms, but are terrestrial ones. Our experiences, as well
as our intuitions, are overwhelmingly terrestrially based. Not surprisingly, our conventional conceptual frameworks for understanding
how marine ecosystem processes may influence population dynamics
are, both at Hjort’s time and at present, rather simple reflections of
terrestrial analogies. But the “marine world” is something qualitatively different and in many ways “beyond our human experience”
(Bakun, 1996). For example, in terms of such references as numbers
of trophic levels or varieties of dynamical feedbacks involved,
marine systems are in nearly all cases much the more complex.
Moreover, as historical data records have lengthened, it has
become ever more evident that on longer time scales, marine ecosystems seem to be functioning as classical complex adaptive systems
(Levin, 1998, 1999), characterized by dynamical non-linearities
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(Hsieh et al., 2005) and self-enhancing feedback loops (Bakun and
Weeks, 2006). Dynamical systems of this type tend towards chaotic,
non-predictable behaviour, calling into question the very efficacy
of scientific management efforts. In particular, since non-linear
mathematics do not necessarily yield unique solutions, potential
consequences of various aspects of global change tend to become
diffused in a nebulous array of multiple possibilities. Certainly,
once it is realized that conventional assumptions of system stationarity are becoming increasingly untenable, the sorts of simple
linear models (e.g. fitting of indices of reproductive success to one
or several indices of correlated environmental or ecosystem mechanisms) that have become traditional in fisheries science, lose
their credibility as reliable harbingers of the future. Fortunately,
such a pessimistic perspective is contradicted by certain striking regularities and temporal-spatial correspondences that seem to evoke
a more promising viewpoint. Among the most remarkable of these
have involved interactions between the anchovy (genus Engraulis)
and sardine (genera Sardinops and Sardina) species groups.
Anchovies and sardines coexist at the crucial wasp-waist position
(Rice, 1995; Bakun, 1996, 2006a; Cury et al., 2000) in the trophic
structures of a surprising variety of important regional marine ecosystems. Their populations tend to be large, often comprising the
greater part of the entire animal biomass of the local ecosystem in
which they function. Therefore, they tend to support quite
massive fisheries, such that variations in production from the
anchovy –sardine pair have often been dominant factors in the
overall variability in world fish production. In turn, the very efficient
and powerful fisheries focused on these stocks exert important controls on their population dynamics.
Notably, the two species groups have historically exhibited a tendency to alternate in ascendancy at the wasp waist of a given regional
ecosystem on time scales of several years to several decades, generating
differing ecosystem effects depending on which may be dominant at a
particular time. For example, anchovies are largely zooplanktivores,
whereas sardines are more omnivorous in that they have greater capability to effectively consume phytoplankton as well as zooplankton.
Thus, anchovy dominance may promote higher ratios of phytoplankton to zooplankton (Cury et al., 2000), perhaps therefore favouring
eutrophication and associated hypoxia. On the other hand, since
herbivorous zooplankton may preferentially consume diatoms over
dinoflagelates, the higher ratios of zooplankton that may be associated
with sardine dominance may favour toxic “red tide” dinoflagelate
blooms (Irigoien et al., 2005). Moreover, sardines tend to spread
their operations over much wider ocean areas, whereas anchovies
tend to remain concentrated in more restricted home-range zones.
Thus, a change in dominance between the two has important consequences with respect to many aspects of geographic patterning of
marine ecosystem processes.
Puzzling issues with respect to the interactions of this pair of
species groups include the following (Bakun and Broad, 2003).
(A) The fact that sardines, which are a species group obviously
adapted to highly productive ocean conditions (upwelling
areas, etc.), often do better, at least in the eastern Pacific,
during El Niño episodes—which paradoxically are characterized by abruptly lowered primary productivity.
(B) The extraordinary fish productivity of the Peru– Humboldt
large marine ecosystem (LME), which largely rests on the productivity of the anchovy –sardine species pair.
A. Bakun
(C) A pervasive tendency for out-of-phase population oscillations
leading to alternating dominance of anchovies and sardines in
any given regional ecosystem.
(D) Basin-scale synchronies in sardine population expansions and
contractions during the 1970s and the 1980s—although the
involved populations exist in very different types of ecosystems, which accordingly could be expected to respond quite
differently to the same large-scale forcing characteristics.
An additional unexplained issue (which can here be labelled “E”)
involves the fact that these two species types manage to cohabit a remarkable number of diversely configured regional-scale marine
ecosystems, in apparent contradiction of the competitive exclusion
principle (Hardin, 1960).
Although it is difficult to rejoice over the existence of conspicuous gaps in our understanding, prominent existing paradoxical
issues such as these do represent remarkable opportunities to
hone directly in on essential mechanisms and thereby avoid becoming lost in irrelevant details and distractions. The wealth of such
“conundrums” represented in the list above (issues A though E) provides an essential inferential basis that underlies the conclusions and
generalizations presented here.
In the many years that fisheries scientists have been puzzling over
these and other seemingly paradoxical patterns of correspondence
and evident interaction, quite a collection of proposed hypotheses
as well as ad hoc explanations have been amassed. At the point
they are proposed, these generally provide a reasonable degree of
empirical fit to the past data that largely motivated them.
However, the degree of fit seldom holds up through subsequent
years. A basic problem is that the standard experimental method
is clearly not practical on the scales at which the earth’s coupled
ocean –atmosphere system and its entrained marine biological processes interact to regulate dynamics of wide-ranging, mobile marine
populations. Moreover, the rises and declines in dominant fishery
resource stocks tend to play out over decadal or multidecadal time
scales, whereas most available in situ dataseries, as well as acceptably
homogeneous fisheries catch dataseries, do not exceed a few decades
in length. As a result, the number of actual realizations of such major
changes available in any real dataseries tends to be too small in any
single regional case to empirically sort out the complexity of interactions among the various driving factors and non-stationary
linkage mechanisms. Although constructing computer-driven
simulation models to explore and demonstrate the outcomes of
combining particular sets of mechanisms and processes is currently
a very popular activity, such simulations can of course only reflect
the knowledge and assumptions that were put into them; they
cannot generate independent new data.
Some alleviation of the insufficiency in empirical degrees of
freedom may be sought via an interregional comparative approach.
This requires a willingness to accept that parallel aspects of essential
processes and relationships controlling the dynamics and interrelationships of highly similar species groups should operate in a generally analogous manner, after allowing for regional particulars, in
different available regional situations. If this willingness exists, the
comparative method (Mayr, 1982) opens the door to considerably
augmented inferential power, although suitable analysis procedures
may not necessarily be simple or straightforward. Generally, if a coherent hypothetical formulation should be found to be capable of
explaining a number of paradoxical, or otherwise remarkable,
observed patterns, scientific confidence expands. If it appears
uniquely so (i.e. no other explanatory basis is found that can
Active opportunist species as potential diagnostic markers for comparative tracking
withstand serious examination), one may reasonably decide, at least
tentatively, to place reliance on it.
MacCall (2009a) listed a number of candidate mechanisms that
may underlie anchovy–sardine interactions, most of which seem
likely to be involved to greater or lesser degree at various times.
For even more potential explanatory “ingredients”, one might
refer to several of the chapters in the “Berlin Workshop” volume
of Journal of Marine Systems (Alheit et al., 2009), and a succession
of other symposium volumes and workshop reports stretching back
to the pivotal “Lima Workshop” (Sharp, 1980). But here we first try
to gain some independent discriminatory power to help navigate the
labyrinth of proposed hypotheses and mechanisms. We do so by
standing back a bit from the details and widening the focus to encompass a more general view of the two species groups in terms of
what might be directly inferred from their apparent evolution,
genetic characteristics, adaptations, and evolved capabilities.
Certainly, the manifested comparative patterns (“A” though “E”,
listed above) are so striking that the idea that they might spontaneously materialize from some variable mix of largely autonomous
mechanisms strains credulity. Rather, a satisfying explanation
would seem to require some overall organizing principle, basic to
all the otherwise puzzling issues listed above, that could somehow
weave together the outcomes of multiple active component mechanisms so as to logically lead to the pervasive patterns that are observed.
Differing evolutions and adaptations
To try to initiate a comparative inferential search at the most basic
evolutionary level possible, it may be useful to begin by considering
the differing developmental origins of the respective anchovy and
sardine species groups. (The discussion that follows in this section
is summarized diagrammatically in Figure 1.)
Anchovies
In gross aspect, the evolution of the anchovy (genus Engraulis)
would seem to have had its primary basis in terrestrially conditioned
habitats (river plume environments, estuaries, run-off-influenced
semi-enclosed seas and bays, broad sedimentary continental
shelves, etc.). For example, because of the westward tectonic movement of the American continents, high mountain barriers and
narrow continental shelves characterize their western continental
boundaries. As a result, the overwhelming portion of continental
run-off flows to their Atlantic Ocean sides, which (being the “trailing” continental edge with respect to tectonic plate movement) tend
to feature much broader continental shelves and very extensive
shallow estuarine systems. Substantial anchovy (Engraulis) populations exist all along the temperate western Atlantic ocean boundary,
with one of the largest anchovy populations of the world (E.
anchoita) stretching along an enormous stretch of very broad
South American continental shelf. In contrast, temperate sardines
(Sardinops or Sardina) are entirely absent from the western side of
the Atlantic. The pattern of association of anchovies with river
plume/estuarine/terrestrial-conditioned environments continues
to hold also on somewhat smaller scales—for example, among the
intricately patterned Mediterranean Sea environments (Palomera
and Rubies, 1996) and also recently within the North and Baltic
Seas (Alheit et al., 2012).
A revealing example comes from the Gulf of California, where
one of the great rivers of North America, the Colorado, used to
flow copiously into its upper (northern) end. That inflow has steadily vanished over the past century as a result of steadily increasing
impoundment to supply agricultural irrigation for much of the
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southwestern United States. In the memory of fishers operating
there in the latter 20th century, an anchovy had never been seen in
the Gulf before 1986 (Hammann and Cisneros-Mata, 1989), when
anchovies briefly appeared following an abrupt collapse of the
local sardine resource. Later, a subsequent analysis of fish scale
deposits in anaerobic sea floor sediments (Holmgren-Urba and
Baumgartner, 1993) indicated that this was not the first time that anchovies had made an incursion into the Gulf of California, but in fact
they had entirely dominated the fish biomass in the Gulf for most of
the 19th century. This was when (and here is the illustrative point)
the Colorado River was still pouring into the Gulf a major portion
of the continental run-off from the great mountain ranges and
high plateaus of the southwestern United States.
The higher degree of affinity of anchovies for estuarine-affected
habitats is clearly reflected in the much coarser gillraker structures
that they employ as food gathering apparatus. As a result, they are
incapable of filtering as small a size of food particles as sardines
can (van der Lingen, 1994; van der Lingen et al., 2006). But anchovies may thus be able to suffer less clogging of these structures with
terrestrial sediment material and other particulate matter that typifies run-off-influenced situations (unblocked flow of water through
gill structures being essential also to respiration, an even more immediate need than food gathering). But crucially, precisely
because of their coarsely meshed gillrakers, anchovies can efficiently
deploy a comparatively much larger “filter basket” (reflected in their
local common name often being some variation on “big mouth”).
Therefore, anchovies are particularly efficient at gathering large
food particles when such particles are plentiful (as they would
tend to be in the run-off-dominated terrestrially conditioned nearcoastal or estuarine situations in which the genus appears to have
primarily evolved). In accordance with this seeming affinity for
terrestrial-conditioned environments, the anchovy seems to be
quite local in its movements, exhibiting a tendency to both feed
and reproduce within restricted, comparatively fixed geographical
contexts (river plume edges, local coastal embayments, island complexes, etc.). Thus, the anchovy has evolved to be a relatively weak
swimmer and migrator. In any case, their coarse filters would
seem to make wide-ranging exploratory activity a risky proposition,
in that once an anchovy may wander away from the geographically
fixed locations where the larger food particles that it can efficiently
gather may be reliably available, it runs serious risk of dangerous
problems in gathering adequate food to sustain itself until it
encounters the next suitable large-particle “oasis”.
Thus, one might surmise that an anchovy would tend to be, in the
terminology of Cury (1994), more “obstinate” than “opportunistic”
in its migrational tendencies. An associated propensity for local
population segmentation is confirmed by the anchovy’s comparatively much greater level of genetic diversity (Hedgecock et al.,
1989; Grant and Leslie, 1996). The implication is that anchovies
expend less of their acquired trophic energy in swimming and migrating than do sardines. Therefore, there is less need for the hydrodynamic advantages associated with larger size, and so the anchovy
can afford to mature earlier and at a smaller size, in the process
allotting a lesser portion of acquired energy to growth and a
greater portion to reproduction and rapid population responses
(Figure 1). Because predation in these highly productive shallow,
near-coastal zones would be expected to be intense on all life
stages, such energetic efficiency and rapidity of population response
may be an absolute requirement for long-term population viability.
The “anomaly” to this pattern presented by the remarkable
success of the anchovy in the open ocean realm off Peru has been
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A. Bakun
Figure 1. Summary diagram representing the adaptive sequences leading from evident “primary ecological origins” to produce the relative
ecological advantages (unshaded text boxes) or disadvantages (shaded text boxes) exhibited by the respective anchovy and sardine species groups.
attributed (Bakun and Weeks, 2008) partially to the special conditions of that very low latitude location which, because of the weakened coriolis effect, presents a particularly benign habitat that is
characterized by strong enrichment, weak turbulent mixing, and
long particle residence times. Except during El Niño situations
when nutrient supply is disrupted, these attributes generate particularly dense accumulations of very large chain-forming diatoms and
associated larger herbivorous zooplankton species. Thus, the
normal Peruvian situation may present analogies to the
comparatively turbid, large-particle conditions found in other
more terrestrially conditioned anchovy habitats. On the other
hand, during an El Niño episode, when the available particle spectrum characteristically shifts to a much smaller size range, the
Peruvian anchoveta would seem to face quite a direct analogue to
the feeding problems that might be faced by a “wandering
anchovy” that attempts to transit between dispersed terrestrially
determined habitats.
Active opportunist species as potential diagnostic markers for comparative tracking
Sardines
Sardines, in contrast, tend to avoid turbid water situations. In particular, they appear to thrive where continental shelves may be
narrow, in upwelling systems, and in the edge zones of strong
oceanic boundary currents. They appear adept at opportunistically
exploiting the benefits of energetically forced eddy fields and of a
variety of transient, sporadically distributed convergent frontal
situations that develop in more offshore oceanic waters. They are
strong swimmers and, particularly for Sardinops, prodigiously
wide-ranging migrators as befits their relative affinity to the less robustly patterned, more variably configured oceanic realm (i.e. the
offshore frontal boundaries where upwelling-conditioned waters
or continental shelf waters meet with oceanic waters, or within
the favourable segments formed within the energetic eddy fields
driven by lateral frictional interactions with strong oceanic boundary current flows). Here, substantial concentrations of food particles
large enough to be efficiently gathered by anchovies tend to be relatively rare, and patches even of much smaller potential food particles
are patchy, transitory, and more or less ephemeral. In such a case, exploration, innovation, and even a degree of “risky” capriciousness
may be advantageous to sardines on an individual basis, while
also yielding as a by-product diffused overall risk to the population
as a whole.
Moreover, in this less productive offshore zone, predation pressure would be relatively relaxed, except in zones of dynamic concentration such as convergent fronts or convergent eddy segments that
may be vital to their reproductive success. But here the sardines’
highly mobile, exploratory tendencies may allow them to “get
there first”, and then “get out” (or at least “do their reproductive
business”) before larger pelagic predators also locating the zones
(e.g. guided by the presence of flotsam and drifting objects that
would begin to progressively accumulate rather immediately after
the particular convergence zones develop) and arriving en masse
to truncate the transient local advantage that the sardines may
have initially enjoyed.
At the population level, sardines are strikingly proficient at opportunistically expanding or altering the geographical locations
and extents of their spheres of operation (Lluch-Belda et al., 1989;
Kuroda, 1991). Their geographical gyrations are matched by
radical abundance variations, suggestive of a “high-risk” opportunistic life strategy that seeks to initially overwhelm and then outmanoeuvre adverse ecological pressures by relentlessly ferreting out
opportune “loopholes” (Bakun and Broad, 2003) in the ambient
predation pressures wherever they might exist.
This impression of wide-ranging, “high-risk” operation by the
sardine is bolstered by genetic data (Lecomte et al., 2004) that, for
example, indicates quite a recent sardine history in the northeast
Pacific (a quarter million years) compared with the anchovy’s (5
million years). Such a comparatively recent “founder event” has
also been supported by allozyme data, which indicated reduced
levels of diversity relative to anchovies and other clupeoids
(Hedgecock et al., 1989; Grant and Leslie, 1996). This degree of shallowness in genetic divergences among regional populations may be
explained by two alternative models of population persistence and
dispersal (Grant and Bowen, 1998). Either (1) Sardinops may have
inhabited a limited area for most of the last 20 million years
before expanding to the temperate corners of the Indian and
Pacific regions in the last few hundred thousand years or (2) the
various regional Sardinops populations may have been extinguished
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repeatedly and subsequently recolonized by opportunistic transoceanic or trans-equatorial migrants.
The intervening “in-play” zones
Thus, on the long term if not necessarily on the very short term, each
of the sardine–anchovy pair in each regional case can probably
pretty consistently be the “superior competitor” in their respective
natural “home segment” of their regional habitat. Otherwise, they
should at some point have been completely eliminated from the regional system. An example of an anchovy “home segment” might be
the western side of the Adriatic Sea, where Coriolis force causes the
plume of the Po River, along with commingling waters from other
rivers flowing out of the Dolomite Alps, to hug against essentially
entire Italian coast of the Adriatic, while the upwelling-conditioned
zone off the Croatian coast on the opposite eastern side of that sea
may better represent natural “sardine waters”. In the northwestern
Mediterranean, the zones near the Rhone and Ebro River plumes
would appear to be zones where the adaptations of the anchovy
would tend nearly always to render it the superior competitor,
whereas the vigorous turbulent eddy fields driven by the winter
Tramontana/Mistral wind jets in the zone between may be difficult
for anchovies while being manageable, and even offering favourable
opportunities, to sardines. In the California system, the plume of the
Columbia River and the run-off influenced near-coastal segments of
the inner Los Angeles Bight (particularly before the impoundment
of most natural run-off sources there) would seem to constitute favourable “home segments” for the respective northern and central
subpopulations of northern anchovy (Engraulus mordax), while
the offshore eddy fields and frontal systems where the upwellingconditioned neritic waters meet the warmer, more saline oceanic
water masses would seem to constitute sardine “home segments”.
[In view of considerations developed here, one may not find surprising the findings of van der Lingen et al. (2006) that natural selection
has apparently optimized the digestive chemistry possessed by
the two species groups to work particularly efficiently with respect
to the size ranges of particles characterizing the “home segments”
on which their viability may at times be totally dependent and to
which the their respective physical capabilities appear likewise to
have been optimized.]
The intervening zones of the rich regional upwelling or boundary
current conditioned systems where the two species groups co-occur
are intermittently dominated by one or the other of the groups,
rather than being characterized by a single superior competitor.
These intervening zones tend to be highly variable on a variety of
scales. And so one might imagine that, as a result, the directions
of the selection pressures may be highly non-uniform in both
time and space. This may have suppressed, or at least delayed,
development of specific adaptations to that intervening zone
itself. In such a case, that rate of immigration of individuals from
the nearby home-base segments could have been sufficient to overwhelm any nascent-specific adaptations to that zone within either of
the sardine or anchovy generic groups.
To sum it up, we evidently have two species groups possessing
differing strongly evolved adaptations simultaneously employing
these adaptations to dominate, when possible, the richly productive
but highly variable regional-scale habitats within which the more
limited home-base segments of each are embedded (Figure 1).
Whenever one or the other may achieve clear dominance, potential
competitors for the dominant nektonic planktivore role are effectively eliminated, or at least “squeezed back” into primary home-base
habitat segments that are particularly forgiving of their specific
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special problems and limitations. In the anchovy case, the home
segment may be limited in extent while being subject to intense predation (e.g. from shore-based seabirds and marine mammals, nearcoastal demersal “ambush” fish predators, etc.). In the sardine case,
lack of consistent availability of adequate food concentrations in
those outer reaches of the neritic system may limit their ability to
grow abundance in the face of a spectrum of predator species that
have been in diverse ways evolutionarily equipped to deal with the
arduous local conditions. This is what appears to render the extensive breadth of rich but variable intervening habitat such a prize.
Excluding the “other”
The process by which the alternative member of the anchovysardine pair may be actually eliminated has been a puzzle. For
example, why do the two species not simply separate spatially,
each occupying a portion of the habitat where its adapted characteristics may render it comparatively superior on average? Rather, one
of the species tends to become overwhelmingly dominant over the
major portion of the shared habitat where the other “subordinate”
species collapses to what might be considered a very low-abundance
“refuge” level (Bakun, 2006a) where it may be found operating
mostly within schools of similar-sized individuals of the much
more numerous “dominant” species (Bakun and Cury, 1999).
Direct competition for food does not seem to be the answer. Nor
does preferential predation on the other species’ eggs and larvae
(each appears to cannibalize its own potential offspring as readily
as the others). The set of “school trap” and associated “school-mix
feedback” effects (Bakun and Cury, 1999; Bakun, 2001, 2005a) could
perhaps hold at least part of the answer. But one wonders if this
group of mechanisms (even acting at several levels: adult energy
efficiency, successful fertilization of eggs, larval mortality, etc.) by
itself could be potent enough to produce the quite consistently repeatable, sweeping nature of the effect. The possibility of involvement of infectious diseases via cycles of increased population
density, associated increased efficiency of disease transmission,
resulting infectious outbreaks and subsequent population collapses
has for some reason been largely neglected in discussions of this set
of issues, but probably should not be discounted in terms of some
degree of possible involvement in the alternating dominance issue
(i.e. item “C” of the list presented in the Introductory section),
but it is not easy to see how disease cycles could constitute any consistent rationalization for the other items (items “A”, “C”, “D”, “E”,
etc.) for which we are seeking a comprehensive theory.
But, whatever the case, there can be no doubt that the very specificity of the respective anchovy and sardine adaptations must
cause the two species groups to often react in strikingly differing
ways to climatic or ecosystem variations. And we seem to drawn
to a general conclusion that a major overall difference between the
evolved ecological strategies of sardines and anchovies is that, of
the two species groups, the sardine seems much more opportunistic
with respect to major ecosystem variations. Anchovies, of course, are
also r-selected (i.e. opportunistic) species, but in a different sense.
That is, the sardine’s evolutionary history has evidently provided
characteristics by which radical ecosystem variation may represent
distinct opportunities that the sardine may be prepared to actively
exploit. In contrast, the anchovy’s evolved characteristics may
allow it to do rather well in a period of rather settled conditions
or comparatively gentle, largely monotonic long-term trends in
which it can take rather steady advantage of superior efficiency,
but be unable to adapt to, and thus be seriously disrupted by,
abrupt ecosystem change. Bakun and Broad (2003) illustrate this
A. Bakun
in terms of a financial stock market analogy, in which anchovies
can be thought of as the “bulls” that do well in “good times” when
conditions are benign, well behaved, and predictable, and sardines
as the contrarian “bears” that during “bad times” are able to turn adversity into opportunity. To put this conceptual template in most
simplistic terms, “normal” (i.e. stable or gently trending) favours
the anchovy, whereas “disruption” (of the “normal”) favours the
sardine.
Resolving conundrums
So, if it is accepted that their differing evolutionary histories may
have effectively assigned the ecological role of obstinate “robust strategist” to the anchovy and the role of “nimble opportunity-seeker” to
the sardine, let us expressly test this “comparative advantage” template terms of its ability to yield a resolution of each otherwise
puzzling pattern of interrelationship (i.e. the “conundrums” “A”
through “E”) outlined in the “Introduction” section. We briefly do
this, item by item.
Item “A”: sardines growing their abundance during
poorly productive conditions
In the eastern Pacific, in both the California Current and Humboldt
Current systems, anchovies do well in highly productive conditions
that characterize the multiyear time intervals between El Niño episodes. This is as is expected for a species obviously oriented to
highly productive ocean zones. A seeming paradox is that sardines,
equally obviously adapted to highly productive ocean zones (upwelling areas, etc.), often do better, at least in the eastern Pacific,
during the conditions of abruptly lowered local low-trophic-level
productivity that characterize El Niño episodes (Niquen and
Bouchon, 2004). The inference drawn by Bakun and Broad
(2003), supported by the empirical finding of Agostini et al.
(2007), is that El Niño disrupts the pervasive larval predator pressures that appear so damaging that many fish species (e.g. coral
reef fish, tunas, salmon, etc.) make extraordinary expenditures of
migrational energy and/or losses of reproductive product to
remove their earliest life stages from proximity to high concentrations of potential larval predators. Sardines, particularly those of
the genus Sardinops, apparently are able to employ their prodigious
long-range swimming capabilities and widely ranging opportunistic
migrational tendencies to ferret out isolated temporal-spatial
“pockets” where a minimally adequate larval food concentration
may be available. This may allow sufficient advantage to be gained
from the reduced levels of predation such that their highly leveraged
reproductive mode can generate a substantial degree of reproductive
success even in the face of rather slow growth, etc., compared with
that possible in much more productive non-El Niño conditions
under which devastating larval predation might completely overwhelm any benefit from accelerated larval growth rate.
Item “B”: the extreme fish productivity of the
Peru– Humboldt LME
The evidently very benign situation off Peru may in large part be due
to its low latitude position which results in strong upwelling-driven
enrichment, uniquely long particle residence times, and low levels of
turbulent mixing energy (Bakun and Weeks, 2008). These factors
apparently combine to promote great abundances of diatom cells
so large that they can be directly collected even by the particularly
coarse filtering apparatus possessed by anchovies, while at the
same time being harvested by a community of exceptionally large
zooplankton that may constitute ideal objects of the raptorial
Active opportunist species as potential diagnostic markers for comparative tracking
feeding mode that appears the one most favoured by anchovies (van
der Lingen et al., 2006). Following each El Niño disruption during
which the ecosystem had been cleansed of profusions of undesirable
components, then reset and renewed, the system remains well
behaved and predictable in a cyclical sense (i.e. in the more or less
repeatable sequence of highly productive transients and the fact
that when there is no active El Niño episode underway, differing intensities of the opposite La Niña state do little to seriously alter the
basic benign situation). It represents the essence of “anchovy
heaven” in which predators of anchovy larvae can be swamped by
the shear productive energy of an explosively growing post-El
Ninõ anchovy population. Therefore, the efficient anchovy can
remain temporarily unimpeded in pursuit of its highly productive
“robust” population strategy.
When the inevitable next El Niño does hit, the anchovy may be
temporarily devastated. However, the sardine may turn the situation
to its own distinct advantage by profiting reproductively from the
associated reproductive failures of planktonic larval predator populations and of the absence of migratory nektonic predators that
need much greater concentrations of zooplanktonic food than
could be supplied from fish larvae alone and therefore may refrain
from entering the habitat at all, either to feed or to deposit their voraciously predatory offspring. Moreover, the system cannot become
durably stunted by development of malignant “eco-feedbacks”, such
as has been hypothesized for the northern Benguella (Bakun and
Weeks, 2006), because of the periodic cleansing and resetting of
the ecosystem by El Niño. [For expanded detail on the cyclic sequence of proposed interacting mechanisms underlying the
overall highly productive Peruvian situation, one may refer to
Bakun and Weeks (2008).]
Item “C”: alternating dominance and item “D”: basin-scale
synchrony
This particular proposed pattern of interaction could also be
expected hold on the longer multiannual to multidecadal time
scales. For example, during the period from the early 1970s to the
mid-1980s, the eastern Pacific upwelling systems appear to have
become more dominated by influence of offshore-oceanic waters
(Alheit and Bakun, 2009), similarly characterized by smaller foodparticle spectra, etc. (To what extent this might represent some separate truly longer term phenomena at its base, or be largely a simple
effect of a period of raised frequency and strength of individual
El Niño episodes is unclear.) But whatever the precise nature of
the cause, it can be understood why anchovies, when food particles
become too small to be effectively filtered by the gillraker structures
of anchovies, might give way to the finer filter-mesh-bearing sardines. In general, this set of considerations would appear to offer
an answer to the alternating dominance issue for the eastern
Pacific systems, at least for the period following 1970 that is the
period for which the indication of alternating dominance may be
truly credible (Bakun, 2005b).
But how does one explain the northwestern Pacific? As stated
earlier, in the neritic ecosystem of the northwest Pacific near Japan
which is under the influence of the extremely energetic Kuroshio
western boundary current system, the anchovy never approaches
peak-abundance parity with the sardine (as is also the case in the
particularly energetic upwelling system of the northern Benguela
region). In these systems, the anchovy has seldom assumed a position of true dominance other than by virtue of the sardines’ abundance falling very low. According to our inferred conceptual
template, sardines appear evolutionarily particularly well-equipped
2287
to take opportunistic advantage of system disruptions. The strong
flows and intense turbulent eddy characteristics of these particularly
energetic systems appear to offer continuous patterns of disrupted
conditions in time and space of exactly the sort that the sardines’
evident adaptations seem designed to accommodate.
More than 30 years ago, Skud (1982) had already identified a
general pattern in a variety of fish that seem to form interrelated
“pairs” (as anchovies and sardine seem to do), such that the population dynamics of the dominant species tends to respond to environmental factors, whereas those of the subordinate species respond
to the abundance variations of the dominant one. Therefore, if we
assign the dominant wasp-waist role in the neritic ecosystem near
Japan as characteristically belonging to the sardine due to the
intense nature of the Kuroshio system in which the regional-scale
population at least partially operates, the observed out-of-phase
alterations fall directly within Skud’s identified pattern.
The early 1970s to mid-1980s period, during which sardine
populations exploded all around the rim of the Pacific, was characterized by a steep decadal scale decline in the Southern Oscillation
Index (SOI) that would of course have been related to an unusual
combination of frequent and intense annual-scale declines (i.e. of
El Niño episodes). Thus, the enhanced “El Niño” character of this
period would naturally seem (see discussion of “item A” above) to
favour sardine population growth in the eastern Pacific, if only in
terms of a sum total of an increased frequency of successful
annual growth episodes. Moreover, the long trend that culminated
in a distinct change in the “mean level” of the various indices undoubtedly represented a degree of continually developing reorganization of various ecosystem distributions and relationships that
probably involved significant natural evolutionary selection of
many short life cycle ecosystem components. The sardine’s intrinsic
exploratory, opportunistic tendencies, and capabilities would be
expected to be invaluable in tracking a favourable ecological response to the rapidly reorganizing ecosystem context (as expressed
in our simplified “comparative advantage” conceptual template, i.e.
that “disruption favours the sardine”).
Moreover, in addition to the uniquely steep decadal scale longterm trends of the early 1970s to the mid-1980s interval (“boxed”
in Figure 2b), the period appears also to have been subject to uniquely energetic shorter 1- or 2-year interannual-scale climatic gyrations.
For example, if one counts all the 1- or 2-year incremental differences in the various smoothed 51-year (1950– 2001) series of
annual climatic indices assembled in Figure 2 of Tian et al. (2004)
[more recently also reprinted as Figure 2 of Alheit and Bakun
(2009)], the 13-year (1970– 83) segment contains: (a) the largest
(‘81–‘82), the 3rd largest (‘75–‘77), the 4th largest (‘72–‘74), and
the 5th largest (‘70–‘72) in the entire 51-year annual mean SOI
series, (b) the largest (‘77–’79), the 2nd largest (‘70–’72), and the
4th largest (‘82–‘83) in the winter North Pacific Index series, (c)
the largest (’76–’77) and the 2nd largest (’70–’72) in the winter
Pacific Decadal Oscillation series, (d) the largest (’76–’77) in the
winter Arctic Oscillation series, and (e) the largest (’77–’79) and
the 2nd largest (‘73–‘74) in the winter Monsoon Index series.
Again the pattern that “disruption favours the sardine” emerges
very distinctly.
In summary, the continual climatic disruptions that appear to
have the characterized the early 1970s to mid-1980s period,
coupled with the inference that “disruption favours the sardine”,
appear to offer a linkage mechanism for the synchronous dynamics
of the widely separated sardine populations located in the far corners
of the Pacific basin. This coupled with the observed pattern of
2288
A. Bakun
Figure 2. (a) Variations in the abundance of the largest sardine stocks of the Pacific Ocean plotted as percentages of maximum annual values for
the period 1970 – 2000, based on landings data taken from the FAO files. (Before the 1990s, most California sardine landings were taken by the
Mexican fishery inside the Gulf of California; beginning in the mid-1990s increasing contributions came from US and Canadian fisheries.) (b)
“Low-passed: (via 5-point running means of annual mean values) versions of several prominent climatic index time-series. The shaded rectangle
indicates the early 1970s to mid-1980s period of steep decadal-scale trends discussed in the text. (Panels redrawn and extended from Bakun and
Broad, 2003).
out-of-phase population variations of anchovies and sardines (Item
C, in our list above) would then work together to rationalize the
observed basin-scale synchrony (Item D).
Item “E”: the “Law of two”
So finally we come to the intriguing item “E” in the list given in the
“Introduction” section. Why are there usually two dominant small
pelagic species, an anchovy and a sardine, rather than just a single
species that turns out to be the superior competitor in each local
situation? And why would this intriguing “law of two” seem to
hold, not only in highly productive temperate coastal upwelling ecosystems and in the likewise highly productive but dynamically quite
different western boundary current situation of the northwest
Pacific, but also reportedly in rather oligotrophic semi-enclosed
peripheral seas such as the Mediterranean. Even within sub-basins
of the Mediterranean, this “law of two” seems to hold in such
quite differing physical/ecological situations as the Balearic and
Adriatic Seas. Moreover, if more than one species, why not more
than two? For example, a “cyclic advantage”-type explanation
would require at least three competing species (Matsuda et al.,
1991; Sinervo and Lively, 1996).
A possibility is that there are ordinarily two, and only two, sufficiently distinct “home-base” habitat segments in any of these
boundary ecosystems. One of these is characterized by terrestrial
influences, significant turbidity, large suspended organic particles,
etc. Here, the anchovy is superior and efficiently outcompetes any
interloping other species of small pelagic planktivore. The other sufficiently distinct segment is at the nebulous, uncertain, temporally,
and spatially extremely patchy offshore edge of the ecosystem where
neritic and oceanic effects merge together. Here, opportunism and
flexibility is at a premium, and food particles may typically be very
small. Here, the sardine has the ability to “hang on” where potential
Active opportunist species as potential diagnostic markers for comparative tracking
small pelagic competitors (vertically migrating mesopelagic fish
representing an essentially different strategy that does not truly
compete with that of the sardine) and extremely damaging concentrations of predator stocks cannot.
Therefore these two alternative species groups, anchovy and
sardine, could be available and ready at any time, when conditions
enable, to break out of their respective “home-base” habitat segments and seize dominance of the extensive intervening in-play
zone (“Item ‘C’: alternating dominance and Item ‘D’: basin-scale
synchrony” section) of the neritic habitat. According to the conceptual framework being inferred here, the enabling conditions for
anchovy breakout might be a period of adequately vigorous
primary productivity during which system disruptions tend to be
minor (e.g. when after an El Niño episode, the system has stabilized
and vigorous primary production resumes). Sardine breakout evidently may be favoured by a major system disruption such as an
abrupt drop in primary production (as during an El Niño episode
in the eastern Pacific) or by a period of steep trend of change (i.e.
continuously progressing disruption) in which a capacity for
nimble opportunism may be at a particular premium.
A separate sardine genus for the North Atlantic
The inference that sardines may depend on system disruption to
most effectively exert their evolved opportunistic advantages
might derive further credibility from the total absence from the
North Atlantic basin of sardines of the genus Sardinops that have
very successfully colonized the suitable temperate neritic boundary
habitats in the Pacific (both hemispheres) and south Atlantic basins
(Sardinops having been the basis of most of the inferences we have
drawn with respect to sardines). Most knowledgeable colleagues
could probably agree that Sardinops may exhibit opportunistic
characteristics to a somewhat greater degree than does Sardina (certainly, Sardinops seems to be much more migratory of the two, as
well as much more prone to abrupt distributional expansions and
contractions). Sardina is the temperate sardine genus that is currently established in the North Atlantic basin which, of all the
major ocean basins on earth, is the one most influenced by continental effects. Land surface possesses little heat storage capacity to
serve as “climatic memory”, whereas water in its liquid state has a
notably large heat storage capacity. The much larger areas of heatstoring ocean surface compared with land surface in the Pacific
and in the southern hemisphere ocean basins allows the climates
of these zones to “wander” on multiannual scales much more
than in the North Atlantic area, where the interaction of heating
and cooling of stationary continental landmasses with a quite precisely cyclic seasonal progression of height of the sun may force
the local ocean climate into greater interannual regularity compared
with the very large seasonal amplitudes to which the local ocean
ecology must be adapted. Thus, one might speculatively conclude
that the evolved opportunistic capabilities of the genus Sardinops
could be less decisive in the North Atlantic than in the other
major basins. Indeed, perhaps much of the evolution of the genus
Sardina might actually have been based within the unique conditions of the Mediterranean where the external climate is dominated
by continentality while the liquid-water environment exhibits a particularly “oceanic” character due to the relative nutrient impoverishment produced by the “negative estuary” mode of water
exchange with the North Atlantic proper. In the continentally influenced North Atlantic, which may thus be less subject to interannual
variation in the degree of its system disruption, the genus Sardina
2289
might simply manage to outcompete the genus Sardinops in the
characteristic “sardine home-base” habitat segments on the
European side of the North Atlantic. The western side of the
Atlantic, with its shallow broad continental shelf and very high
volume of continental run-off, may simply lack significant “homebase” habitat for sardines.
Implications for effects of projected climate changes
The foregoing process of step-by-step rationalization of the list of
prominent conundrums (Subsections “A” through “E”, above) corroborates the earlier gross characterization (that was based on comparative morphological and behavioural aspects, as well as on
inferred evolutionary, aspects) of anchovies as “efficient stay-athome specialists” and of sardines as “nimble wide-ranging opportunists”. Based on this characterization alone, one could guess that
sardines might fare better than anchovies as rapid global changes
transpire. However, our analysis has also pointed out a “home-base”
anchovy environment as being one conditioned by continental
run-off. A fairly recent consensus among climate models (Meehl
et al., 2007) indicates that on a global-average basis, as greenhouse
gases continue to accumulate in the earth’s atmosphere, precipitation will generally increase. This would tend to offer new or
enhanced estuarine and coastal run-off-affected zones where anchovies may turn out to be superior competitors. However, the model
consensus also suggests that a greater proportion of the subtropics
may be affected by drought, which according to the framework
developed herein should favour sardines. This tendency for moist
regions to become wetter while dry regions become drier is in fact
captured by the observational record as well as by models (John
et al., 2009). Moreover, due to the increased atmospheric water
vapour available to be released from a warmed atmosphere as precipitation due to orographic effects, the increase in rainfall
amount is likely to be larger on the windward slopes of mountain
ranges (Christensen et al., 2007). Mountain ranges border some of
the most important marine ecosystems having wasp waists dominated by the sardine–anchovy species pair. In particular, increased
rainfall in the near-coastal zones of Ecuador and Peru, as well as all
along the Asian continental boundary of the northwestern Pacific, is
indicated in the IPCC Regional Climate Projections (Christensen
et al., 2007). Increased precipitation is also projected by IPCC
along the North American Pacific continental boundary north of
408 latitude except during summer and, in the northwestern
Atlantic, throughout the year along the coasts of the North and
Baltic Seas; thus, in these areas, as the anchovy–sardine complexes
expand northwards due to warming, they will be expanding into
areas where precipitation is expected to be increasing as climate
change proceeds, potentially favouring anchovies.
This example discussion has of course only scratched the surface
in terms of available material for such speculative inferences. To
briefly mention another aspect, one currently prominent climate
change projection is that the Pacific trade wind circulation may
decline as climate change proceeds (Vecchi et al., 2006). The implication would seem to be that the ocean –atmosphere system of the
Pacific might shift in the direction of a more chronic, if “low-level”,
El Niño-like state. If so, since El Niño conditions have seemed to
favour sardines over anchovies on both sides of the Pacific, this
aspect might be expected to benefit sardines. But it might presage
less intense individual El Niño episodes, which could lessen the
“boom or bust” aspect of eastern Pacific marine ecosystems, i.e.
perhaps leading to lowered base populations of seabirds and
2290
marine mammals, but conceivably to fewer or less serious incidents
of periodic starvation of these highly visible “charismatic” species.
Yet, another projection that has been put forth is that upwelling
may intensify in the “classical” upwelling ecosystems as climate
change proceeds (Bakun, 1990; Diffenbaugh et al., 2004), although
it should be said that that particular prognosis remains somewhat
controversial (Bakun et al., 2010; Wang et al., 2010). If so, among
other major trophic consequences, because of the greater difficulty
zooplankton have in maintaining population against increased offshore transport associated with intensified upwelling, the ratio of
phytoplankton to zooplankton might be expected to increase
(Bakun et al., 2010). This result, as well as the fact that anchovies
seem to be somewhat less well adapted to intensified flow systems,
would again seem to generally favour the more omnivorous
highly mobile sardines over the largely zooplanktivorous,
weaker-swimming anchovies. The implications are obvious, important, and diverse, e.g. on aspects including hypoxia, marine
“dead zones”, red tides, etc., in addition to distinct effects on
spatial aspects of ecosystem support to fishery resource dynamics,
etc. (the very heavy use of “etc.” reflecting the very broad choice
of potential examples relative to the space that can be afforded to
them in a treatment such as this).
The salient point here is that a simple conceptual framework such
as has emerged from this limited discussion may provide one type of
reference with which to try to gauge and begin to understand the
nature and significance of developing patterns in ecosystems featuring the anchovy –sardine species pair.
Will active opportunist species “steal the stage”?
The early 1970s to mid-1980s period (highlighted in Figure 2), in
which simultaneous sardine population explosions coincided with
steep decadal scale changes in levels of various climatic indices,
has featured prominently in our characterization of sardine as
being adapted to a rapidly changing (i.e. “disrupted”) situation.
Interestingly, this same period also featured strikingly similar
“breakout” population increases and following declines in quite a
large number of other marine species, particularly within the
Pacific Ocean basin [for references, see Benson and Trites (2002)
and many sources cited therein] but also more generally scattered
throughout the entire global ocean system [for references and
sources for additional citations, see Bakun (2005b)]. These included
some of the largest, most important fishery resource populations in
the North Pacific zone (e.g. Alaska pollock, sockeye salmon, pink
salmon, chum salmon, yellowfin sole, Pacific hake, Pacific cod,
and many others). In the tropical Pacific Ocean, additional examples
included yellowfin and skipjack tunas, various lobsters, seabirds,
and coral reef fish, and even phytoplankton and zooplankton distributions. Apparent echoes of this pattern in the Atlantic have
involved various stocks of northern cod, as well as extraordinary
outbreaks of normally rather uncommon fish species such as triggerfish and snipefish. This leads to an intriguing question. Might
the stocks of other species that mirrored the sardine rises during
that unique period of steep climatic trends potentially be likewise
viewed as “active opportunist” species? And might stocks that
appear to have acted during that period in an opposite “anchovy”
sense perhaps be usefully viewed, at least hypothetically, as “efficient
specialists” that may react adversely to rapid ecosystem changes, but
might be able to outpace their less efficient rivals in tracking somewhat more gradual ecosystem trends? If so, we perhaps will have
found a sort of new “philosopher’s stone” for turning ostensibly
random information into distinguishable emerging patterns that
A. Bakun
may aid recognition of some overall order within the apparent
chaos of complex-adaptive marine ecosystem responses.
An initial step could be examination in a similar manner to that
illustrated here (e.g. gleaning some enhanced mechanistic understanding via rationalization of existing apparent conundrums in
each case, etc.) of each of the species groups and ecosystem types
conforming to the same sequential pattern. Undoubtedly such an
interregional pattern –recognition exercise could constitute fascinating collaborative intellectual activity. And if successful, and appropriately coordinated, the effort might well contribute towards
significantly accelerated understanding and enhanced prediction
skill during the coming challenging period of rapid global
changes. [One may guess that a similar envisioned need for a coordinated “broader view” of marine ecosystem operation may have
been what led Johan Hjort to become a “founding father” of the
International Council for the Exploration of the Sea (ICES),
within which he served as the Norwegian delegate from its founding
in 1902 to 1938, when he was elected ICES President, a position he
held until his death in 1948.]
Given the vexing lack, in the full century that has elapsed since
Hjort’s landmark publication, of substantial progress by the
“applied science of fisheries oceanography” towards its major goal
of improving fisheries management and marine conservation
(Hare, this volume; Houde, 2008), a greater degree of “outsidethe-box thinking” would seem to be called for. Hjort’s celebrated
contemporary, Albert Einstien, is said to have remarked that “The
eternal mystery of the world is its comprehensibility”. So why has
not fishery oceanography produced the sort of revolutionary
advances in applications that other sciences have? In answer, it
might perhaps be appropriate to cite a second quote from Doctor
Einstien: “things should be made as simple as possible, but not
simpler”.
The currently prevalent reductionist approach addresses an
expanding multitude of potential simple mechanisms, each of
which is likely to be more or less active at one time or other. One
can of course model and simulate these ad infinitum. But since the
important events to be understood and ultimately predicted (population collapses, etc.) seem most often to occur on interdecadal time
scales, one wonders how the multitude of interacting factors could
ever be sorted out sufficiently confidently to support strong corrective actions (Bakun and Weeks, 2006), even in the unlikely event that
the system structures would be stationary in a temporal sense, which
would seem unlikely in this era of progressing global environmental
change? It seems in fact that fisheries oceanography may be caught in
a sort of quagmire in which ever more resources seem to be required
to follow an ever more reticulated path that seems never to get us
much closer to its major goal. Thus, it may be useful to seek more
integrated, more holistic approaches wherein an expanded “universe” of diverse experiences might be assembled together within innovative conceptual frameworks that could facilitate recognition of
informative emergent patterns ensuing from the superposition of
multiple hierarchies of interacting component mechanisms. The
notion elaborated in this paper of classifying fish populations
according to apparent degrees of evolved opportunistic capabilities
and behaviours might perhaps be considered as one possible initial
step, even if only a “baby step”, in that direction.
Concluding remarks
Some readers might feel frustrated that this attempt at a synthesis focusing on anchovies and sardines may not have pointed very directly
to any concrete model supporting specific predictions with respect
Active opportunist species as potential diagnostic markers for comparative tracking
to that particular pair of species groups. But as stressed in the introductory section of this discussion, we seem to be dealing with
complex adaptive systems that may be governed ultimately by nonlinear feedbacks. Therefore, earlier hopes for effectively employing a
linked sequence of simple linear models appear to be receding
(MacCall, 2009b). Drawing a musical analogy, one might say that
to a careful “listener”, the real generative action in the ocean
system may play less like a set recipe and more like a complex symphony, replete with shifting rhythms and haunting, often scarcely
perceived, recurring themes that may never be precisely repeatable.
Does such a realization signify defeat? One would think not. It
just might have to be accepted that a better approach may be one
much less focused on specific model-based predictions and annually
reformulated management advice, but rather more directed towards
an acquired level of understanding and accumulated experience that
supports reasoned expectations as to the “probability vs. consequence” spectrum of potential outcomes of actions undertaken.
One simple illustrative example taken from an entirely different
context may be that of a particular antibiotic (a different type of likewise valuable, but destructible, resource). One may not be able to reliably predict precisely when a certain antibiotic will begin to fail.
But sufficient understanding and experience have accumulated to
point out what will make it fail more rapidly (e.g. feeding it to
pets and farm animals, ceasing use before a prescribed course of
treatment has been completed, etc.). As Houde (2008) has expressed
it “Understanding the causes of recruitment variability is a desirable
goal; ‘solving the problem’ may be an unrealistic goal”.
The value of seeking a spectrum of outcomes, as opposed to narrowly focusing towards identification and elaboration of a most
probable outcome, is worth stressing. For example, can one afford
to focus totally on maximizing of production of a particularly
favoured resource species while ignoring significantly less likely
but perhaps much more menacing possibilities (such as transformation of the wasp waste of an ecosystem to durable dominance by
infestations of jellyfish, or by hypoxia-producing bacteria, etc.),
which may be potentially lurking as yet unrealized out in the tails
of the probability distributions?
Thus, in the future, instead of management advice that sounds
like “Do such and such, just do not deviate from the plan, and all
will be well”, truly well founded advice may sound more like
“Well, no one can be sure precisely what will happen, but the last
several times someone tried what you propose, differing things happened, but in general, no one was particularly happy with the way
things worked out”. If we are to succeed in preserving our beautifully
intricate ocean systems, we must hope to at least advance to that
basic level. And, happily, advancing to that level should lie within
our scientific reach. From a personal and professional standpoint,
“getting there” should continue to be an extremely engrossing and
fascinating activity.
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