ICES Journal of Marine Science, 63: 1567e1572 (2006)
doi:10.1016/j.icesjms.2006.03.028
Food for thought
Ecosystem-based management of fisheries: is science limiting?
Chris L. J. Frid, Odette A. L. Paramor,
and Catherine L. Scott
Frid, C. J. L., Paramor, O. A. L., and Scott, C. L. 2006. Ecosystem-based management of
fisheries: is science limiting? e ICES Journal of Marine Science, 63: 1567e1572.
Received 10 February 2005; accepted 14 March 2006.
C. L. J. Frid, O. A. L. Paramor, and C. L. Scott: School of Biological Sciences, University of
Liverpool, Crown Street, Liverpool L69 7ZB, England, UK. Correspondence to C. L. J.
Frid: tel: þ44 151 795 4400; fax: þ44 151 795 4404; e-mail: [email protected].
Introduction
With the adoption of the Convention on Biological Diversity (CBD; UN, 1992), managing the environment in an
ecologically sustainable manner has shifted from being an
option to being a legal necessity: sustainability is now the
overarching goal of environmental management policy.
Ecosystems have natural resilience. Reproduction and
adaptability are fundamental biological attributes which respond to human activities. This means that the real challenge for managing the system is determining the key
limits, i.e. the types and levels of human activities that
can be sustained without compromising the functioning of
the ecosystem, and setting in place policies to obtain those
goals. The latter is a socio-political issue, the former is very
much a scientific issue.
The ecosystem approach promotes conservation and equitable, sustainable management of land, water, and living
resources. It relies on scientific understanding of ecosystem
structure, processes, functions, and interactions (CBD,
2000). It recognizes that humans, with their cultural diversity, are an integral component of many ecosystems. It also
emphasizes the fact that, by their very nature, ecosystems
cut across traditional management sectors. Therefore, we
are faced with developing, for example, fisheries management in an ecosystem context, while not necessarily being
able to influence fertilizer applications in the hinterland
that may impact fish nursery areas.
In most jurisdictions the requirements of the CBD are being developed within existing management structures. The
reality is therefore that each sector, within each jurisdiction,
is trying to develop ecosystem-based management regimes.
Here we consider how science is placed to contribute to this
wider fisheries management agenda.
1054-3139/$32.00
Fishing activities influence marine ecosystems in a number
of ways. These include (i) direct removal of target species,
(ii) direct changes in size structure of target populations
(Jennings and Kaiser, 1998), (iii) alteration in non-target populations and communities of fish and benthos (Rumohr and
Krost, 1991; Camphuysen et al., 1995; Tuck et al., 1998),
(iv) alterations in the physical environment (Churchill,
1989; Messieh, 1991; Riemann and Hoffmann, 1991; Auster
et al., 1995; Schwinghamer et al., 1996), (v) alterations in
the chemical environment (ICES, 1998; Percival et al.,
2005), and (vi) food-chain effects such as trophic cascades
(Carpenter et al., 1985) and altered predation pressure (Frid
et al., 1999). It is impossible to harvest a species without
causing (i), and because harvesting is selective, causing
(ii). The challenge for ecosystem-based fisheries management is then to provide the maximum sustainable take of target organisms, with the minimum impact on other ecosystem
components.
Ecosystem measures in fisheries
management
A number of measures can be regarded as addressing ecosystem considerations in the management of the fisheries of
the Northeast Atlantic. The ecosystem issues addressed in
the present management regime are interactions between
species (i.e. through the use of multispecies stock assessment procedures); fisheries effects on the supply of food
for predators (e.g. cod, Gadus morhua, and capelin, Mallotus villosus; ICES, 2001, 2003a) and sandeels (Ammodytes
spp.) for seabirds (ICES, 1999); and the additional fishing
mortality of non-target species (e.g. pingers to prevent cetaceans entering set nets (EC, 2004b). There has been less
progress in providing protection of habitat areas and the
Ó 2006 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.
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C. L. J. Frid et al.
ecological functions they deliver, or in conserving genetic
diversity. It is also recognized that the influence of the ecosystem on fisheries is not well addressed by current management procedures; for example, there is no mechanism
for accounting the variations in climatic factors and hydrography (ICES, 2005).
Climate effects on the marine ecosystem
Ecosystem dynamics are controlled in part by external
drivers such as hydrodynamic/atmospheric factors. These
drivers influence the productivity of phytoplankton (Dickson
et al., 1988; Richardson et al., 1998), and the dynamics of
zooplankton communities (Marshal, 1949; Krause and
Trahms, 1983). The survivorship of fish larvae and hence
recruitment into the adult stock are related to plankton
productivity, while climate variation affects the natural
mortality, distribution, and migration of fish populations
(Jennings et al., 2001).
In future, fisheries management will need to incorporate
these types of external drivers and their impact on ecosystem dynamics to improve the reliability of predictions,
especially in the face of increasing climate variability
linked to global warming. However, the level of uncertainty
in our existing knowledge of the effects of external drivers
on fish stocks will need to be addressed if the information
on the state of external drivers available from ‘‘operational
oceanography’’ is to be used for management purposes.
Protecting habitats
While all habitats are likely to provide ecological services
and the physical environment for certain species or life stages
to exist, not all habitats are equally sensitive to the impacts of
fishing. The OsloeParis Commission (OSPAR) provides the
international regulatory framework for a number of human
impacts in the Northeast Atlantic, although it does not have
competence over fisheries management. OSPAR is, however, the lead body for the application of the UN Convention
on Biological Diversity (UN, 2002) in the regional marine environment, and as such is developing management measures
to ensure that CBD goals are met. OSPAR is in the process of
identifying habitats that are sensitive to various human impacts, including fishing. This categorization obviously requires consideration of the different types of fishing activity
and then a consideration of appropriate management measures (Table 1; ICES, 2002b, 2003b).
In one sense the management measure to protect physical
habitat is straightforward: one simply needs to remove the
damaging activity from the sensitive area. Therefore, the
management measures are inherently spatial. Such closures
to all, or certain damaging types of, fishing gears have now
been implemented for some deepwater coral communities
(EC, 2004a).
The more widespread application of measures based on
protected areas is limited by lack of agreement on the total
fraction of a habitat that should be protected. For rare habitats one can envisage complete protection, but IUCN
guidelines suggest that at least 20e30% of each habitat
type is strictly protected (IUCN, 2003). The lack of highly
spatially resolved maps also hinders this process, although
some European countries have started to map their national
seabed areas using a standard habitat classification scheme
(http://eunis.eea.eu.int/habitats.jsp), so it seems likely that
in the near future the first obstacle, namely knowing what
we have and how it is distributed, will be overcome.
Assuming that we have also agreed on a target proportion
of habitat to protect, we must decide which part(s) of the
whole should be protected. For example, should we distribute a prescribed protection of 20% of the habitat in one
block, two blocks of 10% each, 20 of 1%, 40 of 0.5%, or
some combination of areas of varying size? Nature reserve
theory is much more advanced for terrestrial systems, and
generalities have emerged (Diamond, 1975; Pressey,
1994; Etienne and Heesterbeek, 2000; Kingsland, 2002).
Long-term conservation is best served by a large number
of areas, providing that each is of a sufficient size to hold
viable populations. In terrestrial systems the aim has been
generally to provide protection for one or a few species,
whereas in the marine environment we usually seek to provide protection to a functioning, multispecies assemblage.
Nevertheless, many of the lessons are likely to transfer,
but with additional provisos, occasioned by the open nature
of most marine populations, that decisions need to be made
to determine the optimum spatial distribution of closed
areas on an effective biological scale that considers gene
flow, fish movement, and the transport of planktonic larvae.
The aim will be to have an ecologically linked network of
protected areas.
The spatial configuration of a network of protected areas
will need to consider biological and physicochemical factors, such as patterns of larval dispersal, identification of
where and when adults spawn, the biology and behaviour
of the larvae, and the hydrography of an area (Stobutzki,
2001), in order to maintain the functional integrity of the
ecosystem in those areas. However, there are no absolute
figures as to how close reserves should be (Roberts et al.,
2003), and hard evidence to support the design of reserve
networks is lacking owing to the complexity of the task
and a scarcity of examples.
A model developed to investigate the design of marine reserve networks in the Gulf of California determined that the
space between adjacent reserves should not exceed 100 km,
because of uncertainty about dispersal patterns, and calculated that reserves needed to be sufficiently large (50 km2)
to ensure the local retention of >90% of algal propagules
and >45% of fish and invertebrate larvae (Sala et al.,
2002). However, some argue that the reserves should not
be placed too close to one another to reduce the risk that a
local catastrophe will affect more than one of them (Roberts
et al., 2003). Hydrographic information would also need to
be incorporated into the design of networks, and it has
Ecosystem-based management of fisheries: is science limiting?
1569
Table 1. Matrix of potential mitigating measure for various fishing métiers in OSPAR sensitive habitats (after ICES, 2002b). Shading
indicates fishing activities thought to have no effect.
Key to sensitive habitat types (taken from the draft OSPAR list):
1
Deepwater biogenic habitats: Lophelia pertusa reefs, carbonate mounds, oceanic ridges with hydrothermal vents, seamounts, and deepwater sponge communities.
2
Structural benthic epifauna: Sabellaria spinulosa reefs.
3
Benthic infauna: Seapens and burrowing megafauna communities.
4
Shellfish beds: Ampharete falcata sublittoral community, Ostrea edulis beds, Modiolus modiolus beds, and intertidal mussel beds.
5
Nearshore communities: Zostera beds and littoral chalk communities.
Key to mitigation measures: AC, area closures; R, reseeding/restocking; GM, gear modification.
been suggested that in areas where currents are strongly
directional, the reserves sited in upstream locations will be
more likely to supply recruits to the rest of the management
area than those in downstream locations (Roberts et al.,
2003), so would presumably be of greater value. However,
where currents are complex or reversing, a more even spread
of reserve locations would be preferable.
Although we may now know the sensitive habitats and
where some are, issues concerning the number and spatial
distribution of protected areas remain a major challenge.
Recent advances in understanding of the fine-scale genetic
make-up of benthic populations (Todd, 1998) and in the
dynamics of meta-populations (Grimm et al., 2003) do provide some pointers that may allow the development of appropriate modelling frameworks.
Genetic diversity
Genetic diversity is, potentially, the product of very long
periods of evolution, yet losses may be irreversible and
virtually immediate (Nielsen and Kenchington, 2001;
Kenchington, 2003). This diversity is important for the ability of a species to adapt to extrinsic factors such as pollution or climate change. Loss of populations (extirpation)
most likely equates to a loss of adaptive variation in a species, and a loss of adaptive radiation may ultimately result
in the loss of that species. Management units are rarely
based on population genetic structure. The North Atlantic
blue whiting (Micromesistius poutassou), for example, is
managed as a single stock. However, population genetic
studies have indicated that partially separated stocks of
blue whiting exist in the Mediterranean and in the Northeast Atlantic (Giaever and Stien, 1998). Similarly, Ruzzante et al. (2001) reported on the decadal stability of the
genetic differentiation of five cod populations on spawning
banks off Newfoundland and Labrador, Canada. This genetic structure persisted through the recent population collapse, with only some suggestion of post-collapse mixing
between populations from two of the spawning banks.
This information is critical to recovery management, because it indicates that population re-growth will be the
mechanism for rebuilding the stocks, as opposed to immigration from other areas. Commercially, genetic diversity
is also very important for aquaculture, providing the raw
material for selective breeding programmes and the revitalization of inbred broodstock.
ICES suggests four general measures to mitigate against
the loss of genetic diversity (ICES, 2002a): (i) fishing mortality should be kept sufficiently low to maintain large populations; (ii) the harvest should be widely geographically
distributed among all recruited populations, to avoid local
depletions and fragmentation; (iii) there should be a reduction of fishing effort rather than alternative management
approaches that result in fisheries becoming even more selective; and (iv) there should be a case-by-case evaluation
of the risks associated with the loss of genetic diversity
vs. the benefits of imposed action. These were suggested
as ‘‘common sense’’ approaches for managers to follow
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C. L. J. Frid et al.
until the scientific community could recommend a more rigorous framework for specific stocks. Points (i), (ii), and (iii)
seek to reduce the selective pressure exerted by fishing and
the potential creation of a genetic bottleneck in either the
species (i) or any subpopulation (ii). Point (iii) addresses
concerns that more selective fishing technology may impose
a greater selection pressure than the rather crude size selection imposed by simple nets. Point (iv) aims to provide
a drive to find specific solutions matched to the circumstances of individual stocks. While these measures have
formed part of formal ICES advice to the European Community, no fisheries regulations have been introduced yet specifically targeting conservation or protection of genetic
diversity.
Challenges to implementing
ecosystem-based fisheries management
Two types of barriers inhibit the implementation of ecosystembased advice: (i) a deficiency in our scientific understanding
of the ecosystem, including the human part of it, and (ii)
methodological impediments to using the science as a basis
for management.
Science deficiency: the knowledge gaps
The preceding sections suggest that we currently lack critical understanding of
(i) links between hydrographic regimes and fish stock
dynamics;
(ii) the importance of habitat distributions;
(iii) ‘‘design rules’’ for MPAs, how they should vary by
regions/systems, and how to ensure that they are
ecologically linked;
(iv) ecological dependence/foodweb dynamics;
(v) predictive capabilities in complex systems;
(vi) how to incorporate uncertainty into management
advice;
(vii) the genetics of target and non-target organisms; and
(viii) the response of fishers to management measures.
It is beyond the scope of this paper (and the expertise of
the authors) to provide detailed descriptions of all the science programmes needed to address these knowledge
gaps. It is, however, clear that a number of these gaps are
at the boundaries of traditional discipline areas or are in
need of multidisciplinary approaches. For example, genomic and molecular markers may throw light on the genetics
of marine organisms and will inform our understanding of
sub- and meta-population dynamics. They will contribute
to our understanding of the scale of dispersal and linkages
between spatially distinct populations, the latter being
important for consideration of the potential effectiveness
of MPAs. Similarly, understanding links between physical
drivers, such as hydrography and climate, and biological
responses will be important for improving predictions of
future stock status. Additionally, how the ecosystem, as
a complex set of feedbacks and linkages, buffers/mitigates
these responses adds a further complexity to the predictions, and learning to manage uncertainty is yet another
key challenge. It is clear that as we enter the age of operational oceanography, one of the key users of the information will be those seeking to provide ecosystem-based
management advice for fisheries. However, humans are
also part of the fishery ecosystem, and we need to give as
much consideration to predicting the response of our own
species to the fisheries management regime implemented
(Pascoe, 2006). We cannot be regarded as some sort of simple, additional, predator. The response of fishers to fisheries
regulations varies depending on many factors, including
their degree of perceived ownership of the management regime, their perception of the behaviour of other players
(fleets and individuals), and the economic and social
circumstances.
Impediments to the use of science
It is clear that many gaps in our knowledge can be identified, but it is also apparent that there are a number of issues
that may restrict the use of the knowledge we have. In the
US, Canada, Australia, the EU, and probably many other
fisheries management regimes, management decisions are
made, quite rightly, in a political arena. In a democracy
this is the logical place for the balancing of the various,
potentially conflicting, issues. However, in these cases it
is also true that science travels through a number of filters
before it is considered by the decision-makers. The internal
reports, refereeing, distillation into briefing papers/advice,
and the interpretation of this by civil servants all dilute
the power of the science and, in our opinion, remove the
ability to seek alternatives; indeed the debate is polarized.
There is a need to ensure that science is presented directly
to decision-makers in a manner that allows them to engage
in dialogue. This allows misunderstandings to be avoided
and allows for the scientific evaluation/consideration of
alternatives that might emerge during the political debate.
The reasons for the development of our current administrative frameworks and the development of new ones that
see the removal of these barriers are issues that need to
be addressed by our social and political science colleagues.
In many cases, however, these studies need to proceed as
joint natural and social science initiatives, because only
in this manner can we expect the natural sciences to understand the nature and context for the advice they are being
asked to produce.
The way forward
Effort reduction is widely recognized as being the single
most effective measure that could be implemented to benefit fisheries; it will not on its own provide full protection to
Ecosystem-based management of fisheries: is science limiting?
all ecosystem attributes in need of protection. Closed areas,
whether complete or merely restricting certain métiers
(gear types), are the only protection for habitat features,
and even then we must still understand the necessary scale
and spatial distribution required to provide protection.
Moreover, whereas reducing effort will reduce the selective
pressure on the gene pool, it will not remove it, and although approaches such as gear substitutions have a clear
role to play in protecting habitat features and in reducing
bycatch/incidental mortality, these will not remove the genetic effects of fisheries.
The ecosystem approach is inherently participatory, and
stakeholders must be involved both for democratic governance and pragmatically to gain acceptance of the outcome.
Science has a role in informing stakeholders so that the management objectives set are achievable and arrived at after
due consideration of the options/alternatives. The science
needs of an ecosystem approach are much broader than
those of fisheries science. This will mean some reallocation
of resources if the advice is to come from the best sources.
Decision-makers and stakeholders need to recognize that
cutting-edge science is inherently dynamic and, as such,
there will be no single source for, nor necessarily a strong
consensus on, the best advice. What is clear is that the range
of science needed to input to this process is wider than that
required for present fisheries management.
Acknowledgements
The ideas and perspectives presented here are the authors’
own and do not reflect the views of ICES or any other
organization. However, we acknowledge the intellectual
opportunities that working within the ICES science community has given us. In particular, we acknowledge the
role of the Working Group on the Ecosystem Effects of
Fishing Activities, whose lively and authoritative membership has contributed greatly to the intellectual development
of an ecosystem approach to fisheries management in
Europe. In particular we thank Tom Catchpole, Simon
Greenstreet, Jenny Hatchard, Steve Hall, Louize Hill, Ellen
Kenchington, Gerjan Piet, Jake Rice, Leonie Robinson,
Stuart Rogers, and Simon Thrush for their stimulating exchanges on this and related topics. This work was in part
supported by the EC through study contract Q5RS2001d1685 ‘‘European Fisheries Ecosystem Plans: Northern Seas’’. The clarity of the arguments presented was
improved considerably following the comments of the
editor and two anonymous reviewers; we acknowledge
their efforts and thank them sincerely.
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