dc.description.abstract | This report reviews the methods available for assessing the impacts of interactions
between species and fisheries and their implications for marine fisheries management.
The focus is on modelling methods and multi-species population dynamics effects,
rather than on the full range of ecosystem aspects of fishing which encompass, for
example, environmental effects and technical interactions (e.g. bycatch issues), although
minor mention of these is made.
The first section takes a broad overview of some of the most commonly applied
multi-species/ecosystem approaches to fisheries management. The next section
summarizes the results and conclusions reached by previous studies and workshops
on the subject, including the ICES/SCOR Symposium on Ecosystem Effects of
Fishing, the Workshop on the Use of Ecosystem Models to Investigate Multi-species
Management Strategies for Capture Fisheries, the International Whaling Commission
(IWC) Modelling Workshop on Cetacean-Fishery Competition, the North Atlantic
Marine Mammal Commission (NAMMCO) workshops and the Workshop on
Ecosystem Approaches to Fisheries in the southern Benguela.
A brief description of the various modelling approaches currently in existence is
provided, highlighting particular features of these models which have general relevance
to the field of the ecosystem approach to fisheries (EAF). Models discussed include:
whole ecosystem/dynamic system models, minimum realistic models, individual-based
models and bioenergetic models.
These models are compared in a series of tables and figures, using the following
criteria:
1. the level of complexity and realism, e.g. the number of modelled species, the
representation of size/age structure of the species, and the types of processes
represented (physical and biological);
2. the types of functional responses of predators to changes in abundance of prey
species and their consequences and limitations;
3. how uncertainties in model structure, parameters and data are treated;
4. how environmental effects and interactions with non-target species (e.g. marine
mammals; sea turtles; sea birds) are incorporated;
5. the spatial representation of species interactions and habitat related processes;
6. model suitability for dealing with migratory species, i.e. species that cross
ecosystem boundaries;
7. where possible, model adequacy to allow the analysis of the different types of
management controls in use, such as effort control, minimum size, total allowable
catch, protected areas and closed seasons;
8. model adequacy to allow the assessment of the effects of short, medium and longterm ecosystem changes;
9. model suitability to conduct assessment and policy exploration, considering the
model’s potential use to conduct historical reconstruction of resources to describe
the current status of the ecosystem and to evaluate the potential effects of various
kinds of decisions (short and long term);
10. model transparency of operation and ease of use; and
11. data requirements and model suitability for data poor areas.
A description is also given of model parameters, some important assumptions, data
requirements, technical information such as the computing platform, a list of examples
where the approach has been used, notes on the model history as well as any additional
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useful features of an approach. Some advantages, disadvantages and limitations of each
of the 20 approaches are listed, together with notes on the ease of presentation of model
outputs and the user-level of programming and mathematical skills required.
The most widely used approach is undoubtedly ECOPATH with ECOSIM (EwE),
which is likely to remain a forerunner given the user friendly interface and on-going
improvements to the software. However, faced with incomplete knowledge of ecosystem
functioning, there has been increasing recognition that definitive conclusions cannot be
drawn from a single model structure. There has thus been a parallel increase in efforts
to modularize models so that different components can be easily substituted. Spatial
considerations are similarly playing an increasingly important role in the development
of ecosystem modelling approaches. Nonetheless, even some of the earliest approaches
such as Multi-species Virtual Population Analysis (MSVPA) are still being used and
improved. A summary is presented of some recent advances being planned for the
different modelling approaches.
A set of commonly asked questions pertaining to EAF is identified and the potential
of the various modelling approaches to address these questions is assessed. This
preliminary analysis suggests that a range of different model constructions are needed;
no one model is necessarily superior to all others in all respects. EwE is capable of
addressing the widest range of topical EAF research questions. The model considered to
show the greatest potential to contribute to practical fisheries management advice (such
as changes to total allowable catch (TAC)) is Globally applicable Area Disaggregated
General Ecosystem Toolbox (GADGET). Although still under development, this is
currently the model with the most rigorous statistical framework for testing multispecies based management advice. It is also the modelling approach most capable of
detailed sensitivity investigations to alternative growth, consumption and recruitment
formulations. Additionally, it operates within a spatial framework and overcomes
many of the associated computing constraints by running on multiple computers in
parallel. Nonetheless, it too has limitations in that it is capable of representing only a
relatively small component of the ecosystem and is not suitable for all systems. Models
such as EwE and ATLANTIS are more appropriate for addressing broader questions.
The incorporation of ecosystem considerations into current Operational Management
Procedures (OMPs) and other management strategies for marine resources is also
discussed. ATLANTIS is ranked the best operating model within a simulation testing
framework. Unfortunately it seems unlikely that sufficient data will be available to
implement an ecosystem operating model framework in most marine systems. Further
development is encouraged of approaches that take explicit account of uncertainty
and management issues, for example, through the use of a simulation framework
incorporating feedback control rules used in actual management.
Approaches such as the Extended Single-Species Assessment Models (ESAM)
are often a good first step. Similarly, examples are given of equations that provide a
useful starting template for multi-species modelling approaches, being built up slowly
and in synchrony with data availability. Some of the less well-known (in a global
context) modelling approaches are shown to include some additional useful features,
for example, SEAPODYM’s (Spatial Environmental POpulation DYnamics Model)
habitat index and OSMOSE’s (Object-oriented Simulator of Marine ecOSystem
Exploitation) explorations with simple individual predation rules.
This report is a first step towards initiating more detailed discussions of these models,
their uses and their limitations. This process is considered critical in moving forward
the development of methods for assessing indirect ecosystem impacts of fisheries.
Arguments are presented that whereas a good range of models has been developed
for the task of EAF, greater focus is needed on strengthening these approaches and
conducting the necessary data collection and experimentation to underpin confidence
in these approaches. Would-be model developers are encouraged to assess whether
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they would be adding anything to the current suite of models, given that approaches
such as EwE and GADGET have benefited from an extensive network of collaborators
over a number of years.
Considerable scope exists for significant future developments in multi-species and
ecosystem models, particularly with respect to their use as tools in EAF. Some of the
major areas of current research include:
• investigations pertaining to the effects of model complexity – in particular, the
effect of specific formulations (often feeding functional responses) on model
outputs;
• the treatment of uncertainty;
• representation of socio-economic factors and human behavioural drivers;
• multiple sector dynamics and management (with OMPs being an increasingly
popular method); and
• the effective (and feasible) representation of biodiversity | en_US |