326
14. Dynamics of Multiple Fish Species
The expedited removal of a species from the system under more stringent effort controls than contemplated by previous scenarios is illustrative
of the inherent difficulties in anticipating change in complex systems.
Whereas the more restrictive effort controls of the combined limitation on
days fished and reduction in trawl mesh size would intuitively lead to decreased catch and a corresponding increase in the population sizes of each
of the three species, the indiscriminate nature of trawl fishing continues to
devastate fish populations already threatened by decades of intensive fishing. Such counterintuitive consequences of a change in management exemplify the benefit of modeling complex systems before implementing management schemes.
14.5. Discussion
The dyna mic model of a multispecies fishery has illustrated a modeling approach to the conservation and management of dynamic ecological-economic
systems, and the sensitivity of system dynamics to the choice of parameter
values, initial conditions and functional specifications . The results of this
chapter are presented only for a small set of likely parameter values , various assumptions on technica l change in the fishery, and two possibly complementary management methods. There are two conclusions from the
model runs, one with regard to the conservation and management of the
dynamic ecological-economic system, and a second with regard to future
efforts to generate consensus on data, model structure , and management
implications.
The management methods implemented in the model and discussed here
by no means exhaust the realm of policy options. The analyses above indicate that neither small reductions in effort, nor mesh size increases , are
likely to prevent the further demise of the Georges Bank groundfish. On
the contrary , given interspecies interaction, population dynamics and
changes in age structure together with likely adjustment processes in the
fishing industry , depletion of fish populations may be accelerated through
the introduction of these policy measures. We referred to these problems in
our introduction, and those results are robust for a wide range of choices
for model parameters.
Other management measures seem to be necessary to prevent the collapse of the fishery. Such measures might amount to a combination of various strategies, as represented in our model , in conjunction with a dramatic
change in fishing technology. For instance, it has been suggested that otter
trawl fishing be discontinued in favor of a return to line fishing. Line fishing
may enable a more selective reduction in individual populations, building
on their abilities to recover from harvest , given their interactions with other
populations and the abiotic environment. Our model suggests a significant
14. Dynamics of Multiple Fish Species
The expedited removal of a species from the system under more stringent effort controls than contemplated by previous scenarios is illustrative
of the inherent difficulties in anticipating change in complex systems.
Whereas the more restrictive effort controls of the combined limitation on
days fished and reduction in trawl mesh size would intuitively lead to decreased catch and a corresponding increase in the population sizes of each
of the three species, the indiscriminate nature of trawl fishing continues to
devastate fish populations already threatened by decades of intensive fishing. Such counterintuitive consequences of a change in management exemplify the benefit of modeling complex systems before implementing management schemes.
14.5. Discussion
The dyna mic model of a multispecies fishery has illustrated a modeling approach to the conservation and management of dynamic ecological-economic
systems, and the sensitivity of system dynamics to the choice of parameter
values, initial conditions and functional specifications . The results of this
chapter are presented only for a small set of likely parameter values , various assumptions on technica l change in the fishery, and two possibly complementary management methods. There are two conclusions from the
model runs, one with regard to the conservation and management of the
dynamic ecological-economic system, and a second with regard to future
efforts to generate consensus on data, model structure , and management
implications.
The management methods implemented in the model and discussed here
by no means exhaust the realm of policy options. The analyses above indicate that neither small reductions in effort, nor mesh size increases , are
likely to prevent the further demise of the Georges Bank groundfish. On
the contrary , given interspecies interaction, population dynamics and
changes in age structure together with likely adjustment processes in the
fishing industry , depletion of fish populations may be accelerated through
the introduction of these policy measures. We referred to these problems in
our introduction, and those results are robust for a wide range of choices
for model parameters.
Other management measures seem to be necessary to prevent the collapse of the fishery. Such measures might amount to a combination of various strategies, as represented in our model , in conjunction with a dramatic
change in fishing technology. For instance, it has been suggested that otter
trawl fishing be discontinued in favor of a return to line fishing. Line fishing
may enable a more selective reduction in individual populations, building
on their abilities to recover from harvest , given their interactions with other
populations and the abiotic environment. Our model suggests a significant