1 Fish Farm Wastes in the Ecosystem
41
Account needs to be taken of the uncertainty in the y–x relationship. If the greatest allowable pressure were read at the point on the x-axis of Fig. 1.8 where the
upper limit of the uncertainty crosses the impact threshold on the y-axis, the risk of
an undesirable impact would be minimized. This is giving the benefit of the doubt
to the ecosystem. Alternatively, the benefit could be given to the producers of waste
by using the lower limit to the uncertainty, which will maximize the tolerable pressure. Or, the most probable y–x relationship (the thick dashed line) could be used,
ignoring the risk of some excessive impacts and denying fish-farmers (and other
waste producers) the benefit of some possible assimilative capacity. Carstensen
(2007) has discussed this topic in the context of identifying to which WFD quality
class a water body belongs.
Of course, wastes and pollutants enter ecosystems from many sources. In the
case of nutrients, the anthropogenic sources include diffuse agricultural inputs and
urban waste water discharges as well as aquaculture. Thus, the ability to estimate
the maximum safe loading from all these sources gives regulators the new task of
sharing a water body’s nutrient assimilative capacity amongst its human users –
some of whom have, historically, taken it as an inexhaustible gift of nature rather
than something that they might have to share or pay for.
1.15 Sustainability and the Ecosystem Approach
to Aquaculture
This chapter has mentioned the use of the terms Environmental Quality Standard
and Ecological Quality Objective. Initially, EQSs were made to prevent pollution
by harmful substances, and the term is used in the Water Framework Directive in
exactly this way. The concept of specific EcoQOs came later, and the term is not
always used explicitly: for example, the Water Framework Directive refers to general “environmental objectives” in its main text and to “quality status” in Annex V.
Nevertheless, it is useful to see the statement of precise EcoQOs as a key device for
maintaining the status of components of ecosystem quality or health or to prevent
undesirable impacts. EQS’s and EcoQOs can be enforced only if each is associated
with an indicator than can be monitored. In the case of the highly toxic substances
which are dangerous at any level, the scheme set out in Fig. 1.8 can be bypassed:
the ecosystem has no assimilative capacity for these substances, and the Water
Framework Directive aims to stop their release into the aquatic environment. In all
other cases Fig. 1.8 summarizes the task facing aquacultural managers, regulators
and scientists.
The figure is an outcome from ECASA, a European Commission Framework 6
project, concerned with the Ecosystem Approach to Sustainable Aquaculture.
ECASA’s main product (Box 1.1) is a “virtual toolbox” giving details of the models
and indicators that can be used to apply the approach of the previous section. These
tools do not in themselves guarantee sustainable aquaculture, because this requires
economic efficiency and attention to the needs of local societies in addition to a
41
Account needs to be taken of the uncertainty in the y–x relationship. If the greatest allowable pressure were read at the point on the x-axis of Fig. 1.8 where the
upper limit of the uncertainty crosses the impact threshold on the y-axis, the risk of
an undesirable impact would be minimized. This is giving the benefit of the doubt
to the ecosystem. Alternatively, the benefit could be given to the producers of waste
by using the lower limit to the uncertainty, which will maximize the tolerable pressure. Or, the most probable y–x relationship (the thick dashed line) could be used,
ignoring the risk of some excessive impacts and denying fish-farmers (and other
waste producers) the benefit of some possible assimilative capacity. Carstensen
(2007) has discussed this topic in the context of identifying to which WFD quality
class a water body belongs.
Of course, wastes and pollutants enter ecosystems from many sources. In the
case of nutrients, the anthropogenic sources include diffuse agricultural inputs and
urban waste water discharges as well as aquaculture. Thus, the ability to estimate
the maximum safe loading from all these sources gives regulators the new task of
sharing a water body’s nutrient assimilative capacity amongst its human users –
some of whom have, historically, taken it as an inexhaustible gift of nature rather
than something that they might have to share or pay for.
1.15 Sustainability and the Ecosystem Approach
to Aquaculture
This chapter has mentioned the use of the terms Environmental Quality Standard
and Ecological Quality Objective. Initially, EQSs were made to prevent pollution
by harmful substances, and the term is used in the Water Framework Directive in
exactly this way. The concept of specific EcoQOs came later, and the term is not
always used explicitly: for example, the Water Framework Directive refers to general “environmental objectives” in its main text and to “quality status” in Annex V.
Nevertheless, it is useful to see the statement of precise EcoQOs as a key device for
maintaining the status of components of ecosystem quality or health or to prevent
undesirable impacts. EQS’s and EcoQOs can be enforced only if each is associated
with an indicator than can be monitored. In the case of the highly toxic substances
which are dangerous at any level, the scheme set out in Fig. 1.8 can be bypassed:
the ecosystem has no assimilative capacity for these substances, and the Water
Framework Directive aims to stop their release into the aquatic environment. In all
other cases Fig. 1.8 summarizes the task facing aquacultural managers, regulators
and scientists.
The figure is an outcome from ECASA, a European Commission Framework 6
project, concerned with the Ecosystem Approach to Sustainable Aquaculture.
ECASA’s main product (Box 1.1) is a “virtual toolbox” giving details of the models
and indicators that can be used to apply the approach of the previous section. These
tools do not in themselves guarantee sustainable aquaculture, because this requires
economic efficiency and attention to the needs of local societies in addition to a