250 Fish as feed inputs for aquaculture – Practices, sustainability and implications
culture, as well as by the gradual adoption of joint area management, where companies
operating within an enclosed or semi-enclosed area work to reduce the cumulative
impact of their production.
Various approaches have emerged from the salmon farming industry in Scotland
and Norway that provide useful examples of environmental “best practice” that have
potential for wider replication through Europe, especially in the expanding cage-
culture subsector.- Modelling of sites to set biomass limits: Computer modelling can provide
assessments of both impacts from nutrient loading on waterbody or regional algal
productivity, as well as the benthic effects from sub-cage deposition. The particle
tracking model Depomod has been extensively used in Europe for determining
the theoretical carrying capacity of cage-farming areas as well as assessments of
the deposition of organic matter beneath finfish cages and mussel rafts. Depomod
is limited to near field predictions through the use of a uniform horizontal flow
field – detailed modelling at a waterbody and regional scale requires the capability
to represent two or three dimensional flows, depending on the degree to which
the waterbody is vertically mixed. Various proprietary models exist, for example
Delft3D and Mike21, that can enable detailed assessments of the cumulative effects
from aquaculture activity on water quality, such as nutrients and algal activity, in a
waterbody. While numerical flow and water-quality models of this nature require
considerable effort to set up and calibrate, and the level of effort required increases
with the complexity and scale of the model domain and the water quality processes
of interest, they can provide useful predictions on the carrying capacity of sites
and thus assist in the planning and consenting of aquaculture development. - Setting of EQS: Environmental Quality Standards (EQS) can be used in
assimilative capacity model development. EQS values have to be set for the
different environmental quality variables (EQVs) defined by regulators and
industry bodies, such as dissolved oxygen concentrations. These then provide the
basis for setting environmental quality benchmarks and monitoring targets for
aquaculture areas. - Joint management of sea, semi-enclosed bay, lake and watershed areas: In Scotland,
the use of Area Management Groups has resulted in greater coordination between
different farming interests within a single waterbody that allows joint management
actions, such as the complete fallowing of sea areas between aquaculture
production cycles. This helps control and reduce the cumulative impacts of
intensive aquaculture, especially in areas with limited flushing rates. - Waste reduction strategies: Perhaps the greatest change in intensive aquaculture
over the last ten years has been the reduction of wastage through better
management and monitoring of feeding. Various approaches have been adopted,
including maximizing the bioavailability of feed components through applied
research, as well as better feed delivery management using computer-controlled,
centralized feeding systems. Feeding rates can be further adjusted by the use of
underwater cameras and sensors that detect when feed is passing through cage
systems and not being utilized by the stock, thus invoking a reduction in feeding
rates. - Environmental monitoring: Intermittent monitoring of the benthos and water
column will also provide managers with information on the levels of feed
utilization, wastage and impact from aquaculture systems, especially when
combined with the EQS approach described above.