34 Fish as feed inputs for aquaculture – Practices, sustainability and implications
transmitting viruses from non-endemic feed fish to local wild fish populations, as
has been experienced in Australia (WWF, 2005).Indirect environmental impacts include:- increased trash-fish prices due to high demand for use as aquaculture feed,
placing them out of the economic grasp of the poor and needy for direct human
consumption as an affordable food source (Edwards, Le and Allan, 2004).
5.1.3 Krill fishery
Despite the fact that there are over 85 known species of krill (Nicol and Endo, 1997)
and that total reported krill landings reached over 1 118 165 tonnes in 2004, only one
krill species is currently reported, namely the Antarctic krill (Euphausia superba)
(FAO, 2006a). In view of the important ecological role played by krill in marine food
webs, it is imperative that all krill species be reported and quantified by fishers for
transparency, traceability and the long-term sustainability of the krill fishery sector
(Nicol, 2006; Murphy et al., 2007). Removal of large quantities of krill from the marine
ecosystem may have adverse long-term ecosystem impacts on dependent species, and
in particular for many protected marine mammals and birds (Reid and Croxall, 2001;
Hill et al., 2006).5.2 Examples of environmental “best practice”
Intensive aquaculture has been driven to improve efficiency by a combination of lower
economic margins and an increasingly strict regulatory environment. This efficiency is
reflected by the very low FCRs now experienced in salmonid and marine fish culture,
as well as the gradual adoption of “bay level” management, where different operators
within an enclosed or semi-enclosed area work together to reduce the cumulative
impact of their production.
Various approaches have emerged from the salmon farming industry in Europe
and elsewhere that provide useful examples of environmental “best practice” that have
potential for wider replication, especially in the expanding cage-culture subsector.
These include:- Modeling of sites to set biomass limits: Computer modeling can provide
assessments of the potential impacts of nutrient loading on a waterbody, on
regional algal productivity or on the benthic effects from sub-cage deposition.
The particle tracking model Depomod has been extensively used in Europe to
determine the theoretical carrying capacity of cage farming areas and to assess
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 modeling at a waterbody or 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 licensing of aquaculture development. - Setting of Environmental Quality Standards (EQS): EQS can be used in
assimilative capacity model development. EQS values have to be set for the
different environmental quality variables (EQVs) such as dissolved oxygen
concentrations defined by regulators and industry bodies. These then provide the