254 Fish as feed inputs for aquaculture – Practices, sustainability and implications
regional annual consumption of low-value fish was 2.5 million tonnes but dropped to
150 thousand tonnes by 1997 – and is not predicted to increase to much more than
161 thousand tonnes per year by 2020 (Delgado et al., 2002).
In summary, the use of the main feed-fish species for direct human consumption
is driven by market and other economic factors rather than technical or product
development constraints. As a result, there is unlikely to be any dramatic change in
the production of feed-fish species being used directly as food over the medium term.
However, this depends upon a number of extrinsic factors such as the availability and
price of other feed protein commodities such as soya meal.6.2 Comparative analysis of use in aquafeeds versus for human consumption
As the section above indicates, there are few alternative uses of feedfish for the main
feed fisheries supplying fishmeal production in Europe that are not already being
utilized. In European feed fisheries, a more fundamental question is whether it is more
ecologically efficient if these feed-fish stocks – which are often prey items for both
commercial fish species as well as an integral mid-level component of the food chain in
many European seas – are left in the sea. Essentially, is it more effective to harvest low
trophic-level species in industrial fisheries and convert the biomass obtained to human
consumption fish protein in aquaculture systems, or is it better to leave low trophic-
level fish in the sea where they can be consumed by their natural predators, and then to
harvest species from higher trophic levels in fisheries for human consumption?
This question was asked of ICES by the EC’s DG Fisheries, and its response was
published in the annual report of the ICES’ Working Group on Ecosystem Effects of
Fishing Activities (ICES, 2004). Its conclusions were as follows:- Transfer efficiencies in natural marine food webs: The transfer efficiency of both
energy and carbon between trophic levels along a food chain is not 100 percent.
Energy is required for metabolism and maintenance, and only a fraction of the
food consumed by a predator is actually converted to predator biomass. Transfer
efficiencies in the range from 10 to 15 percent are generally accepted for predator-
prey interactions involving fish predators in marine temperate shelf-sea food webs
(Jennings, Kaiser and Reynolds, 2001). - Transfer efficiencies in aquaculture systems: Taking into account the levels of
fishmeal inclusion and food conversion ratios, the total conversion efficiency of,
say, a sand eel-derived salmon diet in producing a harvestable biomass is around
10–17 percent, which is much in line with natural food webs. - Other energetic factors: In addition to the above efficiencies, the energy/material
“costs” need to be considered. Additional materials are required for production of
fish feeds, as well as the energy involved in processing. However, while the trophic
energy efficiency in marine food chains may be around 10–15 percent, this does
not account for natural mortality due to predation, which may reduce this efficacy
considerably. - Conclusions: ICES concluded that “if one is only concerned about the efficiency
of converting sandeel biomass to human consumption fish biomass, then the
exploitation of sandeels by industrial fisheries for the aquaculture industry is
at least as efficient ecologically”. ICES then goes on to ask the question as to
whether it is of greater benefit to society to exploit lower trophic-level marine
fish resources in industrial fisheries and rely on an aquaculture industry to provide
mankind’s human consumption fish requirements, or is it better to leave these fish
to be processed through the natural marine food web and then to harvest fish in
the higher trophic levels in fisheries for human consumption?
(^10) Low-value fish according to the International Standard Statistical Classification of Aquatic Animals and
Plants (ISSCAAP) include herrings, sardines, anchovies and mackerels.