Fish as feed inputs for aquaculture – Practices, sustainability and implications: a global synthesis 39
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 the members of the International Council for the Exploration
of the Sea (ICES) by the EC’s Directorate-General 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:
- 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 (Pauly et al., 1998; Jennings, Kaiser and
Reynolds, 2001). - Taking into account the levels of fishmeal inclusion and FRCs, 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. - In addition to the above efficiencies, the energy/material “costs” need to be
considered. Additional materials are required for the 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.
ICES concluded that “if one is only concerned about the efficiency of converting
sand-eel biomass to human consumption fish biomass, then the exploitation of sand eels
by industrial fisheries for the aquaculture industry is at least as efficient ecologically”.
ICES examined the premise that if industrial fisheries are reduced, then gains
reflecting 10 percent of the reduction will be made in human consumption landings.
Runs of a Multi-Species Virtual Population Analysis (MSVPA) model were used to
examine this assumption, as was data on the consequences of a four-year closure of
the East of Scotland sand-eel fishery on local gadoid (cod, haddock and whiting)
populations. The results provided no evidence to support the contention that ceasing
industrial fisheries will stimulate catches in the fisheries for human consumption at
the current time and under the prevailing circumstances. ICES goes on to state that so
long as the food conversion efficiencies are regularly reviewed, then a closely regulated
combination of industrial fisheries and fisheries for human consumption may provide
the only solution to the long-term demand for fish protein.
Hecht and Jones (2009) examined the comparative benefits of producing fishmeal
for use in the rapidly expanding South African abalone farming industry versus the
socio-economic benefits of harvesting the fish directly. They concluded that while the
fish that were reduced to fishmeal to supply the abalone culture industry would have
sustained around 741 families for a year had they utilized the fish directly, the abalone
culture industry employed 814 people in 2004 (Troell et al., 2006) who use their salaries
to purchase substantially more than their protein requirement. This example suggests
that the “secondary” use of reduction fishery products is able to sustain more families
indirectly than primary use is able to sustain directly.
6.3 Risks of utilizing feedfish in the food chain
With global aquafeeds so reliant upon fishmeal from wild sources, the aquafeed
industry is potentially vulnerable to economic factors that might change the price of
fishmeal traded with significant consequences for what is now a low-margin farming
process. The industry is also vulnerable to health issues arising from contamination
of fishmeal and fish oil raw materials, either through the concentration of pollutants