3. Results
Financial performance is summarised in Table 1. For
salmon monoculture, price is greater than the annualised
equivalent cost of production, with the result that
NPV is greater than zero and as such can be considered
a financially worthwhile investment. The same conclusion
applies to mussel monoculture, though here the
margin of price over cost is proportionally larger. The
key result, however, relates to polyculture. On the
assumption that growing mussels in close proximity to
salmon cages would enhance productivity by 20%,
investment in an integrated salmon–mussel aquaculture
system is shown to produce a positive NPV (£1.425
million) which exceeds the combined NPV of salmon
monoculture (£0.922 million) and mussel monoculture
(£0.353 million). The difference represents the net
financial benefits of integration (£0.15 million). The
internal rate of return (IRR) from investment in
polyculture is just under 28%, substantially in excess
of the assumed opportunity cost of capital (r) of 8%.
This is depicted in Fig. 2, which also illustrates the effect
of the discount rate on the NPV of the project.
The sensitivity of polyculture NPV to trends in the
price of salmon and mussels is demonstrated in Table 2.
The baseline result of £1.425 million appears in the
centre of the table, corresponding to the assumption
that prices in real terms remain constant throughout the
time horizon of the investment (i.e. 0% annual change in
either price series). Relaxing that assumption signifi-
cantly affects the result, with a downward trend in price
causing a lowering of NPV and vice versa. NPV is more
sensitive to salmon prices than to mussel prices, a
finding that can be accounted for by the much narrower
price–cost margin for salmon than for mussels. What is
striking, however, is that a downward trend in salmon
prices of as little as 2% p.a. in real terms will cause the
NPV of polyculture investment to become negative—in
other words, financially unattractive. That this should