Environmental Engineering Reference
In-Depth Information
10.11
Efficiencies of animal food production. Based on Smil
(2000b).
uid diesel fuels for powering ships and their refrigerators,
and indirect energy costs for building and outfitting the
vessels prorate to less than 10% of the total expense. En-
ergy analyses of U.S. bottom trawling found rates of 35-
40 GJ/t of catch, very similar to the British skippers' rule
of thumb in the 1980s that it takes at least 1 t of fuel (42
GJ) to get 1 t of fish. Tyedmers (2004) reviewed direct
(diesel fuel) energy costs of 29 Atlantic and Pacific fish-
eries and found a wide range of values, with minima of
100-140 L (3.6-5 GJ)/t for herring and mackerel, 15-
30 GJ/t for British Columbia salmon, maxima of 3-3.4
kL (107-121 GJ)/t for shrimp trawling and long-line
tuna fishing, and modal rates around 500 L (18 GJ)/t.
Assuming that 40% of the catch is edible and that it
averages 17% protein, this approximation translates into
an energy subsidy of about 265 kJ/g of protein. For
comparison, Rawitscher and Mayer (1977) calculated
the rates for a dozen U.S. species, ranging from 15 kJ/g
of protein for sardines to 1.8 MJ/g for fresh shrimp, and
Rochereau (1980) found northeastern U.S. fishery aver-
aging just about 75 kJ/g of protein (40 kJ inshore, 174
kJ/g offshore catch). The earlier low rates were due to
the small size of fishing vessels and the natural richness
of the area. This had changed drastically with the collapse
of the region's rich cod stocks during the 1990s.
Tyedmers (2004) notes often rapid increases in energy
subsidies since the 1960s, and only some reduction fish-
eries (catching such species as anchovetta, capelin, and
herring for processing into feed meals and oils) require
less than 2 GJ/t.
Large differences in the energy costs of marine protein
(a spread of 2 OM) are in sharp contrast to the relative
