13. EUPHAUSIIDS IN THE MARINE ECONOMY
387
palatable in its original condition, but others preferred it after it had
been treated with fresh water.
“ Larger quantities of plankton obtained during the November
collection were consumed by three of the investigators. No toxic effects
developed after eating 100-200 g (wet wt) of the material during the
course of a day. Thc maximum quantity eaten by any one of the
subjects a t one time was 1OOg. Larger amounts were definitely
unacceptable and distasteful. It is probable that psychological factors
entered into the matter of the palatability and digestibility of the
plankton in the laboratory and a t sea. Such factors are not easy to
evaluate. It was certainly true that a quantity of only 30-40 g of
plankton gave the impression of remaining undigested in the stomach
for several hours after eating.”
They carried out experiments with rats and showed that when fed
on plankton they derived some nourishment from it but could only
assimilate a small fraction of the food energy that it contained.
Consequently, it seems that some form of pretreatment of euphausiids
may be required in order to make them more assimilable by domestic
animals and human beings.
Schaefer (1965) has recently reviewed present ideas on the magnitude
of the potential harvest that could be cropped from the oceans. He
concludes that, in the past, underestimates of the potential harvest of
offshore areas have been made because in these areas there exist
exploitable fisheries for anchovies, tunas, redfish, jack mackerel,
frigate mackerel and squids. There may also be exploitable stocks of
fish in the Antarctic. Schaefer points out that harvests of 20Ib per
acre are probably too low and instances the fishery in the deep water
areas off the coasts of Peru and northern Chile that is producing over
400 lb per acre. Except for squids, however, Schaefer is discussing the
harvesting of fish species and points out that currently “ 37% of the
marine fishery harvest consists of anchovies, sardines, herring and the
like, some of which feed almost entirely on phytoplankton and others
of which feed on a mixture of phytoplankton and zooplankton ”.
This means that these fish occupy roughly the same position in the
marine food webs as euphausiids although euphausiids, as members of
the plankton, are fed on by some of these fish in certain areas, e.g.
herring on Meganyctiphanes norvegica in the North Sea.
As has been discussed earlier in this book, euphausiids form shoals
and surface swarms. A fishery developed to exploit the surface swarms
or patches of euphausiids would be uneconomic in the northern hemisphere because species in these regions only swarm a t the surface at
irregular times and places ; the Antarctic species, Euphausia superba,
387
palatable in its original condition, but others preferred it after it had
been treated with fresh water.
“ Larger quantities of plankton obtained during the November
collection were consumed by three of the investigators. No toxic effects
developed after eating 100-200 g (wet wt) of the material during the
course of a day. Thc maximum quantity eaten by any one of the
subjects a t one time was 1OOg. Larger amounts were definitely
unacceptable and distasteful. It is probable that psychological factors
entered into the matter of the palatability and digestibility of the
plankton in the laboratory and a t sea. Such factors are not easy to
evaluate. It was certainly true that a quantity of only 30-40 g of
plankton gave the impression of remaining undigested in the stomach
for several hours after eating.”
They carried out experiments with rats and showed that when fed
on plankton they derived some nourishment from it but could only
assimilate a small fraction of the food energy that it contained.
Consequently, it seems that some form of pretreatment of euphausiids
may be required in order to make them more assimilable by domestic
animals and human beings.
Schaefer (1965) has recently reviewed present ideas on the magnitude
of the potential harvest that could be cropped from the oceans. He
concludes that, in the past, underestimates of the potential harvest of
offshore areas have been made because in these areas there exist
exploitable fisheries for anchovies, tunas, redfish, jack mackerel,
frigate mackerel and squids. There may also be exploitable stocks of
fish in the Antarctic. Schaefer points out that harvests of 20Ib per
acre are probably too low and instances the fishery in the deep water
areas off the coasts of Peru and northern Chile that is producing over
400 lb per acre. Except for squids, however, Schaefer is discussing the
harvesting of fish species and points out that currently “ 37% of the
marine fishery harvest consists of anchovies, sardines, herring and the
like, some of which feed almost entirely on phytoplankton and others
of which feed on a mixture of phytoplankton and zooplankton ”.
This means that these fish occupy roughly the same position in the
marine food webs as euphausiids although euphausiids, as members of
the plankton, are fed on by some of these fish in certain areas, e.g.
herring on Meganyctiphanes norvegica in the North Sea.
As has been discussed earlier in this book, euphausiids form shoals
and surface swarms. A fishery developed to exploit the surface swarms
or patches of euphausiids would be uneconomic in the northern hemisphere because species in these regions only swarm a t the surface at
irregular times and places ; the Antarctic species, Euphausia superba,