390
THE BIOLOGY O F EUPHAUSIIDS
If, however, a fishery was prosecuted for euphausiids an economic price
of 250 to 2100 per wet ton might be acceptable to the processing plant,
especially if the euphausiids were being supplied as an item of the
human diet. Thus, the smallest type of craft able to work in the
Antarctic would require to catch a t least 2 tons of euphausiids per
24 hr to cover its costs. Marr estimated a density of forty-one E .
superba per cubic metre in the surface layer, and Nemoto (1968a) has
recently reviewed the difficulties involved in harvesting this animal.
First, there is location of the swarms which might be carried out, as
suggested by Mackintosh (1968), by acoustic scanning techniques.
This is also an important preliminary required to assess accurately the
magnitude of the resource being discussed because not enough is known
about the densities of subsurface populations of this species. Marr’s
figure of forty-one individuals per cubic metre is equivalent to about
20 g wet wt/m3. A net with a mouth area of 2 m2 fishing with 100%
efficiency a t a towing speed of 6 knots would catch a maximum
wet weight of about 6 tons per 24 hr. If the season lasted 3 months,
then a maximum total harvest by one catcher would be about 550
tons wet wt. This catch selling at 240 per ton might just cover the cost
of sending a catcher south. Given that surface swarms can be located
and efficiently netted, an economic return might be obtained.
If efficient fishing methods are evolved then some consideration
should be given to the possible effects on the marine economy, as a
whole, of fishing euphausiids in large quantities. Any fishing industry
must develop by becoming more efficient and this it usually does by
improving its methods of catching. It seems probable that a fishery
for euphausiids will exploit the pre-breeding aggregations, thus making
the fishery seasonal. Most fisheries remove organisms that are several
steps up the food chains from the primary producers and are therefore
usually not a major source of nutrition for other marine organisms.
The euphausiids, however, are a major source of food for many animals
that themselves are commercially exploited and so if over-fishing of
the euphausiids should ever be attained, the stocks of these other
exploited organisms might be adversely affected. It is true that the
populations of baleen whales have been reduced to about one tenth of
their original size and that we might now expect there to be an excess
production of euphausiids, previously harvested by the whales. No data
are available that might be used to discover whether the populations
of euphausiids have indeed increased over the last few years. An
excess of production of euphausiids could, of course, show itself in an
increase in populations of other animals which have benefited, for
example crab-eater seals or sea birds. Exploiters of euphausiids would
THE BIOLOGY O F EUPHAUSIIDS
If, however, a fishery was prosecuted for euphausiids an economic price
of 250 to 2100 per wet ton might be acceptable to the processing plant,
especially if the euphausiids were being supplied as an item of the
human diet. Thus, the smallest type of craft able to work in the
Antarctic would require to catch a t least 2 tons of euphausiids per
24 hr to cover its costs. Marr estimated a density of forty-one E .
superba per cubic metre in the surface layer, and Nemoto (1968a) has
recently reviewed the difficulties involved in harvesting this animal.
First, there is location of the swarms which might be carried out, as
suggested by Mackintosh (1968), by acoustic scanning techniques.
This is also an important preliminary required to assess accurately the
magnitude of the resource being discussed because not enough is known
about the densities of subsurface populations of this species. Marr’s
figure of forty-one individuals per cubic metre is equivalent to about
20 g wet wt/m3. A net with a mouth area of 2 m2 fishing with 100%
efficiency a t a towing speed of 6 knots would catch a maximum
wet weight of about 6 tons per 24 hr. If the season lasted 3 months,
then a maximum total harvest by one catcher would be about 550
tons wet wt. This catch selling at 240 per ton might just cover the cost
of sending a catcher south. Given that surface swarms can be located
and efficiently netted, an economic return might be obtained.
If efficient fishing methods are evolved then some consideration
should be given to the possible effects on the marine economy, as a
whole, of fishing euphausiids in large quantities. Any fishing industry
must develop by becoming more efficient and this it usually does by
improving its methods of catching. It seems probable that a fishery
for euphausiids will exploit the pre-breeding aggregations, thus making
the fishery seasonal. Most fisheries remove organisms that are several
steps up the food chains from the primary producers and are therefore
usually not a major source of nutrition for other marine organisms.
The euphausiids, however, are a major source of food for many animals
that themselves are commercially exploited and so if over-fishing of
the euphausiids should ever be attained, the stocks of these other
exploited organisms might be adversely affected. It is true that the
populations of baleen whales have been reduced to about one tenth of
their original size and that we might now expect there to be an excess
production of euphausiids, previously harvested by the whales. No data
are available that might be used to discover whether the populations
of euphausiids have indeed increased over the last few years. An
excess of production of euphausiids could, of course, show itself in an
increase in populations of other animals which have benefited, for
example crab-eater seals or sea birds. Exploiters of euphausiids would