UPWELLING AND THE PRODUCTION OF FISH
301
Again the major upwellings are also the most intense, but most of the
less intense ones appear to be in the Pacific. An important point is that
the intensity of production in the upwelling areas is greater than elsewhere in the tropics or subtropics. A glance at the distribution of the
intensity of production in the Pacific and Indian oceans (Figs. 13 and
14) shows that the intensity of production in theupwelling areasranges
from O.l-l.OgC/ma per day (and some observations are higher still),
whereas outside them the intensity tends to be less than 0.1 gC/m2 per
day. Effectively, in magnitude, this is the comparison between the
high amplitude discontinuous production cycle of high latitudes and the
low amplitude quasi-steady state one of low latitudes.
B. The production of zooplankton
At the present time, the estimation of secondary production is
difficult because the dependence of the duration of the life stages of
various invertebrates (primarily copepods) upon temperature is only
known sketchily. It is true that this relationship has been established
for a few species, but a generalization is needed for a proper application.
Further, we need t o distinguish between the forms of production, with
perhaps a single generation in high latitudes, from those with many
generations which may be common in the upwelling areas; John
Gulland has suggested to me that the important factor might not be the
generation time but a fraction of it depending on the mortality rate, if
the secondary production were continuous. The material available is
only the simplest, an estimate of stock as sampled by some simple nets,
the constructions of which are common. Because the season of upwelling
has been defined in an earlier section, the duration of the season can be
divided by the generation time and so the average stock is raised by
the number of generations, yielding the roughest estimate of production.
One of the standard nets is the metre net which has been used extensively by American organizations. The mouth is 1 m in diameter, the
mesh size is about 0.25-0-31 mm and the net is hauled vertically from
about 200 m at a speed of about 1 m/sec. The Indian Ocean net is a
very similar net, with a mesh size of 0.33 mm ; off southern Arabia, it
was hauled in strong winds and a wire angle of 45" has been assumed
(from my own observations on R.R.S. " Discovery "). The Russians
working in the Indian Ocean have used a large Juday net, 0.5 m2 in
area, with a mesh size of 0.26 mm ; they express their results as mg wet
wt/l 000 m3, which is essentially the same form of expression as used in
the American and Australian work (ml/l 000 m3). Tranter (1962) has
described the form of net used off north-west Australia and off Java.
Trantcr ( 1 063) has shown that the Juday net with a mesh of 0.26 mm
301
Again the major upwellings are also the most intense, but most of the
less intense ones appear to be in the Pacific. An important point is that
the intensity of production in the upwelling areas is greater than elsewhere in the tropics or subtropics. A glance at the distribution of the
intensity of production in the Pacific and Indian oceans (Figs. 13 and
14) shows that the intensity of production in theupwelling areasranges
from O.l-l.OgC/ma per day (and some observations are higher still),
whereas outside them the intensity tends to be less than 0.1 gC/m2 per
day. Effectively, in magnitude, this is the comparison between the
high amplitude discontinuous production cycle of high latitudes and the
low amplitude quasi-steady state one of low latitudes.
B. The production of zooplankton
At the present time, the estimation of secondary production is
difficult because the dependence of the duration of the life stages of
various invertebrates (primarily copepods) upon temperature is only
known sketchily. It is true that this relationship has been established
for a few species, but a generalization is needed for a proper application.
Further, we need t o distinguish between the forms of production, with
perhaps a single generation in high latitudes, from those with many
generations which may be common in the upwelling areas; John
Gulland has suggested to me that the important factor might not be the
generation time but a fraction of it depending on the mortality rate, if
the secondary production were continuous. The material available is
only the simplest, an estimate of stock as sampled by some simple nets,
the constructions of which are common. Because the season of upwelling
has been defined in an earlier section, the duration of the season can be
divided by the generation time and so the average stock is raised by
the number of generations, yielding the roughest estimate of production.
One of the standard nets is the metre net which has been used extensively by American organizations. The mouth is 1 m in diameter, the
mesh size is about 0.25-0-31 mm and the net is hauled vertically from
about 200 m at a speed of about 1 m/sec. The Indian Ocean net is a
very similar net, with a mesh size of 0.33 mm ; off southern Arabia, it
was hauled in strong winds and a wire angle of 45" has been assumed
(from my own observations on R.R.S. " Discovery "). The Russians
working in the Indian Ocean have used a large Juday net, 0.5 m2 in
area, with a mesh size of 0.26 mm ; they express their results as mg wet
wt/l 000 m3, which is essentially the same form of expression as used in
the American and Australian work (ml/l 000 m3). Tranter (1962) has
described the form of net used off north-west Australia and off Java.
Trantcr ( 1 063) has shown that the Juday net with a mesh of 0.26 mm