UPWELLINQ AND THE PRODUCTION OF FISH
265
200 m contains a resident and sparse population of plants and animals,
very like those in temperate waters in early spring. At the bottom of
the photic layer, the algae start to divide and, as in temperate waters,
the increase in animal production is caused by the increase in plant
population because the reproduction of the animals depends upon this
increased food ; hence the animal production follows the plant production in time. Thc lag between plants and animals may be as much
as half a generation and it allows the production of large stocks of plants,
and, later, of animals as in temperate waters. In contrast, in the deep
subtropical ocean, there is no sudden increase in the production rate of
the plants, and there is no delay between plant and animal production
and there are low stocks (Cushing, 1959).
If the production cycle in an upwelling area were similar to that in
temperate waters, a bell-shaped curve of production would be expected
as a function of distance from the point of upwelling, similar to the
temperate curve as a function of time. The photic layer is usually fairly
deep, up to 50 m, and the rate of upwelling is rather slow, of the order
of 1 m/day (McEwen, 1929; Hidaka, 1954; Yoshida, 1955). So production must rise slowly from the bottom of the photic layer, taking
many days to reach the surface. In the first days of the process, from
the 1% light level to the 5% light level, the increase in production is
necessarily very slow, but it must increase exponentially as upwelling
proceeds. Because the depth of the photic layer is many times the daily
upwelling distance, the peak production is probably reached near the
surface not far from the point of upwelling (the problem is set out
formally in a later section).
On reaching the surface, the plant and animal populations must
move away from the point or line of upwelling and because the rate of
upwelling is a very small proportion of the speed of the eastern boundary
currents, such movement must be at an angle to the coast. The production along this line of movement is high and appears to decrease
slowIy with distance, and the band of maximum production appears to
be rather wide and to decrease rather slowly with distance from the
coast. If the production cycle were symmetrical in time, it would continue for about the same time = the water takes to rise in the upwelling
process. At 4 knot, an upwelling which took 30-60 days to rise through
the photic zone might drift 300-600 miles before the decay process was
complete. This is a simplified view of the process. Because of mixture
and additional divergence offshore, any neat vector of production does
not exist. But the broad band of production declining rather slowly
from the coast is the result of the upwelling production cycle and the
additional processes.
265
200 m contains a resident and sparse population of plants and animals,
very like those in temperate waters in early spring. At the bottom of
the photic layer, the algae start to divide and, as in temperate waters,
the increase in animal production is caused by the increase in plant
population because the reproduction of the animals depends upon this
increased food ; hence the animal production follows the plant production in time. Thc lag between plants and animals may be as much
as half a generation and it allows the production of large stocks of plants,
and, later, of animals as in temperate waters. In contrast, in the deep
subtropical ocean, there is no sudden increase in the production rate of
the plants, and there is no delay between plant and animal production
and there are low stocks (Cushing, 1959).
If the production cycle in an upwelling area were similar to that in
temperate waters, a bell-shaped curve of production would be expected
as a function of distance from the point of upwelling, similar to the
temperate curve as a function of time. The photic layer is usually fairly
deep, up to 50 m, and the rate of upwelling is rather slow, of the order
of 1 m/day (McEwen, 1929; Hidaka, 1954; Yoshida, 1955). So production must rise slowly from the bottom of the photic layer, taking
many days to reach the surface. In the first days of the process, from
the 1% light level to the 5% light level, the increase in production is
necessarily very slow, but it must increase exponentially as upwelling
proceeds. Because the depth of the photic layer is many times the daily
upwelling distance, the peak production is probably reached near the
surface not far from the point of upwelling (the problem is set out
formally in a later section).
On reaching the surface, the plant and animal populations must
move away from the point or line of upwelling and because the rate of
upwelling is a very small proportion of the speed of the eastern boundary
currents, such movement must be at an angle to the coast. The production along this line of movement is high and appears to decrease
slowIy with distance, and the band of maximum production appears to
be rather wide and to decrease rather slowly with distance from the
coast. If the production cycle were symmetrical in time, it would continue for about the same time = the water takes to rise in the upwelling
process. At 4 knot, an upwelling which took 30-60 days to rise through
the photic zone might drift 300-600 miles before the decay process was
complete. This is a simplified view of the process. Because of mixture
and additional divergence offshore, any neat vector of production does
not exist. But the broad band of production declining rather slowly
from the coast is the result of the upwelling production cycle and the
additional processes.