318
D. H. UUSHING
porarily reduce the herbivore numbers considerably, but that the
herbivores would recover after the fish had dispersed ; since writing this
I have found that my colleague, A. C. Burd, who has worked in Peru,
has come to the same conclusion. Thus it appears that the anchoveta
can temporarily play a controlling part in the production cycle ; one is
reminded of the part possibly played by pilchards in the production
cycle in the English Channel (Cushing, 1961 ; Russell, 1936). If the
numbers of herbivores are drastically reduced, the algal numbers
should increase in the surface water after the spawning of the anchoveta ; light and nutrients should be available in excess and, with the
grazing restraint removed, a second algal outburst should occur and it
is quite possible that it is unrelated to the processes of upwelling.
This short account of the biology of an upwelling area listed four
subjects : a rough model of the production dynamics of upwelling, the
vertical and community structure of the system, the possible mechanism
by which the fish stocks remain contained within the area, and the
important part played by the anchoveta in the very simple production
cycle of an upwelling area. The four are obviowly linked in that they
are all parts of a single ecosystem. I n this sense an upwelling area can
be studied as a biological unit, as many people have studied temperate
production cycles. Few of the latter have been linked to the fish stocks
partly because, in temperate seas, the connection between fish stock
and production cycle is not readily made. This is because fish are often
caught at points distant from the region of larval drift (between spawning ground and nursery ground) and so the ecosystem becomes artificially split into separated studies. I n an upwelling area the parts of the
ecosystem coexist and can be studied as a whole with present techniques.
VIII. DISCUSSION
There are three ways of briefly charting the world's upwelling
systems. The most obvious is the chart of phosphatic deposits (Fig.
19A; Tooms, 1967). The four major upwelling systems are shown
clearly ; that in the California Current is continuous from the Mexican
border to the coasts of Washington State. The lack of deposit off Baja
California suggests that the present area of upwelling off Punts San
Eugenio is aberrant and the recent southerly movement of upwelling
since 1949, referred to above, may be an aberration over a geological
time period. The Peruvian upwelling appears to be no different from
its present distribution, except that there is no break south of Arica.
The Canary Current deposits are split at Cap Blanc, but they do not
extend south of Dakar as does the present upwelling area. The Benguela
Current deposits do not appear to extend very far north of the Orange
D. H. UUSHING
porarily reduce the herbivore numbers considerably, but that the
herbivores would recover after the fish had dispersed ; since writing this
I have found that my colleague, A. C. Burd, who has worked in Peru,
has come to the same conclusion. Thus it appears that the anchoveta
can temporarily play a controlling part in the production cycle ; one is
reminded of the part possibly played by pilchards in the production
cycle in the English Channel (Cushing, 1961 ; Russell, 1936). If the
numbers of herbivores are drastically reduced, the algal numbers
should increase in the surface water after the spawning of the anchoveta ; light and nutrients should be available in excess and, with the
grazing restraint removed, a second algal outburst should occur and it
is quite possible that it is unrelated to the processes of upwelling.
This short account of the biology of an upwelling area listed four
subjects : a rough model of the production dynamics of upwelling, the
vertical and community structure of the system, the possible mechanism
by which the fish stocks remain contained within the area, and the
important part played by the anchoveta in the very simple production
cycle of an upwelling area. The four are obviowly linked in that they
are all parts of a single ecosystem. I n this sense an upwelling area can
be studied as a biological unit, as many people have studied temperate
production cycles. Few of the latter have been linked to the fish stocks
partly because, in temperate seas, the connection between fish stock
and production cycle is not readily made. This is because fish are often
caught at points distant from the region of larval drift (between spawning ground and nursery ground) and so the ecosystem becomes artificially split into separated studies. I n an upwelling area the parts of the
ecosystem coexist and can be studied as a whole with present techniques.
VIII. DISCUSSION
There are three ways of briefly charting the world's upwelling
systems. The most obvious is the chart of phosphatic deposits (Fig.
19A; Tooms, 1967). The four major upwelling systems are shown
clearly ; that in the California Current is continuous from the Mexican
border to the coasts of Washington State. The lack of deposit off Baja
California suggests that the present area of upwelling off Punts San
Eugenio is aberrant and the recent southerly movement of upwelling
since 1949, referred to above, may be an aberration over a geological
time period. The Peruvian upwelling appears to be no different from
its present distribution, except that there is no break south of Arica.
The Canary Current deposits are split at Cap Blanc, but they do not
extend south of Dakar as does the present upwelling area. The Benguela
Current deposits do not appear to extend very far north of the Orange