USE OF OCEANOGRAPHY—DEACON 363 
The need to help fishermen to get a good and steady return for their 
work without impoverishing the fishing grounds themselves has done 
more than anything to foster the study of the sea. This practical im- 
mediate aim has led to the specialization known as fisheries science; 
but it has also emphasized the need for precise study of all aspects of 
the ocean. This need has been greatest where there are large numbers 
of people who have long been dependent on food from the sea as well 
as from the land, and where long-established fisheries have become 
uneconomical, either through natural causes or as the result of intensive 
fishing. A paucity of fish unavoidably leads to friction, not only be- 
tween fishermen but also between countries; and the best way of lessen- 
ing such friction is to gain precise knowledge of the life histories, mi- 
erations, and feeding habits of fish in relation to their environment. 
Given sufficient understanding of the changes in numbers and distribu- 
tion, a realistic basis for satisfactory agreement can be established. 
But the task of gaining such knowledge is a very difficult one, because 
fish populations are affected by different conditions during spawning, 
hatching, and larval and adult stages, and we know very little about 
which conditions are favorable and which are not. Bad weather, low 
temperatures, and unfavorable currents may interfere with spawning 
and hatching; the success of the larval stages may depend on the pres- 
ence of a particular current to take the larvae to favorable feeding 
grounds; and further development and growth of the adult may be 
determined by a whole range of physical and biological processes neces- 
sary to insure favorable living conditions and adequate food supplies. 
The International Council for the Exploration of the Sea, formed 60 
years ago by the countries of northwestern Europe, has made good use 
of advances in knowledge and promoted many agreements on measures 
for regulating fisheries in the interests of all concerned. However, the 
number of disputes still occurring shows that much remains to be done 
in establishing facts and principles to prevent misinterpretations and 
misunderstandings. 
A more pressing task, especially in countries with rapidly increasing 
populations, is the need to find and develop new fisheries. Sufficient 
light to cause photosynthesis is the first essential, but in temperate and 
lower latitudes, where there is plenty of sunshine, growth is often 
limited by shortage of nutrient salts, particularly phosphates and ni- 
trates. Some guidance with respect to regions likely to be rich in nu- 
trient salts can be gained by studying water movements. Warm sur- 
face water is generally separated from the colder deep water by a 
clearly defined transition layer in which the decrease in temperature 
causes sufficient increase in density to set up resistance to vertical mix- 
ing. There is thus a layer of relatively light water over one of greater 
density, and while the winter storms in cooler temperate latitudes are 
