414 
NATURE 
oe 
[Marcu 24, 1923 
The Exploitation of the Sea. 
ae very important documents bearing on the 
subject of the rational exploitation of fishing 
grounds have recently become available. The first is 
the report to the Minister of Agriculture and Fisheries 
of the British delegates who attended the meeting 
of the International Council for the Exploration of 
the Sea, held at Copenhagen in September last. 
The other is the Report of the Danish Biological 
Station (xxix., 1922). Both papers are of very 
great interest. 
The British official report emphasises the practical 
nature of the work of the Council and gives an account 
of its organisation. There are four sections (hydro- 
graphy, plankton, statistics, and fish). The work of 
the fish section is carried out by committees, and those 
which deal with the investigation of the herring, 
cod and haddock, and of the biology of the Atlantic 
slope are of great interest to British workers. Pro- 
grammes of the investigations adopted by these 
committees are given in the report. One important 
committee, that on the plaice fisheries, has now 
completed its work, and the recommendations made 
by it have been approved by the Council and are 
given in full. These are that the parts of the North 
Sea situated (1) between the Continental coast and 
the 12-fathom line from N. lats. 52° to 56°, and (2) 
between the 12-fathom and the 15-fathom line, be 
closed to steam trawlers and motor vessels of more 
than 50 h.p., the inner zone throughout the entire 
year and the outer one during the months July to 
March. No size-limits with respect to the fish caught 
are recommended. The Council recognises the diffi- 
culty of enforcing these measures without the 
sympathetic support of the fishing industry, but 
it regards this as a matter for the concern of the 
governments of the participating countries. It is 
considered that the adhesion of Germany to such a 
scheme of regulation will be essential. 
advises the continuance of observations and the 
review of the whole proceedings after three years | 
have elapsed. 
The meaning of the impoverishment of a plaice 
fishing ground is examined by Dr. C. G. J. Petersen 
in the second of the reports noticed. Since 1893 
this distinguished Danish zoologist has studied the 
fisheries in the Limfiord and in the adjacent seas. 
In 1893 the old styles of plaice fishing were super- 
seded by newer and more efficient methods, and Dr. 
Petersen thought then that this meant ‘ the end of 
the golden day,for the fishing industry,” and he had 
similar thoughts about the North Sea plaice fisheries. 
Now-he confesses that later developments have shown 
that he was wrong. What has occurred in the two 
areas is much the same; the quantities of plaice 
taken per day’s fishing by the old types of vessels 
were much greater than those now being taken by 
the newer boats fitted with much more efficient gear. 
Why ? In both areas there was an “ accumulated 
stock ’’ of fish. Vessels of low fishing capacity could 
do well on such grounds. 
The Council | 

How to remedy this “‘ impoverishment’’? There 
are two theories of regulation: (1) to raise more 
young plaice either by protecting the breeding fish 
so as to allow them to reproduce at least once in 
their lifetimes, or by artificial hatching, and (2) to 
legislate and otherwise deal with the fishery so as to- 
increase the gyvowth-vate of the plaice, because it is 
not merely a vast quantity of fish on the grounds that 
is desirable but rather an increased rate of production 
of plaice-flesh. An overcrowded ground may harbour 
small old plaice or young and relatively big ones. 
Plaice which do not grow at all consume from three 
to four times their own weight of food. In the Baltic 
there are fish of 32-36 cm. in length which are 4-5 
years old as well as others of the same sizes but of 
9-18 years old. The best policy is so to regulate the 
fishing as to increase the proportion of the younger, 
more rapidly-growing fish. 
How to do this? The conditions in the North 
Sea illustrate the difficulty—and the remedy. If the 
Dogger Bank ‘were an island surrounded by shallow 
water, vastly more plaice would grow to good market- 
able sizes than donow. As itis, the fishing is probably 
too intense and plaice are caught more rapidly than 
they can migrate out from the overcrowded grounds 
just off the Continental coasts. The restocking of the 
deeper parts, where the fish will grow well, from the 
nurseries (where they grow slowly) must keep pace 
with the depletion of these grounds. This means 
two kinds of measures: (1) size-limits in fishing, and 
(2) transplantation, both being modified according 
to the circumstances. If young plaice do not migrate 
out into favourable parts of the North Sea they — 
must be assisted. Dr. Petersen himself made success- 
ful transplantation experiments in the Limfiord long 
ago, and more recently, English investigators have 
shown, beyond all doubt, that the same measures 
were practicable, and sure to be highly successful, 
in the North Sea. 
The rationale of a continued and still more intensive 
exploitation of the fishing grounds is indicated by 
the scientific investigations. The transplantation 
experiments show which are the favourable grounds ; 
growth-rates are known, and the work now in progress 
by the English investigators is giving results of value 
in regard to the supplies of food on the various 
grounds. The difficulties belong only to the practical 
working of the regulatory measures. Something like 
a scientific ‘‘ nationalisation ’’ of the deep-sea fishin, 
industry appears to be necessary in the interest 0 
an increased food supply, should the apprehensions 
of a failing stock be justified. It seems like a revolu- 
tionary proposal to suggest that permission to exploit 
the offshore fishing grounds should become necessary 
and that this permission should be accompanied by 
certain conditions, yet something of the kind may 
have to come in the near future. Meanwhile the 
scientific work in progress is affording the data 
whereby such proposals can materialise when the 
administrations are ready. feel 

Solar Radiation. 
VOLUME IV. of the Annals of the Astrophysical 
' Observatory of the Smithsonian Institution 
contains the investigations on solar radiation made 
by the director, Prof. C. G. Abbot, assisted by F. E. 
Fowle, L. B. Aldrich, and others. The work in the 
Northern Hemisphere has been transferred from 
Mt. Wilson to Mt. Harqua Hala, Arizona; that in 
Chile from Calama to Mt. Montezuma. In 1914 
NO. 2786, VOL. I11| 
pyrheliometers were taken up to a height of 25 km. 
by small balloons. The atmospheric pressure was 
3 cm. of mercury; the value of the solar constant 
indicated was 1-84 calories per cm.?, in good agree-— 
ment with the adopted value. 
Mr. Clayton compared the variations of solar 
radiation measured in 1913-14 with the temperature 
records in various parts of the world; he found a 
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