714 NATIONAL OCEANOGRAPHIC PROGRAM—1965 
baltic in the mid 15th century, the Hanseatic league of cities that depended on 
them faded and the Dutch became the premier fishmongers of Europe for their turn. 
No one knows why the herring of the Baltic disappeared -- perhaps some change of 
conditions in the sea -- and they have never returned. 
As yet, we have no way of adjusting to these fluctuations in natural popu- 
lations of fishes in the sea. For example, while it is generally believed that 
the sardines of the California coast declined because of changes in the tempera- 
ture of the ocean, brought about perhaps by changes in the currents, it is also 
suspected that a very heavy fishery at a period of unfavorable environmental 
change contributed to the decline of the fish stocks. Conversely, however, we 
have some evidence that a fairly heavy fishery of adults during favorable years 
might have the reverse effect -- that is, removing the mature large fish makes it 
possible for the young fishes to grow faster and replace the older ones that have 
been removed. 
Whatever happens in nature, it is doubtful that major population changes are 
as simple as driving cattle off a range and turning sheep loose on it. Less than 
- hyndred years ago it was believed by many eminent authorities on fisheries prob- 
lems t -t the sea was so vast and the populations of fishes so immense that the 
efforts of man, however intense, could have no effect on the populations, It 
needed only a minute fraction of the population to replace the entire stock, so 
abundant is the spawn of most fishes. Now we have evidence concerning the extra- 
ordinary vulnerability of hatching and larval fish to changes in the environmert -= 
how a drop of a degree or so of temperature may delay hatching perhaps several 
days, so that the egg drifts beyond the point of no return, or hatches at a time 
when other creatures that would eat it are just a little larger than they should 
be, and thus eat more fish. These small changes apparently have a way of piling 
up to produce unexpectedly large effects. And we have the example of the Baltic 
herring to suggest that the process may not always be reversible. 
Mankind has had two great lessons concerning the effect of his fishing activ- 
ities on the stock of fishes. The bottom fish of the North Sea and waters around 
the British Isles had been fished intensively up to 1°1h, and the catches were 
dropping off, and the average size of the fish was decreasing. Fishing had gone 
beyond that stage in the fishery when a harvest of the old mature fish enabled 
the smaller and younger ones to srow up to take their place -- the whole fish- 
eries curve was dropping. But the war of 191-18 made fishing impossible, and 
imposed a closed season on the stocks of the North Sea. When fishing was resumed 
in 1919, the fish were more abundant and larger. But man did not learn the lesson, 
and by 1938 things were back to where they were in 191) -- or perhaps worse. 
Then World War 2 imposed another long closed season, and the stocks again im- 
proved. Now many nations that depend on the north sea fisheries have regulations 
requiring that the mesh of the nets be large enough for the smaller fish to ex- 
cape, but in no field of international relations is uniformity and compliance so 
difficult to achieve as in fishery regulations. 
When success is apparently attained, as in the halibut fishery of the United 
States and Canada, the suspicion arises in some minds that the fishery is not 
being regulated so mich on conservation grounds as on lines to maintain the 
highest price for the fish. In any event, it was impossible for the fisheries 
experts to be certain that the halibut was being fished to capacity in the east 
Bering sea grounds, so in 1963 the Americans and Canadians grudgingly opened 
these grounds to Japanese fishing. 
