22 
(c. 90) journals, for which I beg to express my best thanks. These cutters 
are fishing particularly for plaice, and therefore use their seines in the 
same way, and chiefly at the same fishing-grounds, all the year round. 
When they do not catch any cod, the reason is, therefore, that there are 
none, and the table on p. 23 shows from this reason, approximately, the 
number of cod in the Cattegat in the various months of the year. We see 
immediately how frequent the cod is in the winter half-year, especially in 
January, February, and March, and how rare it is in the summer. I must 
here call attention to this, as another proof of the fact that the great 
multitude of cod leaves the Cattegat every year in the summer, and returns 
in the coldest months. — The Great and the Little Belt, however, do not 
become as empty of cod every year as the Cattegat. When we know how 
long the water at Samsø and in the Belts, on the deep, can keep its winter 
temperature — much longer than that of the Cattegat — it is not surprising 
that a great number of cod remain here through a considerable part of the 
summer, nay, perhaps all the summer, while, as above mentioned, good cod 
are exceedingly scarce in the Cattegat at this time of the year. The way 
from the Cattegat to the North Sea, certainly, is also shorter and easier 
to find. — Earll (loc. cit.) mentions how the shark (Squalus acanthias), con- 
sequently just our common Dog-fish, on the shores of North America is the 
worst enemy of the cod. It remains there from May till September; the 
shoals devour everything, drive the cod away, and put a stop to the fisheries. 
This reminds us very much of the conditions on the western shore of Jutland 
and in the Cattegat (see Report X, p. 33). Perhaps these sharks are of far 
greater significance in the household of nature, than we are generally 
inclined to think. As yet they have not been systematically studied in our 
seas, but in 1901 Mr. H. Lorentzen, the fish-exporter, of Frederikshavn, 
informed me that he had now for two years been commissioned to get 
sharks for the University, for Professor H. Jungersen; but in the winter it 
had been impossible for him to deliver any: the first did not arrive till the 
month of June every year. When we know how regularly the fishery at 
Frederikshavn is carried on with the same apparatus all the year round, 
this is an excellent proof that the shark is missing in the Cattegat in the 
winter. It is a fact, however (see Report of the Biol. Station X, p. 33), 
that some "winter” in our southern seas (analogous to the ""summering” of 
the cod); but, on the whole, the shark must be said to be a summer guest 
in our seas, as shortly mentioned also by Winther in his "Prodromus”. 
A third important addition to our knowledge of the cod has also been 
obtained this year, viz. that no fry of the cod was found thus year at Born- 
holm. In spite of all searching with seines and hooks, and in spite of dy- 
namiting where the fishermen thought the fry must be, none at all was 
found. I must suppose that the tender fry of the cod cannot thrive at all in the 
whole Baltic Sea, and that all the cod which, in considerable multitudes, 
are fished as far north as Finland, have immigrated into these parts through 
