Herring observed in the Sound. 297 
many foreign places; but in this case an explanation of the 
phenomenon can be given. In the Sound a herring-period 
lasts eight years. At the commencement the fish are few and 
small; but there is a steady increase in quantity and quality 
until the fifth and sixth years, which are the best, and are 
followed by two years of decrease in quantity, after which the 
large fish suddenly disappear; and in the ninth year only 
smaller herrings are taken, and the quantity is likewise defi- 
cient. How great the difference between the fish in the bad 
and the good years is, may be concluded from the fact that 
the length of the meshes of the nets used in 1874, when 
the last completed period terminated, was 56 millims., 
whilst in the nets used in 1867, when that period com- 
menced, it was only 39°5 millims. In 1875, when a new 
period came on, hardly any large fish were taken, but only 
small ones; and the question naturally arises, What has 
become of the large breed, and where does the small breed 
come from? ‘The former evidently have remained in the 
Kattegat; and the latter were of the southern or Baltic 
variety, which had spread over the excellent spawning- 
ground north of the Flinterende, which in ordinary years is 
occupied by the northern variety, but in that year was free. 
Having thus established themselves in the northern portion 
of the Sound, they have gone north into the Kattegat after 
the breeding-season, instead of returning to the Baltic, as 
this kind usually do. From the Kattegat they will now 
return every year to the Sound; and from living in a 
larger basin, and perhaps on account of the water being more 
salt there, they will increase in size until the Sound becomes 
too confined for them ; then the shoals, led as they always are 
by the biggest individuals, will seek other spawning-grounds 
in the Kattegat, leaving the one north of the Flinterende 
untenanted ; this will then be occupied by another instalment 
of Baltic herrings, probably in 1883. According to this view 
the Bundsild of the Danish fishermen is merely the Baltic 
herring, or Kiviksill, improved by emigration to more favour- 
able localities, where it remains till the improvement has been 
carried still further ; then they cease to return to the sound, but 
remain in the more open water of the Kattegat. Something 
quite analogous seems to hold good with regard to the herring 
in the Great Belt, and perhaps also with regard to other 
species of fish in these waters. It has not yet been observed 
whether the converse, a degeneration of races penetrating into 
the Baltic from the Kattegat, does not take place occasionally. 
In any case a similar explanation is very likely to afford the 
explanation of similar fishing-periods in other places. 
Ann. & Mag. N. Hist. Ser. 5. Vol.i. 20 
