332
THE
SEAS
that these six year old sh absolutely outnumber the sh
of all other ages indicatesthat six years before there was a
great survival of young herring, far and above those born
in the years immediately previous and succeeding.
That
year is then known as a good
“
survival year,” and it may
.
be found that for several years the catches will be domin—
ated by sh born then.
For
many
consecutive years
Norwegian investigators
studied the age composition of their shoals, and the domination of the catches by a single year—class derived from a
good “survival year
”
is clearly shown by the following
instance.
In the year 1908 the 1904 year-class (i.e. sh
born in 1904) appeared in large quantities in the catches.
_
From that year until 1919 these 1904 sh were still predomînant, by which time they were fteen years of age.
For eight years, 1909 to 1916, they had in fact practically
supported
,
the
herring shery industry-;
but
in
1919
1
there appeared in the catches a new set of sh hatehed in
-
1914, that is six years old, which nearly equalled the 1904
sh in
.
Not until 1924 did the 1904 sh die out
from the catches, and about this time the 1914 class was
also on the "wane, but in 1922 a new brood appeared which
was still predominating in 1926 (Fig. 63).
-
'
Thus
are faced with the amazing conclusion that the
main stock of herrings on which we draw may consist
for several, years of the production of a particular year’s
spawning, and the outlook for the herring shèries will beserious if this stock is depleted before there has been another
good "‘ survival year "’ to keep the supply up to the demandi
It is one of the main aims'0f shery research to nd
‘
out what isthe exact combination-of conditions necessary to -»
:
bring about a good
“' survival year,” and this knowledge can
only be gained by taking very full-and detailed observations
over a 10ng period oiyears; 'With such know1edge-Ëit W0uld- '
THE
SEAS
that these six year old sh absolutely outnumber the sh
of all other ages indicatesthat six years before there was a
great survival of young herring, far and above those born
in the years immediately previous and succeeding.
That
year is then known as a good
“
survival year,” and it may
.
be found that for several years the catches will be domin—
ated by sh born then.
For
many
consecutive years
Norwegian investigators
studied the age composition of their shoals, and the domination of the catches by a single year—class derived from a
good “survival year
”
is clearly shown by the following
instance.
In the year 1908 the 1904 year-class (i.e. sh
born in 1904) appeared in large quantities in the catches.
_
From that year until 1919 these 1904 sh were still predomînant, by which time they were fteen years of age.
For eight years, 1909 to 1916, they had in fact practically
supported
,
the
herring shery industry-;
but
in
1919
1
there appeared in the catches a new set of sh hatehed in
-
1914, that is six years old, which nearly equalled the 1904
sh in
.
Not until 1924 did the 1904 sh die out
from the catches, and about this time the 1914 class was
also on the "wane, but in 1922 a new brood appeared which
was still predominating in 1926 (Fig. 63).
-
'
Thus
are faced with the amazing conclusion that the
main stock of herrings on which we draw may consist
for several, years of the production of a particular year’s
spawning, and the outlook for the herring shèries will beserious if this stock is depleted before there has been another
good "‘ survival year "’ to keep the supply up to the demandi
It is one of the main aims'0f shery research to nd
‘
out what isthe exact combination-of conditions necessary to -»
:
bring about a good
“' survival year,” and this knowledge can
only be gained by taking very full-and detailed observations
over a 10ng period oiyears; 'With such know1edge-Ëit W0uld- '