318
THE BIOLOGY» OF FISHES
'
,
For
latter purpose he has devised an apparatus to
take large samples of the_bottom‘-soil. It ”descends through
the water open and the heavy wings bite deep
into
'
the soil, if not too'hard, to collect a known quantity… By
means of a falling weight the wings are then allowed to close
5
and the apparatus brings up a sample of one square foot,
;
or even more according to size, from which the mud and
'
sand are passed through sieves of various grades, leaving the
animals behind.
These are then counted and identied -
and their {Cod value determined by chemical analysis.
With the aid of this bottom-sampler Petersen has made
—
a quantitative comparison of the various Danish waters, and
the method has also been employed by others in the North
Sea.
An ordinary dredge is also able, of course,
to give an
,
approximate‘ estimate of the richhess of any given ground
in
method is much more accurate
and reliablm
The acCompanying gures represent. the
quantities taken at two stati0ns in— the Kàttegat;. As a rule
the majority of the animals in the bottom—soil are useless
as food to the Plaice, which lives chiey othé smaller
‘
Mollüscâ and
hence the quality rather than the '
‘
quantity of the ground is of importance,
not
'
expect
to ndthe same unvarying, quantity or
from
one year or even season to another.
-‘
.
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—
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.
'
3‘. RESOURCES QF THE SEA '._Regarding
as oneoftheagentsmuencmg
'
the Ways
life ofshes, we;come nowtoa fi11iiiriber of
,
,
interest.
'
Mari takes aheavytollof theshes year1yand the
_
“of deciding.
bétWeçh different classes of
shermen man,—different
has led to intensive“
_
investigations and, the "acoumulationof a weighty literature.
' The freShwater she's, under—conditions to a great eXtent '
own ina-king and soinewhat
those of "
plant icr0ps and pbultry breeding, need "not be considered f
AS
the
of the sea.
,