216
N. A . IIOLME
members of the epifaiina the grab was a rather poor sampling instrument. The trawl WRS rather better, and the camera gave acceptable
est.imates with thc additional advantage that the distribution of
individual niiimals ovw the groirid could bc determined.
VT. C J I ~ I C E
OF A SAMPLER
It is customary to discuss quantitative sampling by grabs or corers
separately from t,he more qualitative sampling by dredges or trawls.
I have decided to consider all together, partly because of the existence
of samplers of an intermediate nature, such as the anchor-dredge, and
also because dredges may a t times lw used for semi-quantitative work,
and grabs may be used for non-quantitative collecting.
The choice of a sampler for any given purpose must always be a
compromise, based on such considerations as :
(1) The size, density, and habits of the animals to be collected.
(2) Whether qualitative or quantitative samples are desired.
(3) The nature of the deposit.
(4) The size of shipand facilities for working heavy gear.
( 5 ) Whether sampling is to be under open sea conditions and, if so,
whether extra time is available so that in the event of bad
weather sampling caii be post poncd until conditions improve.
(6) Depth of water.
It is perhaps usual whrn starting benthos work to insist that
samples be as nearly as possible fully quantitative, to a depth at which
all the animals present will be taken, and covering a sufficient area
to obtain a reasonably reliable estimate of densities. The acquisition
of such samples, however, demands reasonably calm conditions, a ship
anchored or with precautions taken to avoid excessive drift, and a
sampler such as the Knudsen, which can only be operated under mch
conditions. However, ship time is at a premium, and very often it
will be necessary to work under conditions which test gear and patienoe
to the utmost, and on these occasions samplers tend to bring up a
smaller and less satisfactory sample than usual. T h l s each worker
must select the sampler most suitable for his needs and, paradoxically,
it may sometimes be found that a more-nearly quantitative sample
may be taken by a dredge than is obtainable by a quantitative sampler
such as a grab (cp. Smith, 1932).
The following notes are offered merely as a guide to the choice of
samplers for different conditions.
N. A . IIOLME
members of the epifaiina the grab was a rather poor sampling instrument. The trawl WRS rather better, and the camera gave acceptable
est.imates with thc additional advantage that the distribution of
individual niiimals ovw the groirid could bc determined.
VT. C J I ~ I C E
OF A SAMPLER
It is customary to discuss quantitative sampling by grabs or corers
separately from t,he more qualitative sampling by dredges or trawls.
I have decided to consider all together, partly because of the existence
of samplers of an intermediate nature, such as the anchor-dredge, and
also because dredges may a t times lw used for semi-quantitative work,
and grabs may be used for non-quantitative collecting.
The choice of a sampler for any given purpose must always be a
compromise, based on such considerations as :
(1) The size, density, and habits of the animals to be collected.
(2) Whether qualitative or quantitative samples are desired.
(3) The nature of the deposit.
(4) The size of shipand facilities for working heavy gear.
( 5 ) Whether sampling is to be under open sea conditions and, if so,
whether extra time is available so that in the event of bad
weather sampling caii be post poncd until conditions improve.
(6) Depth of water.
It is perhaps usual whrn starting benthos work to insist that
samples be as nearly as possible fully quantitative, to a depth at which
all the animals present will be taken, and covering a sufficient area
to obtain a reasonably reliable estimate of densities. The acquisition
of such samples, however, demands reasonably calm conditions, a ship
anchored or with precautions taken to avoid excessive drift, and a
sampler such as the Knudsen, which can only be operated under mch
conditions. However, ship time is at a premium, and very often it
will be necessary to work under conditions which test gear and patienoe
to the utmost, and on these occasions samplers tend to bring up a
smaller and less satisfactory sample than usual. T h l s each worker
must select the sampler most suitable for his needs and, paradoxically,
it may sometimes be found that a more-nearly quantitative sample
may be taken by a dredge than is obtainable by a quantitative sampler
such as a grab (cp. Smith, 1932).
The following notes are offered merely as a guide to the choice of
samplers for different conditions.