Vol. 53 - Alaska Resources Library and Information Services

In our annual report (Armstrong et al. 1981), all larval abundance
data were reported in units of numbers/1000 m³. This volumetric basis
for representing mean abundance was abandoned because it did not include
larvae below 60 m depth (although the error introduced by this omission
was small) and because it was not an accurate reflection of how larvae
are distributed in the ocean.
The units presently used (number/100 m
of sea surface) include all larvae sampled and provide no misconception
about "uniform distribution."
Estimates of abundance from the annual
report can be compared with the data provided here in the following way.
In virtually all cases the majority of larvae were found above 60 m
(Tanner crab mainly in the upper 20 m), so this was considered a lower
limit for calculations of numbers/1000 m³. The surface area of a
1000 m volume extending to 60 m depth is about 16.7 m 2 . To convert the
volumetric estimates of abundance to units of numbers/100 m², a multiplication
factor of 5.99 is used (100 ÷ 16.7 = 5.988).
For sampling in
depths less than 60 m this multiplier changes.
For example, density
values for larvae caught in 40 m of water will be only four times greater
in units of 100 m² than 1000 m³ .
However, few samples reported in
the 1981 annual report were integrated over water columns of less than
60 m depth.
2.6 Data Sensitivity and Accuracy
The volume (or mass) of plankton retained by the comparatively
large mesh of the Bongo nets was frequently much smaller than that retained
by the finer mesh nets used on MOCNESS.
Yet the estimated volume
of water sampled by nets of the two devices (according to the flow
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