Lascara et al: Acoustically-Derived Dist. of Krill, Eos 73:319, 1992

Lascara, C.M., E.E. Hofmann, R.M. Ross and L.B. Quetin. 1992 
ABSTRACT 
  
Acoustically-Derived Distribution of Krill (Euphausia superba) 
Swarms off the Antarctic Peninsula during Austral 
Spring 1991 (LTER Program) 

Eos 73: 319


A multidisciplinary cruise was conducted during austral spring 1991
as part of the Palmer Long Term Ecological Research program (LTER) off
the Antarctic Peninsula. Fifteen stations were occupied along 3 transects
oriented from the ice edge seaward towards the shelf break. Replicate acoustic
tows were made over short distances (avg 3km) at each station 
using a downward-looking 120 kHz echosounder. Patch-finding routines
were applied to the high-resolution echo integration data 
(7 m horizontal by 2 m vertical)
to generate the following statistics for each krill swarm: horizontal
length, vertical dimension, depth from surface, cross sectional area,
distance and angle to nearest neighbor and mean, peak and variance
of volume backscattering.

Cohesive swarms with simple to moderately 
complex shapes were detected throughout the sampling area.
Eighty percent of the 482 krill swarms were <  60m in length,
<  10m in height, positioned in the upper 100 m of the water column
and had mean volume backscattering values <  4 x 10  m2 /m3 .
The concentration of krill was highest in three areas: the coastal waters
near Gerlache Strait, open waters within 20 km of the ice edge, 
and an offshore station
located over Circumpolar Deep Water. Factors contributing to higher
krill concentration differed among stations and 
included greater number of swarms per km, larger
areal extent of swarms, and/or higher mean volume backscattering values.
These characterizations
suggest that the observed spatial distributions of krill
result from different processes.  One of the goals of the LTER is
to quantify the physical and biological mechanisms important in
structuring the spatial distribution of krill.