TITLE:     Palmer LTER: Seasonal and geographic variability in the
           distribution of Antarctic krill, Euphausia superba, west of the 
	   Antarctic Peninsula
AUTHOR     CM Lascara, EE Hofmann, JM Klinck, RM Ross and LB Quetin
PAGE:      161 of SCAR SIXTH BIOLOGY SYMPOSIUM, Antarctic Communities: Species,
           Structure and Survival 
ABSTRACT:  Acoustic estimates of krill biomass in the waters west of the
Antarctic Peninsula were collected during several multidisciplinary cruises to
investigate patterns of geographic and seasonal krill distribution in relation
to other habitat characteristics; in particular, the concentration and
composition of food resources, ice history, large-scale flow regimes, and
hydrographic and optical properties of the upper ocean.  This study was
conducted between November 1991 and September 1993 as part of the Palmer
Long-Term Ecological Research (LTER) program and included sampling during all
four seasons.  Replicate acoustic tows were made over short distances (1-2 km)
at stations within a large-scale grid west of the Antarctic Peninsula.  The
acoustically-derived distributions of krill biomass were analyzed to quantify
patch characteristics and to compute the mean biomass (integrated from 10-200
m) at each station.  For all cruises combined, over 80% of the 2440 swarms wer
< 45 m in horizontal length, < 10 m in vertical thickness, and were positioned
< 66 m from the surface.  The cumulative frequency distributions of patch
characteristics were similar between seasons with the exception that swarms
were shallower in the summer and less dense during the winter.  The percentage
of acoustics events per cruise which were positive (at least one krill swarm)
varied with season: 90% in spring and summer, 35% in fall, and 8% in the
winter.  There was a distinct difference between seasons in the station mean
krill biomass (g m-2) which ranged from 0-95 in spring (n=15 stations), 0-460
in summer (n=39), 0-44 in fall (n=96), and 0-80 in winter (n=33).  During
spring mean krill biomass exceeded 50 g m-2 in three areas: coastal waters
near Dallman Bay coincident with high phytoplankton concentrations, open
waters within 20 km of the ice edge and an offshore station located over
Circumpolar Deep Water.  Krill were most abundant during the summer and
biomass values exceeding 100 g m-2 were found at the inner stations along most
transects, where the influence of ice melt on the hydrographic structure and
water column stability was evident.