Palmer LTER: Observations in Foraging Areas of Adelie Penguins During the January 1995 Cruise Langdon B. Quetin, Janice L. Jones, Robin M. Ross, Raymond C. Smith Marine Science Institute and Institute for Computational Earth System Science University of California at Santa Barbara Santa Barbara, CA, 93106 Karen S. Baker, Maria Vernet Scripps Institution of Oceanography University of California at San Diego La Jolla, CA 92093 William R. Fraser, Wayne Z. Trivelpiece, Laura Sommerville Polar Oceans Research Group, Biology Department Montana State University Bozeman, Montana 59717 Britta Denise Hardesty Point Reyes Bird Observatory Stinson Beach, CA 94970 One objective of the annual January LTER cruise is to characterize both the physical and biological nature of the foraging areas of Adelie penguins nesting near Palmer Sta- tion in order to examine the interaction between local prey availability and reproductive success. In January 1995 a "picket line" sampling strategy identified both the direc- tion of travel and the distance of foraging trips of Adelie penguins leaving the Palmer area rookeries (Smith et al., this issue). Once the foraging areas had been located, a high density sampling grid was run within these areas to characterize the physics, optics, chemistry and biology within the foraging area. Based on the results of the picket line and penguin tracking observations three areas were determined as likely Adelie penguin foraging areas and selected for more inten- sive sampling (see Smith et al., this issue). The high den- sity (HD) sampling rids (HD Grid 1, HD Grid 2, HD Grid 3) were 10 kilometers by 20 kilometers, with nine transects 2.5 kilometers apart. Each was covered at a ship speed of 4 knots during daylight of one day. Along-track, continuous measurements of surface salinity, temperature, chlorophyll a, acoustic biomass with a BioSonics 120 kHz transducer, and penguin numbers were recorded. The zooplankton biomass detected acoustically in this region is dominated in most years by Antarctic krill, Euphausia superba, but also includes other euphausiids, salps and shelled pteropods. At five stations on each grid BOPS (Bio-Optical Profiling Sys- tem) was deployed to a maximum depth of 500m to obtain hydrographic and optical data, and water for chlorophyll a and primary production measurements. The orientation of the grids and cruise track with respect to Palmer Station and the picket lines (Smith et al., this issue) is shown in Figure 1. HD Grid 1 begins 3.7 km from Palmer Station and is contiguous with HD Grid 2 to the southwest. HD Grid 3 is at a right angle to HD Grid 1 and HD Grid 2 and extends to the northwest. On HD Grid 2 the cruise track of the RV Polar Duke was modified to avoid the Myriad Islands. However, due to calm weather during the sampling period, a zodiac following a GPS course was able to complete the grid where it intersected the island group and record seabird observations not often obtained on oceano- graphic cruises in the Antarctic (Figure 2). The cruise track of HD Grid 3 also had to be modified to avoid Buff Island, but weather conditions prevented completion of the grid bird observations with a zodiac (Figure 1). Each grid was surveyed once during the cruise and HD Grid 1 was surveyed three times during the cruise (Table 1). Both HD Grid 2 and 3 were covered the day after HD Grid 1. In a summary of the observations, some trends are apparent (Table 1). For both HD Grids 2 and 3 the normalized acous- tic biomass was greater than in HD Grid 1 the previous day. During the three surveys of HD Grid 1 acoustic biomass increased by two orders of magnitude. Based on observations of swarm density and shape, this increase is likely due to krill swarms moving into the area. Normalized penguin counts followed a different pattern. Adelie penguin counts during HD Grid 1b were double or greater than Adelie penguin counts from either HD Grids 1a and 1c. These numbers suggest a change in the foraging pat- tern of penguins from the rookeries in the vicinity of Palmer Station which may be related to the density of krill in the foraging area. The doubling in penguin numbers sug- gests either that (1) during HD Grid 1b both penguins from each nesting site were foraging in the area rather than one, possibly due to the low food available at the beginning of the sampling period, or (2) that penguins that had been foraging elsewhere temporarily moved into the area. This period coincides with the time when most of the adult Adelie penguins abandoned the colonies near Palmer Station and went to sea to feed, leaving only a small proportion of the adults to guard the chicks. Temporally, total acoustic biomass does not follow the same pattern as chlorophyll a and primary production. Total acoustic biomass continually increased in HD1 over the three weeks, whereas the highest values for chlorophyll a and pri- mary production were for HD1b. Primary production values are not available for HD1c. Palmer LTER research team members, both on shore and at sea, personnel from Antarctic Support Associates, and the Captain and crew of the RV Polar Duke were all essential to the success of this multidisciplinary effort. This research was supported by National Science Foundation grant DPP90- 11927 and is Palmer LTER contribution No. 062. References R.C. Smith, J.L. Jones, L.B. Quetin, R.M. Ross, W. R. Fraser, W.Z. Trivelpiece, Laura Somervill, Denise Hardesty, Palmer LTER: Sea bird picket line sampling and zodiac track- ing during the January 1995 cruise. Antarctic Journal of the United States (this issue), K.J. Waters, R.C. Smith. 1992. Palmer LTER: A sampling grid for the Palmer LTER program. Antarctic Journal of the United States 27(5): 236-239. Palmer LTER Contribution #004.