Mysticete whales are top-predators of euphausiids (krill), but whale populations were so severely depleted by commercial whaling during the 20^th century that their role in the existing Antarctic ecosystem is unknown. The primary goal of this project is to determine seasonal occurrence and minimum population size of mysticete whales within the WAP study area through year-round detection of their calls. Eight autonomous acoustic recording packages (ARPs) were deployed between 18 March and 13 April 2001 offshore the Antarctic Peninsula to record calls from baleen (mysticete) whales. The ARPs are bottom-moored, with a hydrophone suspended roughly 5 m above the seafloor. Their sample rate is 500 Hz and, with a total hard disk storage capacity of 36 Gbytes, they are capable of a 400-day deployment. Blue whales (Balaenoptera musculus) and fin whales (B. physalus) produce repetitive low frequency calls (~20 Hz), which can be reliably identified and detected at ranges of 20-30 km. These species were nearly extirpated during the whaling era, and obtaining an accurate population estimate from visual surveys is virtually impossible. Humpback whales (Megaptera novaeangliae) and minke whales (Balaenoptera acutorostrata) produce calls at higher frequencies (40-2000 Hz), the lower ends of which are well within the sampling capability of the ARPs. For these two species we anticipate describing seasonal occurrence and minimum population density estimates both from acoustic and visual detections, as they are far more numerous. Whale calls also were detected and recorded via sonobuoy deployments during several SoGLOBEC cruises including: NBP01-03, from 23 April to 6 June, and NBP01-04, from 22 July to 31 August. Recordings made during these cruises can be coordinated in real-time with visual observations and form a basis for identification of calls recorded on the ARPs. The ARPs are scheduled for recovery (and redeployment) in February-March 2002, with the data processing beginning immediately thereafter.