Acoustic and visual surveys for bowhead whales in the western Beaufort and far northeastern Chukchi seas

Two types of passive-acoustic survey were conducted to investigate the seasonal occurrence of bowhead whales (Balaena mysticetus) in the western Beaufort and far northeastern Chukchi seas: (1) an over-winter (2003–04) survey using autonomous recorders deployed northeast of Barrow, Alaska, and (2) a summertime dipping-hydrophone survey along the 2005 NOAA Ocean Exploration (OE) cruise track northwest of Barrow. The longest continuous sampling period from the over-winter survey was 3 October 2003 to 12 May 2004. During that period, bowhead whale calls were recorded from 3 to 23 October, intermittently on 6–7 and 22–23 November, then not again until 25 March 2004. Bowhead calls were recorded almost every hour from 19 April to 12 May 2004, with a call rate peak on 30 April (ca. 9400 calls) and a few instances of patterned calling (or, “song”) detected in early May. Bowhead whale calls were never detected during the NOAA OE cruise, but calls of beluga whales (Delphinapterus leucas) were recorded at 3 of 16 acoustic stations. Opportunistic visual surveys for marine mammals were also conducted during the NOAA OE cruise from the ship (65 h) and helicopter (7.8 h), resulting in single sightings of bowhead whales (3–5 whales), beluga (16–20 whales), walrus (1), polar bear (2=sow/cub), and 17 sightings of 87 ringed seals from the ship and 15 sightings of 67 ringed seals from the helicopter.