Target strengths and echotraces of whales and seals in the Canadian Beaufort Sea

Abstract

Active acoustics as a tool to detect and avoid Arctic marine mammalswas assessed in the Canadian Beaufort Sea. The target strengths and shape of the echoes of whales and seals were characterized using a bi-frequency (38 and 120 kHz) split-beam scientific echosounder in winter 2003/2004 and a scientific scanning sonar (20-30 kHz) in summer 2011. The echosounder detected 452 signals of diving ringed seals and the sonar detected 59 bowhead whales, 13 ringed seals, and 2 bearded seals. Target strengths of diving ringed seals tracked by the echosounder ranged from 256 to 212 dB re: 1 m2 and did not vary with the depth of the animal. Target strengths of animals tracked by the sonar varied from 215 to 10 dB for bowhead whales and from 237 to 23 dB for seals. Marine mammals presented higher target strength values near broadside than near tail- or head-on. The sonar detected whales at a distance up to 2000 m and their echoes were discriminated from that of seals. This study suggests that active acoustic technology can be used as a complementary tool for marine mammal surveys in the Arctic.