Ecological studies of marine mammals using a seabed-mounted echosounder

Abstract

Abstract Doksæter, L., Godø, O. R., Olsen, E., Nøttestad, L., and Patel, R. 2009. Ecological studies of marine mammals using a seabed-mounted echosounder. – ICES Journal of Marine Science, 66: 1029–1036. A seabed-mounted, upward-looking, 38 kHz echosounder (Simrad EK60) was used to monitor cetaceans for 128 d between July 2004 and June 2005. The echosounder was placed at 52°N 30°W at a depth of 910 m, in a frontal area with continuous upwelling creating a hotspot of marine life at all trophic levels. Echo tracks were observed, apparently resulting from one or more animals in close temporal and spatial proximity. The 69 “acoustic detections” were examined with a principal component analysis (PCA) considering mean target strength (TS), group size, and maximum dive depth and duration. The PCA conservatively classified 45 of the acoustic detections as “cetaceans”. Their mean TS values varied between −5 and −36 dB, in agreement with earlier TS measurements of whales and dolphins. Several of the supposed cetaceans were apparently feeding in the “deep-scattering layer” when this ascended at night. This study demonstrates that cetacean behaviour, including swimming, feeding, and vocalizing, can be observed and monitored with stationary active-acoustic instrumentation.