Cetacean presence on the northern Mid Atlantic Ridge revealed through passive acoustic monitoring

Abstract

Cetaceans are known to utilise the Mid-Atlantic Ridge, a key topographical feature in the Atlantic Ocean, for migratory and feeding purposes. Passive acoustic monitoring was used over a one-year period (2007/2008) to identify cetacean vocalisations that occurred on a location near the Charlie Gibbs Fracture Zone. Using species-specific vocalisations that have previously been documented in the North Atlantic, six cetacean species were identified: fin whales, blue whales, sei whales, humpback whales, minke whales and sperm whales; and three non- biological soundscape components were also identified: earthquakes, airguns from seismic exploration and shipping vessels. Call types from fin whales (20 Hz pulse and 40 Hz downsweep) and blue whales (A-B call and D-call) were identified separately, to explore intraspecific call variation. Temporal trends were identified in blue whales, sperm whales and humpback whales; whereas minke whales did not display a clear presence pattern. Fin whales and sei whales were present year-round. Fin whale 20 Hz pulses showed a peak in detections during winter, as did the 40 Hz downsweep, despite the low audible area ranges during these times due to strong fin whale choruses. The sei whale downsweep, however, was relatively constant throughout the entire year. Environmental and biological variables did not appear to explain much of the variation in cetacean presence, indicating that cetaceans use the MAR for migration purposes.