Marine Mammal Acoustic Operations Summary
CalCOFI 1108, R/V New Horizon, Chief Scientist: Dave Wolgast
July 27 – August 13, 2011
Marine Physical Laboratory, SIO
Acoustic monitoring for marine mammals was conducted concurrently with visual observations during daylight hours. A six-element hydrophone array was towed during daylight transits between stations, and expendable Navy sonobuoys were deployed upon arrival at stations. Two marine mammal observers were present on the bridge during all daylight transits. Acoustic signals from the hydrophone array and sonobuoys were continuously recorded and monitored by the acoustician.
The six-channel hydrophone array was deployed during all daylight transits where at least 1.5 hours of data could be recorded. The array was towed 300 meters behind the ship and about 17 meters below the surface. Acoustic signals from the hydrophone array were continuously recorded with a sampling rate of 192 kHz for channels 1, 2, 3 and 6 and 500 kHz for channels 4 and 5. The acoustician monitored channels 1, 2, 3 and 6 aurally as well as visually by a scrolling spectrogram via Ishmael.
For all stations that were at least 3nm from shore and approached during daylight hours, two sonobuoys were deployed 1nm prior to arriving on station: one omnidirectional (omni) 57B and one Directional Frequency Analysis and Ranging (DiFAR) 53F. Both use a VHF carrier frequency to transmit acoustic signals to the ship, where the signals are received by ICOM R100 radios and recorded with a sampling rate of 48 kHz. Omni sonobuoys were monitored aurally as well as visually via a scrolling spectrogram in Ishmael.
In total there were 33 array deployments for a total of 95.5 hours and 860 nm and 63 sonobuoy deployments at 31 CalCOFI stations for a total of 139 hours. Throughout all of the hydrophone array deployments, 63 cetacean groups were detected with associated acoustic signals recorded by the acoustician, 21 of which had corresponding sightings by the visual observers. During the sonobuoy deployments, 29 detections were logged, three of which had visual confirmation. Species recorded included short-beaked common dolphins (Delphinus delphis), long-beaked common dolphins (Delphinus capensis), risso’s dolphin (Grampus griseus), sperm whales (Physeter macrocephalus) as well as unidentified odontocetes and unidentified large whales. Anthropogenic sounds such as ship noise, mid-frequency sonar, underwater communications and explosions were also noted.