Acoustic Marine Mammal Surveys
Another focus of passive acoustic research at NEFSC is the development and testing of methods for monitoring spatial and temporal trends in relative cetacean abundance using passive acoustic technologies. When used in conjunction with visual surveys, passive acoustic monitoring provides a means to detect marine mammals while submerged, during the night, and whenever weather conditions limit visibility. In addition, acoustic monitoring allows us to detect animals that may generally be difficult to see (such as harbor porpoises or beaked whales). These data can then be integrated with visual sightings to improve marine mammal abundance estimates.
Acoustician Denise Risch monitors the towed hydrophone array on board the Henry B. Bigelow
A towed hydrophone array is deployed during shipboard surveys to detect and record cetacean vocalizations. In addition to helping inform visual survey data, these recordings provide baseline data on the vocalization characteristics of lesser known species. Strategically deployed sonobuoys also provide opportunistic recordings of target species.
Towed hydrophone array on the deck of the ship
During acoustic surveys we continue to test newly developed passive acoustic monitoring software (see www.pamguard.org), which will improve our ability to detect, localize and acoustically track cetacean groups as they pass the survey vessel. Increased automation will streamline data collection and processing, and provide consistent results that can be compared across different regions and seasons.
Lastly, we are investigating the effects of active acoustic technologies, such as the ship’s echosounders, on detection capabilities, as well as any behavioral response by marine mammals to the echosounders.
Map of acoustic marine mammal detections during a cetacean abundance survey in 2011
To further improve our data collection methods, NMFS science centers convened for a toward array workshop at the Southwest Fisheries Science Center. Here, acousticians from 6 of the science centers developed and built towed arrays so that data collection across centers will be standardized.
Danielle Cholewiak and Robert Valtierra building a towed array at the SWFSC workshop