"Some people talk to animals. Not many listen though. That's the problem."

-A.A. Milne

Acoustic Marine Mammal Towed Hydrophone Array Surveys

Shipboard Acoustic Lab
Acoustician Denise Risch monitors the towed hydrophone array on board the Henry B. Bigelow
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.

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 array
Towed hydrophone array being spooled on the ship deck
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.

Building the towed array
Danielle Cholewiak and Robert Valtierra building a towed array at the SWFSC workshop
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.

Our towed array research is one component of how we are working within the Atlantic Marine Assessment Program for Protected Species (AMAPPS) program. This component focuses on using acoustics to estimate densities for sperm and beaked whales. In addition we are focused on improving visual sighting data and species identification through improved integration and use of passive acoustic data.

Tracking sperm whales in PAMGUARD
Tracking Sperm whales in PAMGUARD:
Top: Bearing-time display in Pamguard. Detected clicks are indicated by triangles. Orange triangles indicate clicks that were manually assigned to one click train series; black triangles represent clicks that are unassigned to individuals. Bottom (from left to right): The waveform display of one selected click (indicated by the gray circle in the top panel), the frequency spectrum, and Wigner plot.
Figure from Cholewiak et al. 2013.
Acoustic Detections AMAPPS 2011
Map of acoustic marine mammal detections during a cetacean abundance survey in 2011

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(File Modified Sep. 06 2016)