Acoustic Recording Packages Research Articles

High-frequency Acoustic Recording Package (HARP) for long-term monitoring of marine mammals

Advancements in low-power and high-data-capacity computer technology during the past decade have been adapted to autonomously record sounds from whales over long time periods. Acoustic monitoring of whales has advantages over traditional visual surveys including greater detection ranges, continuous long-term monitoring in remote locations under various weather conditions, and lower cost. One currently used tool for providing long-term acoustic monitoring of marine mammals is an autonomous acoustic recording package (ARP) which uses a tethered hydrophone above a seafloor-mounted instrument frame. Since 2000, ARPs have been deployed to record baleen whale sounds in the Bering Sea, in the Beaufort Sea, in the Gulf of Alaska, off the coast of southern California, around Antarctica and near Hawaii. ARP data have provided new information on the seasonal presence, abundance, call character and patterns of calling whales. The need for a broader-band, higher-data capacity system capable of recording odontocete whales, dolphins and porpoises for long time periods has prompted the development of a High-frequency Acoustic Recording Package (HARP). The HARP design is described and data analysis strategies are discussed using examples of HARP broad-band (sample rates up to 200 kHz) recorded data.

Blue and fin whales in the Southern California Bight: Using long-term acoustic records and acoustic recording tags

Blue and fin whales have been the subject of acoustic investigation for decades, but recent advances in technology, including acoustic tags, autonomous recorders, computer automated signal detectors, and genetic sex-identification allow us to examine fine scale patterns in acoustic behavior. Northeast Pacific blue whales are known to produce at least five separate call types, and North Pacific fin whales at least three. Since August 2000, we have been acoustically monitoring blue and fin whales in the Southern California Bight using acoustic recording packages (ARPs), acoustic recording tags, and through genetic sampling of vocal whales. There are patterns of occurrence of particular call types with nonacoustic behaviors, and sex-biases exist in the production of certain calls. Acoustic sampling from several sites in the region indicates there are significant changes in the detection of various call types both within and between years, and among sites. Hourly detection patterns also vary, potentially serving as an indicator of feeding activity. An understanding of the temporal and spatial patterns of occurrence of individual call types, and the behavior associated with each, will lead to more efficient methods to monitor habitat, distribution, and abundance of these species.

Location and range of calling blue and fin whales off the Western Antarctic Peninsula

Blue and fin whales were heavily whaled from the Southern Ocean during the 20th century and their populations today remain at extremely low levels. Both species produce loud, low-frequency calls that are well suited for long propagation. Eight acoustic recording packages (ARPs) were deployed off the Western Antarctic Peninsula, with instrument spacing from 100 to 180 km. Blue and fin whale calls were commonly heard and two different methods were used to determine locations and ranges to the calling whales. Blue whales were localized using the differences in call arrival times to three different instruments. It also was possible to calculate ranges to blue whales from multipath arrivals of their calls and verify the results obtained by the difference in arrival times method. Short detection ranges for fin whales precluded localization, but multipath arrival difference allowed range estimation. Source levels for both species were calculated using these ranges and the measured received levels.

Seasonality of blue and fin whale calls and the influence of sea ice in the Western Antarctic Peninsula

The calling seasonality of blue (Balaenoptera musculus) and fin (B. physalus) whales was assessed using acoustic data recorded on seven autonomous acoustic recording packages (ARPs) deployed from March 2001 to February 2003 in the Western Antarctic Peninsula. Automatic detection and acoustic power analysis methods were used for determining presence and absence of whale calls. Blue whale calls were detected year round, on average 177 days per year, with peak calling in March and April, and a secondary peak in October and November. Lowest calling rates occurred between June and September, and in December. Fin whale calling rates were seasonal with calls detected between February and June (on average 51 days/year), and peak calling in May. Sea ice formed a month later and retreated a month earlier in 2001 than in 2002 over all recording sites. During the entire deployment period, detected calls of both species of whales showed negative correlation with sea ice concentrations at all sites, suggesting an absence of blue and fin whales in areas covered with sea ice. A conservative density estimate of calling whales from the acoustic data yields 0.43 calling blue whales per 1000 n mi2 and 1.30 calling fin whales per 1000 n mi2, which is about one-third higher than the density of blue whales and approximately equal to the density of fin whales estimated from the visual surveys.

Autonomous Acoustic Recording Packages (ARPs) for Long-Term Monitoring of Whale Sounds

Advancements in low-power and high-data capacity computer technology during the past decade have been adapted to autonomously record acoustic data from vocalizing whales over long time periods. Acoustic monitoring of whales has advantages over traditional visual surveys including greater detection ranges, continuous long-term monitoring in remote locations and in various weather conditions, and lower cost. An autonomous acoustic recording package (ARP) is described that uses a tethered hydrophone above a seafloor-mounted instrument frame. ARPs have been deployed to record baleen whale sounds in the Bering Sea, off the coast of southern California, near the West Antarctic Peninsula, and near Hawaii. ARP data have provided new information on the seasonal presence, abundance, call character, and patterns of vocalizing whales. Current development is underway for a broader-band, higher-data capacity system capable of recording odontocete whales, dolphins, and porpoises for long time periods.

Acoustic and visual monitoring for marine mammals at Cortez and Tanner Banks

We have implemented continuous acoustic monitoring for baleen whales in the region surrounding Cortez and Tanner Banks, offshore of Southern California, complemented by bimonthly ship-based visual and acoustic observations. Our objective is to develop methods for acoustic monitoring of baleen whales using seafloor acoustic recording packages, the results of which will be used to produce abundance estimates. The joint acoustic and visual effort will answer questions regarding the probability for acoustic detections of individual animals, the quantitative association of calls with a particular species, and how well the number of animals in an area can be assessed acoustically. These findings can then be used to generate a detectability curve for each baleen whale species, from which the seafloor recorder data can be translated into absolute abundance estimates. The use of continuous acoustic monitoring with seafloor recording packages offers the potential for efficient and economical monitoring of marine mammals. The continuous acoustic census approach will be discussed, and compared to opportunistic visual and acoustic survey methods.

Onboard acoustic recording from diving northern elephant seals.

This study was the first phase in a long-term investigation of the importance of low-frequency sound in the aquatic life of northern elephant seals, Mirounga angustirostris. By attaching acoustic recording packages to the backs of six translocated juveniles, the aim was to determine the predominant frequencies and sound levels impinging on them, and whether they actively vocalize underwater on their return to their rookery at Ano Nuevo, California, from deep water in Monterey Bay. All packages contained a Sony digital audio tape recorder encased in an aluminum housing with an external hydrophone. Flow noise was minimized by potting the hydrophone in resin to the housing and orienting it posteriorly. The diving pattern of four seals was recorded with a separate time-depth recorder or a time-depth-velocity recorder. Good acoustic records were obtained from three seals. Flow noise was positively correlated with swim speed, but not so high as to mask most low-frequency sounds in the environment. Dominant frequencies of noise impinging on the seals were in the range 20-200 Hz. Transient signals recorded from the seals included snapping shrimp, cetacean vocalizations. boat noise, small explosive charges, and seal swim strokes, but no seal vocalizations were detected. During quiet intervals at the surface between dives, the acoustic record was dominated by respiration and signals that appeared to be heartbeats. This study demonstrates the feasibility of recording sounds from instruments attached to free-ranging seals, and in doing so, studying their behavioral and physiological response to fluctuations in ambient sounds.