Passive Acoustic Monitoring

Deployment of a High-frequency Acoustic Recording Package with collaborators from Cascadia Research off the Kona coast. Photo by Robin Baird.
Deployment of a High-frequency Acoustic Recording Package with collaborators from Cascadia Research off the Kona coast. Photo by Robin Baird.

Passive acoustics are useful for augmenting visual surveys and assessing temporal and spatial changes in the density and behavior of some marine animals. They can also provide important details about the acoustic environments of cetaceans. Our Program uses a variety of acoustic recording instruments to study cetaceans in the Pacific Islands Region (PIR), including towed hydrophone arrays, bottom-mounted long-term acoustic recording devices, acoustic recording underwater gliders, miniature recorders for use on mobile or dynamic platforms, and acoustic recording tags that temporarily attach to dolphins and whales using suction cups.

Long-term Acoustic Monitoring

In collaboration with researchers at the Scripps Institution of Oceanography, we are using bottom-mounted passive acoustic data recorders called High-frequency Acoustic Recording Packages, or HARPs, to monitor cetaceans. The HARP data loggers are moored to the sea bottom and remain there for several months. When the HARP is later retrieved from its mooring, the acoustics data are downloaded. Currently several HARPs are deployed around the PIR - at Palmyra Atoll, off the Kona coast of Hawaii Island, near Kauai, at Pearl & Hermes Reef in the Northwestern Hawaiian Islands, at Wake Atoll, and near Saipan in the Mariana Islands. The results of these long-term data sets provide the ability to assess baleen whale movements through the tropical Pacific, population structure based on differences in call types, seasonal presence, and changes in vocal behavior in response to sound sources or changing environmental conditions.

HARPs deployed throughout the PIR to monitor cetacean occurrence and seasonality.  Red = currently deployed, yellow = part deployments.
HARPs deployed throughout the PIR to monitor cetacean occurrence and seasonality. Red = currently deployed, yellow = part deployments.

Acoustic Monitoring to Understand Dolphin Interactions with Fisheries

BJ the bottlenose dolphin testing the miniature HARP at the Hawaii institute of Marine Biology.  Photo provided by Ali Bayless.
BJ the bottlenose dolphin testing the miniature HARP at the Hawaii institute of Marine Biology. Photo provided by Ali Bayless.

We have recently started to deploy miniaturized HARPs for acoustic recording of whale interactions with the commercial longline fishing fleet. A recent Take-Reduction Team for false killer whales identified several areas of priority research needed to determine how false killer whale find longline gear and their behavior around the gear once located. The new miniature HARPs are being deployed on longline gear in cooperation with the Hawaii Longline Association and the Hawaii Institute of Marine Biology, with the aim of identifying the mechanism of false killer whale – fishing gear interactions in finding solutions to mitigate that interaction for the benefit of the whales and the fishermen.

Acoustic Tags to Understand Vocal Behavior and Response to Noise

Pantropical spotted dolphin near Kona carrying an Acousonde acoustic recording tag.  Photo by Robin Baird, Cascadia Research Collective.
Pantropical spotted dolphin near Kona carrying an Acousonde acoustic recording tag. Photo by Robin Baird, Cascadia Research Collective.

Passive acoustic recording tags, equipped with additional environmental sensors, including depth, temperature, 3-D acceleration (pitch, roll, yaw) and a 3-D compass, are being tested by our Program, in collaboration with Cascadia Research and Greeneridge Sciences for use in evaluating dolphin vocal behavior, identification of species-specific vocalizations, and in examining dolphin responses to anthropogenic sounds. This work has recently expanded from baleen whales to small delphinids with the introduction of a new hydrodynamic tag (the Acousonde) that is small enough for deployment on small animals.

Technology Development: Acoustics and Underwater Gliders

Distribution and abundance of cetacean stocks is traditionally carried out using visual line transect surveys and distance sampling analyses to generate abundance estimates. With limited ship time and resources, and an expansive largely unsurveyed region, we're presented with an often insurmountable challenge if relying on traditional ship-based methods. To overcome this, we are turning to new technology in order to meet our assessment mandates. Recent developments in glider technology, including initial tests with onboard passive acoustic sensors could provide an autonomous analog to line-transect ship surveys. With funding from the NMFS Advanced Sampling Technology Working Group, and in collaboration with the Ecosystems and Oceanography Division at PIFSC, our Program is testing and developing new acoustic underwater glider technology in hopes of identifying a new tool for conducting cetacean assessments in remote regions.

Gliders are autonomous, re-usable, underwater vehicles designed to glide along a sawtooth trajectory from the ocean surface to a programmed depth, measuring a suite of oceanographic quantities along their path. Gliders can be deployed from a pier or from a small boat requiring far less logistical support than a large-scale ship survey. In addition, the sensor suite of a glider provides the capability to collect the oceanographic measurements that help to put cetacean occurrence in the proper habitat context. PIFSC and partner UH have conducted several tests deployments to date and working on integration of the DMON, a new acoustic sensor package from Woods Hole Oceanographic Institution to advance the acoustic capabilities of the glider.

Acoustic Monitoring of the Hawaii Longline Fishery for Interactions with False Killer Whales

HARP figure
Figure of HARP mounted on longline fishing gear.

False killer whales are known to take catch and bait from the Hawaiʻi longline fishery at high rates in certain areas of the Pacific. These interactions can incur large financial losses to fishermen and can also result in the hooking, entanglement or even death of the animal in some cases. However, observations of these interactions are limited since most occur at depth and animals are rarely seen. False killer whales make specific vocalizations that are easily detected and identified, which makes sound a great way of investigating whale-fishery interactions. Using a High-frequency Acoustic Recording Package (HARP) designed specifically for deployment on longline fishing gear, we can monitor the sounds associated with these types of interactions. The HARP is a single unit that consists of a hydrophone (underwater microphone) and a pressure case housed in a black tube. The package is directly attached to the mainline and then placed overboard to be activated by a saltwater switch, recording all animal, gear and vessel sounds in the vicinity of the line. By monitoring the sounds associated with these interactions, we may better understand exactly what is attracting animals to the vessel and how we might be able to deter them.

Figure of hydrophone mounted within the cylindrical pressure case of a HARP.
Figure of hydrophone mounted within the cylindrical pressure case of a HARP.