Relationships of cetacean and prey densitiesPredator-prey relationships are important indicators for change in an ecosystem. Predictive models for higher-trophic level organisms have predominantly been relying on distant indicators such as data from surface satellite imagery that may not be representable to what is occuring in the water column and at depth and is collected on spatial and temporal scales that may not align with predator-prey interacations. Using actual predator and prey density measurements is an intriguing opportunity that may be feasible with combined passive and active acoustics. Verifying these measurements with optics and net tows as well as augmenting models with oceanographic information will provide a closer look and deeper understanding about important food web links and animal-environment interactions.
Sound Production by Mesopelagic SpeciesA new area of interest is the investigation of sound produced by mesopelagic species within the deep-scattering layer (DSL), comprising a variety of mesopelagic fishes, and squids, siphonophores, crustaceans, and other invertebrates. Some of the DSL species migrate from depth during daylight to feed near the surface at night, transitioning during dusk and dawn.
Long-term passive acoustic data from several sites in the North Pacific show a diel pattern of ambient sound with elevated levels at night. A number of indicators point to the DSL being the origin for this ambient sound. With the combination of passive- and active-acoustic, and CTD sensors, we documented that DSL organisms produced sound, between 300 and 1000 Hz, and the received levels were highest when the animals migrated past the recorder during ascent and descent. Mesopelagic fish are most likely producing the recorded sounds.
These fishes probably contain the largest global fish biomass with an estimated 1000 million tons. Diel vertical migration of them and other DSL species is a global phenomenon and contributes significantly to the vertical flux of carbon from the surface water to the mesopelagic zone and is hence crucially important in the context of climate change. Additionally, they are preferred prey for numerous large marine predators, e.g. cetaceans, seabirds, and economically relevant fishes. We believe that this potentially ubiquitous acoustic phenomenon has wide-reaching implications for deep-sea ecology, behavior, evolution, economics, and management opportunities for anthropogenic impact. The pelagic realm of ocean soundscape is understudied. Sound travels farther than light or chemicals and thus can be sensed at larger distances by predators, prey, and mates. The animals of the DSL may have evolved to use sound to optimize their fitness, and it is conceivable that other marine species in the deep sea take advantage of sound for essential life functions as well.
We recently presented initial findings during the Ocean Sciences Meeting 2016 and received considerable public interest (e.g. NPR, Science News, BBC World Service Radio).
Beaked Whale Behavior and EcologyOver the past years we have become a leading group in beaked whale acoustics. Beaked whales appear to be acoustically discriminable to species level and are therefore well suited for long-term acoustic studies. Very little is known about beaked whales’ life history or population numbers due to their elusive behavior, and most species’ IUCN Red List status is “data deficient”. Evidence suggests that these species are affected by anthropogenic noise, particularly navy sonar. Therefore research results improving our current knowledge of beaked whales are essential for the development of management and mitigation plans. We are investigating the impact of anthropogenic noise, particularly naval mid-frequency active sonar and fishery-related explosions, on the acoustic behavior of beaked whales based on long-term passive acoustics. We are documenting long-term changes in beaked whale densities, seasonal occurrence patterns, and habitat preference.
Listen to a short interview with Dr. Baumann-Pickering on this topic on the National Geographic Society weekend radio show, or to a long evening lecture within the Jeffrey B. Graham Perspectives on Ocean Sicence Lecture Series: 'Listening in the Deep - Using Sound to Study Animals We Cannot See'
Detection and Classification of Acoustic SignalsTo deal with long-term acoustic data, automated routines need to be established to detect and classify acoustic signals. We have been working on the description and discrimination of species-specific properties in echolocation clicks of toothed whales. We have ongoing projects to improve detection and classification algorithms, to explore the echolocation click parameters of species that are currently not discriminable, and to develop new methods.
Acoustic Metadata Database - TethysAcoustic metadata is varied (e.g. recording equipment, location, trajectory paths, number and types of sensors, detection algorithms) and a convenient database to organize and share great amounts of data has been missing. We are contributing to a large collaborative effort to develop a database system that stores acoustic metadata, allows for data sharing, and provides access to external sources retrieving physical or biological oceanographic as well as ephemeris data, particularly convenient for behavioral or habitat modeling purposes. We are using Oracle’s open source Berkeley dB/XML database and XQuery as the querying language. The languages for interfacing with the database server are Java, Matlab, and the R Project for Statistical Computing. More specific information can be found under Tethys Metadata - Integrating bioacoustics and habitat data.