PASCAL: Passive Acoustic Survey of Cetacean Abundance Levels

Chief Scientists: Jay Barlow and Jeff Moore
Survey Coordinator: Annette Henry

SWFSC will conduct a dedicated acoustic survey for cetaceans throughout the California Current off the U.S. West Coast in 2016. The survey will be called PASCAL: Passive Acoustic Survey of Cetacean Abundance Levels. Focal study species are beaked whales (family Ziphiidae), which due to their cryptic nature are less amendable to visual survey than most other cetacean species. Other species of interest for acoustic survey are sperm whales, and dwarf and pygmy sperm whales. This survey will be conducted from the NOAA ship Bell M. Shimada, which is quieter vessel than the older vessels used in the past. Data will be collected from a network of approximately 20 drifting acoustic spar buoy recorders (DASBRs; Griffiths and Barlow 2015) which will be deployed during the first leg of study and retrieved during the second. DASBR hydrophones are suspended 100 m below the surface. Because of this, and since the DASBRs are away from the ship, there is little noise to mask cetacean detections, and the depth of hydrophone improves detection of deep-diving species. Using twenty DASBRs, deployed for approximately 20 – 30 days each, should allow us to collect far more acoustic data for the species of interest than have ever been collected to date. We will also be towing a hydrophone array between deployment and retrieval stations to gather additional data on the geographic and depth distribution of beaked whales and to visually validate species identification for some beaked whale acoustic signals. This is truly an unprecedented opportunity to collect data on these cryptic species for which NOAA stock assessments contain relatively little information. Cuvier's beaked whale by Charlotte Dunn

Between DASBR deployments, we will conduct dedicated towed hydrophone array work in high-density beaked whale areas for the purposes of (a) providing information to estimate the depth profile of acoustic recordings, which are needed to estimate the horizontal range of DASBR detections (for density estimation) and (b) provide visual confirmation of the species identification associated with different beaked whale call types within the genus Mesoplodon. Currently we can identify acoustic signals to this genus but not to species within this genus, which compromises the information content and hence the value of marine mammal stock assessments for these species. Once we can accurately assign species ID to Mesoplodon calls, then the DASBR data can be used to generate species-specific estimates of density (our density estimates are currently at the genus level for beaked whales).

The primary objective of this project is to estimate density of beaked whales and other acoustically surveyable species (e.g., sperm whales Physeter macrocephalus, and pygmy and dwarf sperm whales (genus Kogia)) throughout the California Current ecosystem using new survey technology and increased acoustic sampling effort compared to past large-scale transect surveys (which have been more visually focused). PASCAL is expected to provide far more acoustic detections than during previous large-scale cetacean assessment surveys, thus providing improved estimates of density (and in turn, improving existing spatial models and trend estimates). A secondary objective is to improve our ability to identify acoustic calls to the species level. For example, many beaked whale detections are identifiable to the genus level (e.g., Mesoplodon), but we lack paired visual sighting confirmation to allow Mesoplodon calls to identified to species. Once calls are identified to the species level, we will be able to provide species-specific density estimates in the CA Current for the first time.

This study was funded in part by the U.S. Department of the Interior, Bureau of Ocean Energy Management through Interagency Agreement Ml6PG000l1 with the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Science Center. Additional funding was provided by Southwest Fisheries Science Center. 

Cuvier’s beaked whale photo credit: Charlotte Dunn.