Acoustic survey methods can be used to estimate density and abundance using sounds produced by cetaceans and detected using hydrophones if the probability of detection can be estimated. For passive acoustic surveys, probability of detection at zero horizontal distance from a sensor, commonly called g(0), depends on the temporal patterns of vocalizations. Methods to estimate g(0) are developed based on the assumption that a beaked whale will be detected if it is producing regular echolocation clicks directly under or above a hydrophone. Data from acoustic recording tags placed on two species of beaked whales (Cuvier's beaked whale—Ziphius cavirostris and Blainville's beaked whale—Mesoplodon densirostris) are used to directly estimate the percentage of time they produce echolocation clicks. A model of vocal behavior for these species as a function of their diving behavior is applied to other types of dive data (from time-depth recorders and time-depth-transmitting satellite tags) to indirectly determine g(0) in other locations for low ambient noise conditions. Estimates of g(0) for a single instant in time are 0.28 [standard deviation (s.d.) = 0.05] for Cuvier's beaked whale and 0.19 (s.d. = 0.01) for Blainville's beaked whale.
Tagging in Hawaii was conducted under Scientific Research Permit No. 731, 774, and 540-1811 issued by the U.S. National Marine Fisheries Service (NMFS). Dtagging in European waters was conducted under US NMFS permits 981-1578-02 and 981-1707-00 and annual permits from the Canary Islands Government to the University of La Laguna. Tagging in the Bahamas was conducted under US NMFS permits issued to John Boreman (Permit No. 1121-1900) and to Peter Tyack (Permit No. 981-1578), and issued by the Government of the Bahamas to the Bahamas Marine Mammal Research Organisation (Bahamas permit No. 01/09) and Ian Boyd (Bahamas permit Nos. 02/07 and 02/08). The Dtagging was approved by the WHOI and BMMRO Institutional Animal Care and Use Committees and the Animal Welfare and Ethics Committee of the University of St Andrews. Funding for this work was provided by the U.S. Navy (N45 and ONR), the U.S. Strategic Environmental Research and Development Program (www.serdp.org), the U.S. Chief of Naval Operations Submarine Warfare Division, the U.S. National Oceanic and Atmospheric Administration (National Marine Fisheries Service, Office of Science and Technology) (http://www.st.nmfs.noaa.gov/), U.S. National Oceanic and Atmospheric Administration Ocean Acoustics Program (http://www.nmfs.noaa.gov/pr/acoustics/), NMFS's Southwest Fisheries Science Center, NMFS's Pacific Islands Fisheries Science Center, the M.R. and Evelyn Hudson Foundation, the Wild Whale Research Foundation, the Joint Industry Program on Sound, National Ocean Partnership Program, the Packard Foundation, the Canary Islands Government, the Spanish Ministries of Defense and Environment, the project LIFE-Indemares, the Cabildo Insular de El Hierro, and the Marine Life Program of the International Association of Oil and Gas Producers (www.soundandmarinelife.org). N.A.S. is currently funded by a Marie Curie fellowship from the 7th EU Frame Program. This manuscript was improved by helpful reviews by Jeffrey E. Moore, William F. Perrin, and Jeffrey L. Laake. The authors gratefully acknowledge the invaluable support of field personnel in all tagging locations, especially Patricia Arranz, Alex Bocconcelli, Andrea Fais, Erin Falcone, Jeff Foster, Leigh Hickmott, Allan Ligon, Peter T. Madsen, Jacobo Marrero, Lucia Martin, Dan McSweeney, and Daniel Webster. We thank Dave Moretti and his team from the Marine Mammal Monitoring on Ranges, and the support from the Navy's Southern California Offshore Range.
I. INTRODUCTION II. METHODS A. Field data collection B. Statistical analyses of dive data C. Estimation of detection probability 1. Line-transect g(0) estimation 2. Point-transect g(0) estimation 3. Robust estimates of uncertainty III. RESULTS A. Tagging studies B. Estimates of g(0) IV. DISCUSSION A. Diving and echolocation behavior B. g(0) estimates V. RECOMMENDATIONS