This case study used a single hydrophone at AUTEC to estimate density of beaked whales around the sensor, based on counts of detected beaked whale clicks. Using propagation modelling, information about the source level of the clicks and characteristics of the automatic click detector, the effective detection radius around the hydrophone was estimated. Together with information about clicking rates of beaked whales, this enabled density of beaked whales around the hydrophone to be estimated. These data were used to characterize the performance of the automatic detector. A 6-minute recording from hydrophone 57 was manually checked for beaked whale clicks. This 6-minute section was part of the main 6-day dataset used in the case study. The automatic detector was used on the same sound file, and the results compared. For each manually detected click, the signal-to-noise ratio (SNR) was calculated, the quality of the click was judged and it was noted whether or not the click was detected by the automatic detector. Time zone is GMT. Note hydrophone location is approximate. Original data can be downloaded at http://www.creem.st-and.ac.uk/decaf/decaf-data-files under Case Study 4a: Beaked whale data. The sound file can be downloaded at http://www.mobysound.org/odontocetes.html (click the 'from the Bahamas: AUTEC' under the Blainville's Beaked Whale, Mesoplodon densirostris, subheading). Sound file name: Set4-A5-092705-H57-0600-0618-1435-1453loc_filter.wav. Dataset credit = Density Estimation of Cetaceans from passive Acoustic Fixed sensors (DECAF) (http://www.creem.st-and.ac.uk/decaf/)