Effects of duty-cycled passive acoustic recordings on detecting the presence of beaked whales in the northwest Atlantic

Abstract

This study investigated the effects of using duty-cycled passive acoustic recordings to monitor the daily presence of beaked whale species at three locations in the northwest Atlantic. Continuous acoustic records were subsampled to simulate duty cycles of 50%, 25%, and 10% and cycle period durations from 10 to 60 min. Short, frequent listening periods were most effective for assessing the daily presence of beaked whales. Furthermore, subsampling at low duty cycles led to consistently greater underestimation of Mesoplodon species than either Cuvier's beaked whales or northern bottlenose whales, leading to a potential bias in estimation of relative species occurrence.

Using passive acoustic monitoring to document the distribution of beaked whale species in the western North Atlantic Ocean

“…Data for the remaining 319 days at MGL were collected at a sampling rate of 128 kHz, providing insufficient recording bandwidth to reliably detect the higher-frequency Sowerby's beaked whale clicks. Cuvier's beaked whales were present less frequently at MGL, and were detected on 26% of the 605 recording days, although their daily presence may be underestimated as a result of the duty-cycled recordings, which are likely to have greater effects on the assessment of daily presence of rarely detected species (Stanistreet et al 2016).…”

“…At GBK, Sowerby's and Cuvier's beaked whales were detected on 15% and 13% percent of the 304 recording days, respectively, and Gervais' beaked whales were detected only once. Based on analyses by Stanistreet et al (2016), it is likely that these results significantly underestimate daily presence, particularly of the Mesoplodon species, since data at this site were collected using a low duty cycle (less than 10% recording time; see Table 1). At NFC, recordings were made continuously, and Sowerby's, Cuvier's, and Gervais' beaked whales were detected on 36%, 20%, and 15% of the 289 recording days, respectively.…”

“…We performed these comparisons at the level of daily presence rather than on finer temporal scales to reduce potential bias in detection rates that may result from comparing data collected using different duty-cycled recording schedules. A detailed analysis of the effects of using duty-cycled recording schedules to detect different beaked whale species was performed by Stanistreet et al (2016) using similar data sets, and we discuss these potential biases in our results.…”

“…Sowerby's beaked whale (panel E) clicks are labeled as such based on a posited species identification of this click type. 5 min at a time (Stanistreet et al 2016). Finally, we found the lowest overall beaked whale presence at the Jacksonville (JAX) recording site, where Gervais' and Blainville's beaked whales were detected on only four (1.4%) and two (0.7%) of the 278 recording days, respectively.…”

Specimens of opportunity provide vital information for research and conservation regarding elusive whale species

“…A single animal was successfully tagged, but the animal immediately dislodged the tag (Visser 2012). Recently, a few acoustic recordings have been made of Sowerby's beaked whales, laying the groundwork for passive acoustic monitoring for the presence of this species (Cholewiak et al 2013, Stanistreet et al 2016, Stanistreet et al 2017, Clarke et al 2019. There are no data regarding this species' abundance or movement behaviour anywhere in its range.…”