Signals from the deep: Spatial and temporal acoustic occurrence of beaked whales off western Ireland

PLoS One. 2018 Jun 21;13(6):e0199431. doi: 10.1371/journal.pone.0199431. eCollection 2018.

Abstract

Little is known of the spatio-temporal occurrence of beaked whales off western Ireland, limiting the ability of Regulators to implement appropriate management and conservation measures. To address this knowledge gap, static acoustic monitoring was carried out using eight fixed bottom-mounted autonomous acoustic recorders: four from May to December 2015 on Ireland's northern slope and four from March to November 2016 on the western and southern slopes. Recorders ran for 205 to 230 days, resulting in 4.09 TB of data sampled at 250 kHz which could capture beaked whale acoustic signals. Zero-crossing-based automated detectors identified beaked whale clicks. A sample of detections was manually validated to evaluate and optimize detector performance. Analysis confirmed the occurrence of Sowerby's and Cuvier's beaked whales and Northern bottlenose whales. Northern bottlenose whale clicks occurred in late summer and autumn, but were too few to allow further analysis. Cuvier's and Sowerby's clicks occurred at all stations throughout the monitoring period. There was a significant effect of month and station (latitude) on the mean daily number of click detections for both species. Cuvier's clicks were more abundant at lower latitudes while Sowerby's were greater at higher latitudes, particularly in the spring, suggesting a spatial segregation between species, possibly driven by prey preference. Cuvier's occurrence increased in late autumn 2015 off northwest Porcupine Bank, a region of higher relative occurrence for each species. Seismic airgun shots, with daily sound exposure levels as high as 175 dB re 1 μPa2·s, did not appear to impact the mean daily number of Cuvier's or Sowerby's beaked whale click detections. This work provides insight into the significance of Irish waters for beaked whales and highlights the importance of using acoustics for beaked whale monitoring.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustics* / instrumentation
  • Animals
  • Atlantic Ocean
  • Circadian Rhythm / physiology
  • Geography
  • Ireland
  • Signal Processing, Computer-Assisted*
  • Spatio-Temporal Analysis*
  • Time Factors
  • Vocalization, Animal / physiology*
  • Wavelet Analysis
  • Whales / physiology*

Grants and funding

This study is part of the ObSERVE Acoustic project that was initiated and funded by the Department of Communications, Climate Action and Environment in partnership with the Department of Culture, Heritage and the Gaeltacht under Ireland’s ObSERVE Programme. The Galway-Mayo Institute of Technology (GMIT) is the lead organization in ObSERVE. JASCO Applied Sciences was contracted by GMIT to provide acoustic recorders, analysis services, and to prepare a final report, but did not have any additional role in the study design, data collection, or decision to publish. JASCO provided internal funding in the form of salaries for authors (KK, JD, and BM) to prepare the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.