Abstract
Beaked whales are deep diving elusive animals, difficult to census with conventional visual surveys. Methods are presented for the density estimation of beaked whales, using passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period during and following the Deepwater Horizon oil spill (2010–2013). Beaked whale species detected include: Gervais’ (Mesoplodon europaeus), Cuvier’s (Ziphius cavirostris), Blainville’s (Mesoplodon densirostris) and an unknown species of Mesoplodon sp. (designated as Beaked Whale Gulf — BWG). For Gervais’ and Cuvier’s beaked whales, we estimated weekly animal density using two methods, one based on the number of echolocation clicks, and another based on the detection of animal groups during 5 min time-bins. Density estimates derived from these two methods were in good general agreement. At two sites in the western GOM, Gervais’ beaked whales were present throughout the monitoring period, but Cuvier’s beaked whales were present only seasonally, with periods of low density during the summer and higher density in the winter. At an eastern GOM site, both Gervais’ and Cuvier’s beaked whales had a high density throughout the monitoring period.
Highlights
Beaked whales in the Gulf of Mexico (GOM), all confined to the northern region[1]
Passive acoustic monitoring data were used to detect the presence of four species of beaked whales over more than three years, at three sites on the GOM continental slope in deep water (Fig. 1): Green Canyon (GC), Mississippi Canyon (MC), and Dry Tortugas (DT)
Four beaked whale acoustic signatures were detected in the GOM passive acoustic monitoring data (Fig. 2): Cuvier’s beaked whale, Gervais’ beaked whale, Blainville’s beaked whale, and a sound believed to be a beaked whale but of an unidentified species that we designate as “Beaked Whale Gulf ” (BWG)
Summary
Beaked whales in the GOM, all confined to the northern region[1]. Sowerby’s beaked whales are thought to inhabit regions outside of the GOM, with only one stranding record there[7]; this species is more typically found in northern temperate waters of the North Atlantic. A cue counting approach was presented for estimating Blainville’s beaked whale densities using a hydrophone array in the Bahamas[18], where the cues were individual echolocation clicks and detection probability was estimated using animal-borne digital acoustic tags. Another form of cue counting analysis was applied to the same species and location, using the onset of echolocation by groups of diving whales as the cue[19]. These continental shelf sites are presumably too shallow to be beaked whale foraging habitat
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