Underwater click detectors are used to detect actively vocalising cetaceans in industry and research worldwide and, inter alia, to mitigate potential harmful effects of man-made (anthropogenic) activities on marine mammals.
Underwater click detectors are used to detect actively vocalising cetaceans in industry and research worldwide and, inter alia, to mitigate potential harmful effects of man-made (anthropogenic) activities on marine mammals. Please click the following links for more information on how to detect echolocating cetaceans with the variety of click detectors available, including autonomous underwater click detectors called C-PODs and T-PODs. Ocean Science Consulting (OSC) provides a range of underwater marine mammal acoustic Passive Acoustic Monitoring (PAM) click detectors, and the following information summarises recent application of such devices used to track elusive beaked whales (Ziphiidae).
All beaked whales use a biological sonar, called echolocation for orientation, navigation, and foraging purposes (Griffin et al. 1960; Johnson et al. 2004). Echolocating animals produce short pulses of sound and interpret returning echoes to gain a snapshot of their environment (Madsen et al. 2013). Beaked whales are members of the Odontoceti suborder of toothed cetaceans, which is slightly misleading semantics, as most have only a handful of teeth. In fact, only Shepherd's beaked whale: Tasmacetus shepherdi) has a full set of teeth, and females of some beaked whale species lack teeth all together. One of the reasons that they are grouped in the Odontoceti suborder is that they share the feature of a single blowhole. Beaked whales are found in every ocean, from the poles to the equator, typically in water deeper than 300 m (Jefferson et al. 2015); however, little is known about the biology of some of the most elusive species, due to their deep-diving behaviour. Some of these (sub-)species can only be identified to species level through stranded animals and have never actually been recorded alive at sea e.g. spade-toothed whale (Mesoplodon traversii).
Shearer et al. (2019) used satellite tags to study the diving behaviour of Cuvier’s beaked whales (Ziphius cavirostris) off Cape Hatteras, North Carolina from 2014 to 2016. Researchers tagged 11 individuals and recorded a total of 3,242 hours of behaviour footage. Median values were established for deep and shallow dives and noted that most surface intervals were kept short (median 2.2 minutes) with increasing surface times at night; however, no diel (24-hour) variations were observed.
Tyack et al. (2006) used tags to record sound and body orientation in order to analyse dive profiles of ten individuals from Cuvier’s and Blainville’s (Mesoplodon densirostris) beaked whale. Each tag comprised a pressure sensor, a three-axis accelerometer, and a magnetometer to calculate and record whale orientation, and a hydrophone to record acoustic data. Study results demonstrated that all whales tagged for longer than 15 minutes undertook deep dives, and they were rarely found at the surface. Cuvier’s beaked whales were tagged in the Ligurian sea (part of the Mediterranean) and reached maximum depths of 1,888 m. Blainville’s beaked whales were tagged off the Canary Islands (Atlantic Ocean) and dived to 1,251 m. Deep dive duration was correlated significantly to maximum depth (i.e. duration increased with increased depth) for Blainville’s whales, whereas no correlation was observed for Cuvier’s. Descents were always faster than ascents, with each species descending at a specified constant speed, regardless of final depth, and at a very steep angle, 60°–83°. In contrast, ascents occurred in shallow angles, and speed changed during each ascent, possibly to aid stabilisation. Foraging dives could be distinguished by presence of long sequences of echolocation clicks whilst, non-foraging dives were relatively silent, with only a few isolated noises. The author’s results showed that foraging dives were far deeper (always in excess of 500 m) than non-foraging dives.
In a similar study in Hawai’i, Baird et al. (2006) recorded maximum dive depths of 1,450 m for Cuvier’s and 1,408 m for Blainville’s beaked whales. Akin to Tyack et al. (2006), Baird et al. (2006) found similar results for ascent rates and shallow dive patterns. The study also found that Blainville’s beaked whales spent more time in the upper portion of the water column compared to Cuvier’s. Since Cuvier’s beaked whales also performed dives close to maximum depth more frequently, it has been discovered recently that Cuvier’s beaked whale is the deepest diving marine mammal in the world, reaching a depth of 2,995 m with a duration of 2 hours and 43 minutes, in this case probably as a result to stress (Falcone et al. 2017).
Baird et al. (2008) investigated diel variation in diving behaviour of Blainville’s and Cuvier’s beaked whales using time-depth recorders. Similar patterns were observed to the Tyack et al. (2006) study, in terms of maximum depth, ascent and descent rates. For both Blainville’s and Cuvier’s beaked whales, deep foraging dives occurred as often during the day as at night. There were also no significant diel differences for ascent or descent rates, mean or maximum depths, or durations of dives for Blainville’s beaked whales. Similar trends were evident in Cuvier’s, but unfortunately sample size prevented statistical analysis; however, mid-water dives of Cuvier’s to depths of 100–600 m occurred 4.5 times more frequently during the day than at night. They were also observed to spend more time in shallow water at night, probably as a result to a reduced predation pressure at night from near-surface, visual predators, such as large sharks. Being able to stay near the surface is advantageous, as it allows them to rest and recover between deep, foraging dives, spending less energy compared to ‘hiding’ at mid-water depths. Baird et al. (2006) also observed Blainville’s beaked whales spending greater amount of time near the surface during the night; however, limited data prevented a comparison to Cuvier’s beaked whales.
Contrary to Cuvier’s and Blainville’s beaked whales, descent and ascent rates for Northern bottlenose whales (Hyperoodon ampullatus) varied with depth during deep dives (Hooker & Baird 1999), with longer dives having significantly faster descent than ascent rates. For this study, five time-depth recorders were tagged on northern bottlenose whales off the coast of Nova Scotia, showing that this species dives regularly deeper than 800 m, with a maximum depth of 1,453 m, often close to the sea floor, suggesting benthic foraging. The study also included active fish finding sonar system to track non-tagged whales to calculate diving descent rates. Descent rates were similar to those recorded from tagged whales undertaking deep dives. The sonar system had a limited range of 600 m, but none of the sonar traces appeared to level out, suggesting the whales were still diving when the traces were lost, again, demonstrating their elusive nature.
Like marine mammals, the military use Sonar to locate submarines and vessels. Military sound pulses have been shown to affect sensitive echolocation organs in cetaceans, in particular, beaked whales. For information on beaked whales and effects of military sonar, please click here. Sonar systems are being used currently to quantify anthropogenic impacts on beaked whales (Hooker et al. 2019; Wensveen Paul et al. 2019).