Cuvier's Beaked Whale

Threats

The IUSN classifies Cuvier’s beaked whale as of least concern, and, in the worst case scenario, the global reduction in population could be as high as 30% in as little as 3 generations (Taylor et al., 2008). Mass stranding events of Ziphius are worryingly common, in the region of areas where naval mid-frequency sonar exercises have occurred. All of the mass stranding events that coincided within the range and time of mid-frequency sonar exercises consisted wholly or partly of Ziphius (D’Amico et al., 2009). However, it is not fully understood how mid-frequency sonar causes such events.

Dead Cuvier's beaked whale after a mass stranding event.

Dead Cuvier’s beaked whale after a mass stranding event.

Ziphius are highly effected by and extremely sensitive to anthropogenic sound, and even the noise produced by boats can cause them to stop foraging. Mid-frequency active sonar causes Ziphius to swim rapidly away from the source of the sonar (DeRuiter et al., 2013), adding extra energy expenditure, the results of which could be fatal (Fahlman et al., 2014). This panic response could partially explain the mass beaching events recorded. It could result in a faster than normal attempt to rise to the surface, which, because of the huge pressure at the depths that Ziphius are known to dive to, could cause extreme decompression sickness (DeRuiter et al., 2013). Bubbles form when dissolved gasses (primarily nitrogen as it is inert), become less soluble due to a  reduction in pressure (Fahlman et al., 2014). Furthermore, the increased activity of the whales as they move away from the sonar source could lead to high levels of supersaturation of CO2 in the tissues and blood of the whale, increasing the likelihood that bubbles will form (Fahlman et al., 2014). These bubbles are commonly found in the tissues of deep diving marine mammal, and grow by diffusion, resulting in lesions and gas emboli, symptoms often described in the bodies of stranded Ziphius (Fernández et al., 2005) . It is not however, clear why Cuvier’s beaked whale is the most susceptible to sonar induced stranding events, but it is possibly related to their specific diving strategies (Hooker et al., 2009). It could also be as a result of the numerous shallow dives they carry out in between deep dives, as if the lungs are not fully compressed during a dive it can result in nitrogen supersaturation (Zimmer & Tyack, 2007).

In order to prevent mass standings from occurring, and so conserve the Cuvier’s beaked whale, identification of areas where high numbers of beaked whales are present is important (Ferguson et al., 2005). Cañadas & Vázquez (2014) suggest that we could use the knowledge of these locations to prevent further reduction of populations by establishment of marine protected areas.

PHOTOGRAPH BY TUI DE ROY, MINDEN PICTURES/CORBIS

PHOTOGRAPH BY TUI DE ROY, MINDEN PICTURES/CORBIS

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