Beaked Whales Share Oddity, Beaked Whales Have Recently What Appear to Be Similar Foraging Received Substantial Public Attention Niches
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Magazine R1 similar but genetically distinct a largely overlooked zoological Quick guide species of beaked whales share oddity, beaked whales have recently what appear to be similar foraging received substantial public attention niches. Beaked whales routinely after a series of mass-strandings Beaked whales dive deeper than 1km for an hour or caused by mid-frequency naval more, and surface for such a short sonars. Peter T. Madsen1*, Natacha Aguilar time that they are very difficult to de Soto2, Peter L. Tyack3 and Mark sight (Figure 1). This cryptic lifestyle Why do beaked whales dive so Johnson3 has, until recently, left us with very deep? The need to understand why little information about some of the beaked whales may respond so What is a beaked whale? The world’s biggest predators beyond strongly to navy sonar has prompted beaked whales (Ziphiidae) belong what can be gathered from stranded the development of techniques to a little known cetacean family specimens. This second largest to study these elusive predators of more than 22 species that range family of toothed whales is so of the high seas. Deployments of in size from 3 meters and a few little known that two new species, electronic tags have revealed the hundred kilograms to more than Perrin’s beaked whale and the underwater behavior of bottlenose, 10 meters and 12 tonnes. Even pygmy beaked whale, have been Blainville’s and Cuvier’s beaked though beaked whales all belong identified in the last 25 years, and a whales, showing that these species to the suborder ‘toothed whales’, few more beaked whale species may routinely dive to mesopelagic most species, ironically, have few if be awaiting discovery. It is thought- depths, where they hunt for small, any erupted teeth, and those serve provoking that there are possibly deep-water squid and fish. These as tusks in male-male interactions elephant-sized mammalian predators food resources are found so deep rather than for foraging. Despite few still roaming the world’s oceans that that beaked whales often dive to geographical boundaries in their science has not yet even named. more than 1000 meter depths for deep ocean habitat, superficially However, after many years of being around an hour (Figure 1) routinely 0 A B 200 Dive depth Echolocation Buzzes 400 600 ) Depth (m C 800 1000 1200 1400 0306090 120 150180 Time (mins) Current Biology Figure 1. Beaked whales above and below. (A) Dive profile of a Blainville’s beaked whale. Echolocation clicks (yellow line) are only made during the deep foraging dive where red dots mark foraging buzzes. (B) Male Blainville’s beaked whale with barnacles on its large tusks. (C) Male Cuvier’s beaked whale of El Hierro in the Canary Islands. Both photos courtesy of University of La Laguna under permit from the Canarian government. Current Biology Vol 24 No 16 R2 exceeding their calculated aerobic energy returns during intense bouts What is their conservation status? dive limit. They therefore return of foraging with durations that are Although mass-strandings of to the surface with a substantial limited by breath-hold dives. beaked whales provide a dramatic oxygen debt that is paid off in a example of the vulnerability of prolonged surface time that includes Do they have a social life? Little is these species to human activities, a series of shallow non-foraging known about the social structure sonar exposure is not the only, nor dives (Figure 1). Recently, a tagged of beaked whales, but the smaller necessarily the most important Cuvier’s beaked whale was recorded species seem to live in groups of conservation threat to these large diving more than 3000 meters females and young with a single predators. Beaked whales live in during a two-hour dive that is by mature male. The heavily scarred areas that are hard to survey and far the deepest dive recorded for older males may be seen with their diving behavior precludes any air-breathing endotherm. How different groups of females over reliable visual counts, leading the a mammal can hold its breath for time, suggesting that they fight IUCN to list most species as ‘data so long and survive a hydrostatic over access to the females using deficient’. Currently, we know next pressure of >300 kg/cm2 is still very their tusks. Females are often larger to nothing about how beaked whale much a mystery. But a consequence than males, which may relate to the populations are affected by potential of this deep water food source is large birth weight of beaked whale environmental stressors, such as that beaked whales spend <20 % calves enabling them to achieve toxins, shipping noise, or bycatch in of their time foraging, which may deep diving capabilities sooner. fisheries, nor do we know anything explain why they are often found Beaked whale groups remain close about their global population sizes. around islands and in upwelling together but, unlike in other toothed However, their distinctive frequency- areas that provide stable and dense whales, this is not mediated by modulated clicks with potential patches of food resources at depth. social calls at the surface, at least in species-specific differences now the smaller species, which seem to enable acoustic surveys to estimate How do they find and catch food in keep track of one another at depth habitat use and population sizes. the deep sea? The task of locating, by eavesdropping on one another’s The echolocation clicks, vital for approaching and catching small, echolocation clicks. Blainville’s their foraging, may thus also provide agile prey in the cold, dark abyss beaked whales also produce social researchers with a unique window may seem almost impossible to us sounds but these are made at to study and protect some of the humans. Beaked whales and other depths below 200 meters, which largest and most cryptic predators toothed whales have solved that together with long silent ascents alive. problem by emitting ultrasonic clicks from deep dives suggest a strategy and listening for returning echoes of acoustic crypsis perhaps to Where can I learn more? to hunt by echolocation. When the reduce the risk of predation from Aguilar Soto, N., Madsen, P.T., Tyack, P., Arranz, first sound recording tags were killer whales that seldom dive P., Marrero, J., Fais, A., Revelli, E. and deployed on Blainville’s beaked deep. Larger species, such as the Johnson, M.P. (2011). No shallow talk: Cryptic strategy in the vocal communication whales, we were astounded to find bottlenose and Baird’s beaked of Blainville’s beaked whales. Marine that not only could the tags record whales, may have a more relaxed Mammal Science, http://dx.doi.org/10.1111/ j.1748-7692.2011.00495.x the emitted echolocation clicks, but crypsis, forming larger groups Cox, T.M., Ragen, T.J., Read, A.J., Vos, E., also the echoes returning from prey, while making some sounds near the Baird, R.W., Balcomb, K., Barlow, J., allowing us a unique opportunity surface. Caldwell, J., Cranford, T., Crum, L. et al. (2006). Why do beaked whales strand? to tap into the sensory stream Report of workshop to understand the of a predator hunting in the wild. Why do some beaked whales strand impacts of anthropogenic sound. J. Cetacean Res. Manag. 7, 177–187. Because of this, beaked whales when exposed to navy sonars? The Dalebout, M.L, Baker, C.S., Cockcroft ,V.G., are now among the best-studied anti-predation strategies of beaked Mead, J.G., and Yamada, T.K. (2004). A animals that use echolocation to whales may also explain why some comprehensive and validated molecular taxonomy of beaked whales, family hunt, and they have become a very beaked whale species are prone Ziphiidae. Journal of Heredity 96, 459–473. unlikely model for how toothed to strand in conjunction with naval Hooker, S.K., and R.W. Baird. (1999). Deep-diving behaviour of the northern bottlenose whale, whales in general operate their sonar exercises. Recent playback Hyperoodon ampullatus (Cetacea: Ziphiidae). sonars in the wild. Tagged whales studies suggest that the strandings Proceedings of the Royal Society, London B. emit some 3500 echolocation happen as a result of strong 266, 671–676. Madsen, P.T., Aguilar Soto, N., Arranz, P., clicks to detect and approach behavioral responses that appear to and Johnson, M. (2013). Echolocation in about 25 prey per dive (Figure 1A). be elicited by low level sonar pulses Blainville’s beaked whales (Mesoplodon densirostris). J. Comp. Physiol. A 199, When whales catch their prey, they at frequencies around 3–4 kHz. 451–469. accelerate the click rate to a ‘buzz’, Playbacks of killer whale calls in a Tyack, P.L., Johnson, M., Aguilar Soto, N., as is the case for echolocating bats, similar frequency range also evoke Sturlese, A., Madsen, P.T. (2006). Extreme diving of beaked whales, Journal of revealing a remarkable functional strong flight responses, suggesting Experimental Biology 209, 4238–4253. convergence of biosonars in air that the sonar pulses may trigger an and water. Analysis of echo data antipredator avoidance behaviour 1 from two species of beaked whale with potential physiological Zoophysiology, Dept. of Bioscience, Aarhus University, Denmark. 2BIOECOMAC, shows that they ensonify many more consequences that may include La Laguna University, Tenerife, Spain. organisms than they try to capture, decompression sickness from 3SMRU, University of St. Andrews, indicating careful prey selection repeated dives to escape the Scotland. via echo information to optimize perceived threat. *E-mail: [email protected].