Species Profile and Threats Database

For information to assist proponents in referral, environmental assessments and compliance issues, refer to the Policy Statements and Guidelines (where available), the Conservation Advice (where available) or the Listing Advice (where available).
In addition, proponents and land managers should refer to the Recovery Plan (where available) or the Conservation Advice (where available) for recovery, mitigation and conservation information.

EPBC Act Listing Status Cetacean
Adopted/Made Recovery Plans
Policy Statements and Guidelines Industry Guidelines on the Interaction between offshore seismic exploration and whales (Department of the Environment and Water Resources (DEW), 2007h) [Admin Guideline].
Information Sheets Australian National Guidelines for Whale and Dolphin Watching (Department of the Environment and Heritage, 2005e) [Information Sheet].
Non-statutory Listing Status
IUCN: Listed as Data Deficient (Global Status: IUCN Red List of Threatened Species: 2013.1 list)
Scientific name Mesoplodon mirus [54]
Family Ziphiidae:Cetacea:Mammalia:Chordata:Animalia
Species author True,1913
Infraspecies author  
Distribution map Species Distribution Map

This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.

Illustrations Google Images

Scientific name: Mesoplodon mirus

Common name: True's Beaked Whale

True's Beaked Whale was discovered and described by the American biologist Frederick True in 1913. The specific name, mirus, is the Latin word for 'wonderful' and reflects his excitement at the discovery (Leatherwood & Reeves 1983; Martin 1990). No subspecies are recognised (Rice 1998), although slight cranial differences are present between northern and southern populations of this well-defined taxon (Ross 1984). Based on analysis of nuclear DNA, True's Beaked Whale appears to be most closely related to Gervais' Beaked Whale, M. europaeus, and to the Ginko-toothed Beaked Whale, M. ginkgodens (Dalebout 2002).

True's Beaked Whale is a medium sized beaked whale, and is not known to differ substantially from other mesoplodonts, although they do have a slightly bulging forehead and prominent beak (Jefferson et al. 1993). The lower jaw and the cheeks are pale grey to whitish in colour in the Southern Hemisphere (Ross 1984; Shirihai 2002), with black 'lips' (Tove 1995). True's Beaked Whale is medium grey to brownish grey above, and pale grey beneath (Tove 1995). In Northern Hemishere animals, Tove (1995) described a distinctive dark blaze along the upper back from posterior to (behind) the melon to well behind the dorsal fin, with an even darker grey dorsal fin. In contrast, based on a live-stranded specimen from the Eastern Cape Province, South Africa, Ross (1984) described the rear third of the body as being white, including the dorsal fin through to the tail stock, the uro-genital area and the underside of the flukes. The upper surface of the tail flukes is dark grey in colour. There is a clear, almost oval, darker pigmentation around the eye (Ross 1984; Tove 1995).

True's Beaked Whale is also characterized by the position of the mandibular teeth at the very tip of the lower jaw (Leatherwood & Reeves 1983). The teeth are oval in cross section, lean slightly forward, and are visible outside the closed mouth of adult males (Jefferson et al. 1993).

The dorsal fin is small and triangular, slightly falcate (sickle-shaped) in shape and is placed at two thirds of the body length (measuring from the tip of the beak) (Ross 1984). The short flippers have a rounded apex (Ross 1984), are dark in colour, and fit into the characteristic mesoplodont flipper depression on the side of the body (Pitman 2002). The tail flukes have no caudal notch and a concave trailing edge (Shiriahi 2002).

The largest recorded length for True's Beaked Whale is 5.34 m in males, and 5.18 m in females (Ross 2006). Physical maturity is reached at about 4.8 m in length. The maximum recorded weight of is 1.4 tonnes, for a 5.1 m South African adult female (Ross 1984).

Almost nothing is known about the social behaviour of True's Beaked Whale, but it is assumed to follow most mesoplodont characteristics of living primarily on their own, but occasionally seen in small groups of up to about six individuals (Shirihai 2002).

Only a few True's Beaked Whales have been recorded in Australia, including two strandings from Western Australia, one from Victoria and one from Tasmania, in the period up to 1994 (Ross 2006). No key localities are known for True's Beaked Whale in Australian waters (Bannister et al. 1996).

The paucity of sightings for True's Beaked Whales precludes calculation of the current extent of occurrence. However, it is presumed to be greater than 20 000 km² (based on the Australian Economic Exclusion Zone (EEZ) (200 nm, between approximately 30° S and 50° S, and deeper than 200 m) (Peddemors & Harcourt 2006, pers. comm.). Increasing ocean temperatures predicted by climate change scenarios could potentially decrease the extent of occurrence, with warmer water extending southwards beyond 30° S.

The area of occupancy of True's Beaked Whales cannot be accurately calculated due to the paucity of records for Australia. However, it is likely to be greater than 2000 km² (Peddemors & Harcourt 2006, pers. comm.). Future expansion of high-seas pelagic gillnet fisheries may result in increased incidental catches, potentially depleting local waters and leading to a decrease in area of occupancy.

True's Beaked Whales are considered to occur in one location as deep water is not a barrier to movement in this species, and there are no known unsurpassable pelagic boundaries. Thus, distribution fragmentation is not anticipated for True's Beaked Whales in Australian oceanic sub-Antarctic and temperate waters.

No distribution fragmentation is anticipated for True's Beaked Whales in Australian oceanic sub-Antarctic and temperate waters.

The distribution of True's Beaked Whale in the Northern Hemisphere appears limited to the North Atlantic, northwards from approximately 30°–50° N. It occurs from Florida, San Salvadore Island in the Bahamas, and Ilas Canarias north to Nova Scotia and Ireland (an incorrectly reported record from the Outer Hebrides is now known to represent Cuvier's Beaked Whale, Ziphius cavirostris, (Herman 1992; Rice 1998). In the Southern Hemisphere, True's Beaked Whales are known from the Cape Province, South Africa, and Australia (Rice 1998; Ross 2006).

No estimates of population size exist for True's Beaked Whale and no records of human exploitation exist. According to Pitman (2002) so few mesoplodonts have been reliably identified at sea that it is impossible to accurately determine the population status of any species. Based on stranding and sighting data, True's Beaked Whale may be rare (Pitman 2002).

As there are no estimates of True's Beaked Whale population size, either globally or for Australia, the proportion of the global population in Australian waters remains unknown. It is unlikely that Australian True's Beaked Whales are a distinct population, as no subspecies are currently recognized (Dalebout et al. 2004; Rice 1998). As True's Beaked Whale is presumed to be a deep water species primarily living off the continental shelf, incidental bycatch of animals in neighbouring countries and/or international waters may affect the Australian population.

World-wide, True's Beaked Whale is not well surveyed. Their distribution is primarily assumed from beach-cast animals, for all areas.

Although no population size estimates are available for True's Beaked Whale, they are not considered abundant as sightings and strandings are rare.

All cetaceans are protected within The Australian Whale Sanctuary under the EPBC Act. The Sanctuary includes all Commonwealth waters from the three nautical mile (nm) State waters limit out to the boundary of the Exclusive Economic Zone (i.e. out to 200 nm and further in some places). True's Beaked Whales are also subject to International Whaling Commission (IWC) regulations and protected within the Indian Ocean Sanctuary and Southern Ocean Sanctuary.

True's Beaked Whales are thought to prefer deep oceanic waters of cool temperate (10–20 °C) regions (Pittman 2002; Ross 2006), rarely venturing into continental seas. No information on habitat is available, but the only confirmed sighting of live True's Beaked Whales occurred with the whales travelling parallel to a steep drop-off between 600 and 1000 fathoms (1097–1828 m) (Tove 1995).

Shipboard surveys of beaked whales (Mesoplodon spp. and Ziphius cavirostris) from 1991–1998 along the shelf edge and Gulf Stream waters off the northeast United States showed that these species frequent shelf-edge habitats (Waring et al. 2001). Beaked whales were present mostly along the colder shelf edge and associated significantly with canyon habitats (Waring et al. 2001). However, a more recent survey of the same area found that this previous proposed definition of beaked whale habitat may be too narrow, as suggested that beaked whales may be found from the continental slope to the abyssal plain, in waters ranging from well-mixed to highly stratified (Ferguson et al. 2006). It is likely that such habitats are utilised by beaked whales along much of Australia's extensive coastline (Ross 2006).

Beaked whales exhibit a propensity to be closely associated with colder shelf edge waters and canyon habitats (Waring et al. 2001). As for many species of beaked whale, True's Beaked Whale are also found close to undersea features such as submarine escarpments & sea mounts (Tove 1995), where prey are believed to aggregate (Balcomb 1989). In the eastern tropical Pacific, beaked whales were sighted an average of 1000 km offshore, with a range of approximately 40–3750 km. The mean water depth of Mesoplodon beaked whale sightings in this region was just over 3.5 km, with a maximum depth of approximately 5.75 km (Ferguson et al. 2006).

Almost nothing is known regarding reproduction in True's Beaked Whales. Longevity data for mesoplodonts are virtually non-existent, although they may be quite long lived (Pitman 2002). The maximum recorded age for the related Baird's Beaked Whale (Berardius bairdii) is 84 years, and for all other beaked whales recorded age is between 27 and 39 (Mead 1984, cited in MacLeod & D'Amico 2006). Natural causes of mortality are poorly understood, but are thought to include predation, disease and effects associated with 'old age' (MacLeod & D'Amico 2006).

The length at birth of True's Beaked Whale calves is about 2.2 m, with weaning occurring at about one year and a length of approximately 3.5 m (Ross 2006). Calves are born in the summer (Bannister et al. 1996), but calving areas are unknown (Bannister et al. 1996; Ross 2006).

There are no known reproductive behaviours that may make True's Beaked Whale particularly vulnerable to a specific threatening process. However, a suspected calving interval of at least three to four years leads to a slow reproductive capacity.

The diet of True's Beaked Whale is presumed to be mainly mid- and deep-water squid and some fish (Ross 2006), although Ross (1984) did report the occurrence of some common inshore squid (Loligo reynaudi) in the stomach of a stranded adult female from South Africa.

True's Beaked Whale is presumed to actively pursue prey, but the mode of capture is not known. It is possibly capable of deep dives. Only adult males have functional teeth, consisting of one pair at the tip of the lower jaw, but these appear to be used more as weapons during agonistic encounters than in capturing prey (Ross 2006). Lacking functional gripping teeth, prey may be seized and disabled using the hard edges of the mandibles and the rostral palate (Bannister et al. 1996). The pair of V-shaped throat grooves typical of this Family may enable distension of the throat, creating a sucking pressure and allowing larger prey to be swallowed whole (Bannister et al. 1996).

In the Southern Hemisphere, the tooth positioning at the tip of the lower jaw in male True's Beaked Whales allows identification (Jefferson et al. 1993). Following the single live sighting of this species, Tove (1995) suggested that their colouration may also allow discrimination of the species in the North Atlantic.

The presence of a distinct melon, beak and the forehead shape, plus the lack of any jaw arching allows distinction from Blainville's Beaked Whales (M. densirostris), while the prominent dolphin-like beak, rounded melon and lack of lateral flattening of the head allows distinction from Gervais' Beaked Whale (M. europaeus) in the north-west Atlantic.

Notes on the behaviour and detectability of True's Beaked Whales are based on the single observation of a group of three individuals in the north-west Atlantic (Tove 1995). The typical blow-and-roll sequence of True's Beaked Whales takes about 10–12 seconds, the animals rising to the surface at an angle and bringing the rostrum clear of the water. This is followed by the head, rising to above the level of the eye, but rotating forward so that by the time the eye is visible the head is parallel to the water surface. The blow is indistinct, but cumular and roughly equivalent in height to the length of the head. The roll is then followed by a downward thrusting of the head and submergence back to the level of the dorsal fin, which is the last part visible in the respiratory roll sequence. Normally, a single blow is followed by one of two minutes of submerged swimming, but this behaviour changes to two or three blows with three to four minute submergence times when evading vessels (Tove 1995). These observations confirm the typical inconspicuous surface behaviour of mesoplodonts and highlight the difficulty observers experience when trying to sight True's Beaked Whales.

Recommended methods
Cetacean surveys are constrained by several important factors including weather (e.g. sea state and light conditions), area to be covered, aim of the survey (abundance estimate versus ecological studies), the activities of the animals themselves (e.g. travelling, resting, surface versus deep feeding), and the type of craft used for the survey.

Surveys for oceanic cetaceans such as beaked whales have primarily been boat-based transects. There are almost no dedicated cetacean surveys conducted in temperate Australian waters, but surveys conducted en route to the Antarctic have covered substantial portions of potential range of True's Beaked Whales. Unfortunately, much of this range is in areas experiencing few calm days, leading to difficulty in sighting beaked whales. During non-dedicated surveys, a minimum requirement is to record all cetacean sightings encountered with corresponding GPS position, environmental data (sea conditions and habitat) and behavioural observations. From fishing vessels, all incidentally caught animals should be recorded with corresponding GPS position, and basic biological information from dead animals should be obtained (Peddemores 2006, pers. comm.).

Although there has never been a directed fishery targeting True's Beaked Whale, some mesoplodonts are occasionally taken by opportunistic whalers (Pitman 2002). However, it is thought that incidental entanglement in gillnets is more likely to be a potential threat than incidental whaling (Reeves et al. 2003). Four True's Beaked Whales were recorded from a total bycatch of 46 beaked whales in an investigation of incidental captures in the pelagic drift gillnet fishery off the north east United States coast (Waring et al. 2001). This highlights that entanglement in drift nets and other nets set, lost or discarded in international waters should be considered as a current and potentially increasing threat to True's Beaked Whales (Bannister et al. 1996; Reeves et al. 2003; Ross 2006).

Recently, there have been a number of studies investigating the impacts of anthropogenic noise on beaked whales, particularly activities that transmit sounds into the water column. These studies have, in part, been driven by mass strandings of beaked whales coinciding temporally and spatially with naval manoeuvres (MacLeod & D'Amico 2006). For example, necropsies (autopsies) of stranded Blainville and Cuvier's beaked whales following low frequency acoustic sonar tests have revealed tissue trauma associated with an acoustic or impulse injury that caused the animals to strand (Frantzis 1998). It has been noted that beaked whales with group sizes of less than 20 (including the Mesoplodon spp.), and particularly groups composed primarily of immature, juvenile or cow-calf pairs, may be more susceptible to strandings associated with anthropogenic noise, although it is not known why this might be the case. Anthropogenic sounds may disrupt or interfere with the sounds produced by beaked whales, including disruption of navigation, and/or interfere with social communication. While data is limited, where there is data beaked whales appear to use relatively high frequency echolocation (up to 120 kHz or more) and non-echolocation sounds in the region of one to 16 kHz (MacLeod & D'Amico 2006).

Although little is known about reproduction in beaked whales, it is likely that True's Beaked Whales have a low reproductive rate, producing one offspring every three to four years. This means that population recovery is a slow process.

Bannister and colleagues (1996) and Ross (2006) recommended the following actions be taken to better understand the threats to True's Beaked Whale:

  • Determine the distribution and monitor abundance of True's Beaked Whale in Australian waters to assess the possible impact of threats, particularly the effect of direct and indirect fishing activities. This should be done via a sighting program to monitor numbers, particularly in southern waters.
  • Obtain information on True's Beaked Whale diet to determine their trophic level and assess any possible impact of the fishing industry on beaked whale food resources.
  • Obtain basic biological information (including confirmation of colouration variations, diet, pollutant levels and genetic samples) from incidentally-caught and stranded True's Beaked Whale specimens, and ensure specimens are made available to appropriate scientific museums to enable collection of life history data and tissue samples for genetic analysis.

Current projects initiated to address these threats include a requirement to report all incidental catches made within the Australian EEZ (Bannister et al. 1996); conducting disentanglement workshops, and developing suitable action plans for the species.

The Action Plan for Australian Cetaceans (Bannister et al. 1996) and the Review of the Conservation Status of Australia's Smaller Whales and Dolphins (Ross 2006) provide brief biological overviews and management recommendations of this species. In addition, Industry Guidelines on the Interaction between offshore seismic exploration and whales (DEW 2007h), and Australian National Guidelines for Whale and Dolphin Watching (DEH 2005c) have been published.

No threats data available.

Balcomb, K.C. (1989). Baird's Beaked Whale Berardius bairdii Stejnegeri, 1833: Arnoux's Beaked Whale Berardius arnuxii Duvernoy, 1851. In: Ridgway, S.H. & R. Harrison, eds. Handbook of Marine Mammals Vol. 4: River Dolphins and the Larger Toothed Whales. Page(s) 261-288.

Bannister, J.L., C.M. Kemper & R.M. Warneke (1996). The Action Plan for Australian Cetaceans. [Online]. Canberra: Australian Nature Conservation Agency. Available from:

Dalebout, M.L. (2002). Species identity, genetic diversity and molecular systematic relationships among the Ziphiidae (beaked whales). Ph.D. Thesis. University of Auckland, New Zealand.

Dalebout, M.L., C.S. Baker, J.G. Mead, V.G. Cockcroft & T.K. Yamada (2004). A comprehensive and validated molecular taxonomy of beaked whales, Family Ziphiidae. Journal of Heredity. 95(6):459-473.

Department of the Environment and Heritage (2005e). Australian National Guidelines for Whale and Dolphin Watching. [Online]. Available from:

Department of the Environment and Water Resources (DEW) (2007h). Industry Guidelines on the Interaction between offshore seismic exploration and whales. [Online]. Available from:

Ferguson, M.C., J. Barlow, B. Reilly, S.B. & T. Gerrodette (2006). Predicting Cuvier's (Ziphius cavirostris) and Mesoplodon beaked whale population density from habitat characteristics in the Eastern Tropical Pacific Ocean. Journal of Cetacean Research and Management. 7(3):287-299.

Frantzis, A. (1998). Does acoustic testing strand whales?. Nature. 392:29.

Herman, J.S. (1992). Cetacean specimens in the National Museums of Scotland. National Museums of Scotland Information Series. 13:1-68.

Jefferson, T.A., S. Leatherwood & M.A. Webber (1993). FAO species identification guide. Marine Mammals of the World. [Online]. Rome: United Nations Environment Programme, Food and Agricultural Organization. Available from: [Accessed: 15-Aug-2007].

Leatherwood, S. & R.R. Reeves (1983). The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books.

MacLeod, C.D. & A. D'Amico (2006). A review of beaked whale behaviour and ecology in relation to assessing and mitigating impacts of anthropogenic noise. Journal of Cetacean Research and Management. 7(3):211-221.

Martin, A.R. (1990). Whales and Dolphins. London, UK: Salamander Books Ltd.

Mead, J.G. (1989). Beaked Whales of the Genus Mesoplodon. In: Ridgway, S H & R. Harrison, eds. Handbook of Marine Mammals Vol. 4: River Dolphins and the Larger Toothed Whales. Page(s) 349-430. Academic Press, London.

Peddemors, V.M. (2006). Personal Communications. Sydney: Graduate School of the Environment, Macquarie University.

Peddemors, V.M. & R. Harcourt (2006). Personal Communication. Sydney: Graduate School of the Environment, Macquarie University.

Pitman, R.L. (2002). Mesoplodont Whales Mesoplodon spp. In: Perrin, W.F., Wursig, B. & Thewissen, J.G.M., eds. Encyclopedia of Marine Mammals. Page(s) 738-742. London, Academic Press.

Reeves, R.R., B.D. Smith, E.A.Crespo, & G. Notarbartolo di Sciara, eds. (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans. Switzerland and Cambridge: IUCN/SSC Cetacean Specialist Group. IUCN, Gland.

Rice, D.W. (1998). Marine mammals of the world. Systematics and distribution. Special publication number 4. Kansas: Society for Marine Mammalogy.

Ross, G.J.B. (1984). The smaller cetaceans of the south-east coast of southern Africa. Annals of the Cape Provincial Museums (Natural History). 15:173-411.

Ross, G.J.B. (2006). Review of the Conservation Status of Australia's Smaller Whales and Dolphins. Page(s) 124. [Online]. Report to the Australian Department of the Environment and Heritage, Canberra. Available from:

Shirihai, H. (2002). The Complete Guide to Antarctic Wildlife. Princeton & Oxford: Princeton University Press.

Tove, M. (1995). Live sighting of Meosplodon cf. M. mirus, True's beaked whale. Marine Mammal Science. 11 (1):80-85.

Waring, G.T., J.M. Quintal & S.L. Swartz (2001). U.S. Atlantic and Gulf of Mexico marine mammal stock assessments - 2001. NOAA Technical Memorandum. NMFS-NE168.

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This database is designed to provide statutory, biological and ecological information on species and ecological communities, migratory species, marine species, and species and species products subject to international trade and commercial use protected under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). It has been compiled from a range of sources including listing advice, recovery plans, published literature and individual experts. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. Individuals and organisations should consider all the available information, including that available from other sources, in deciding whether there is a need to make a referral or apply for a permit or exemption under the EPBC Act.

Citation: Department of the Environment (2014). Mesoplodon mirus in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: Accessed Tue, 29 Jul 2014 12:49:30 +1000.