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 as Mesoplodon layardii|
|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].
Australian National Guidelines for Whale and Dolphin Watching (Department of the Environment and Heritage, 2005e) [Information Sheet].
|Non-statutory Listing Status||
|Scientific name||Mesoplodon layardii |
|Other names||Mesoplodon layardi |
This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.
Scientific name: Mesoplodon layardii
Common name: Strap-toothed Beaked Whale
Other names: Layard's Beaked Whale
The Strap-toothed Beaked Whale is a recognised species and no subspecies have been described or recognised (Rice 1998). Analysis of nuclear DNA supports a close relationship with M. carlhubbsi (Hubb's Beaked Whale, which occurs in the north-east Pacific), while in the Southern Hemisphere, Andrew's Beaked Whale (M. bowdonii) is also closely related to these species (Dalebout 2002; Dalebout et al. 2004).
The body shape of the Strap-toothed Beaked Whale is rather indistinctive, having many of the characteristics shared by other Mesoplodonts, such as a prominent slender dolphin-like beak with a straight mouthline and a very slight melon-shaped forehead (Jefferson et al. 1993; Leatherwood & Reeves 1983; Shirihai 2002). The low, falcate (sickle-shaped) dorsal fin, short narrow flippers, and broad un-notched, almost triangular tail flukes are also characteristic for the genus. The distinctive feature for Strap-toothed Beaked Whales is a sexually dimorphic trait where the males' teeth form uniquely shaped long tusks emerging from near the middle of the lower jaw and then curl backward and inward, extending over the upper jaw and often preventing it from opening more than a few centimetres.
The complex colour pattern of Strap-toothed Beaked Whales is better known than for many other Mesoplodonts, due to a large number of specimens (Jefferson et al. 1993). The body is mostly grey or black, sometimes with a purple or brown tinge. Much of the underside is white, particularly the areas around the urogenital opening, between the flippers and up the throat to the lower jaw. The white throat patch extends as a band of variable width around the head to behind the eye and links into a light grey dorsal blaze from the melon to about two-thirds of the way to the dorsal fin. There is often extensive scarring on the body of Strap-toothed Beaked Whales (Shirihai 2002).
Almost nothing is known of the natural history of Strap-toothed Beaked Whales, and this overview is therefore based on limited data from Australian and New Zealand specimens. The length at birth is approximately 2.22.4 m. Male Strap-toothed Beaked Whales reach a maximum length of 6.13 m and females 6.25 m, at about 2 tonnes in weight (Ross 2006), making it one of the largest beaked whales.
From very few sightings of live animals it appears that the Strap-toothed Beaked Whale is often solitary, but may be found in small groups of up to three individuals (Shirihai 2002).
The Strap-toothed Beaked Whale is the most commonly stranded beaked whale in Australia, with 68 events to 1994, occurring on the southern coast of Western Australia (five events), South Australia (27), Victoria (five), Tasmania (13), NSW (14), Queensland (four), as well as on Macquarie Island (two) and Heard Island (one) (Bannister et al. 1996; Dixon 1980; Kemper & Ling 1991; Nicol 1987).
The current extent of occurrence for the Strap-toothed Beaked Whale is estimated to be greater than 20 000 km² (based on the Australian EEZ (200 nm, between approximately 30° S and about 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 the Strap-toothed Beaked Whale cannot be 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.
Strap-toothed Beaked Whales are considered to occur in one location, without any strong distribution fragmentation, in Australian oceanic sub-Antarctic and temperate waters. Deep water is not a barrier to dispersal in this species.
No distribution fragmentation is anticipated for the Strap-toothed Beaked Whale in Australian oceanic sub-Antarctic and temperate waters.
Pitman (2002) suggests that the Strap-toothed Beaked Whale is one of the more widespread and common beaked whales in the Southern Ocean and adjoining waters, occurring between approximately 30° S and the Antarctic Convergence. It has been recorded from Australia, New Zealand, both coasts of South America, the Falklands, Namibia, South Africa, and Kerguelen Island in the Indian Ocean (Rice 1998).
No estimates of population size exist for the Strap-toothed Beaked Whale and there are no records of human exploitation. 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, although, based on stranding data, Strap-toothed Beaked Whale may not be as rare as the sighting records indicate.
It is unlikely that Australian Strap-toothed Beaked Whales are a distinct population, as no subspecies are currently recognized. As the Strap-toothed Beaked Whale is 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, the Strap-toothed Beaked Whale is not well surveyed. Their distribution is primarily assumed from incidental sightings, plus beach-cast (stranded) animals, for all areas.
There are no available estimates of the population size of Australian Strap-toothed Beaked Whales, however they are not considered abundant as sightings and strandings are rare.
Strap-toothed Beaked Whales are thought to occur in areas south of 38° S throughout the year. In contrast, their occurrence north of 38° S appears to be seasonal, suggesting that the Strap-toothed Beaked Whale may undergo some limited migration to lower latitudes during local winter (Pitman 2002). Insufficient data exists as to the proportion of the population undergoing this seasonal movement, and whether this would constitute an extreme fluctuation in numbers. In Australia, the majority of strandings occur from January to April, indicating a seasonal influx during mid- to late summer (Bannister et al. 1996) with the frequency of strandings suggesting that the Strap-toothed Beaked Whale may be seasonally common off southern Australia.
All cetaceans are protected within the Australian Whale Sanctuary under the EPBC Act. The Sanctuary includes all Commonwealth waters from the 3 nm State waters limit out to the boundary of the EEZ (200 nm and further in some places). Strap-toothed Beaked Whales are also subject to International Whaling Commission (IWC) regulations and protected within the Indian Ocean Sanctuary and Southern Ocean Sanctuary.
The Strap-toothed Beaked Whale apparently prefers deep oceanic waters of temperate (1020 °C) to subantarctic (18 °C) regions (Pittman 2002; Ross 2006). No information on habitat is available, although these whales are presumed to feed at depth on mid- and deep-water squid (Sekiguchi et al. 1996). Shipboard surveys of beaked whales (Mesoplodon spp. and Ziphius cavirostris) from 19911998 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, suggesting 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).
As for many species of beaked whale, the Strap-toothed Beaked Whale may also be found close to undersea features such as submarine escarpments and sea mounts 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 403750 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).
Although no information is available on whether the Strap-toothed Beaked Whale uses different habitats for different activities, the majority of strandings in Australia occur from January to April, indicating a seasonal influx during mid- to late summer (Bannister et al. 1996). These data suggest that Strap-toothed Beaked Whales may feed seasonally in zones of higher productivity adjacent to the Australian continental slope, as well as using adjacent waters for calving (Bannister et al. 1996; Ross 2006).
Life history data for the Strap-toothed Beaked Whale are extremely limited. Sexual maturity is reached at about 5 m (Ross 2006). Life expectancy is unknown, although the maximum recorded age for 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).
Breeding areas and habitat are unknown, but are presumed to be oceanic. Mating is thought to occur in summer and, after an inferred gestation period of between nine to 12 months, calves are born from summer through autumn (Ross 2006). No calving areas are known for Australian waters (Bannister et al. 1996), although the possible inshore movement of Strap-toothed Beaked Whales in summer and autumn may be associated with breeding.
Due to the substantial scarring in Strap-toothed Beaked Whales it is believed that there is extensive physical competition for partners.
There are no known reproductive behaviours that may make the Strap-toothed 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 food habits of Strap-toothed Beaked Whales were examined in detail by Sekiguchi and colleagues (1996) from stomach contents of 14 stranded whales found on South African and New Zealand coasts. Although a few unidentified fish otoliths and crustacean remains were found in two of these stomachs, 24 species of oceanic squids (some of which occur at a great depth) accounted for 94.8% of counted prey items. Histioteuthis sp. and Taonius pavo were the predominant prey species for Strap-toothed Beaked Whales. The presence of these sub-Antarctic squid species suggests a northward migration to South African waters in late summer/autumn. A similar movement has been suggested for Strap-toothed Beaked Whales off Australia (Bannister et al. 1996).
Sekiguchi and colleagues (1996) also compared prey sizes between males with fully grown strap-teeth and females/immature males without erupted teeth. Although Strap-toothed Beaked Whale females and immature males ate longer squids than mature males, there was no significant difference in estimated squid weights eaten by both groups. The presence of fully-erupted teeth in adult male Strap-toothed Beaked Whales, therefore, does not seem to influence the size of prey ingested, even though an adult male could only open its jaws about half as wide as a female.
Strap-toothed Beaked Whales are active predators and presumed to be strong swimmers capable of deep dives in pursuit of prey, but the mode of capture is not known. It is thought that prey are seized and disabled between the hard edges of the mandibles and the rostral palate (Ross 2006). 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.
Most records of Strap-toothed Beaked Whale in Australian waters are in summer and autumn, possibly related to a movement onto the continental shelf edge to feed, and/or to mate and calve in the warmer coastal waters (Bannister et al. 1996).
As one of the largest of the beaked whales, the Strap-toothed Whale is also one of the few Mesoplodon species that can be readily identified at sea. The melon-shaped small head, grey pigmentation band coming up behind the head and joining with a light grey dorsal blaze are distinctive, but the most interesting and diagnostic feature is the strap-shaped pair of teeth that emerge from the lower jaw, well behind the tip of the beak, in males (Leatherwood & Reeves 1983).
Unfortunately, the Strap-toothed Beaked Whale is rarely seen in the wild, although it is known to bask at the surface on calm, sunny days (Culik 2003c). Generally the animals are hard to approach, especially in large vessels, so their positive identification is difficult. Strap-toothed Beaked Whale flukes do not normally show above the surface at the start of a dive. Limited observations suggest that Strap-toothed Whales sink slowly beneath the surface, barely creating a ripple, then rise and blow again 150200 m away. A typical dive time is 10 to 15 minutes (Carwardine 1995).
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 vs ecological studies), the activities of the animals themselves (e.g. travelling, resting, surface vs 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 Strap-toothed 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, plus attempts should be made to obtain basic biological information from dead animals.
Although there has never been a directed fishery, some mesoplodonts are occasionally taken by opportunistic whalers (Pitman 2002). It is not known to what extent, if any, Strap-toothed Beaked Whales were taken. Incidental entanglement in gillnets is more likely to be a potential threat (Reeves et al. 2003). Investigations of incidental captures in the pelagic drift gillnet fishery off the north-east United States coast indicated that 46 fishery related mortalities of mesoplodonts occurred between 1989 and 1998, 24 of which were Sowerby's Beaked Whales (M. bidens), four were True's Beaked Whales (M. mirus) and 17 were unidentified beaked whales (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 Strap-toothed 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. 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 116 kHz (MacLeod & D'Amico 2006).
Although little is known about reproduction in beaked whales, it is likely that Strap-toothed 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 the Strap-toothed Beaked Whale:
- Determine the distribution and monitor abundance of the Strap-toothed 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 the Strap-toothed 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 diet and pollutant levels) from incidentally-caught and stranded Strap-toothed 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), and the preparation of disentanglement workshops.
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 (EA 2001k), and Australian National Guidelines for Whale and Dolphin Watching (DEH 2005c) have been published.
No threats data available.
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Bannister, J.L., C.M. Kemper & R.M. Warneke (1996). The Action Plan for Australian Cetaceans. [Online]. Canberra: Australian Nature Conservation Agency. Available from: http://www.environment.gov.au/resource/action-plan-australian-cetaceans.
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Nicol, D.J. (1987). A Review and Update of the Tasmanian Cetacean Stranding Record to the end of February 1986. University of Tasmania Environmental Studies Working Paper. 21:96 pp.
Peddemors, V.M. & R. Harcourt (2006). Personal Communication. Sydney: Graduate School of the Environment, Macquarie University.
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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.
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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 layardii in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Wed, 24 Sep 2014 04:30:26 +1000.