|Scientific Name:||Mesoplodon densirostris|
|Species Authority:||(Blainville, 1817)|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L.|
|Reviewer/s:||Hammond, P.S. & Perrin, W.F. (Cetacean Red List Authority)|
There is limited information on global abundance and none on trends in abundance for this species. It is not believed to be uncommon but it is potentially vulnerable to low-level threats and a 30% global reduction over three generations cannot be ruled out (criterion A).
|Range Description:||Blainville's beaked whales (also referred to as densebeaked whales) occur in temperate and tropical waters of all oceans (Mead 1989). This species has the most extensive distribution of any species of the genus Mesoplodon, and is also the most tropical of the genus (Pitman 2002; MacLeod et al. 2006). Sightings are common around some oceanic archipelagos, like the Hawaiian (USA) and Society Islands (French Polynesia). They occur in many enclosed seas with deep water, such as the Gulf of Mexico, Caribbean Sea, and the Sea of Japan. However, there are only rare records of this species occurring in the Mediterranean, and therefore the species is considered to be a vagrant there.|
Native:Angola (Angola); Australia (New South Wales, Northern Territory, Queensland, South Australia, Tasmania, Western Australia); Bahamas; Belize; Brazil; Cameroon; Canada (Nova Scotia); Cape Verde; Cayman Islands; Chile; China; Cocos (Keeling) Islands; Colombia; Comoros; Costa Rica; Ecuador; Fiji; Guam; Guatemala; Guyana; Honduras; India; Indonesia; Japan; Kenya; Kiribati; Madagascar; Malaysia; Marshall Islands; Mauritania; Mauritius; Mayotte; Micronesia, Federated States of; Morocco; Mozambique; Myanmar; Namibia; Nauru; New Caledonia; New Zealand (Chatham Is., North Is.); Nicaragua; Nigeria; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Portugal (Azores, Portugal (mainland)); Réunion; Saint Helena, Ascension and Tristan da Cunha (Ascension); Sao Tomé and Principe; Seychelles; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Taiwan, Province of China; Tanzania, United Republic of; Tokelau; Tonga; United Kingdom; United States; United States Minor Outlying Islands (Midway Is.); Uruguay; Vanuatu; Venezuela; Viet Nam; Wallis and Futuna; Western Sahara; Yemen
|FAO Marine Fishing Areas:||
Atlantic – northeast; Atlantic – eastern central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Mediterranean and Black Sea; Pacific – western central; Pacific – eastern central; Pacific – northwest; Pacific – southwest; Pacific – southeast
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Overall, the species appears to be fairly common in most tropical seas, and it is one of the most common of all the species of Mesoplodon (Reeves et al. 2003). Estimates of abundance are generally not available for most areas, but there are estimated to be 2,138 (CV=77%) in Hawaiian waters (Barlow 2003). In the northern Gulf of Mexico, an estimated 106 (CV=41%) mesoplodonts occur, and these are considered to be either M. densirostris or M. europaeus (Mullin and Fulling 2004). Ferguson and Barlow (1999) estimate a total abundance of 32,678 beaked whales in the genus Mesoplodon in the eastern Pacific (corrected for missed animals). The majority of these are M. peruvianus and M. densirostris (Pitman and Lynn 2001).|
|Habitat and Ecology:||
Like other beaked whales, these whales are found mostly offshore in deep waters, but they may sometimes occur reasonably close to shore (MacLeod and Zuur 2005). A detailed analysis of habitat preferences in the Bahamas, where this species is commonly encountered, indicated that Blainville’s beaked whales were found preferentially in waters of intermediate depth gradients and depths between 200 and 1,000 m (continental slope waters). These may be areas of increased prey availability caused by interactions of currents and local topography (MacLeod and Zuur 2005). Observations around Hawaii seem to indicate that animals prefer water depths of 700-1,000 m (Baird et al. 2006). Ritter and Brederlau (1999) sighted Mesoplodon densirostris 24 times between September 1995 and August 1997 off La Gomera, Canary Islands. Of the seven sightings for which such information was recorded, mean depth was 320 m (SD = 270 m), and mean distance from shore was 4.39 km (SD = 1.85 km).
Squid are apparently the main food items, but some deepwater fish may be taken as well. Like most other ziphiids, they are thought to be suction feeders (Heyning and Mead 1996).
Some Blainville's beaked whales have been taken incidentally by Japanese tuna boats off the Seychelles and Western Australia, as well as directly by small cetacean hunters in various areas. Dolar (1994) investigated directed fisheries for marine mammals in central and southern Visayas, northern Mindanao and Palawan, Philippines from archived reports and visits to sites where such fisheries are conducted. Hunters at Pamilacan Island take some small whales, including Mesoplodon densirostris. Dolphins and whales are taken by hand harpoons or, increasingly, by togglehead harpoon shafts shot from modified, rubber-powered spear guns. Jefferson et al. (1993) reported that some specimens have been incidentally taken in the North Pacific by Taiwanese fishermen, and accidentally by Japanese tuna fishermen in the Indian Ocean.
In 1993, an adult Blainville's beaked whale was found washed ashore in southern Brazil (Secchi and Zarzur 1999). Stomach analysis revealed the presence of a bluish bundle of plastic threads occupying a large part of the main stomach chamber. Both stomach and intestines were completely free of parasites, as well as food remains and faeces, indicating that the whale had not fed for some time. The ingested plastic may have resulted in a false sensation of satiation for the animal, which could have reduced the whale's appetite and meal size and, in turn, led to the death of the whale. This form of pollution may be increasing and could be a threat to the species.
In recent years, there has been increasing concern that loud underwater sounds, such as active sonar and seismic operations, may be harmful to beaked whales (Malakoff 2002). The use of active sonar from military vessels has been implicated in mass strandings of Blainville’s beaked whales (Balcomb and Claridge 2001, Jepson et al. 2003; Wang and Yang 2006; Yang et al. 2008). A stranding of two Cuvier’s beaked whales in the Gulf of California was also closely correlated with a seismic survey (Malakoff 2002). The mechanistic cause of the strandings is not well understood, but gas bubble formation (Fernandez et al. 2005) from a behaviourally mediated response to sound has been proposed (Cox et al. 2006).
Predicted impacts of global climate change on the marine environment may affect this species of whale, although the nature of impacts is unclear (Learmonth et al. 2006).
The species is listed in Appendix II of CITES.
The species is poorly known with respect to abundance, migratory patterns, bycatch and direct catch rates. It should be ensured that artisanal whale fisheries operate within sustainable limits and do not export products illegally.
|Citation:||Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. 2008. Mesoplodon densirostris. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 19 May 2013.|
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