Mesoplodon densirostris (de Blainville, 1817)

English: Blainville's beaked whale
German: Blainville-Zweizahnwal
Spanish: Zifio de Blainville
French: Mésoplodon de Blainville

Family Ziphiidae

Mesoplodon densirostris © Wurtz-Artescienza (see links).

1. Description

The main colour pattern of this species is rather inconspicuous, dark above, light below. There is an eye patch which is also dark, with females alone developing both white upper and lower jaws. The lower jaw is highly arched in the same fashion?? as the Right Whales', with a prominent tooth erupting at the peak of this arch in males, making it very distinctive among mesoplodonts. The dark areas of larger animals tend to have round or oval white scars and widely separated, paired scratches, presumably in males. There often is an orangish sheen (presumably due to diatoms) covering the head. Maximum recorded length has been 4.7 m and body mass reaches up to 1,000 kg (Jefferson et al. 2008; Wang et al. 2006). Females seem to reach sexual maturity at about 9 years age (Pitman, 2009).

2. Distribution

In tropical oceans, M. densirostris is one of the more widespread and common beaked whales (Pitman, 2002). Blainville's beaked whale ranges north to Nova Scotia, Wales, Portugal, the western Mediterranean, Japan, Midway Islands, and central California; and south to Rio Grande do Sul in Brazil, South Africa, Tasmania, and central Chile (Rice, 1998). Baker and van Helden (1999) also indicate its presence in New Zealand waters. McAlpine and Rae (1999) report on a stranding in New Brunswick, Canada. Aguayo et al. (1998) report on sightings between Valparaiso and Easter Island in the south-eastern Pacific Ocean.

Distribution of Mesoplodon densirostris (Taylor et al. 2008; © IUCN; enlarge map). It is found in
all tropical and warm temperate oceans and is probably the most widespread and perhaps
most abundant mesoplodont (Pitman, 2009).

3. Population size

M. densirostris appears to be widespread and fairly common in tropical oceans, and Pitman (2009) suggests it may be one of the most common of all the species of Mesoplodon. Estimates of abundance are generally not available for most areas, but there are estimated to be 2,138 in Hawaiian waters. In the northern Gulf of Mexico, an estimated 106 mesoplodonts occur, and these are considered to be either M. densirostris or M. europaeus.

In the eastern Pacific the total abundance is estimated around 30,000 beaked whales in the genus Mesoplodon (Taylor et al. 2008 and references therein). Pitman and Lynn (2001) believe that the majority of these are M. peruvianus and M. densirostris.

4. Biology and Behaviour

Habitat: Macleod and Zuur (2005) investigated habitat utilization in Blainville's beaked whale in the northern Bahamas associated with seabed gradient. The whales preferred gradients from 68 to 296 m/km and depths from 136 to 1,319 m. The authors hypothesize that the relationships between habitat utilization and these topographic variables relates to interactions between a deepwater current and the seabed topography on preferred prey. Locally, prey animals may be concentrated in areas with a northeast aspect, intermediate gradients and depths between 200 and 1,000 m where the Deep Western Boundary Current is forced towards the surface by the local topography. These are the areas where Blainville's beaked whales preferentially occurred.

According to Casinos and Filella (1995 and references therein) M. densirostris seems to prefer water depths of 700- 1000m. Ritter and Brederlau (1999) sighted M. densirostris off La Gomera, Canary Islands over mean depths of 320 m, with mean distance from shore of 4.4 km.

McSweeny et al. (2007) investigated site fidelity, patterns of association, and movements of Blainville's beaked whales using a 21-yr photographic data set from the west coast of Hawaii. Resightings of individuals spanned 15 yr, suggesting long-term site fidelity to the area. Long-term resightings were documented primarily from adult females. Among adult females, although repeated associations occurred up to 9 yr apart, individuals were seen separately in intervening years. Individuals seen on multiple occasions were typically documented in multiple months-seasons, suggesting they may use the study area throughout the year. Such long-term site fidelity has implications both for potential population structure and for susceptibility of beaked whale populations to anthropogenic impacts.

Behaviour: Baird et al. (2008) investigated diel variation in diving behaviour using time-depth recorders deployed on six Blainville's beaked whales. Deep foraging dives (>800 m) occurred at similar rates during the day and night. Series of progressively shallower 'bounce' dives were documented to follow deep, long dives made during the day; at night whales spent more time in shallow (<100 m) depths. Dives to mid-water depths (100-600 m) occurred significantly more often during the day. This diel variation in behaviour suggests that beaked whales may spend less time in surface waters during the day to avoid near-surface, visually oriented predators such as large sharks or killer whales (Orcinus orca).

Tyack et al. (2006) used sound-and-orientation recording tags (DTAGs) to show that M. densirostris hunt by echolocation in deep water between 222 and 1885 m, attempting to capture about 30 prey/dive. The food source is so deep that the average foraging dives were deeper (835 m) and longer (47 min) than reported for any other air-breathing species. A series of shallower dives, containing no indications of foraging, followed most deep foraging dives. The average interval between deep foraging dives was 92 min. This duration may be required for beaked whales to recover from an oxygen debt accrued in the deep foraging dives, which last about twice the estimated aerobic dive limit.

These results confirm earlier findings by Baird et al. (2006) who investigated beaked
whales in Hawaiian waters using suction-cup-attached time-depth recorders. Blainville's beaked whales were found over median depth of 922 m and regularly dove for 48-68 min to depths greater than 800 m (maximum 1408 m).

Schooling: Group sizes are small and most groups had only a single adult male present. Repeated associations between adult females and adult males were documented for all resightings of adult males over periods from 1 to 154 d. (McSweeny et al. 2007).

Most strandings involved single individuals, although groups between 3 and 7 animals were observed in tropical waters (Jefferson et al. 1993). Ritter and Brederlau (1999) estimated group size to range from 2 to 9 individuals (mean 3.44). Adult males and calves were both observed during many encounters.

Food: Single specimens of Blainville's beaked whale stranded on the Canary Islands had eaten both fish and cephalopod prey. The most numerous prey remains belonged to gadid fish. This is consistent with the limited published data on diet in these species, with Mesoplodon species having a relatively higher proportion of fish in the diet whereas Ziphius specialises on cephalopods (Santos et al. 2007).

5. Migration

Unknown.

6. Threats

Direct catches: According to Houston (1990c), the species is of no commercial interest. However, Dolar et al. (1994) investigated directed fisheries for marine mammals in the Philippines, where small cetaceans, including M. densirostris are taken around Pamilacan Island by hand harpoons or togglehead harpoon shafts shot from modified, rubber-powered spear guns. Around 800 cetaceans are taken annually at seven sites, mostly during the inter-monsoon period of February-May. The meat is consumed or sold in local markets and some skulls are cleaned and sold as curios. Although the Department of Agriculture issued Fisheries Administrative Order No. 185 on 16 December 1992: 'banning the taking or catching, selling, purchasing, possessing, transporting and exporting of dolphins', the order did not stop dolphin and whale hunting but seems to have decreased the sale of dolphin meat openly in the market (Dolar et al. 1994).

Similarly, Baker et al. (2006) report the results of molecular monitoring of 'whalemeat' markets in the Republic of (South) Korea based on nine systematic surveys from February 2003 to February 2005. The only legal source of these products was assumed to be incidental fisheries mortalities ('bycatch') as reported by the government to the IWC . Species identification of 357 products using mitochondrial DNA control region or cytochrome b sequences and the web-based programme "DNA-surveillance" also included Blainville's beaked whales.

Incidental catches: Jefferson et al. (1993) report that some specimens have been taken in the North Pacific by Taiwanese whalers, and accidentally by Japanese tuna fishermen in the Indian ocean. Forney and Kobayashi (2007) report on by-catch of a Blainville beaked whale in the Hawaii-based longline fishery .
Pollution: Concerns regarding the impact of man-made debris in the marine environment are increasing. Pollution in the form of plastic debris has been recognised as a major threat to marine wildlife, in terms of ingestion and entanglement. In 1993, a 419cm adult female Blainville's beaked whale stranded near Sao Jose do Norte, southern Brazil had a 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. Mistaken ingestion of debris due to its resemblance to preferred prey is usually not thought to occur in odontocete cetaceans because of their echolocation capabilities. 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. In turn, this would have compromised the energy consumption and health of the animal and subsequently (at least indirectly), led to the death of the whale (Secchi and Zarzur, 1999).

One individual stranded in the Mediterranean sea was investigated with respect to chlorinated hydrocarbons. Levels found were lower than in other cetacean species (Jefferson et al. 1993).

Naval exercises: At least one animal died in September 2002 during a naval exercise conducted around Gran Canaria, Spain (Vidal Martin, pers. comm.). Another two specimens live stranded during a naval exercise off The Bahamas in March 2000 (Waring et al. 2001). High intensity Low Frequency Active Sonar (LFAS) was used by US and NATO vessels in both these areas, respectively, which led to a multi species mass stranding also including Ziphius cavirostris.

But Moretti et al. (2006) report that passive sonar detection of beaked whales has become increasingly important as part of the Office of Naval Research (ONR) Marine Mammal Monitoring on Navy Range (M3R) program. There is hope that based on these real-time data, trained observers can verify the species on site and in time to avoid further conflicts.

7. Remarks

Confirmed and inferred Range states (Taylor et al. 2008) :
Angola; Australia; Bahamas; Belize; Brazil; Cameroon; Canada; Cape Verde; Cayman Islands; Chile; China; Cocos 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; Nicaragua; Nigeria; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Portugal; Réunion; Saint Helena; Sao Tomé and Principe; Seychelles; Solomon Islands; Somalia; South Africa; Spain; Sri Lanka; Taiwan, Province of China; Tanzania; Tokelau; Tonga; United Kingdom; United States of America; Uruguay; Vanuatu; Venezuela; Viet Nam; Wallis and Futuna; Western Sahara; Yemen.

For recommendations on South American stocks, please see Hucke-Gaete (2000) in Appendix 1 and for south-east Asian stocks Perrin et al. (1996) in Appendix 2.

IUCN status: "Data Deficient". The species is not listed by CMS. Listed in Appendix II of CITES.

8. Sources and further information

see "Genus Mesoplodon - Beaked whales: Introduction and Sources"

© Boris Culik (2010) Odontocetes. The toothed whales: "Mesoplodon densirostris". UNEP/CMS Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza. © Maps by IUCN.