Mesoplodon bidens, Sowerby, 1804

Russell A. Mittermeier & Don E. Wilson, 2014, Ziphiidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 326-357 : 356

18.

Sowerby’s Beaked Whale

Mesoplodon bidens

French: Baleine-a-bec de Sowerby / German: Sowerby-Zweizahnwal / Spanish: Zifio de Sowerby

Other common names: North Atlantic Beaked Whale, North Sea Beaked Whale

Taxonomy. Physeter bidens Sowerby, 1804 ,

UK, Scotland, “stranded on the estate of James Brodie, Esq. F. LL. S., in the county of Elgin.”

This species is monotypic.

Distribution. Restricted to the cooler waters of the N Atlantic Ocean from 71° 30" N in the Norwegian Sea, Iceland, and [Labrador (Canada) in the N, to Madeira, Azores, and NE USA to the S; single records from the Gulf of Mexico and E Mediterranean Sea are thought to represent vagrant individuals. In general, this species appears to be more widespread in E Atlantic Ocean than in W Atlantic Ocean, which may be related to preferences for cooler water temperatures.

Descriptive notes. Total length 450-550 cm; weight 1000-1500 kg. Body of Sowerby’s Beaked Whale is spindle-shaped, with greatest girth around its midpoint. Flukes are wide in relation to body length, and tailstock is compressed laterally. Dorsalfin is small and set approximately two-thirds the distance between tip of the beak and end of the tail. Coloration is typically dark brown, dark gray, or black on top and paler underneath. Rostrum and lowerjaw form a long, well-defined beak, and there are two grooves on the throat. Adult males have two triangular tusks midway along the lower jaw that stick up alongside the upperjaw. Tusks can become heavily worn in older males, and they do not erupted in juveniles and adult females. Adult males may also have many long pale scars that are caused by the tusks of other males during male-male combat.

Habitat. Generally restricted to water depths greater than 200 m. Most sightings of Sowerby’s Beaked Whales are associated with areas of complex seabed topography, such as shelf edges, canyons, seamounts, and oceanic islands, but they may also occur in other oceanic habitats. Distribution of Sowerby’s Beaked Whaleis restricted to cooler waters, and most records come from waters cooler than 15°C.

Food and Feeding. Sowerby’s Beaked Whale is one of the few species of beaked whales that seems to primarily consume deep-water fish rather than deep-water squid. It is known to take a wide range of bentho-pelagic fish, including deep-water gadoids. Almost all of its prey is 1-6% of an individual’s total body length, with a clear mode at 2-3%. In common with other species of beaked whales, feeding likely occursat great depth, often over 500 m and possibly as deep as 3000 m or more. Foraging dives may be up to an hourin length.

Breeding. Little is known about breeding in Sowerby’s Beaked Whale. Although unconfirmed,it is thought that reproduction is seasonal, with offspring born in spring or summer, and that gestation is twelve months.

Activity patterns. There is no information available for this species.

Movements, Home range and Social organization. There is no specific information available for this species, but as with other species of Mesoplodon , Sowerby’s Beaked Whale is seen in small groups, typically of five individuals or less, and groups larger than ten individuals are rarely encountered. Small groups tend to consist of females and immature individuals with one adult male. Larger groups may contain more than one adult male.

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The [UCN Red List. There are no estimates of global population size of Sowerby’s Beaked Whale. It is one of the most commonly encountered species of Mesoplodon within much ofits distribution. As with other species of beaked whales, Sowerby’s Beaked Whale may be at risk from climate change, noise pollution, bycatch by driftnetfisheries, and ingestion ofplastic debris. Nevertheless, nothing is known about the form or extent of these potential impacts.

Bibliography. Hooker & Baird (1999b), Macleod (2006), MacLeod & DAmico (2006), MacLeod, Perrin et al. (2006), MacLeod, Santos & Pierce (2003), Mead (1989b).

Figures

On following pages: 18. Sowery's Beaked Whale (Mesoplodon bidens); 19. Blainville’s Beaked Whale (Mesoplodon densirostris); 20. Andrews's Beaked Whale (Mesoplodon bowdoini); 21. Spade-toothed Whale (Mesoplodon traversil); 22. Gervais's Beaked Whale (Mesoplodon europaeus).

Distribution. Restricted to the cooler waters of the N Atlantic Ocean from 71° 30" N in the Norwegian Sea, Iceland, and [Labrador (Canada) in the N, to Madeira, Azores, and NE USA to the S; single records from the Gulf of Mexico and E Mediterranean Sea are thought to represent vagrant individuals. In general, this species appears to be more widespread in E Atlantic Ocean than in W Atlantic Ocean, which may be related to preferences for cooler water temperatures.