Mesoplodon bidens (Sowerby,
English: Sowerby's beaked whale, North Atlantic beaked whale
Spanish: Zifio de Sowerby, ballena picuda de Sowerby
French: Mésoplodon de Sowerby; Baleine à bec de Sowerby
Mesoplodon bidens ©
Wurtz-Artescienza (see links)
Adults are bluish grey or slate coloured, with grey to white flanks
and belly. Young are generally paler and have fewer scars than the
adults. The two flattened, triangular tusks of adult males erupt
from the lower jaw, at about 37% of mandible length from the tip
of the rostrum (Macleod and Herman, 2004; Jefferson et al. 2008).
The largest specimen was 5.5 m long (Reidenberg and Laitman, 2009).
M. bidens has one of the most northerly distributions of
all the beaked whales, which should help with identification. However,
parts of its range overlap with other Mesoplodon species,
especially Gervais' beaked whale, Blainville's beaked whale, and
True's beaked whale, and it is likely to be difficult to distinguish
it from these with any certainty at sea (Carwardine, 1995), however
documented sightings are reported (Hooker and Baird, 1999).
Sowerby's beaked whale occurs in the temperate North Atlantic,
the distribution range being delimited clockwise from Massachusetts
to the Labrador Sea, Iceland, northern Norway south to the Azores,
Madeira and the Canary Islands (Jefferson et al. 2008). There are
no records off the NW African continent (K. van Waeebeek, pers.
Distribution of Mesoplodon bidens (Taylor
et al. 2008; © IUCN; enlarge
map): temperate and
subarctic waters in the eastern and western North Atlantic (Pitman,
According to C.D. MacLeod (pers. comm.) Sowerby's beaked whale
is known mainly from approx. 150 strandings, an exceptionally high
number for the genus. In the western North Atlantic, 11 strandings
were reported (Lien and Barry, 1990). Most records stem from the
eastern North Atlantic, especially around Britain. However, Carlstroem
et al. (1997) observed two Sowerby's beaked whales at 71° 30'N,
04°00'E in the Norwegian Sea. Kinze et al. (1998) reported a
stranding from the Danish North Sea coast and Smeenk (1995) found
a stranded specimen on the Dutch coast.
Sowerby's beaked whale is unlikely to live in the Baltic Sea, where
the water is too shallow (Carwardine, 1995). There is one stranding
report from Italy (Carwardine, 1995), but the species is only vagrant
in the Mediterranean (Jefferson et al. 2008). Stray specimens have
also been recorded from Florida (C.D. MacLeod, pers. comm.). Although
there are more recorded strandings of this whale on British and
European coasts, its range appears to be generally offshore throughout
the cooler parts of the North Atlantic.
M. bidens is the most northerly recorded mesoplodont species in
the North Atlantic, followed by M.
mirus. The distribution of Mesoplodon species may relate
to variations in water temperature (MacLeod, 2000).
3. Population size
4. Biology and Behaviour
Habitat: Although it is one of the most commonly stranded
Mesoplodon species, there have been few sightings at sea,
and it is poorly known. De Buffrénil (1995b and references
therein) mentions that two sightings north of Scotland and west
of the Orkney Islands were in waters several hundreds of meters
deep. Hooker and Baird (1999) observed groups of Sowerby's beaked
whales in the Gully, a submarine canyon off eastern Canada, on four
occasions ,in water depths of between 550 and 1500 m.
Behaviour: Hooker and Baird (1999) observed Sowerby's beaked
whales to dive for between 12 and 28 minutes. Blows were either
invisible or relatively inconspicuous. During all surfacings the
long beak projected from the water well before the rest of the head
or back was visible. While surfacing behaviour was generally unremarkable,
one individual tail-slapped repeatedly.
Schooling: According to De Buffrénil (1995b and references
therein) stranded animals usually occur singly. In those cases where
two animals stranded together, these were mother-calf pairs. However,
at least occasional formation of larger groups is supported by two
strandings of M. bidens in Newfoundland; one in 1986 with
6 individuals and a second stranding in 1987 which involved 3 whales
(Lien et al. 1990). Hooker and Baird (1999) found that group size
in the Gully varied from 3 to 10 individuals. A mixed-composition
group was observed on one occasion, consisting of at least two female-calf
pairs and 2 to 4 adult males (based on the presence of visible teeth
and extensive scarring). Another group consisted of three quite
heavily scarred and therefore presumably male animals.
Food: Stomachs of freshly killed M. bidens primarily
contained bottom-dwelling deep-water (greater than 400m) fish of
between 100 and 200mm length (Gannon et al. 1998). Ostrom et al.
(1993) evaluated the diet of Sowerby's beaked whales based on isotopic
comparisons among north-western Atlantic cetaceans and found that
the species feeds mostly on small, offshore squid.
Little is known about migration; most northerly animals may migrate
with advancing and retreating ice, and some populations may move
towards the coasts during summer. Year-round strandings are recorded,
but most occur from July to September. Animals probably live some
distance offshore (Carwardine, 1995; de Buffrénil, 1995b
and references therein).
According to Mead (1989) there does not seem to be any seasonality
in the European stranding records. The only country for which enough
records exist (n =41) to allow an analysis of seasonality is the
United Kingdom. Strandings have been reported in every month except
February, with a tendency towards a broad peak in the summer (July-September).
According to C.D. MacLeod et al. (pers. comm.) most strandings of
Sowerby's beaked whales on eastern coasts of the UK occurred in
late summer and autumn which may coincide with a southward movement.
Occasionally, individuals were caught incidentally in fishing gear
(De Buffrénil, 1995b), e.g. in Newfoundland small-scale fishery
(Jefferson et al. 1993). A number have been incidentally killed
by whalers off Newfoundland, Iceland and in the Barents Sea (Jefferson
et al. 2008).
Waring et al. (2001) report that for 1989-1998 observed by-catch
rates in pelagic drift gillnets along the US East Coast amount to
24 Sowerby's beaked whales. These were caught exclusively in the
area from Georges Canyon to Hydrographers Canyon along the continental
shelf break and (continental) slope during July-October. Catches
of other beaked whale species were significantly lower.
Range states (Taylor et al. 2008) :
Belgium; Canada; Canary Islands (Spain), Denmark; France; Germany;
Gibraltar; Iceland; Ireland; The Netherlands; Norway; Portugal;
Spain; Sweden; United Kingdom; United States of America (USA).
The species is categorised as "Data Deficient" by (the)
IUCN and is not listed by CMS. Listed in CITES Appendix II.
Mesoplodon - Beaked whales: Introduction and Sources"
© Boris Culik (2010) Odontocetes.
The toothed whales: "Mesoplodon bidens". UNEP/CMS
Secretariat, Bonn, Germany. http://www.cms.int/reports/small_cetaceans/index.htm
© Illustrations by Maurizio Würtz, Artescienza.
© Maps by IUCN.