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Sowerby's beaked whale

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Sowerby's beaked whale
Size compared to an average human
CITES Appendix II (CITES)[2]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Ziphiidae
Genus: Mesoplodon
Species:
M. bidens
Binomial name
Mesoplodon bidens
Sowerby, 1804

Sowerby's beaked whale (Mesoplodon bidens), also known as the North Atlantic or North Sea beaked whale, is a species of toothed whale. It was the first mesoplodont whale to be described. James Sowerby, an English naturalist and artist, first described the species in 1804 from a skull obtained from a male that had stranded in the Moray Firth, Scotland, in 1800. He named it bidens, which derives from the two teeth present in the jaw, now known to be a very common feature among the genus.[3]

Physical description

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  • Profile of an adult female
    Profile of an adult female
  • Adult male
    Adult male
  • Adult male head, showing teeth.
    Adult male head, showing teeth.

Sowerby's beaked whale has a typical body shape for the genus, and is mainly distinguished by the male's dual teeth positioned far back in the mouth. The whale's beak is moderately long, and the melon is slightly convex. The colouration pattern is a grey with light countershading on the bottom, and frequently has cookiecutter shark bites and scars from teeth (in males). The whale reaches 5 metres (16 ft) in females and 5.5 metres (18 ft) in males, with a weight of 1000-1300 kilograms (2200-2900 lb). The gestation period lasts for 12 months and the young are born at a length of 2.4 to 2.7 metres (8 to 9 ft) with a weight of around 185 kilograms (400 lb).

Diet

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The diet of Sowerby's beaked whales consists primarily of small mesopelagic and benthopelagic fish, with cephalopods accounting for a much smaller proportion of the diet.[4]

Population and distribution

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Sowerby's beaked whale on Faroese stamp.

Sowerby's beaked whale ranges from Nantucket to Labrador in the western North Atlantic and from Madeira to the Norwegian Sea in the eastern North Atlantic. They typically range in waters 200 to 1,500 metres (650 to 5,000 ft) deep. No population estimates have been made. In 1991, there were about 90 records of the species, 80 from the eastern North Atlantic and less than ten from the western North Atlantic; the majority of the records are from around the British Isles.[5]

On 10 January 2009, a female Sowerby's beaked whale was found at the port of Fethiye on the Aegean coast of Turkey, far away from her natural habitat. The whale was successfully saved and released back to the open sea.[6]

On 25 July 2015, biologists with the New England Aquarium investigated the death of a beaked whale in Massachusetts. The carcass of the 17 ft (5.2 m) long female, which weighed almost 1 short ton (0.91 t), was found on Plymouth Long Beach in Plymouth, Massachusetts. Biologists from the aquarium and the International Fund for Animal Welfare said they would perform a necropsy at the Woods Hole Oceanographic Institution. The whale was initially identified as a Sowerby's beaked whale, but the aquarium said a more thorough examination and consultation with additional experts was needed as staff had not seen a beaked whale since 2006.[7]

On 26 October 2018, a 4.2 m (14 ft) whale was found beached near the town of Saltdean, on the UK coast. The carcass was subsequently taken to the Natural History Museum, London for post-mortem.[8] On 29 August 2019, a stranded whale was rescued from Dungarvan Bay, in southeast Ireland.[9] On 4 July 2020, a whale became disorientated and strayed into Wicklow, harbour on the east coast of Ireland but was later discovered dead on Wicklow, beach.[10]

On 21 August 2020, a 3.86 m (12.7 ft) long female Sowerby's beaked whale washed up on the shore of a beach in Caister-on-Sea, Norfolk. Emergency services assisted the whale out to sea in an attempt to encourage the animal to live. Unfortunately the next morning a report was received to suggest the whale was stranded and deceased at Lowestoft, on the UK coast, following reported sights of 2 whales in the nearby towns of Brancaster and Blakeney in Norfolk earlier in the month.[11]

On successive days in October 2020, two Sowerby's beaked whales were washed up on separate beaches in East Lothian. Both animals died.[12] The necropsy revealed that one of the whales had an unusually high density of small gas bubbles in the lung tissue, and both whales showed signs of gas emboli in the mesenteric arteries. These symptoms are often associated with decompression sickness, however it was not clear if this was the cause in this case. The MOD later revealed that, one day before the first whale stranded, airborne ASW sonar exercises had been carried out within 80 nmi (150 km; 92 mi) of the stranding sites. There was not enough evidence from the necropsy to confirm decompression sickness as the cause of death, so the Scottish Marine Animal Stranding Scheme still consider these as live strandings. However, given the otherwise good physical health of the beaked whales combined with the unusual proximity in both time and location of their strandings, the use of sonar in the surrounding area should still be considered a possible factor in the stranding.[13]

On 28 September 2024, the bodies of two Sowerby's beaked whales, initially thought to be large dolphins, were sighted on a beach of near Eculleville, France on the Cotentin Peninsula. Before their bodies could be examined, they were pulled off the beach by the tide and washed up 50 km further down the coast off Biville, three days later. The whales were identified as an adult female and her young daughter. The local coast guard hypothesized that the adult became disoriented during a recent storm and ended up lost and unable to return to her usual swimming grounds and the daughter followed her to end up later beached, where both perished.[14]

Behaviour

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A whale breaching

Sowerby's beaked whales are reclusive creatures that stay away from ships and are rarely sighted. The whales are occasionally seen in groups of up to 10 individuals (males, females, and calves) and have been known to strand in groups as well. They hunt at depths greater than 500m, and dive to more than 1000m while foraging. Their swimming and diving behaviours are more similar to deep-diving delphinids such as Risso's dolphins and pilot whales than to other mesoplodonts. Compared to Blainville's beaked whales, a mesoplodont of similar body size, Sowerby's beaked whales swim faster while descending and while actively foraging. Their dives are also relatively short and generally last between 30 and 40 minutes. Sowerby's beaked whales cover long distances between dives by swimming at speed just below the surface of the water, as opposed to the typical beaked whale strategy, where time near the surface is minimised by travelling on shallow dives at depths between 100 and 200m.[15]

Conservation

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Skull of Sowerby's beaked whale.

The species has been hunted infrequently by Norwegians, but such practices have long since been abandoned. There are some deaths due to entanglement in fishing gear, but it is unlikely to be very damaging to the species.[citation needed] Sowerby's beaked whale is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS)[16] and the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS).[17] The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).[18]

See also

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Notes

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  1. ^ Pitman, R.L.; Brownell Jr.; R.L. (2020). "Mesoplodon bidens". IUCN Red List of Threatened Species. 2020: e.T13241A50363686. doi:10.2305/IUCN.UK.2020-3.RLTS.T13241A50363686.en. Retrieved 18 November 2021.
  2. ^ "Appendices | CITES". cites.org. Retrieved 14 January 2022.
  3. ^ Sharks and Whales (Carwardine et al. 2002), p. 358.
  4. ^ Pereira, J.N.; Neves, V.C.; Prieto, R.; Silva, M.A.; Cascao, I.; Oliveira, C.; Cruz, M.J.; Medeiros, J.V.; Barreiros, J.P.; Porteiro, F.M.; Clarke, D. (November 2011). "Diet of mid-Atlantic Sowerby's beaked whales Mesoplondon bidens". Deep Sea Research Part I: Oceanographic Research Papers. 58 (11): 1084–1090. Bibcode:2011DSRI...58.1084P. doi:10.1016/j.dsr.2011.08.004. hdl:10400.3/1574.
  5. ^ Klinowska, M. (1991). Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. Cambridge, U.K.: IUCN.
  6. ^ Hürriyet daily newspaper: "Balinaymış". Published on January 12, 2009. Retrieved on January 12, 2009.
  7. ^ Caspari, Sarah (26 July 2015). "Rarely seen beaked whale washes ashore in Massachusetts". The Christian Science Monitor. Retrieved 26 July 2015.
  8. ^ "Sad scenes as rare 14-foot whale washes up on beach". 27 October 2018. Retrieved 30 October 2018.
  9. ^ Aherne, Sinead (30 August 2019). "Unusual rescue for County Waterford lifeboat crew". WLR FM. Retrieved 30 August 2019.
  10. ^ O hOchtun, Ceaneacht (4 July 2020). "Whale in Wicklow harbour dies". Wicklow News. Retrieved 4 July 2020.
  11. ^ "Rarely sighted whale washes up on Lowestoft beach". ITV News. 22 August 2020. Retrieved 22 August 2020.
  12. ^ Duncan, Emma (18 October 2020). "Two rare whales wash up and die on two beaches in East Lothian". East Lothian Courier. Retrieved 24 June 2023.
  13. ^ "SMASS Annual Report 2020" (PDF).
  14. ^ ""C'est une espèce rarissime en Manche" : deux cadavres de baleine à bec retrouvés sur des plages du Cotentin". France 3 Normandie (in French). 10 April 2024. Retrieved 5 October 2024.
  15. ^ Visser, F.; Oudejans, M.G.; Keller, O.A.; Madsen, P.T.; Johnson, M. (12 May 2022). "Sowerby's beaked whale biosonar and movement strategy indicate deep-sea foraging niche differentiation in mesoplodont whales". Journal of Experimental Biology. 225 (9): jeb243728. doi:10.1242/jeb.243728. PMC 9163448. PMID 35417009.
  16. ^ Official website of the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas
  17. ^ Official website of the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area
  18. ^ Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia

References

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