As interns, we were given the fortunate privilege to attend a field necropsy on a stranded sperm whale (Physeter macrocephalus). The adult female was found on Porth Neigwl (Hell’s Mouth) Beach on the south coast of the Llŷn Peninsula in North Wales at around 8 a.m. on Sunday, 8 May 2023 (Deaville, 2023). The whale initially live stranded but died fast in the surf side. The post-mortem was carried out by a team from the UK Cetacean Strandings Investigation Programme (CSIP) and took place on the beach two days after the stranding.
About sperm whales
Sperm whales are the largest species of toothed whales (Odontoceti; Jaquet, 1996; Whitehead, 2018) with females reaching a length of about 11 m and males of 16 m which is a great display of sexual dimorphism in terms of body length and weight (Whitehead, 2018). They have a cosmopolitan distribution which means they can be found in all oceans, ranging from the equator to the drift ice in the North and South (Jaquet, 1996; Watwood et al., 2006; Engelhaupt et al., 2009). The global sperm whale population is currently estimated at about 360 000 animals (Whitehead, 2018).
Among Odontoceti, sperm whales are considered the deepest divers (Jaquet, 1996). They forage for deep-sea squid (Jaquet, 1996; Watwood et al., 2006; Whitehead, 2018) at depths of about 600 m. They perform deep dives of sometimes over 1 000 m that last about 45 min in average and intermittently surface to breathe for about 9 min (Watwood et al., 2006). By actively searching using this high diving efficiency and long-range echolocation, sperm whales effectively locate prey in the deep ocean (Watwood et al., 2006). The sounds sperm whales use to echolocate prey are formed in the head and focused through their spermaceti organ into long ranged clicks. Aside from foraging, these clicks are also used for communicating with conspecifics (Whitehead, 2018).
Sperm whales are highly social animals. Females stay in matrilineal groups of about 10 females and their offspring that travel, forage and raise offspring together. Some matrilineal groups join and regularly associate in temporary units (Jaquet, 1996; Whitehead, 2018). Young males sometimes form bachelor groups after leaving their matrilines (Engelhaupt et al., 2009; Whitehead, 2018). As the males age and grow, they move to higher latitudes and aggregation sizes decrease. Once sexual maturity is reached in their late 20s males return to breeding grounds (usually areas of high primary productivity) in lower latitudes (Whitehead, 2018). While little is known about rates and causes of natural mortality, longevity is expected to be at least 50 years (Whitehead, 2018).
About sperm whales
Sperm whales are the largest species of toothed whales (Odontoceti; Jaquet, 1996; Whitehead, 2018) with females reaching a length of about 11 m and males of 16 m which is a great display of sexual dimorphism in terms of body length and weight (Whitehead, 2018). They have a cosmopolitan distribution which means they can be found in all oceans, ranging from the equator to the drift ice in the North and South (Jaquet, 1996; Watwood et al., 2006; Engelhaupt et al., 2009). The global sperm whale population is currently estimated at about 360 000 animals (Whitehead, 2018).
Among Odontoceti, sperm whales are considered the deepest divers (Jaquet, 1996). They forage for deep-sea squid (Jaquet, 1996; Watwood et al., 2006; Whitehead, 2018) at depths of about 600 m. They perform deep dives of sometimes over 1 000 m that last about 45 min in average and intermittently surface to breathe for about 9 min (Watwood et al., 2006). By actively searching using this high diving efficiency and long-range echolocation, sperm whales effectively locate prey in the deep ocean (Watwood et al., 2006). The sounds sperm whales use to echolocate prey are formed in the head and focused through their spermaceti organ into long ranged clicks. Aside from foraging, these clicks are also used for communicating with conspecifics (Whitehead, 2018).
Sperm whales are highly social animals. Females stay in matrilineal groups of about 10 females and their offspring that travel, forage and raise offspring together. Some matrilineal groups join and regularly associate in temporary units (Jaquet, 1996; Whitehead, 2018). Young males sometimes form bachelor groups after leaving their matrilines (Engelhaupt et al., 2009; Whitehead, 2018). As the males age and grow, they move to higher latitudes and aggregation sizes decrease. Once sexual maturity is reached in their late 20s males return to breeding grounds (usually areas of high primary productivity) in lower latitudes (Whitehead, 2018). While little is known about rates and causes of natural mortality, longevity is expected to be at least 50 years (Whitehead, 2018).
About sperm whale strandings
A cetacean strandings in general is defined as an individual found beached or washed up onto land, dead or alive, sometimes holding the possibility of re-floating the animal (Coombs et al., 2019). In the past 100 years, over 20 000 strandings have been recorded in the UK and Ireland. Cetacean strandings may be cause by a variety of reasons. Suggested causes for strandings include meteorological or oceanographic disturbances that may displace or injure cetaceans, changes in the sea surface temperature which may influence prey abundance and distributions, starvation due to overfishing, or damaging to fatal anthropogenic influences such as intensive sound disturbances and physical contact with ship or fishing gear (Bearzi et al., 2011; Coombs et al., 2019).
For sperm whales specifically, it has been proposed that geomagnetic fluctuations may affect the whales’ geomagnetic-based navigation, misdirecting them into shallower waters where they strand (Vanselow et al., 2018). Alternatively, it has been proposed that strandings along coastal areas facing shallow continental shelf waters, may be caused by sperm whales becoming trapped in areas of insufficient food availability for extended periods of time, causing starvation (Bearzi et al., 2011).
The stranding of the female sperm whale on Porth Neigwl Beach was highly unusual. As females tend to aggregate in lower latitudes (less than 40°) with water deeper than 1000 m and sea surface temperatures higher than 15 °C (Whitehead, 2018), their occurrence in British waters with latitudes of over 50° (Porth Neigwl Beach at 52°) is noticeably out of habitat. This whale was the fourth female ever recorded stranded in the UK, and only the second one ever in Wales. According to CSIP the animal was in markedly poor nutritional condition with no evidence of recent feeding and notably protruding ribs. However, it remains unclear what ultimately lead to the animal’s stranding (Deaville, 2023).
The increase in recent cetacean strandings is notable. Within the last two months alone there has been amongst others another sperm whale stranding near the Humber estuary, a fin whale stranding in Bridlington, several common dolphins, harbour porpoises and our very own bottlenose dolphin, Graham (Deaville, 2023). Due to factors such as increasing anthropogenic activities and climate change, continued stress on marine mammal health and as a result, increasing numbers of cetacean strandings are predicted (Boys et al., 2021). While this causes concerns for long-term population trends of the species, strandings also provide data that opens doors for potential monitoring strategies. Stranded individuals provide information such as life history, diet, distribution, nutritional status, disease burden and environmental contaminants of local populations (Williamson et al., 2021). Especially for cetaceans that are difficult to monitor in situ, strandings provide a valuable opportunity for monitoring this species, providing management insights for potentially disturbing human activities and mitigating large-scale human-wildlife interactions (IJsseldijk et al., 2020). As interns for the Sea Watch Foundation, we are thankful to have been provided with the unique learning opportunity to attend the post-mortem of a stranded sperm whale.
Hannah Carstens
Research Intern
References
Bearzi, G. et al. (2011) ‘Overview of sperm whale Physeter macrocephalus mortality events in the Adriatic Sea, 1555-2009’, Mammal Review, 41(4), pp. 276–293. doi: 10.1111/j.1365-2907.2010.00171.x.
Boys, R. M. et al. (2021) ‘Deathly silent: Exploring the global lack of data relating to stranded cetacean euthanasia’, Animals, 11(5). doi: 10.3390/ani11051460.
Coombs, E. J. et al. (2019) ‘What can cetacean stranding records tell us? A study of UK and Irish cetacean diversity over the past 100 years’, Marine Mammal Science, 35(4), pp. 1527–1555. doi: 10.1111/mms.12610.
Deaville, Rob. (2023) [Twitter] Available at: https://twitter.com/strandings_man?ref_src=twsrc%5Egoogle%7Ctwcamp%5Eserp%7Ctwgr%5Eauthor (Accessed 22/05/2023).
Engelhaupt, D. et al. (2009) ‘Female philopatry in coastal basins and male dispersion across the North Atlantic in a highly mobile marine species, the sperm whale (Physeter macrocephalus)’, Molecular Ecology, 18(20), pp. 4193–4205. doi: 10.1111/j.1365-294X.2009.04355.x.
IJsseldijk, L. L. et al. (2020) ‘Spatiotemporal mortality and demographic trends in a small cetacean: Strandings to inform conservation management’, Biological Conservation, 249(108733). doi: 10.1016/j.biocon.2020.108733.
Jaquet, N. (1996) ‘How spatial and temporal scales influence understanding of Sperm Whale distribution: A review’, Mammal Review, 26(1), pp. 51–65. doi: 10.1111/j.1365-2907.1996.tb00146.x.
Vanselow, K. H. et al. (2018) ‘Solar storms may trigger sperm whale strandings: Explanation approaches for multiple strandings in the North Sea in 2016’, International Journal of Astrobiology, 17(4), pp. 336–344. doi: 10.1017/S147355041700026X.
Watwood, S. L. et al. (2006) ‘Deep-diving foraging behaviour of sperm whales (Physeter macrocephalus)’, Journal of Animal Ecology, 75(3), pp. 814–825. doi: 10.1111/j.1365-2656.2006.01101.x.
Whitehead, H. (2018) ‘Sperm Whale’, in Encyclopedia of Marine Mammals, pp. 919–925. doi: 10.1016/b978-0-12-804327-1.00242-9.
Williamson, M. J. et al. (2021) ‘Cetaceans as sentinels for informing climate change policy in UK waters’, Marine Policy, 131(104634). doi: 10.1016/j.marpol.2021.104634.
