Editing Narwhal (section)

=== Longevity and mortality factors ===
[[File:A polar bear (Ursus maritimus) scavenging a narwhal whale (Monodon monoceros) carcass - journal.pone.0060797.g001-A.png|thumb|A polar bear [[scavenging]] a narwhal carcass|alt=Polar bear feeding/scavenging on a beached narwhal carcass.]]
Age determination techniques using the number of [[periosteum]] layers in the [[lower jaw]] reveal that narwhals live an average of 50 years, though techniques using [[amino acid dating]] from the [[Lens (vertebrate anatomy)|lens]] of the eyes suggest that female narwhals can reach 115{{Nbsp}}±{{Nbsp}}10 years and male narwhals can live to 84{{Nbsp}}±{{Nbsp}}9 years.<ref>{{Cite journal |last1=Garde |first1=Eva |last2=Heide-Jørgensen |first2=Mads Peter |last3=Hansen |first3=Steen H. |last4=Nachman |first4=Gösta |last5=Forchhammer |first5=Mads C. |date=28 February 2007 |title=Age-specific growth and remarkable longevity in narwhals (''Monodon monoceros'') from West Greenland as estimated by aspartic acid racemization |url=http://dx.doi.org/10.1644/06-mamm-a-056r.1 |journal=Journal of Mammalogy |volume=88 |issue=1 |pages=49–58 |doi=10.1644/06-mamm-a-056r.1 |issn=0022-2372}}</ref>

Death by [[suffocation]] often occurs when narwhals fail to migrate before the [[Climate change in the Arctic|Arctic freezes over]] in late autumn. This is known as "sea-ice entrapment".<ref name="Macdonald" /><ref name=":7">{{Cite journal |last1=Laidre |first1=Kristin |last2=Heide-Jørgensen |first2=Mads Peter |last3=Stern |first3=Harry |last4=Richard |first4=Pierre |date=1 January 2012 |title=Unusual narwhal sea ice entrapments and delayed autumn freeze-up trends |url=https://doi.org/10.1007/s00300-011-1036-8 |journal=Polar Biology |language=en |volume=35 |issue=1 |pages=149–154 |bibcode=2012PoBio..35..149L |doi=10.1007/s00300-011-1036-8 |issn=1432-2056 |s2cid=253807718}}</ref> Narwhals drown if open water is no longer accessible and ice is too thick for them to break through. Breathing holes in ice may be up to {{convert|1450|m|ft|-1|abbr=on}} apart, which limits the use of foraging grounds. These holes must be at least {{convert|0.5|m|ft|abbr=on}} wide to allow an adult whale to breathe.<ref name=":8">{{Cite journal |last1=Williams |first1=Terrie M. |last2=Noren |first2=Shawn R. |last3=Glenn |first3=Mike |date=April 2011 |title=Extreme physiological adaptations as predictors of climate-change sensitivity in the narwhal (''Monodon monoceros'') |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1748-7692.2010.00408.x |journal=Marine Mammal Science |language=en |volume=27 |issue=2 |pages=334–349 |bibcode=2011MMamS..27..334W |doi=10.1111/j.1748-7692.2010.00408.x |issn=0824-0469}}</ref> Narwhals also die of [[starvation]] from entrapment events.<ref name=":21" />

In 1914{{endash}}1915, around 1,000 narwhal carcasses were discovered after entrapment events, most occurring in areas such as [[Disko Bay]] in [[West Greenland]].<ref>{{Cite journal |last=Porsild |first=Morten P. |date=1918 |title=On 'savssats': a crowding of Arctic animals at holes in the sea ice |url=https://www.jstor.org/stable/207815 |journal=Geographical Review |volume=6 |issue=3 |pages=215–228 |bibcode=1918GeoRv...6..215P |doi=10.2307/207815 |issn=0016-7428 |jstor=207815}}</ref> Several cases of sea entrapment were recorded in 2008–2010, during the Arctic winter, including in some places where such events had never been recorded before.<ref name=":7" /> This suggests later departure dates from summering grounds. Wind and currents move sea ice from adjacent locations to Greenland, leading to fluctuations in concentration. Due to their tendency of returning to the same areas, changes in weather and ice conditions are not always associated with narwhal movement toward open water. It is currently unclear to what extent sea ice changes pose a danger to narwhals.<ref name=":18" /><ref name=":7" /><ref>{{Cite book |last1=Macdonald |first1=David Whyte |url=https://books.google.com/books?id=rdRFAAAAYAAJ |title=Mammals of Britain & Europe |last2=Barrett |first2=Priscilla |date=1993 |publisher=HarperCollins |isbn=978-0-00-219779-3 |pages=173 |language=en}}</ref>

Narwhals are preyed upon by [[polar bear]]s and [[orca]]s. In some instances, the former have been recorded waiting at breathing holes for young narwhals, while the latter were observed surrounding and killing entire narwhal pods.<ref name="Macdonald" /><ref>{{Cite book |url=https://books.google.com/books?id=2rkHQpToi9sC&q=narwhals+attacked+by+polar+bears&pg=PA929 |title=Encyclopedia of Marine Mammals |publisher=Academic Press |year=2009 |isbn=978-0-08-091993-5 |editor-last=Perrin, William F. |pages=929–930 |access-date=18 November 2020 |editor-last2=Wursig, Bernd |editor-last3=Thewissen, J. G. M. 'Hans' |archive-url=https://web.archive.org/web/20240128092123/https://books.google.com/books?id=2rkHQpToi9sC&q=narwhals+attacked+by+polar+bears&pg=PA929#v=snippet&q=narwhals%20attacked%20by%20polar%20bears&f=false |archive-date=28 January 2024 |url-status=live}}</ref><ref>{{Cite journal |last1=Ferguson |first1=Steven H. |last2=Higdon |first2=Jeff W. |last3=Westdal |first3=Kristin H. |date=30 January 2012 |title=Prey items and predation behavior of killer whales (''Orcinus orca'') in Nunavut, Canada based on Inuit hunter interviews |journal=Aquatic Biosystems |volume=8 |issue=1 |pages=3 |bibcode=2012AqBio...8....3F |doi=10.1186/2046-9063-8-3 |issn=2046-9063 |pmc=3310332 |pmid=22520955 |doi-access=free}}</ref><ref>{{Cite web |date=19 November 2014 |title=Invasion of the killer whales: killer whales attack pod of narwhal |url=https://www.pbs.org/wnet/nature/invasion-killer-whales-killer-whales-attack-pod-narwhals/11165/ |url-status=live |archive-url=https://web.archive.org/web/20161022071130/http://www.pbs.org/wnet/nature/invasion-killer-whales-killer-whales-attack-pod-narwhals/11165/ |archive-date=22 October 2016 |access-date=23 October 2016 |publisher=Public Broadcasting System}}</ref> To escape predators such as orcas, narwhals may use prolonged submersion to hide under [[ice floe]]s rather than relying on speed.<ref name=":8" />

Researchers found bacteria of the ''[[Brucella]]'' genus in the bloodstreams of numerous narwhals throughout the course of a 19-year study. They were also recorded with [[whale lice]] species such as ''[[Cyamus monodontis]]'' and ''[[Cyamus nodosus]]''. Other [[pathogen]]s that affect narwhals include ''[[Toxoplasma gondii]]'', [[morbillivirus]], and [[papillomavirus]].<ref>{{Cite journal |last1=Barratclough |first1=Ashley |last2=Ferguson |first2=Steven H. |last3=Lydersen |first3=Christian |last4=Thomas |first4=Peter O. |last5=Kovacs |first5=Kit M. |date=July 2023 |title=A review of circumpolar Arctic marine mammal health—a call to action in a time of rapid environmental change |journal=Pathogens |language=en |volume=12 |issue=7 |pages=937 |doi=10.3390/pathogens12070937 |issn=2076-0817 |pmc=10385039 |pmid=37513784 |doi-access=free}}</ref> In 2018, a female narwhal was recorded with an [[alphaherpesvirus]] in her system.<ref>{{Cite journal |last1=Nielsen |first1=Ole |last2=Rodrigues |first2=Thaís C. S. |last3=Marcoux |first3=Marianne |last4=Béland |first4=Karine |last5=Subramaniam |first5=Kuttichantran |last6=Lair |first6=Stéphane |last7=Hussey |first7=Nigel E. |last8=Waltzek |first8=Thomas B. |date=6 July 2023 |title=Alphaherpesvirus infection in a free-ranging narwhal (''Monodon monoceros'') from Arctic Canada |url=https://www.int-res.com/abstracts/dao/v154/p131-139/ |journal=Diseases of Aquatic Organisms |language=en |volume=154 |pages=131–139 |doi=10.3354/dao03732 |issn=0177-5103 |pmid=37410432 |doi-access=free}}</ref>