Editing Gray whale (section)

===Reproduction===
{{See also|Whale reproduction}}
[[File:Embryos of Eschrichtius robustus (illustrations) and outline of head showing spouthole in 1874 detail, from- The marine mammals of the north-western coast of North America (Plate III) BHL16226079 (cropped).jpg|thumb|[[Embryo]]s of gray whale (1874 illustration) and outline of head showing spouthole]]
Breeding behavior is complex and often involves three or more animals. Both male and female whales reach puberty between the ages of 6 and 12 with an average of eight to nine years.<ref name="The Grey Whale">{{cite journal|url=http://spo.nmfs.noaa.gov/mfr464/mfr4643.pdf |archive-url=https://web.archive.org/web/20081031201305/http://spo.nmfs.noaa.gov/mfr464/mfr4643.pdf |archive-date=2008-10-31 |url-status=live |author=Rice, D. |author2=Wolman, A. |author3=Braham, H. |name-list-style=amp |year=1984 |title=The Gray Whale, ''Eschrichtius robustus'' |journal=Marine Fisheries Review |volume=46 |issue=4 |pages=7–14}}</ref> Females show highly synchronized reproduction, undergoing oestrus in late November to early December.<ref name="Gray-Whale">{{cite journal|url=http://lsiecosystem.org/wp-content/uploads/2010/07/Jones-Gray-Whale-Calf-Production-byPhoto-ID-Analysis-1984.jpg.pdf |journal=Rep. Int. Whal. Comm. |issue=t2 |page=177 |author=Jones, Mary Lou |title=The Reproductive Cycle in Gray Whales Based on Photographic Resightings of Females on the Breeding Grounds from 1977–82 |url-status=dead |archive-url=https://web.archive.org/web/20120426022201/http://lsiecosystem.org/wp-content/uploads/2010/07/Jones-Gray-Whale-Calf-Production-byPhoto-ID-Analysis-1984.jpg.pdf |archive-date=2012-04-26 }}</ref> During the breeding season, it is common for females to have several mates.<ref Name="Swartz-Rugh-Taylor">{{cite journal|url=http://lsiecosystem.org/wp-content/uploads/2010/07/Swartz-Rugh-Taylor-GW-Stock-ID-June-06.pdf |title=Gray whale ''Eschrichtius robustus'' population and stock identity |doi=10.1111/j.1365-2907.2006.00082.x |year=2006 |last1=Swartz |first1=Steven L. |last2=Taylor |first2=Barbara L. |last3=Rugh |first3=David J. |journal=Mammal Review |volume=36 |pages=66–84 |issue=1 |url-status=dead |archive-url=https://web.archive.org/web/20120426022248/http://lsiecosystem.org/wp-content/uploads/2010/07/Swartz-Rugh-Taylor-GW-Stock-ID-June-06.pdf |archive-date=2012-04-26 }}</ref> This single ovulation event is believed to coincide with the species' annual migration patterns, when births can occur in warmer waters.<ref Name="Swartz-Rugh-Taylor"/> Most females show biennial reproduction, although annual births have been reported.<ref name="Gray-Whale"/> Males also show seasonal changes, experiencing an increase in testes mass that correlates with the time females undergo oestrus.<ref Name="Swartz-Rugh-Taylor"/> Currently there are no accounts of twin births, although an instance of twins ''in utero'' has been reported.<ref name="Gray-Whale"/>

The gestation period for gray whales is approximately 13&nbsp;{{frac|1|2}} months, with females giving birth every one to three years.<ref name="The Grey Whale"/><ref>{{Cite web |last= |title=Gray Whale {{!}} The Marine Mammal Center |url=https://www.marinemammalcenter.org/animal-care/learn-about-marine-mammals/cetaceans/gray-whale |access-date=2024-11-22 |website=www.marinemammalcenter.org |language=en}}</ref> In the latter half of the pregnancy, the fetus experiences a rapid growth in length and mass. Similar to the narrow breeding season, most calves are born within a six-week time period in mid January.<ref name="The Grey Whale"/> The calf is born tail first, and measures about 14–16&nbsp;ft in length, and a weight of 2,000&nbsp;lbs.<ref name="Fisheries"/> Females lactate for approximately seven months following birth, at which point calves are weaned and maternal care begins to decrease.<ref name="The Grey Whale"/> The shallow lagoon waters in which gray whales reproduce are believed to protect the newborn from [[shark]]s and [[orca]]s.<ref>{{cite web|url=http://www.graywhalefoundation.org/gray-whales.htm|title=The Gray Whale Foundation|last=Solutions|first=Gray Whale Foundation {{!}} Rosodigital Creative|website=www.graywhalefoundation.org|language=en|access-date=2018-02-02|archive-url=https://web.archive.org/web/20180203064444/http://www.graywhalefoundation.org/gray-whales.htm|archive-date=2018-02-03|url-status=dead}}</ref><ref name=BANG/>

On 7 January 2014, a pair of newborn or aborted [[conjoined twin]] gray whale calves were found dead in the Laguna Ojo de Liebre (Scammon's Lagoon), off the west coast of Mexico. They were joined by their bellies.<ref>{{Cite web|url=http://www.independent.co.uk/environment/nature/conjoined-gray-whale-calves-discovered-in-mexican-lagoon-could-be-worlds-first-ever-documented-find-9046110.html |title=Conjoined gray whale calves discovered in Mexican lagoon could be|date=January 8, 2014|website=The Independent}}</ref>