Narwhal pregnancy test: the power of progesterone

Have you ever wondered why you feel hungry, or you suddenly crave more sleep? The answer is in part because of tiny messengers called hormones. Hormones are inside all living things and communicate messages, such as how fast a living thing is growing, when animals are awake or when to prepare for pregnancy. Pregnancy is very sensitive to hormone changes and scientists can figure out which stage a pregnancy is at by measuring the levels of certain hormones, such as progesterone, estrogen and testosterone, in animals’ bodies. However, when scientists have tried to infer whether whales are pregnant based on hormone measurements taken from the whales’ blubber, they have based their estimations on hormone measurements from other pregnant mammals, confirming their estimates later by observing whether whale calves were born the following year. Therefore, Justine Hudson, at Fisheries and Oceans Canada, and her colleagues in Nunavut and the University of Manitoba, decided to study hormones in narwhals (Monodon monoceros) to figure out whether these messengers in blubber can tell us about the whales’ pregnancies.As narwhals are sustainably harvested by members of the Inuit communities around Naujaat, Kugaaruk and Pond Inlet, Nunavut, Hudson was able to obtain samples of blubber from 19 female narwhals that they hunted and two that had become trapped in ice, to see whether she could pair blubber hormone measurements from the animals with the condition of their reproductive organs (the ovaries and uteruses), which would show whether a narwhal was pregnant, not pregnant but capable of becoming pregnant, or too young to get pregnant.After studying the narwhals’ reproductive organs, Hudson found that five of the narwhals were pregnant, five were not pregnant but were sexually mature and capable of becoming pregnant, and three were too young to get pregnant. And when she looked at the progesterone levels in the blubber, she found that all of the pregnant whales had higher progesterone measurements (4.90–704.77 ng per gram of blubber) than the whales that were not pregnant (0.62–2.35 ng per gram of blubber). This was an exciting finding because it confirms that blubber progesterone measurements can indicate pregnancy.Because of this discovery, Hudson outlines that any female narwhal with blubber progesterone measurements above 90 ng per gram of blubber can be considered pregnant. In fact, three narwhals in which it was not possible to determine pregnancy from the ovaries or uteruses had progesterone levels greater than 90 ng, meaning that the whales were likely pregnant. Hudson further explains that narwhals with blubber progesterone measurements less than 4 ng per gram of blubber could be classified as not pregnant, while it was not possible for Hudson to determine whether narwhals with blubber progesterone measurements between 4 and 90 ng per gram of blubber were pregnant. Interestingly, one narwhal that was carrying a calf had a blubber progesterone measurement below 90 ng per gram of blubber, which Hudson suggested could be an indication that this narwhal was in the process of miscarrying the pregnancy.The findings of Hudson and colleagues are an exciting step forward in determining whether narwhals are pregnant, which may be applicable to other whale species too. Not only is measuring hormones in blubber a more efficient technique than analyzing the reproductive organs after a whale has died, but this may also help scientists figure out how fast a whale population can grow. Ultimately, knowing this will aid the conservation and management of narwhals and other endangered whale species.

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