Bowhead Whales Have the Longest Pregnancy for a Mammal in the Animal Kingdom

Bowhead Whales Have the Longest Pregnancy for a Mammal in the Animal Kingdom

Whales, the majestic giants of the ocean, have long captured the fascination of humans. Yet, despite our curiosity, there remains an aura of mystery around these magnificent creatures.

Among them, the bowhead whale stands out as a species that has managed to keep its secrets hidden from us, even as we nearly pushed it to the brink of extinction.

Nadine Lysiak, a dedicated marine biologist, has been on a quest to unravel the enigma surrounding the bowhead whale and other baleen whales, shedding light on their reproduction, growth, and Conservation needs.

One of the most astounding discoveries from Lysiak’s research is the potential for female bowhead whales to harbor a truly extraordinary feat of nature – pregnancies lasting up to 23 months.

This discovery, published in the journal Royal Society Open Science, has put the bowhead whale’s reproductive mysteries in the spotlight.

If confirmed, this would surpass the already impressive elephant pregnancies, making bowhead whales the champions of prolonged gestation in the mammalian kingdom.

Understanding the reproductive patterns of these creatures is crucial for their conservation, especially in the face of a changing climate that poses further challenges to their survival.

Unfortunately, studying free-ranging mammals like bowhead whales presents a significant challenge due to their elusive nature. Scientists have had to rely on field observations, surveys, and the examination of washed-up carcasses to gather information.

However, Lysiak and her team adopted a unique approach for this study, examining samples taken from the baleen of 10 female bowhead whales collected by Inuit hunters in the eastern Canadian Arctic and West Greenland.

The baleen, those fibrous off-white bristles in the mouths of whales, proved to be a treasure trove of information. Unlike blubber or skin tissue samples, which provide only a snapshot of an animal’s life, baleen offers a more comprehensive view. Acting like teeth-like projections, the baleen retains a molecular record of the body’s circulating hormones.

By analyzing these hormones—progesterone (produced during pregnancy), estradiol (associated with the heat or estrus cycle), and corticosterone (a biomarker of stress that affects fetal development)—researchers gained valuable insights into the bowhead whale’s reproductive journey.

The data analysis returned surprising results, suggesting two possible scenarios for the duration of bowhead pregnancies. The first scenario proposed that the pregnancy lasts for an astonishing 23 months.

The second scenario, on the other hand, hypothesized that the whales experienced a prolonged state of estrus or ovulation during the initial surge in progesterone, and the actual pregnancy lasted around 14 months.

While the second scenario aligns with what is known about bowhead whale fetus sizes, the first scenario points to a phenomenon that biologists previously discounted in baleen whales—delayed implantation, also known as embryonic diapause.

Delayed implantation is a survival advantage found in many marine mammals, terrestrial animals, and even some seals, bears, and otters. It allows the mother’s body to decide the most favorable time for giving birth, pausing the pregnancy at a certain point after fertilization until external conditions become more conducive to the newborn’s survival.

Although further research is needed to confirm whether bowhead pregnancies indeed last 23 months, these findings come at a critical juncture when the species is at risk.

Human activities, climate change, and environmental disturbances continue to threaten the survival of these majestic creatures.

Understanding their reproductive complexities can aid Conservation efforts by providing valuable information for decision-making.

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This article by Trinity Sparke was first published by One Green Planet on 22 October 2023. Image Credit :Vladimir Chebanov/Shutterstock.

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