Finback whale female cycles

From: Pieter Folkens (animalbytes@earthlink.net)
Date: Fri Mar 28 2003 - 02:12:02 EST

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    > Do you know the length in time of the finback whale's uterine and
    > ovarian cycle?  If you do please email me at
    > volleyballpower_34@hotmail.com.  Thank you very much.  If you could
    > get it to me before Friday 28 of March, I would greatly appreciate it.

    In general, pairing and parturition extends over the winter with a
    peak in June-July (south), December-January (north). Pregnancy lasts
    about 11 months followed by 7 months of lactation. Typically the
    subsequent pregnancy does not occur until the winter following weaning.
    However, plenty of evidence suggests cows are capable of of becoming
    pregnant immediately in the second year as a result of a successful
    post-partum ovulation. This condition seems to appear more commonly in
    stressed (endangered) populations of a variety of mammals, including
    whales. Indeed, N.A. Macintosh noted in 1942 a marked increase in the
    percentage of pregnant fin whales and suggested that this might be a
    reaction to the impact on the population caused by whaling. Similarly,
    the age of first reproduction becomes earlier in stressed populations.

    There was evidence that (at least in humpbacks) that there were two to
    three ovulations per 2-year cycle, increasing the opportunity to become
    pregnant.

    R.M. Laws fine-tuned the data to conclude that gestation is thought to
    last 11.25 months with post-partum ovulation occurring 3-4 weeks later
    with conception roughly at the end of July (mid-winter in the south).

    Immature females ovulate for the first time between June and November
    (possibly into December) in the southern oceans. From January to May
    the ovarian activity is at a minimum. This data indicates that the
    breeding season extends over a protracted period.

    Sources:
    Laws, R.M., 1961. Reproduction, Growth, and Age of Southern Fin Whales.
    Discovery Reports Vol.XXXI, Cambridge At The University Press
    Slijper, E.J., 1949. On some phenomena concerning pregnancy and
    parturition. Bijd. Dierk. Vol. XXVIII
    Mackintosh, N.A. & J.F.G. Wheeler, 1929. Southern Blue and Fin Whales.
    Discovery Reports Vol. I

    I hope this helps,

    Pieter Folkens
    Alaska Whale Foundation



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