Morphometric Correlates of the Ovary and Ovulatory Corpora in the Bowhead Whale, Balaena mysticetus

Abstract

Gross morphology and morphometry of the bowhead whale ovary, including ovulatory corpora, were investigated in 50 whales from the Chukchi and Beaufort seas off the coast of Alaska. Using the presence of ovarian corpora to define sexual maturity, 23 sexually immature whales (7.6-14.2 m total body length) and 27 sexually mature whales (14.2-17.7 m total body length) were identified. Ovary pair weights ranged from 0.38 to 2.45 kg and 2.92 to 12.02 kg for sexually immature and sexually mature whales, respectively. In sexually mature whales, corpora lutea (CLs) and/or large corpora albicantia (CAs) projected beyond ovary surfaces. CAs became increasingly less interruptive of the surface contour as they regressed, while remaining identifiable within transverse sections of the ovarian cortex. CLs formed large globular bodies, often with a central lumen, featuring golden parenchymas enfolded within radiating fibrous cords. CAs, sometimes vesicular, featured a dense fibrous core with outward fibrous projections through the former luteal tissue. CLs (never more than one per ovary pair) ranged from 6.7 to 15.0 cm in diameter in 13 whales. Fetuses were confirmed in nine of the 13 whales, with the associated CLs ranging from 8.3 to 15.0 cm in diameter. CLs from four whales where a fetus was not detected ranged from 6.7 to 10.6 cm in diameter. CA totals ranged from 0 to 22 for any single ovary, and from 1 to 41 for an ovary pair. CAs measured from 0.3 to 6.3 cm in diameter, and smaller corpora were more numerous, suggesting an accumulating record of ovulation. Neither the left nor the right ovary dominated in the production of corpora. Anat Rec, 299:769-797, 2016. V C 2016 Wiley Periodicals, Inc.Grant sponsors: North Slope Borough Department of Wildlife Management, Barrow, AK, to Texas A&M University; Grant numbers: C3469, E1621, 20177, 16840, 83-58, 58-58, 84-91, 85-62, 86-61, 87-123, 88-134, 93-293, 19980490, 19981343, and 1999226; Grant sponsor: U.S. National Marine Fisheries Service Scientific Permits; Grant numbers: 345 and 519 (to T.F. Albert) and 780 (issued to R.J. Tarpley).

Validation of a blubber-based endocrine pregnancy test for humpback whales

“…It has been shown in horses, that pseudopregnancy is common after mating (25%) but occurs less frequently in non-mated mares (4%) ( Ginther, 1990 ). Work by Tarpley et al (2016) noted the presence of large mature CLs among four bowhead whale ovaries even in the absence of a foetus, indicating the potential for either an early, pseudo or non-fertile pregnancy. Additionally, Robins (1954) found contrary evidence among several examined mature female humpback whales that ovulated more than once without a successful fertilization and showed signs of rapid CL regression with no signs of a prolonged CL.…”

Endocrine profiling of reproductive status and evidence of pseudopregnancy in the Pacific walrus (Odobenus rosmarus divergens)

“…Hunters were trained by USFWS personnel and given field notebooks to document each animal hunted. Sexual maturity was determined by presence of a CL within the ovary [36][37][38][39]. Ovaries indicated if the female was reproductively active during her current cycle by presence of the CL, whereas ovaries lacking a CL were termed inactive.…”

Reproductive parameters of Bering‐Chukchi‐Beaufort Seas bowhead whales

“…This is because we made no adjustment to account for the difference between an early fetus and a term fetus in spring, and classified all whales with any sized fetus as pregnant. Tarpley et al (2016) and Tarpley and Hillmann (1999) estimated pregnancy rates ranging from 0.22 to 0.43 depending on the data set used. In addition, their smallest mature female was 14.2 m (using data through 1992), and their pregnancy rate estimates might be inflated as smaller whales were not included.…”