OBSERVATIONS ON THE OVARIES OF AN ISOLATEDMINKE WHALE: EVIDENCE FOR SPONTANEOUS
STERILE OVULATION AND STRUCTURE
OF THE RESULTANT CORPUS

HELENE MARSH*ABSTRACT

Examination of the reproductive organs of a parous "dwarf' minke
whale who spent the last three months of her life alone in a Great Barrier
Reef lagoon indicated that this animal ovulated spontaneously during thisperiod despite illness. The structure of the resultant ovarian corpus provides further evidence that corpora lutea of "ovulation" cannot be distinguished from those of pregnancy in this species.
INTRODUCTION

Information from the reproductive organs of a minke whale*, Balaenoptera
acutorostrata, which spent the last three months of its life in isolation in a smalllagoon on the Great Barrier Reef, is relevant to two controversial topics incetacean reproduction: (1) whether corpora derived from sterile ovulations
can be distinguished from those of pregnancy and (2) whether ovulation canbe spontaneous in wild cetaceans.
MATERIALS AND METHODS

The minke whale, first sighted in a small (approximately 250m x 150m xlOm deep) lagoon on Hook Reef (l9°50'S, 149°13'E) on August 31, 1983, remained there until immediately before her death. Her carcass was found on
the adjacent reef flat within four hours of death on November 28, 1983.
While in the lagoon, the whale was checked several times each day by thepilots of light aircraft ferrying tourists to nearby reefs, the pilots reporting
their observations to the Great Barrier Reef Marine Park Authority. No otherwhales were observed in the area during this time.

* Zoology Department, James Cook University, Townsville 4811, Australia.
The colouration of the flippers, shoulder regions and baleen of this minke resembled those of thediminutive form reported by Best 1985; this volume pp. 1-33 off Durban. This colour form is notincluded in the photographic records of 1200 minkes from the Antarctic which are held by Mr S. Wada,
Far Seas Fisheries Research Laboratory, Shimizu, Japan and which he kindly allowed me to check.
Sci. Rep. Whales Res. Inst.,
No. 36, 1985, 35-39

MARSH36

Necropsy commenced about 48hr after death. The whale was measured
according to the standards of Norris (1961). The ovaries were excised andformalin-fixed for subsequent macroscopical and histological examination
using methods similar to those outlined in Marsh and Kasuya (1984). Theuterus was measured using a flexible tape, examined carefully for the presence of an embryo, and sampled for histology at the midlength of eachcornu. The right mammary gland was likewise measured and sampled; in addition the depth of the gland was measured using vernier calipers. All histological samples were processed as outlined in Marsh and Kasuya (1984).
The earplugs were not collected as they had disintegrated.
RESULTS

Details of the reproductive organs are summarized in Table 1. I had nodifficulty interpreting their histology despite the interval between death andnecropsy. Conspicuous stretch marks in the uterine serosa (see Benirschke,Johnson and Benirschke, 1980) and the histology of the mammary gland (seeMackintosh and Wheeler, 1929) indicated that the 7.lm long whale was parous and that she was not lactating. This agrees with Best's (Best, 1982) observations that whales of this colour form reach puberty at a smaller size thantypical southern minke whales.
TABLE 1.

DETAILS OF THE REPRODUCTIVE ORGANS OF THE MINKE WHALE
ALL TERMINOLOGY AS IN MARSH AND KASUYA (1984)

Component

LeftRight

Ovary weight (g)Mean diameters of ovarian structures (mm)Corpus luteum/albicans

100.692.0

Old corpora albicantia
Corpus atreticum a

Corpus atreticum b
Largest follicle
Diameter of each uterine cornu (cm)Depth of mammary gland at midlength (cm)33.3
13.5,12.5,11.0
18.4

6.0
3.0
8.8

Histological details

As in Marsh & Kasuya (1984)
Fig. 19a.

13.5,10.9
As in Appendix B to Workshop
Report Fig. 2c, d (Perrin et al.,1984)
3.58.81.8

Endometrial glands welldeveloped and crowded; somehyalinzation of stroma beneathsurface epithelium; as in
Benirschke et al. (1980) Figs 21&22
Completely involuted as in
Mackintosh and Wheeler(1929) Fig. 138

The right ovary contained what appeared to be a well-established yellow
corpus luteum with a fibrin-filled centre (Fig. 1). The corpus was 33.3mm in
Sci. Rep. Whales Res. Inst.,
No. 36, 1985

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38MARSHKirby and Ridgway ( 1984) concluded on the basis of hormonal monitoring of captive dolphins, that Tursiops truncatus and Delphinus delphis can ovulate spontaneously. If the minke ovulated spontaneously while alone in the lagoon she did so despite the fact that she was ill during this period. The
pathologist present at the necropsy (Dr R. Speare, Graduate School of Tropical Veterinary Science, James Cook University) could not determine the causeof death but reported that (1) the whale had suffered (and recovered) fromchronic peritonitis at least one month before death (2) a chronic gastric ulcer
and two acute gastric haemorrhages were present in the second stomach (3)the blubber especially in the neck region was oedematous indicating starvation. This last symptom was consistent with the progressive encaving of theneck region which was photographically documented during the whale'stenure in the lagoon. Ridgway ( 1972) cites this as a sign of severe weight loss
m porpoises.
If the whale last ovulated before entering the lagoon, the corpus in Fig. 1
must have been at least three months old. This seems unlikely in view ofthe observations of Sawyer-Steffan, Kirby and Gilmartin (1983) who monitored five, assumed ovulations in captive T. truncatus. The assumed ovulations
were assessed by elevated serum progesterone levels which dropped markedly
within one month, suggeting the corpus luteum of each of these animals wasactive for only a few weeks. I conclude that the minke whale ovulated spontaneously while alone in the lagoon despite her illness.

ACKNOWLEDGEMENTS
The Great Barrier Reef Marine Park Aut_hority funded several trips tomonitor the whale during its tenure in the lagoon as well as the necropsy. I
gratefully acknowledge their support, the field assistance of numerous volunteers, and Christina Lockyer for a stimulating correspondence on the subjectof minke whale ovaries, and Toshio Kasuya and Peter Best for their comments on an earlier draft of this manuscript.

REFERENCESBENIRSCHKE, K. M., L. JOHNSON and R.J. BENIRSCHKE, 1980. Is ovulation in dolphins, Stenella longirostris andStenella attenuata, always copulation induced? Fish. Bull. U.S., 78: 507-528.
BEST, P.B., 1982. Seasonal abundance, feeding, reproduction, age and growth in minke whales off Durban(with incidental observations from the Antarctic). Rep. lnt. Whal. Commn, 32: 759-786.
KIRBY, V.L. and S.H. RIDGWAY, 1984. Hormonal evidence of spontaneous ovulation in captive dolphins,
Tursiops truncatus and Delphinus delphis. Rep. Int. Whal. Commn. Spee. Iss., 6: 459-464.
MACKINTOSH, N.A. and j.F.G. WHEELER, 1929. Southern blue and fin whales. Discovery Reports, 1: 257-540.
MARSH, H. and T. KASUYA, 1984. Changes in the ovaries of the short- finned pilot whale, Globicephala macrorhynchus, with age and reproductive activity. Rep. Int. Whal. Commn Spee. Iss.,6: 311-335.
NORRIS, K.S. (ed.), 1961. Standardized methods for measuring and recording data on the smaller cetaceans.
]. Mamm., 42: 471-476.

Sci. Rep. Whales Res. Inst.,
No. 36, 1985

MINKE WHALE OVARIES39

PERRIN, W.F., R.L. BROWNELL, Jr. and D. DE MASTER. (eds.), 1984. Appendix B to Workshop Report. Rep.
Int. Whal. Comm Spee. Iss.,6.
RIDGWAY, S.H., 1972. Homeostatis in the aquatic environment. pp. 590-747. In S.H. RIDGWAY (ed.)
Mammals of the Sea: Biology and Medicine. CHARLES C. THOMAS, Springfield Illinois. 812pp.
ROBINS, J.P., 1954. Ovulation and pregnancy corpora lutea in the ovaries of the humpback whale. Nature,173: 201-203.
SAWYER-STEFFAN, J.E., V.L. KIRBY and w.c. GILMARTIN, 1983. Progesterone and estrogens in the pregnant
and non-pregnant dolphin, Tursiops truncatus, and the effects of induced ovulation. Biol. of Repro.,28: 898-901.

Sci. Rep. Whales Res. Inst.,
No. 36, 1985