Beluga whale

Delphinaptera leucas

Order: Cetacea
Family: Monodontidae

1) General Zoological Data

Belugas, also referred to as ‘white whales', are distributed circumpolar and are estimated to number between 62,000 and 80,000 animals (NMFS, 2004). They are thus arctic or subarctic whales. Numerous studies of these animals come from the St. Lawrence River estuary in Canada . They ascend rivers frequently and also migrate south for some distance. Delphinapterus refers to: dolphin a=not pterus feather or wing (no dorsal fin, according to Gotch (1979); she refers to beluga as deriving from belyi (Russian) as white . The animal is also often named ‘belukha'. Males weigh up to 1,500 kg, females 1,360 kg (Nowak, 1999). Weigl (2006) lists maximal life span as 34 years.

2) General Gestational Data

Gestation is 14-14.5 months long and the single newborn weighs 80 kg (Nowak, 1999), while Stewart & Stewart (1989) indicated 35-85 kg.

3) Implantation

Information is available on their implantation or placentas (Mossman (1973).

4) General Characterization of the Placenta

I have had the opportunity of studying four specimens of Beluga whale placentas from the Aquarium for Wildlife Conservation in Brooklyn , N.Y. All of them were bred at the facility and specimens were obtained immediately when the placenta was expelled, about 8 hours after the birth. They were all similar in their appearances and measured and weighed as follows:

This is a typical thin villous, epithelio-chorial placenta that, so it would appear, extends into both uterine horns. The horn with fetus is much larger in width. The trophoblast sits on a thin basal membrane and is unicellular. No trophoblastic inclusions were identified and there are no binucleated cells. There was no pigmentation, although one animal had hemosiderin deposits. The tips of their placental ends were covered with villi.

5) Details of fetal/maternal barrier

No implanted placenta has been available and therefore, it is inferred that the interface is similar to that of common dolphins. Occasional endometrial fragments came detached and lay in between the villi.

6) Umbilical cord

The umbilical cord of the specimen shown here was 55 cm long and virtually not twisted at all. It had numerous plaques consisting of squamous metaplasia on its surface and there was extensive capillarization beneath these plaques. Some squamous plaques are ‘buried' beneath the cords' surface, as illustrated below. Other cord lengths are listed in the table above. There are four large fetal vessels and numerous small blood vessels with or without musculature; many are clustered around the large allantoic duct. The duct has a very thin, flat single-layered epithelium.

7) Uteroplacental circulation

No studies are known to me.

8) Extraplacental membranes

The membranes are thin, have no blood vessels and few squamous plaques, mostly over the vascular branches. There was no decidua.

9) Trophoblast external to barrier

There is no known trophoblastic invasion.

10) Endometrium

Although no implanted placenta has been available, inferring from other cetacean, there is no decidua.

11) Various features

The basal body temperature of a captive beluga was ascertained at 2-4 week intervals by Katsumata et al. (2006) in order to detect ovarian cycles. Highest temperatures were at the peak of progesterone levels; the cycle was 36 days long. Details on the anatomy of male genitalia were provided by De Guise et al. (1994a).

12) Endocrinology

I am not aware of any studies.

13) Genetics

Beluga whales have 44 chromosomes that are shown below. These karyotypes were donated by Dr. D. Duffield and were published in Hsu & Benirschke (1977). Jarrell & Arnason (1981) provided banded karyotypes. Remarkably, a true hermaphrodite beluga was found in the St. Lawrence Estuary (De Guise et al., 1994b). The animal had two testes, two ovaries and their respective ducts, but cervix, vagina and vulva were absent. The testes contained spermatozoa and there were several involuted corpora lutea. Hybrids have not been described (Gray, 1972).

14) Immunology

The purification of T-lymphocytes from splenic tissue was studied by Bernier et al. (2000), and Philippa et al. (2004) ascertained the prevalence of antibodies against a variety of antigens (adenovirus, herpesvirus etc.) in Canada .

15) Pathological features

In contrast to many other species I have reviewed in these chapters, there is an abundance of neoplasms reported in beluga whales. This is frequently attributed to the pesticides and other residues that have accumulated and that have been analyzed from this species. Whether these are true relationships remains to be established, but the number of cancers identified in belugas is remarkable. Here are some of the reports: De Guise et al. (1994c) reported on 21 tumors identified in 12 of 24 stranded carcasses and reviewed even earlier reports of tumors in belugas and drew the conclusion that there must be relation to carcinogenic contaminants (which are referred to).Martineau et al. (1995a) also reported from the St. Lawrence river estuary on intestinal cancers. Then, Lair et al. (1997a) identified unusual adrenal lesions (hyperplasia, cysts) and also considered xenobiotics as causes. Later (1998b) they reported a uterine adenocarcinoma in a 26 year-old animal with peritoneal spread. Mikaelian et al. (1999), also reporting from the same estuary, found mammary adenocarcinomas in two belugas. Ridgway et al. (2002) reported from San Diego on a poorly differentiated carcinoma after having identified it in the brainstem with MRI. Again from St. Lawrence River , Martineau et al. (2002b) estimated that there are 650 belugas in the estuary of which they examined 129 carcasses (of 263 stranded animals) over 17 years. Cancers were found in 18%, parasites in 22%, protozoal and other infections in 17%. They observed cancer overall in 27% found dead. McKinney et al. (2006) analyzed the organochlorines in the belugas from the same estuary and detailed their varied results. Thus, there may be a definite relationship of xenobiotics and cancers, at least in that river.

In addition to the neoplastic lesions reported, there are many studies of various types of infection occurring in belugas. Thus, candidiasis was successfully treated by Dunn et al. (1982); a herpetic infection occurring 3.5 months after capture occurred in a beluga that cleared up spontaneously (Barr et al., 1989). Mikaelian et al. (2000) reported toxoplasmosis in two free-ranging belugas that stranded perhaps due to this affliction and they found titers in another 27% of stranded animals. Trichinella infection in a beluga was reported by Forbes (2000). Harper et al. (2002) isolated a new helicobacter species from a captive beluga (and other dolphins) with problems of regurgitation and some having esophageal ulcers. A 16 year-old beluga died from a necrotizing dermatitis with ruptured aorta etc. and tuberculous organisms (Bowenkamp et al., 2001). In stranded belugas from the St. Lawrence estuary, Mikaelian et al. (2001) found skin lesions from which they isolated a dermatophilus-like organism. Finally, from the same estuary, De Guise et al. (1995d) reported non-neoplastic lesions in 24 carcasses, such as periodontitis, esophageal ulcers, pneumonia due to parasites and adrenal gland cysts.

16) Physiologic data

Cornell et al. (1988) published the results of hematologic and chemistry values of 31 captive belugas. More recently, Tryland et al. (2006) studied a wide variety of chemistries (urea, creatinine, bilirubin, enzymes, hormones, etc.) from 21 free-ranging belugas. Most interesting data on the composition of milk from belugas and Minke whales were assembled by Urashima et al. (2002). Miller et al. (2002) did ultrastructural comparative studies on spermatozoa of three odontocetes and found significant differences in their structures. Detailed examination of the myoglobin structure and function was published by Stewart et al. (2004).

17) Other resources

None are known to me, although there are many animals in Oceanaria and material should there be available.

18) Other remarks – What additional Information is needed?

Time and nature of implantation and a study of an implanted term placenta would be desirable.

Acknowledgement

The animal photographs in this chapter come from Dr. Sam Ridgway, San Diego . Dr. Paul P. Calle of New York provided most of this material for which I am grateful.

References

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