Reproduction

Southern Right Whales (Eubalaena australis) mate and calve during the winter calving season of June spanning until late October or early November. Peak calving takes place in August. This baleen whale species is polygamous. During copulation one might observe as many as seven males to a single female.
Reproduction takes place in one of four major breeding grounds: Argentina, South Africa, Australia and New Zealand (NMFS, 2007; Patenaude et al., 2007). Females mate every third year and it is common for them to travel long distances to reach a mating ground during this year (Burnell, 2001). Females are more likely to frequent the same mating site than are their male counterparts.

The actual reproduction can be observed beginning near the surface of the water. A single female rolls onto her back holding her breath for long periods of time, in an attempt to hide her genital slit until she is ready to mate. Male Eubalaena australis in a group of 3-7 whales join her and disrupt the water by rubbing bodies and stroking flippers. When the female is prepared to mate she rolls into a berthing position. Males pull along side the female (stroking her back with a flipper) or rise from underneath her. The male performs a roll and sinks under the female to mate belly up. The unsheathed E. australis penis is extremely motile and eventually ejaculates gallons of sperm into the female. Several males will attempt to (successfully) mate with the female until she breaks away. Due to the large quantities of semen expelled in each ejaculation, the last whale may have the greater chance of impregnating the female than the initial whale (Best et al,. 2010). This mating may last from 1 to 2 hours. The female undergoes a gestation period of 365 days (1 year) before producing one offspring which will accompany her for the following year. Female E. australis use the following year to replenish their stores of energy before beginning the breeding cycle again.

The Eubalaena australis are separated into three age categories: calf, juvenile and adult. Calves are small in size and consistently observed with a large whale. Juveniles are smaller than adult female yet larger than calves. At this age the whales lose the dip in their posterior which was observed in calves. Identifying juveniles is more ambigious than calf or adult. Adult E. australis are large and sexually mature. E. australis reach sexual maturity at age 9 or 10 in both male and females. It is difficult for even a qualified biologist to distinguish male from female Eubalaena australis.

Female Eubalaena australis are slightly larger than males. However the size difference is not statistically significant as there is a great deal of overlap. A male E. australis can be immediately identified by the presence of a penis. The male E. australis has the largest whale penis (approx. 12 ft) and the largest testes of any mammal, which weigh up to a ton. Despite their size, penis sighting are uncommon.

Both male and female Eubalaena australis have a genital slit on their ventral side. The male genital slit is more than two times as long as the female genial slit. The whales’ white ventral coloring masks size of the slit for the untrained eye. The location of the genital slit is  varied between the sexes. The male E. australis genital slit originates near the umbilicus and the females further posterior. The males slit branches into a Y towards the whales posterior while the females does not bifurcate. Another distinctive characteristic of male E. australis is an anus distinctly separate from the genital slit. The anus is located towards the posterior end separated from the genital slit by a distance approximately equal to the slit. The anus is distinctive, slightly raised and appearing similar to a tiny volcano. Sighting of an anus without genital slit is a definite male status. Biologists cannot assume a whale is female solely based on unobserved separate anus unless absolutely certain an anus would have been seen if present. (Payne, et al., 1983). In females, the genital slit is not separate from the anus. Males have been observed with uniform and smooth genital slits while reproductive females display creased and uneven slits.  

Female Eubalaena australis have easily observable mammary slits on either side of their genital slits. This observation leads to a fairly conclusive sex identification although there have been instances when this trait appeared in males. Nipples are seen only on reproductive females. Lactation typically occurs for 4-6 months before the calf is weaned. Female E. australis may have protruding nipples even after their calf is weaned. Similar to other mammals, one nipple may be significantly larger than the other due to the calf feeding on one teat more frequently.

It is difficult to observe both the dorsal and ventral sides, without information from both distinguishing physical differences can be challenging. As a result, biologists may resort to behavioral norms to distinguish sex (Best et al,. 2010). Reproductive females are identified due to their association with calves. These whales travel very little and stay close to shore, where these  Eubalaena australis are more frequently observed. These mothers are observed facing their ventral side to the sky to either avoid nursing or play with their calves (a distinctly non male characteristic). Although mature E. australis are polygamous, the calves appear to monogamously cling to one adult. The female and her calf tend to stay isolated from other whales during the calves first year.

Identifying a male through behavior patterns is based on three main criteria.

1.  A number of consecutive years being seen as an adult without a calf. This is evidence of sex as females are rarely without their calves. Females bear calves about every there years and are only observed on years of reproduction.
2. A whales participation in a mating group. This group is categorized as three-seven mature E. australis huddled together by no less than the length of one whale. These groups are observed near the surface and create white water as a result of their rolling, turning and diving.
3. A whale observed as a companion to another known male. In non-mating situations males tend to associate with other males (Payne, et al 1983).

Eubalaena australis display strong, successful reproductive abilities. However as a result of whaling massacre their numbers are still significantly depleted. Rebuilding the population is a slow and arduous journey for a species in which a female produces a single offspring only every three years.

 

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