REPRODUCTION
Narwhals exhibit bilateral symmetry and sexual dimorphism. On average, adult males are longer and heavier than females. Males reach a maximum length of about 460 cm and a maximum weight of 1,645 kg. Adult females, on the other hand, have a maximum length of 400 cm and a weight of 900 kg. Only a small percentage of females are likely to develop a tusk, but this feature is most commonly found in all adult males. The maximum life span is estimated to be 40 to 50 years.
Male narwhals mature sexually at lengths exceeding 390 cm and at 16-17 growth layers. Males display protracted maturation and a possible annual cycle of spermatogenesis. Female narwhals mature sexually at lengths exceeding 340 cm and at 12 growth layers. They reach sexual maturity between 7 and 9 years of age. Females are seasonally polyoestrous, experiencing up to four consecutive ovulations during the breeding season. The season of conception is From March to May is the season for conceiving. During July and August is when calving occurs. On average, female narwhals have one calf every 3 years. About 20% of females conceive at the first breeding season following the birth of their calves.
After a male Narwhal finds a suitable mate, they will proceed to copulate in shallow waters in a vertical position from belly to belly. An infant is usually implanted in the left uterine horn of a female. As a result of this, normally only a single calf is born. However, there have been records of the birth of twin calves. Gestation is thought to last about fourteen months inside the narwhal, followed by twenty months of lactation. Following the birth of a calf, the mother nurses the newborn calves for about four months.Males are thought to have some parental investment because males and females generally do not travel together unless there is a calf with them. This is based on observation of traveling narwhals, however, whether the males provide food or protection for the offspring is unknown.
Image retrieved from: https://www.tuscaloosanews.com/story/opinion/2020/11/01/ecoviews-narwahls-marine-unicorn-arctic-ocean/3747328001/.
Reproduction in the Male
The attainment of sexual maturity by male odontocetes (toothed whales) is not necessarily accompanied by maximum fertility or the capacity to impregnate females. It is not known whether the male narwhal is fully fertile when it attains sexual maturity, but because of the intense competition for females among the males of a polygynous species, social maturity may be attained only after a further increase in body size and/or testis size. Delayed sexual maturity of males leads to a relative excess of mature females.
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Reproduction in the Female
Many odontocetes (toothed whales) appear to have polyoestrous breeding cycles. The female narwhal is polyoestrous, experiencing up to four successive ovulations during a two-month-long breeding season which comprises the latter part of the lactation period, or the period following weaning of the second-year calf. Female narwhals do not appear to ovulate after parturition.
The milk of lactating narwhals is a thick turbid green fluid, often seen oozing from the mammary slits when the whale is rolled up the beach. The mammary glands of some females in early pregnancy and those of some resting females contain a light brownish or greenish translucent oily fluid, referred to as post-lactation oil.
Most mature female narwhals fall into one of the four main reproductive categories: non-lactating, pregnant (weaned two-year calf); full-term/postpartum; lactating (one-year calf); and resting (non-pregnant; non-lactating; ovulated unsuccessfully). This means that there is a basic three-year reproductive cycle, and because most early-pregnant females have weaned their calves, the lactation period exceeds one year but is less than two years. The logical conclusion is that simultaneously pregnant and lactating whales are nursing yearling calves, and therefore they have conceived about nine months after parturition (Hay et al., 1984).
