The life history of the narwhal Monodon monoceros was studied utilizing animals captured by the Inuit in northern Baffin Island. Segregation by age and sex within this population is evident, with summering groups consisting of mature females with calves, immature and maturing males, and large mature males. The diet consists of arctic cod, shrimp, and squid during June and July, but feeding activity declines markedly during the open-water months of August and September. Growth layers in the unerupted teeth and periosteal zone of the mandible were found to be related to age but absolute rates of accumulation of these layers are uncertain. The maximum life span is estimated to be 40 to 50 years. Male narwhals, which mature sexually at lengths exceeding 390 cm and at 16-17 growth layers, display protracted maturation and a possible annual cycle of spermatogenesis. Females, which mature sexually at lengths exceeding 340 cm and at 12 growth layers, are seasonally polyoestrous, experiencing up to four consecutive ovulations during the breeding season. The gestation period is estimated to be 15.3 months. The season of conceptions is March to May and calving occurs during July and August. Since the lactation period exceeds 12 months, the interval between successive conceptions is usually three years, but about 20% of females conceive at the first breeding season following birth of their calves. The annual population birth rate is calculated to be about 0.07. The basic life history features of the narwhal are similar to those of other medium-sized toothed whales.

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