Life History

            The reproductive strategies of the narwhal have eluded researchers for many years. It is commonly believed that narwhals mate in late May to early June. A study done by M.P. Heide-Jørgensen and E. Garde in 2010 compared the length of narwhal fetuses and newborn narwhals compared to the date they were observed (2011). This study was done because no mating rituals have yet been documented in the wild, and this type of study was the only indication as to when the mating period might take place. Using the data collected and several different types of best-fit lines, the researchers found themselves in agreement with the popular theory of a late May to early June time of reproduction. The length of gestation is thought then to be around 13 months, with mothers giving birth around the months of July and August (Heide-Jorgensen & Garde 2011).

            Mothers usually give birth to only one calf at a time, however twins have been reported. The calf is usually around 1.6 meters long and weighs approximately 80 kilograms (~176 pounds). There is a period of the mother nursing her offspring, however the length of nursing is unknown (Reeves & Tracey 1980). Female narwhals are believed to reach sexual maturity faster than males, taking only four to seven years as compared to the males taking eight to nine years. Physically, females will grow to be about 900 kilograms (~1984 pounds) and 4 meters long. Males will grow to be about 1600 kilograms (~3527 pounds) and 4.7 meters long (Reeves & Tracey 1980).

            In the history of their species, narwhals are believed to have gone through a bottleneck. The bottleneck effect describes a situation where the species nearly goes extinct, but manages to rebound. Other species have similarly gone through a bottleneck, such as cheetahs, California condors, and northern elephant seals. Evidence for narwhals having gone through a bottleneck comes from a study conducted by P.J. Palsbøll, M.P. Heide-Jørgensen, and R. Dietz in 1996. Palsbøll, Heide-Jørgensen, and Dietz sequenced part of the narwhal mitochondrial DNA and compared them (1996). When the diversity is high, it indicates a more diverse species that has had many individuals and has had enough time to develop changes in the DNA sequence that are passed to offspring.  They found that the diversity of the DNA was very low which suggests a recent bottleneck effect, acknowledging that recent could indicate tens of thousands of years. The reason for this bottleneck effect are unknown but could be attributed to past glacier effects limiting the habitat of the narwhal (Palsbøll et al. 1996).

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Created November 2013.