Life history parameters of narwhals (Monodon monoceros) from Greenland

Life history parameters for narwhals (Monodon monoceros) were estimated based on age estimates from aspartic acid racemization of eye lens nuclei. Eyes, reproductive organs, and measures of body lengths were collected from 282 narwhals in East and West Greenland in the years 1993, 2004, and 2007–2010. Age estimates were based on the racemization of L-aspartic acid to D-aspartic acid in the nucleus of the eye lens. The ratio of D- and L-enantiomers was measured using high-performance liquid chromatography. The age equation used, 420.32X – 24.02·year where X is the D/L ratio, was determined from data from Garde et al. (2012). Asymptotic body length was estimated to be 405 ± 5.8 cm for females and 462 ± 16.2 cm for males from East Greenland, and 399 ± 5.9 cm for females and 456 ± 6.9 cm for males from West Greenland. Due to several indeterminant age class estimates, age at sexual maturity was subjectively assessed based on data from reproductive organs and was estimated to be 8–9 years for females and 12–20 years for males. Pregnancy rates for East and West Greenland were estimated to be 0.38–0.42 and 0.38, respectively. Maximum life span expectancy was found to be approximately 100 years. A population projection matrix was parameterized with the data on age structure and fertility rates. The annual rate of increase of narwhals in East Greenland was estimated to be 3.8% while narwhals in West Greenland had a rate of increase at 2.6%.