AGE-SPECIFIC GROWTH AND REMARKABLE LONGEVITY IN NARWHALS (MONODON MONOCEROS) FROM WEST GREENLAND AS ESTIMATED BY ASPARTIC ACID RACEMIZATION

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Abstract

Eyes from 75 narwhals (Monodon monoceros) were collected in West Greenland in 1993 and 2004 for the purpose of age estimation. 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 aspartic acid racemization rate (kAsp) was estimated to be 0.001045/year ± 0.000069 SE by regression of d/l ratios on age estimated by length from 15 young narwhals (≤298 cm) and by earplug laminations from 13 fin whales (Balaenoptera physalus). The d/l ratio at age 0 ((d/l)0) was estimated to be 0.0288 by regression of d/l ratios against the estimated age of the 15 young narwhals. The intercept of the regression slope, providing twice the (d/l)0 value, was 0.05759 ± 0.00147 SE. The maximum estimated age was a 115-year-old (± 10 SE) female. Asymptotic body length was estimated to be 396 cm for females and 457 cm for males, and asymptotic body mass was estimated to be 904 kg for females and 1,645 kg for males. Using the von Bertalanffy growth model, age at sexual maturity was estimated to be 6–7 years for females and 9 years for males.

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