IMPROVED ESTIMATES OF SOME LIFE-HISTORY PARAMETERS OF THE PELAGIC SUBSPECIES OF BRYDE’S WHALE IN THE WESTERN NORTH PACIFIC

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Estimates of several life-history parameters of the pelagic subspecies of Bryde’s whale (Balaenoptera edeni brydei) in the western North Pacific were made based on samples collected from the second phase of the Japanese Whale Research Program under Special Permit in the Western North Pacific (JARPNII) from 2000 to 2016. A total of 730 individuals were sampled in the western North Pacific, between the Japanese coast and 170°E and between 35°N and approximately 42°N. Age information was obtained from earplugs of 475 individuals (65.2%). The growth curves were estimated as L_t=12.65 (1−e^{−0.189 (t+5.250)}) and L_t=13.30 (1−e^{−0.170 (t+4.929)}) for males and females, respectively. The mean age at sexual maturity was estimated as 7.72 (SE=0.49) and 8.56 (SE=0.39) years, and the mean body length at sexual maturity was estimated as 11.41 m (SE=0.25) and 11.75 m (SE=0 .23) for males and females, respectively. The annual ovulation rate was estimated as 0.526/year. Increased readability of earplug age in the JARPNII resulted in improved estimates of age-related life-history parameters for the western North Pacific Bryde’s whale compared with those based on samples collected during the past commercial whaling period.