Determining sexual maturity in female Antarctic minke whales during the feeding season based on concentrations of progesterone in blubber
Satoko Inoue, Genta Yasunaga and Luis A. Pastene
International Whaling Commission
The relationship between concentration of progesterone in blubber and reproductive status in the Antarctic minke whale was investigated by examining 230 female Antarctic minke whales sampled during the 2015/16 austral summer survey of the New Scientific Whale Research Program in the Antarctic Ocean (NEWREP-A). The study was conducted in response to a recommendation from the NEWREP-A review workshop to ‘Examine use of hormones in blubber to detect sexual maturity’. Progesterone concentrations in blubber of the sampled whales were related to their reproductive status determined by the traditional method of examining reproductive organs (56 immature, 11 resting, 6 ovulating and 157 pregnant females). Significant differences were found in median progesterone concentration between all reproductive categories except in the case between ovulating and pregnant females. However, the ranges of progesterone concentration overlapped between each reproductive status with the exception of the cases immature/ovulating and immature/pregnant. The results of the present study indicate that the progesterone concentration in blubber samples, which potentially can be obtained by biopsy sampling, cannot be used as a diagnostic index to discriminate between mature and immature female Antarctic minke whales. Discrimination between immature and mature females is fundamental information for population dynamics models such as the catch-at-age analysis (SCAA). Therefore, at this stage, lethal sampling is required to obtain information on sexual maturity of female Antarctic minke whales for use in population dynamic models.