Preliminary results in stable isotope analysis along edge of baleen plates in the Antarctic minke whales to estimate duration of time on feeding grounds
Mayuka Uchida, Ippei Suzuki, Tsutomu Tamura, Takeharu Bando, Kenji Konishi and Yoko Mitani
International Whaling Commission
The stable isotope of 16 Antarctic minke whales (Balaenoptera bonaerensis) sampled in the New Scientific Whale Research Program in the Antarctic Ocean (NEWREP-A) in 2016 and 2017 were examined. The stable carbon (δ13C) and nitrogen isotope ratios (δ15N) were determined along the edge of baleen plates of 10 pregnant females in the Ross Sea and 6 immature females of the Antarctic minke whale. Each baleen plate was examined at an interval of 5mm to investigate if there were records of feeding in the δ15N and δ13C derive from the long-term feeding profile. In the pregnant females, about 4 cycles of nitrogen were seen at each baleen plate and the mean length of cycle was 7.7±2.0cm (mean±SD, range: 6.0-10.0cm), while two individuals had nitrogen cycles more than 12cm. No constant cycle was observed in δ13C. The trophic enrichment factor of the Antarctic minke whale is calculated as 3.48‰, assuming the mean δ15N value at base of baleens derived from feeding on the Antarctic krill. From the analyses in immature animals, the δ15N kept high value before birth to the end of lactation followed by a rapid down, suggesting feeding on krill causes lower δ15N. The cycles of stable isotope values in immature animal were longer than those in pregnant females, suggesting the baleen plates in younger animals have higher growth rate. The value of δ13C is difficult to interpret its change compare to that of δ15N in the Antarctic minke whales. The fluctuation range of δ15N in the pregnant females was 0.97 ± 0.21 ‰, suggested that they highly depend on only the Antarctic krill. The duration of feeding period of the Antarctic minke whales on feeding grounds remains unknown. However further experiments with the baleen samples obtained at lower latitude during Austral winter possibly show the change of δ15N during fasting that can estimate the timing of leaving Antarctic Waters. As an alternative way, if possible to examine, the growing ratio of baleen plates can estimate the seasonal change of δ15N, and the duration of time on feeding ground could be calculated.