Reproductive endocrine profiles in blue whales from the Eastern North Pacific Ocean

The goal of this project is to define progesterone profiles for different reproductive states in blue whales (Balaenoptera musculus) from the Eastern North Pacific and determine how samples stored in different ways alter these levels. While extensive work has been conducted using photo-identification and tagging to estimate population abundance and movements, physiological parameters regarding reproduction are fundamental for describing population dynamics and defining growth. In this study, blubber progesterone concentrations were combined with sighting history as a tool to determine pregnancy status in blue whales. To determine the feasibility for hormone analysis of archived samples stored in Dimethyl Sulfoxide (DMSO) a pilot experiment was designed and carried out: pieces of blubber were placed in DMSO and analyzed after 2, 4 and, 8 weeks. The outcomes indicate that blubber stored for at least 8 weeks in DMSO showed no significant difference in progesterone concentration compared to blubber stored frozen (p-value > 0.05). Additionally, preliminary results of progesterone in 23 blubber biopsies and in three stranded individuals support the hypothesis that high concentrations of progesterone are indicative of an ongoing pregnancy. Observational data confirmed pregnancy status for two out of six adult biopsied whales with high progesterone, as they were seen with calves the following year and for one stranded individuals, as it was carrying a fetus at the time of necropsy. Furthermore, very low concentrations of progesterone were found in immature (i.e. less than 10 years old) individuals. Analysis of blubber depth profile suggests that progesterone is more concentrated in shallow layers (0-2 cm) than in deeper ones (4-5.5 cm). Further steps for this project include measuring progesterone in blubber, feces and blow samples from the breeding grounds and processing additional archived blubber samples stored in DMSO, now that we have verified this storage method does not invalidate results.

Citation:

Melica, V., A. Kameroff-Steeves, J. Calambokidis, D. Gendron. 2017. Reproductive endocrine profiles in blue whales from the Eastern North Pacific Ocean. Abstract (Proceedings) 22nd Biennial on the Biology of Marine Mammals, Halifax, Nova Scotia, October 22-27, 2017.