Resumen del producto

The goal of the present study was to complement existing data of testosterone and progesterone in blue whale(Balaenoptera musculus) blubber from the eastern North Pacific Ocean to evaluate effects of seasonality andlocation on these hormones and to better assess reproductive status of individuals. Physiological parametersregarding reproduction are fundamental for describing population dynamics, and hormones can be a valid tool toestimate those for wildlife populations. In this study, blubber tissue was validated for testosterone and progesteroneassays. Hormone concentrations were measured in 69 (35 males and 34 females) blubber samples fromlive (n = 66) and stranded (n = 3) animals collected between 2002 and 2016 from a known winter reproductiveground in the Gulf of California (GoC) and summer feeding areas along the United States West Coast (USWC),specifically off the states of California and Oregon. Results were combined with sighting histories as a tool todetermine reproductive status of individual whales. Testosterone concentrations in adult male blue whales weresignificantly higher (p < 0.05) in blubber biopsies sampled off the USWC between the months of June andNovember compared to those sampled in the GoC between February and April. Elevated testosterone concentrationslikely indicate physiological preparation for reproductive activity while the animals were present off theUSWC. Progesterone concentrations were significantly elevated in pregnant females, confirming progesterone asan indicator of pregnancy in blue whales. Probabilities of being pregnant were estimated for adult females withunknown sighting histories based on progesterone concentrations. Testosterone in females was detected andmeasured only in pregnant whales suggesting its biosynthesis or metabolism is altered during gestation. Theseresults provide updated and new information on the reproductive cycle of blue whales in the eastern NorthPacific, posing new milestones to better estimate the timing of the mating season for this endangered population.

Palabras clave: blue whales; testosterone; Progesterone; Reproductive endocrinology; Breeding-feeding habitat

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