Annual Changes in Serum Reproductive Hormone Levels in the Captive Female Bottle-nosed Dolphins

Abstract

To describe the changes in reproductive hormone levels in the bottle-nosed dolphin Tursiops truncatus gilli, serum samples were obtained at 5-7 day intervals or biweekly from three sexually mature females kept in captivity wlthout adult males for period of 13 or 31 months from June 1982 through December 1984. Serum levels of estradiol, progesterone and LH were measured by radioimmunoassay (RIA). In spring through fall, 2 to 7 cyclic rises of progesterone, some of which were preceded by estradiol elevations, occurred at about one month intervals. No cyclic rise of progesterone was found in winter. A markedly elevated level of LH assumed to be a pre-ovulatory surge was detected. These changes in serum hormone levels were considered to represent sexual cycles with ovulations occurring spontaneously in the species. One female, however, showed prolonged luteal phase lasting about 5 months twice for three years, which was taken to be indicative of false pregnancy. Another female exhibited no elevation of progesterone levels through a one year period.