UC San Diego

This compilation of research describes the development, validation, and application of a novel approach to assess life-history states in free-ranging cetacean populations. Two assays were developed in which reproductive hormone concentrations were quantified in readily available skin samples to assess 1) pregnancy state and 2) male maturity state, information that can be in turn used to assess reproductive output and demographic structure of dolphin groups in the wild. Toward these ends and important for the validation of this approach, new procedures were developed to verify reproductive state in dead female specimens in which reproductive tract was at hand (Chapter 1). Here several histological characters of the corpus luteum were used to help differentiate females undergoing ovulation from those who were pregnant. Using these new procedures to identify reference samples (females of known pregnancy condition) a pregnancy assay for use on skin biopsies was developed and validated on three species of small delphinids (Chapter 2). Levels of blubber progesterone in dolphins of known pregnancy state were determined from carcasses collected from fishery-bycatch and local strandings. Pregnant short-beaked common dolphin blubber were found to contain dramatically more progesterone (16 times) than the blubber of non-pregnant mature and immature females. In addition, no overlap was found between the pregnancy states such that pregnancy diagnosis was unambiguous. Using these concentrations as reference we quantified the levels of progesterone in the blubber connected to projectile biopsies of wild pan- tropical spotted dolphins and found that animals exposed to higher levels of tuna-fishing effort were less likely to be pregnant (Chapter 4). Finally, unlike with blubber progesterone and pregnancy, blubber testosterone was less precise in determining the maturity state of individual male dolphins. However, with a sufficient reference collection of blubber testosterone concentrations from male dolphins of known maturity state we developed a Bayesian method to estimate the probability of maturity of individual animals, which could be used in turn to estimate the proportion of males that were mature within any given group of biopsy samples (Chapter 3)