REPRODUCTIVE MORPHOLOGY AND STATUS OF FEMALE HAWAIIAN MONK SEALS (MONACHUS-SCHAUINSLANDI) FATALLY INJURED BY ADULT MALE SEALS

Female Hawaiian monk seals at Laysan Island in the Northwestern Hawaii an Islands seasonally risk aggressive mating attempts by groups of adu lt male monk seals. These attacks, which also target immature female a nd male seals at a lower frequency, result in injuries that are often fatal and are termed mobbings. This study was undertaken to assess the reproductive status of nine female seals that died after mobbing atta cks and to obtain basic morphological data of reproductive tracts from ten females. Reproductive morphology of the seals indicated that the lengths of the uterine body and both uterine hems were significantly s horter in nulliparous than in parous seals. Seven of the nine seals we re periovulatory, on the basis of gross morphology of the ovaries at d eath. The ovaries of the other two seals possessed immature follicles. Histological studies of the vagina and uterus confirmed the reproduct ive status of the seals. When the reproductive status at the time of f irst injury was estimated, all seals were in the follicular phase of t he oestrous cycle. At least four of these seals were estimated to be i n oestrus at the time of their first injury, and seven of the seals su stained at least one injury during the estimated period of oestrus (2- 6 days). These results support the hypothesis that most adult female H awaiian monk seals that die following an attack by male monk seals are periovulatory, and that the majority of the attacks occur during oest rus.