Project Description
After 2 decades of relative stability, the population of fur seals in the Pribilof Islands has declined at an annual rate of 6% since 2000. The reason for the current decline is unknown but may be related to a decrease in reproductive rates. The NMML is expanding on a successful test of trans-rectal ultrasonography to detect ovulation and implantation in northern fur seals on St Paul Island with a 3-year program to assess ovulation, implantation and pupping in ~200 northern fur seals. Adult female fur seals were captured, examined with ultrasonography and equipped with VHF radio flipper tags in November 2007 and will be again in 2008, and their pupping success determined the following summers. This program will determine if early term pregnancy rates have declined since they were estimated from lethal studies in the 1950s and 60s, and whether decreased pupping rate may be contributing to the current population decline.
Issues & Justification
By the 1970s the population of northern fur seals (Callorhinus ursinus) on the Pribilof Islands had declined to one-third of their historic numbers. They were declared depleted under the Marine Mammal Protection Act in 1988. After nearly two decades of relative stability in major rookeries, censuses of pups and breeding bulls indicate a new decline beginning in 2000 at an annual rate of ~6%. The reason for the current decline is unknown but may be related to a decrease in reproductive rates. From pelagic collections taken when the seal population was near its peak, fecundity was estimated to be high; i.e., >80% of adult females between 7 and 16 yr of age were pregnant. However, there are no current estimates of pregnancy or pupping rates that may be used to determine if reduced fecundity is contributing to the present population decline. The Conservation Plan for the Northern Fur Seal calls for monitoring of reproductive rates using nonlethal techniques. Diagnostic, B-mode ultrasonography has been used for more than two decades as a safe and effective tool for characterizing reproductive events in domestic and wild species. The safety and efficacy of this approach was established with a pilot study in northern fur seals in November 2005 (Adams et al., 2007, Marine Mammal Science), in which we were able to detect corpora lutea in 10/10 adult females, and embryonic vesicles as small as 3mm in diameter, denoting an implanted embryo in 9/10. We are expanding on this successful effort with a 3-year program to assess ovulation, implantation and pupping in ~200 northern fur seals to determine if changes in these rates have declined since they were estimated from lethal studies in the 1950s and 60s, and may be contributing to the current population decline.
Goals
- Use ultrasonography to detect ovulation and implantation in ~200 northern fur seals in November, 2007 and 2008.
- Use VHF flipper tags to monitor their subsequent return and pupping success in summer, 2008 and 2009
Methods
November reproductive assessments
Approximately 100 adult female fur seals will be examined annually by a trained theriogenologist (veterinary reproductive specialist) in 2007 and 2008. We will capture and restrain fur seals from Polovina Cliffs from November 12-19, obtaining standard body measurements and blood samples in addition to video ultrasonography of the reproductive tract. The presence, size and number of corpora lutea in the ovaries and embryonic vesicles in the uterus will be determined, as well as levels of estrogen and progesterone in the blood. Each fur seal will be equipped with a standard numbered flipper tag and a VHF radio flipper tag, duty cycled to restart transmission by 15 June 2008.
Summer pupping success
From ~15 June-30 August a VHF receiving and data-logging station will be maintained over the rookery at Polovina Cliffs to monitor the presence of radio-tagged fur seals that were examined ultrasonographically the previous November. Visual confirmation of pupping success will be sought for each animal present, and compared to the attendance pattern expected for the appropriate pupping category (i.e., females with pups should exhibit normal suckling/foraging cycles and those without should not). Visual searches for flipper-tags may also determine pupping success of females that may lose their VHF tag during winter.