Graduate Thesis Or Dissertation
 

Photoperiod and the timing of pupping in the Pacific harbor seal (Phoca vitulina richardsi) with notes on reproduction in northern fur seals and Dall porpoises

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  • Birth and pupping season records of Pacific harbor seals (Phoca vitulina richardsi) were used in an analysis of photoperiod effect on the timing of birth in this species. Dates and latitudes of births were converted into photoperiods using a photoperiod equation. Sequential dates from parturition were converted into photoperiods and plotted as a function of latitude. The resulting functions of latitude vs. photoperiod were regressed to determine the point during the reproductive cycle at which latitude did not have an effect on photoperiod. The Pacific harbor seal can be divided into two geographic subgroups by their respective pupping seasons. Seals inhabiting the Puget Sound / Strait of Georgia (PS/SG) System give birth to pups an average of 88 days (P < 0.01) later than do seals of the North American west coast. The dine in the pupping season of coastal harbor seals can be defined by a 13.8 h/day photoperiod occurring at 68 days post partum. PS/SG harbor seals experience a significantly different photoperiod (P <0.001) of 10.8 h/day at 68 days post partum. Progesterone and testosterone levels support an hypothesis that these two populations may be reproductively isolated, as coastal male seals show low testosterone levels during the breeding season for PS/Sc seals. A proposed photoresponse at 68 days post partum occurs at the midpoint between estrus and implantation. This period is characterized by secondary follicular activity in the ipsilateral ovary and other changes occurring in the uterus and corpus luteum. A response to a specific photoperiod terminating the follicular activity and leading to a specific implantation date is suggested.
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