Environmental and physiological factors controlling the reproductive cycles of pinnipeds

The reproductive pattern of pinnipeds is characterized by embryonic diapause, annual reproduction, and synchronous breeding cycles. Active gestation generally last c8 months. In most species, implantation occurs when day length is declining, and a photoperiod of c12h may provide the signal for implantation in some species. Other proximate factors may include sea temperature. Pinnipeds have reproductive cycles with an active and an inactive phase. The inactive phase may be equivalent to the period of embryonic diapause. Transition from the inactive to the active phase and reactivation of embryonic growth are probably controlled by the same environmental cues. -from Author