Photoperiod and reproduction in captive female Northern fur seals*

The reproductive cycles of captive female Northern fur seals (Callorhinus ursinus) were unaffected over two consecutive years by a photoperiod that differed substantially from that of the natural range. Breeding was observed in July and August, or at the same time as in the wild. Growth was comparable in captive and wild fetuses, indicating a similar timing of delayed implantation of the blastocysts.