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Keywords:

  • Zalophus californianus;
  • California sea lion;
  • reproduction;
  • photoperiodism;
  • seasonality;
  • birth timing;
  • captivity;
  • delayed implantation

Abstract

A population-based analysis was used to evaluate the role of photoperiod in regulating the precise annual birth timing of captive California sea lions. Latitudinal variation of 463 birth dates was explained by a response to a common photoperiod, 11.48 h/d, occurring 242 d pre-partum and immediately before blastocyst implantation. The lengths of the pupping seasons at the 18 largest captive colonies were significantly correlated to those estimated by the photoperiod model. Hence, the phenology of birth in this species is defined by photoperiod.