The authors have retracted this article because they discovered after publication that the observer did not observe the birth moment of the seal pup twins as stated in the article. The authors also stated that the observations were done daily throughout the survey period; however, they have now discovered that the observations were done weekly although it was done daily at near twin observation period. As these factors directly influenced the conclusions of the study, the authors have agreed to retract the paper. All authors agree to this retraction.

The online version of this article contains the full text of the retracted article as Supplementary Information.