In the North Atlantic, conception takes place from December to May with a peak month of February with birth taking place from October to March with a peak in December. In the North Pacific off Japan there appears to be two phases of conception, the majority of which occurs from February to March but also from August to September, with births occurring from December to January and June to July. In the Yellow Sea stock these two phases have not been noted with conception occurring from July to September and birth peaking from May to June.