First documented evidence of a mating event of blue shark ( <i>Prionace glauca</i> ) in the pelagic zone off Baja California Peninsula

Understanding the reproductive behavior of elasmobranchs (sharks and rays) remains a significant challenge due to the elusive nature and habitat preferences of many species. In addition, relatively few species are successfully bred in captivity. The blue shark ( Prionace glauca ) is one of the most abundant and wide-ranging pelagic shark species, yet the species’ mating behavior or even courtship attempts have never been documented. Here, we report the first direct observation of P . glauca mating behavior in the pelagic zone off the southern tip of the Baja California Peninsula. This rare behavioral sequence provides critical insight into the reproductive ecology of the species and represents the first in situ account of any kind of copulatory behavior in a pelagic carcharhinid shark. Our findings underscore the value of opportunistic behavioral observations by recreational divers and the urgent need for increased behavioral monitoring in the pelagic realm to support the effective conservation of vulnerable and declining elasmobranch populations.