The giant devil ray is an indubitably fantastic name for an aquatic creature, and it certainly lives up to it. Technically known as Mobula mobular, this beastie is not only the largest of its genus, reaching lengths of 6.5 meters (21 feet), but its head’s downward-pointing cephalic fins certainly give it the appearance of some hellish horns.
Plenty about its life cycle remains enigmatic, however, which is why a new study, spotted by New Scientist, is such a boon. It describes the first observation of the courtship behavior of the giant devil ray, with an accompanying video featuring one pregnant female fending off the advances of four males.
The New Zealand Journal of Zoology study has just two authors: Scott Tindale, a recreational fisherman from Albany, and Clinton Duffy, an Auckland-based marine technical officer at the New Zealand Department of Conservation.
Their footage, obtained in March 2017 in the temperate southwest Pacific Ocean off the coast of Aotearoa, not only documents a never-before-seen phenomenon, but the presence of the pregnant female also confirms that M. mobular breeds (at unknown intervals) in this part of the world, to which they migrate seasonally.
This research isn’t just a curiosity, by the way: it’s vital. Giant devil rays are listed as endangered, according to the International Union for Conservation of Nature (IUCN). Their populations appear to have declined precipitously in recent decades, not only because they have a low reproductive capability, giving birth to a single pup at once, but also thanks to fishing pressures.
The more we understand about their life cycle, the better chance we have at preserving their species.
The incident involved what they refer to as a “mating train” consisting of a full-term pregnant female and four mature males, observed over a period of 147 minutes. In general, you could describe it as an unwelcome chase, as the female spent the entirety of the time evading capture, intentionally swimming close to the surface to stop any of the males successfully mounting her.
The mating train feature, along with such patterns of female avoidance, has been observed in other large mobulid rays. Conversely, the paper notes that, in this instance, “biting of the female was not observed,” possibly because of her near-surface evasive action. No mating scars were spotted. On other occasions, the males appeared to try and bite the female’s pectoral fins, also in vain.
At the same time, no aggression between the competing males was observed.
Whenever the female stopped at the surface, the lead male would essentially prod her abdomen and her cloaca, an all-purpose orifice. All in all, the authors suggest that the mating behavior was very similar to that of the bay ray, Mylobatis californica, both of which belong to the same family.
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