Because they live in environments which are challenging for scientists to see, there are many things we do not yet know about sharks... Especially elusive are shark mating rituals. In fact, there are many species of sharks that we have never witnessed mating in the wild. So do sharks have courtship rituals? And how do they mate? Well... it turns out, quite violently!
Hammer Time
Recently a research team were lucky enough to see hammerhead sharks (Sphyrna lewini) mating in the Isla del Coco National Park (aka the Cocos Islands), in the Eastern Pacific Ocean. They were able to describe how these hammerheads go about making baby sharks - identifying 6 distinct parts to the mating ritual:
1. THE OPEN-WATER ENCOUNTER (the approach)
The female hammerhead was approached by the male for mating (no surprise there, huh, ladies?!). He swam up to her, high in the water column, far from the ocean floor. Both sharks were of a similar size (2.5 m total length) and initially wall in parallel to each other near to the surface of the water (within 5m of the surface) (Salinas-de-León et al, 2017).
2. PRE-COPULATORY BITING (the flirt)
The male grasped the female's pectoral fin in his mouth. This move is common amongst sharks as mating begins- it seems to be a universal shark flirting signal. At this point the male also arched his pelvis forwards, in order to keep his claspers (the male reproductive organs) near to the female's cloaca (female reproductive opening). This phase only lasted 24 seconds! (Salinas-de-León et al, 2017).
3. THE COPULATION (the good bit)
The sharks slowed their swimming considerably and the male inserted one of his two (yes, two!) claspers into the female and began vigorous thrusting. The female remained motionless with her jaws wide open (*blush*). The male remained latched onto the pectoral fin with his teeth during this phase and the next... (Salinas-de-León et al, 2017).
4. THE FREE FALL (the post-coital embrace)
Both sharks completely stopped swimming and began to sink, in a spiral trajectory, towards the ocean floor. They remained motionless on the bottom for 18 seconds, still entwined (Salinas-de-León et al, 2017).
5. SEPARATION (it's all over)
The male withdrew both his claspers and his teeth...
6. POST-COPULATORY FOLLOWING (a long goodbye)
Both sharks returned to their normal swimming orientation and the male followed the female around, at a distance of 1 metre, for 30 seconds, as she slowly swam near to the "substrate" (aka ocean floor) (Salinas-de-León et al, 2017). these sharks' mating rituals
From start to finish the whole event lasted 01 min 32 sec... disappointing?!... Not to us sharks nerds! Because witnessing this event taught us a lot about the mysterious behaviour of these sharks (Salinas-de-León et al, 2017).
Free Falling
The researchers noted that they witnessed many behaviours (biting and lying on the bottom, for instance) that are seen when other species of sharks mate, like the whitetip reef shark (Triaenodon obesus) (Salinas-de-León et al, 2017).
But they also noticed that there were behaviours which made the scalloped hammerhead mating unique; namely the freefall. Instead of commencing mating near to the bottom, like many reef sharks do, mating began near to the surface and the couple sank as much as 40 metres though the water column whilst mating, before reaching the ocean floor. The researchers suggested that, in fact, it seems likely that this freewill might often be even longer and deeper, as mating is thought to occur commonly further out to sea (Salinas-de-León et al, 2017).
Getting Schooled
Scientists suspect that scalloped hammerheads come to the Cocos Islands and form large schools on a specific schedule, so that they can find a mate. But this study shows us that may not be the case. It is possible that this couple met whilst in the school, but the copulation itself took place in a relatively private space, away from the rest of the group and after the act was complete, they headed back into the school separately (Salinas-de-León et al, 2017).
Sharks do not mate for life or stay together to rear their offspring, in fact, they do not invest in caring for their offspring at all after they are born... The pregnant female would eventually move back towards to coast to give birth to her pups, around March to April (around 12 months later). The babies would be left in a mangrove region which acts as a "nursery ground"; offering the young ample food supplies and relative safety from predators, until they themselves are grown enough to venture out to sea... When they reach sexual maturity at approximately 2 metres total length (around 4 or so years of age, depending on how rapidly they grow)... the whole cycle can begin again (Heupel et al, 2007; Salinas-de-León et al, 2017).
Alright, Mate!
You might think it's a bit creepy that scientists are so curious about how sharks mate, but in fact, we are not just being seedy! Understanding where and how sharks breed is vital for conservation and management planning. Now that we know that this area is a critical scalloped hammerhead mating habitat, we can ensure that the region is correctly protected. As these hammerheads are considered Critically Endangered, it will be essential to continue to the protect the beautiful Cocos Islands, so that this species can continue to mate and reproduce, and bolster their population sizes on a global scale (Salinas-de-León et al, 2017; IUCN, 2017).
To learn about other shark's mating rituals, you can check out Fifty Shades of White.
References
Heupel MR, Carlson JK & Simpfendorfer CA (2007). Shark nursery areas: Concepts, definition, characterisation and assumptions. Marine Ecology Press Series, 337, 287-297. Access online.
IUCN (2017). The International Union for Conservation of Nature Red list of Threatened Species. Access online.
Salinas-de-León P, Hoyos-Padilla EM & Pochet F (2017). First observation on the mating behaviour of the endangered scalloped hammerhead shark Sphyrna lewini in the tropical
Eastern Pacific. Environmental Biology of Fishes, 100:11, 1603-1608. Access online.
By Sophie A. Maycock for SharkSpeak
