• SharkieSophie

Do a Little Dance, Make a Little love

Updated: Apr 27

Because they live in environments which are challenging for scientists to see, there are many things we do not yet know about sharks... What is especially elusive are shark mating rituals. In fact, there are many species of sharks that we have never witnessed mating in the wild.


However, 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 and were able to describe how they go about making baby sharks...


The researchers described the mating sequence in 6 sections:

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).

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!

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...


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.


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).


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 behaviour of these sharks that we did not know before. 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 m 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).


In this region, these hammerheads form large schools seasonally, which were thought to be for finding a mate. 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. After the act was complete, they headed back into the school separately and it is more than likely that that was that- 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 m total length (or around 4 or so years of age, depending on how rapidly they grow)... the whole cycle can begin again.


The reproductive migration cycle of scalloped hammerheads (Salinas-de-León et al, 2017)

To learn about other shark's mating rituals, you can check out Fifty Shades of White.



References

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.

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