They are some of the ocean’s most fearsome predators.
Now, a study has revealed that sharks can be just as dangerous to their mates as they are to their prey.
Gruesome footage reveals the horrendous injuries inflicted by male sharks as they grasp females with their teeth while they mate.
These bloody love bites are now helping scientists piece together the hidden secrets of sharks’ sex lives.
To mate, sharks have to press their bellies together while the male penetrates the female.
That’s a fairly straightforward process for smaller, more nimble species.
However, larger sharks often struggle to line themselves up for long enough.
This means that male sharks often violently bite down on the fins or gills of their mate to hold them in place, inflicting deep cuts in the process.
The researchers looked at ‘mating wounds’ sustained by sand tiger sharks, a species which can grow up to three metres (10ft) in length.
Because these sharks spend most of their time as solitary hunters who mate out at sea, scientists don’t know many of the intimate details of their sex lives.
Although cases of mating in the wild have only rarely been observed, the researchers realised that they could look at mating wounds instead.
Lead author Dr Jennifer Wyffels, of the University of Delaware, told LiveScience: ‘Sharks and rays use their mouths to hold and position females and therefore, mating wounds are common during the reproductive season.
‘Observations of mating for any shark or ray species are very rare so we used mating wounds as indirect evidence for reproductive behavior.’
First, Dr Wyffels and her team observed a group of sand tiger sharks housed at Ripley’s Aquarium of Canada Marine Science Center.
During this time the researchers recorded the sharks mating and saw how the male left severe wounds on the female.
The deepest injuries cut through the female’s skin down to the muscle but were surprisingly quick to heal – closing completely in just 22 days.
By recording those injuries and the healing process, the researchers developed a scale for describing the severity and healing stages of mating wounds.
The scale ranges from fresh, open stage one wounds to stage four wounds which have started to scar over.
Dr Wyffels and her co-authors then applied this scale to photos in the Spot A Shark USA database which collects citizens’ shark sighting images.
They analysed 2,876 pictures of 686 individual sand tiger sharks taken between 2015 and 2020.
These images revealed that the number of stage one wounds rose sharply in late May, suggesting that this is the peak of the breeding season.
By July, the number of fresh wounds had levelled off which indicates that the sharks were either mating less frequently or were doing so less violently.
In their paper, published in Environmental Biology of Fishes, the researchers write: ‘By mid to late summer, mating has ceased based on the lack of stages 1 and 2 mating wounds on females.’
The fact that the number of fresh wounds was highest off the coast of North Carolina also suggests that this is a popular breeding ground for sand tiger sharks.
Likewise, the researchers noticed that this region had a high number of female sharks bearing wounds which had been healing for much longer.
They write: ‘The presence of stages 1 and 2 mating wounds on sand tiger sharks in North Carolina suggests the area is used for mating while females with stages 3 and 4 mating wounds provide evidence that the area also serves as gestation habitat for this species.’
In addition to providing new insights into the lives of these elusive creatures, it also confirms their incredible powers of healing.
In the wild, sharks have been observed to live for long periods of time after suffering seemingly deadly wounds.
During the study, the researchers even found sand tiger sharks which were living with their jaw almost torn off and parts of their skull exposed by wounds.
However, they also found that wounds suffered by the aquarium sharks closed after 22 days and finished scarring over 85 days after being injured.
This rapid healing factor might explain how sharks survive for so long after injuries and why their mating wounds very rarely lead to long-term damage.
WHAT GIVES RISE TO SHARKS’ ‘SIXTH SENSE’?
The ampullae of Lorenzini are visible as small pores in the skin around the head and on the underside of sharks, skates, and rays.
Each pore is open and connected to a set of electrosensory cells by a long canal filled with a clear, viscous jelly.
The AoL jelly likely contributes to this electrosensing function, yet the exact details of this contribution remain unclear.
‘Skates and sharks have some of the most sensitive electroreceptors in the animal world,’ said Dr David Julius, professor and chair of physiology at UCSF and senior author of a recent study on the mechanism.
‘Understanding how this works is like understanding how proteins in the eye sense light – it gives us insight into a whole new sensory world,’ he said.
