Marine Creature of the Month March '20

Marine Creature of the Month

Famous Fish: Jaws

Poster from arthipo

Great White Shark 

As March is my Birthday Month (yes, I milk it for that long) I thought it was high time I covered the OG Famous Fish on #MCotM. 

Photo from Oceana

Kingdom: Animalia

Class: Chrondrichthyes

Conservation Status: Vulnerable

WHAT IS JAWS?

Thanks to the 1975 blockbuster, Jaws, the great white shark is possibly one of the most famous sharks swimming about in the ocean. It belongs to the Mackerel Shark family, which also contains basking sharks, goblin sharks, and thresher sharks. Great whites are known for their size, being among the biggest sharks alive today. Females are larger than the males, averaging at 4m (13ft) for the males and 4.9m (16ft) for the females. Certain specimens have been known to grow as large as 6m (20ft), like the one living off the coast of Mexico known as Deep Blue. 

Like all sharks, great white skeletons are made out of cartilage rather than calcium, like our bones, with the exception of their jaws and teeth. This is why fossils found of sharks tend to only be their jaws and teeth. You can even find loose teeth along the coast, as their teeth regularly fall out. Instead of swimming about toothless, sharks have a constant conveyor belt of teeth which move forward and grow to replace those that have fallen out. This continues throughout their life, seemingly never running out. (Check out this Today I Found Out video for more on shark teeth!)

Sharks have been on our planet for longer than flowers. (Yeah, wrap your noodle around that one!) They are at their evolutionary peak and have largely remained unchanged for millions of years. Great white sharks are apex predators, meaning they are at the top of their food chain and not generally predated themselves. Everything about the great white has been perfected to making them the efficient hunters we know and love.

WHAT DOES JAWS LOOK LIKE?

Think of a stereotypical shark - torpedo shaped, dorsal fin, teeth. Yep, that is a great white. Now, you would think a shark named a great white would be entirely white but it's not. Because humans are actually fantastic at naming things. (I'm looking at you, killer whale.) They use a camouflage tactic many other aquatic creatures have evolved too; they are light on their underside and dark on their topside. This protects them from being sighted from both above and below as they blend in. Looking up, they are protected by the light; looking down, they are the same colour as the water. This is known as countershading.

Their skin is made of denticles which are tiny teeth! This is common across all sharks and gives them a rough texture, rather than scaled. In other species, fish have been observed to scratch dead scales off their sides using the rough skin of a shark - but I doubt many are brave enough to use a great white as a scratching post! I certainly wouldn't be and I love me a great white shark! 

Across their snout and face, great whites have what look like they could be freckles but are in fact ampullae de Lorenzini. These dark spots detect the electromagnetic field emitted from all living things. Sharks use these when hunting their prey, being able to pick up the slightest movement. The great whites can use these to detect half a billionth of a volt because theirs are incredibly sensitive! This translates to being able to detect an immobile fish from its heartbeat alone. How incredible?!

From my own shark diving experience!

WHAT DOES JAWS GET UP TO?

Great white sharks are migratory fish, meaning they are constantly swimming. They are the type of shark which actually has to always be swimming in order to force water over its gills and breathe. Some sharks can buccal breathe (pump their gills to create movement in the water) but great whites are not among those that can. They also cannot swim backwards because of this, so Jaws 3D check your facts! (Also, how hilarious is that CGI!)

As mentioned before, great whites are hunters. They generally eat seals, sea turtles, big fish like tuna, rays, and other sharks, crustaceans, porpoises... the list goes on. These bad boys will eat whatever they can get their teeth on. When attacking their prey at the waters' surface, they tend to approach quickly from the underside and breach the water as they chomp down on their dinner. They burst to the surface at speeds of 40 km/h (25mph) and can jump up to 3m (10ft) above the waters' surface. They are adaptable hunters, though. How they attack their prey varies on where they are. With bigger prey, they will bite and hold on until they've bled out. They have been observed dragging prey to great depths to stop their struggling.

But an important source of their diet comes from whale carcasses, which shows that they are scavengers too. 30kg (66lbs) of whale blubber can feed a great white for a month and a half, although the only evidence of this happening comes from whale carcasses washing ashore. Whales tend to die in remote areas and get nibbled at as the currents carry to body. When biting on their prey, whatever size, great whites shake their head to utilise the serrated edges of their teeth. This tears through their prey's flesh and leaves the shark with a happy tummy. Their diet is generally made of fatty marine animals, so great whites are actually warm blooded, even in colder waters, to aid in digestion.

Great white sharks tend to live in mid-temperature waters across the globe. They are found off the coast of Mexico, South Africa, Japan, Australia. A lot of great white habits actually remain largely unknown because they can dive up to 1,200m (3,900ft). They tend to live in isolation but have a size dictated hierarchy - the large ladies rule. Their social structure is a little more complex than that and that is probably down to the fact that we can't observe them at certain depths. Some sport bite mark scars which would suggest fighting between sharks but as it occurs so infrequently it is postulated that they give each other warning bites rather than full out fisticuffs. 

It takes great whites about twenty-five years to reach sexual maturity. Their life span is seventy years on average and the females carry their young for twelve months. They have a slow reproductive cycle, which has led to a decline in their numbers (but more on that later). Great whites are ovoviviparous sharks, meaning they carry eggs which hatch inside them and then give birth to live young. There can be anything between two and thirteen pups birthed. (Hands up who'd rather the lower end of the scale!) Their mating and birthing habits have yet to be observed, maybe they get down at 1,200m! It has only been confirmed how they give birth by pregnant sharks being caught and studied. (Or, tragically, killed.)

WHAT THREATENS JAWS?

Being an apex predator, great whites have few predators themselves. Juveniles and smaller sharks are at risk from orcas who take advantage of the fact that sharks will go into a state of tonic immobility when held upside down. Do it long enough and the shark will suffocate as water is not moving across their gills. Orcas are alone in being their only natural threat.

Once again, humanity is directly responsible for the great white sharks' vulnerable conservation status. This is largely because of their slow reproductive cycle. Great whites are not quick breeders. Nor do they mature quickly. As a result, their populations simply cannot keep up with the amount of sharks being killed by humans - either directly for shark fins or indirectly from pollution. Great whites are rarely the target of commercial fishing, but they are susceptible to being a by-catch and ghost fishing. Ghost fishing is where nets and fishing equipment are just left in the ocean and trap unsuspecting fish and marine mammals. If a great white gets caught in a net, it will suffocate.

The other main problems facing great whites is the bad reputation they have unwillingly grown over the years. This is largely attributed to Jaws once again. After the film aired in 1975, media platforms took to sensationalising shark sightings every summer after that. They are referred to as killers or man-eaters, and rarely noted for their beauty and migratory habits. This has lead to a global fear of sharks and great whites in particular. Which seems to give many a "free pass" for killing them. Countries create shark culling programmes despite also listing them as a protected species. Shark charity Bite Back have a Mind Your Language campaign, calling out news articles which do this very thing. It seems the world has forgotten that Jaws was a work of fiction. Barely any sharks are "man-eaters" and very few which venture towards the coast actually bite people.

Not to minimise the damage that a great white can do to a person because those teeth are sharp. They are predators. But, the likelihood of being attacked by a great white is phenomenally small. The numbers vary, but it's something like sharks fatally attack less than five people a year whereas we kill them in the millions. Remember how you always used to be told as a kid that "the spider is much more afraid of you than you are of it"? I think this is something we need to remember and take into consideration when reporting on sharks just swimming about.

Photo from Bloomberg

FUN FACTS

• Not directly about great whites, but Jaws was the first blockbuster film because people queued around the block waiting to see it in the cinema.
• And the animatronic puppet shark was called Bruce (hence every shark since being called Bruce).
• He kept breaking down and delaying production, giving the film a lot of media attention, hype, and the eventual summer release.
• Enough about Jaws now. Sorry, not sorry. Jaws facts are my ice breakers!
• A great white shark has been recorded swimming 17,703km (11,000miles) in just nine months!
• The biggest great white recorded was 7m (22ft) long.
• The largest clutch of pups was fourteen which was unfortunately found out by cutting open a pregnant great white.
• It is difficult to keep great whites in captivity. A few larger aquariums have tried with very little success. The sharks tend to die after only a few days.
• The longest one was kept in captivity for was 30 days.
• Great whites hunt during the day time.
• They roll their eyes back during the final stages of the hunt, to protect them from their thrashing prey.
• The biggest of their teeth measure 5cm (1.9inches) long.

I should probably call it a day there. It seems I could talk about sharks for days. I was even bombarding my six month old nephew-ish (my cousin's kid) with all the shark facts! He sort of enjoyed it!

Photo from WWF

Which is your favourite shark? Know any other good facts about great whites? Can you name any other types of sharks featured in films? (Creature feature frankensteinien sharks allowed.)

Who should be me next Famous Fish? Lemme know, below!

Listening to: Cheesy Hits