Grey Reef Shark Profile
Sharks in the family Carcharhinidae are known as the Requiem sharks. This name likely doesn’t originate from the same route as the Catholic mass for the dead, but there’s still a certain aptness in the name. These sharks are almost ethereal; effortless in their motions, yet bringing, as sharks often do, a level of ominousness and death to the table.
Many species are reef sharks, and these have perhaps the most optimal balance between speed and agility. Of these, the Grey reef shark, found in one of the most biodiverse habitats on earth, is one of the fastest, but also one of the rarest.
Grey Reef Shark Facts Overview
| Habitat: | Reefs; clear tropical waters from the surface to 280m |
| Location: | Indian and Pacfici Oceans |
| Lifespan: | 20 years |
| Size: | 2.6m (8.5 ft) long |
| Weight: | 33.7 kg (74 lb) |
| Colour: | Grey, countershaded, with a black caudal fin |
| Diet: | Cephalopods, crustaceans, sometimes fish |
| Predators: | Larger sharks: hammerheads, tiger sharks, etc |
| Top Speed: | Possibly more than 40km/h (25mph) |
| No. of Species: | 1 |
| Conservation Status: | Endangered (IUCN) |
Grey reef sharks are native to the Indian and Pacific Oceans and surprisingly rough for their size, and this keeps them competitive in a diversity hotspot with lots of competition.
They’re high-speed animals, though prefer to eat slower food, and are quick to let you know if you’re upsetting them with a peculiar and unmistakable threat display.
Despite their moderate size and being preyed upon by other larger sharks, they have an aggressive demeanor and often dominate many other shark species in coral reefs.
Grey reef sharks are social creatures though, and will often form groups between 5-20 individuals, near their home range of a coral reef.
Sadly, they’re one of the many species coming to the end of the line, evolutionarily and literally, as the fishing industry bleeds them toward extinction.
Interesting Grey Reef Shark Facts
1. They’re faster than most
These are robust, muscular reef sharks with powerful yet streamlined bodies. Like all reef sharks, they’re agile, but unlike many, they’re exceptionally fast.
Some reports suggest they can reach speeds of up to 50km/h, and there are at least credible records of them hitting 40km/h, but typically they prefer to cruise about below 8km/h outside of hunting or chasing bursts.
But they don’t often eat fast food. Instead, they prefer to ambush slow-moving cephalopods and crustaceans: animals that hide in the rocks, rather than flee at pace.
And evolution doesn’t favour traits that have no survival benefit to an organism; those resources would be better spent elsewhere.
So, why did they evolve to swim at such speeds?
2. They’re not apex predators
One reason might be that these aren’t the biggest fish in the pond. While grey reef sharks are formidable, ancient predators, they have the disadvantage of being smaller than some of the even more formidable and ancient predators above them.
As such, they’re common food for much larger sharks like the infamous Tiger shark, who will eat just about anything. So, swimming away quickly could be a good strategy for predator avoidance.
3. They live in one of the most biodiverse ecosystems on Earth
These sharks commonly occupy a region known as the Coral Triangle. This is an area of reef that includes waters around Indonesia, Malaysia, the Philippines and Papua New Guinea – countries that are well known for their biodiversity on land, but all of which also have astonishing marine habitats too.
There are almost 600 species of coral in these reefs, and consequently, around 2,000 species of fish. The reefs are teeming with life, and when that’s the case in any ecosystem, it means they’re also teeming with competition.
Grey reef sharks compete directly with Sandbar sharks, which are also requiem sharks, roughly the same size, and eat more or less the same thing in the same environment. As such, areas where Greys are present have lower levels of Sandbars, and vice-versa.
So, it may pay to be speedy – not simply to chase prey, but to get to it before the competition does.
But there are other reasons to be fast. 1
4. They engage in courtship ‘chases’
We typically frown upon and discourage this behaviour in our societies, but physically chasing down a mate is actually a very common and effective way (in other species) for a female to select the fittest individuals to produce offspring with.
In Grey reef sharks, this courtship ritual involves several males trying to keep up with a female and demonstrating their genetic advantages in the process. The faster the male, the faster his offspring is likely to be, and the more likely they will then be to outpace a predator on the reef when their time comes.
So, there’s a sexually-selected element to this shark’s exceptional speed, too, as only the fastest will have the best chance of passing on their genes with a mate. Once the female decides on a mate, however, things don’t get any easier for her. 2
5. The catch is really violent and dangerous
On catching the female, the male will, for some reason, bite into her body and fins as part of the copulatory routine, causing a worrying amount of damage.
These bites may contribute some stability to what is essentially a zero-G manoeuvre, but it can cause substantial damage and exhaustion to both parties and when mating is complete, this can leave the sharks vulnerable to predation by much larger dangers like Great Hammerheads. 3
6. Grey reef shark are viviparous
This means the embryo is developed inside the body of the mother through a placental connection.
Grey reef sharks will give birth to litters of between 1-6 pups every other year and the gestation period ranges from 9-14 months.
7. They are opportunistic feeders
Grey Reef sharks are mesopredators. This is a term used to generalise a type of predator that occupies a level somewhere between the big boys at the top and the tiny little arthropod eaters at the lower levels of the trophic hierarchy.
It’s not a strict term, but it is useful in understanding where, roughly, an animal sits in its ecosystem.
On land, mesopredators are things like foxes, coyotes and jackals. One thing that’s very common among them is unfussed they are about where their food comes from, and this is something grey reef sharks have also taken onboard.
While the predominant prey items in the Greys’ diets are crabs, squid and octopus, they are partial to some fish now and then.
This ability to hunt is more likely a by-product of their speed, rather than a cause of it, as they don’t appear to be very good at the practice.
One study showed that the vast majority of attacks on fusiliers fish resulted in around 5% of ‘investigations’ and 16% of bite attempts actually hitting their mark.
As such, this is more of a product of a generalist predator than a specialist; one that feeds at various levels in the trophic web and will take what they can get. The perfect strategy for an ecosystem with a diverse range of potential prey.
Sometimes, the victims are divers.
8. They’ll attack people
These sharks give off one of the most obvious threat displays of any shark when they’re feeling nervous.
This aggressive posture and willingness to back it up with violence are what allows them to maintain their position in the reef against, sometimes, much larger species of shark.
The threat display consists of a contorted and stiff body position that suggests the shark is very uncomfortable with how close you’re getting.
Unfortunately for divers, it’s also what makes them one of the commonest sharks implicated in attacks on the reef. No deaths have been recorded, on account of the shark’s relatively small size and the fact that we probably taste awful, but this doesn’t imply the bites are particularly fun or safe to receive.
They’ve even been known to attack submersibles that they deem unworthy. 4
9. They have an incredible sense of smell
Their sense of smell is extraordinarily sensitive, capable of detecting one part tuna extract in ten billion parts sea water.
Grey reef sharks may be stirred into a feeding frenzy in the presence of lots of food. One documented event witnessed an undersea explosion that killed multiple snappers and one of the sharks engaged was attacked and consumed by the others.
10. They’re in serious trouble
Populations of these beautiful animals are in steep decline, and this is in huge part related to the inefficient and destructive practices of the global fishing industry.
Grey reef sharks make up a portion of the 100,000,000 sharks killed by mistake every year (yes, you read that correctly, 100 million sharks each year) in nets and on longlines aiming for food species for global demand.
Fisheries targeting reef teleosts like grouper and snapper commonly snag Greys, killing them in the process. In the Papua New Guinea Shark Longline Fishery, they’re the second commonest species of shark brought up.
In East Africa, they’re one of the specifically targeted species, and they’re also collected for private and public aquarium collections.
As fish stocks reduce, the human response is to send more ships. As nets and lines increase, stocks decrease even further, and the bycatch of sharks increases.
Climate change is also leading to reduced reef health and coral bleaching events, essentially destroying these rich habitats for the sharks.
As a result, this species, like many others, is on its way out. Few species-specific programs are focussing on its protection, but general reef conservation efforts do show promise if they are enforced. Ongoing training and capacity building are crucial to the success of this species. 5
Grey Reef Shark Fact-File Summary
Scientific Classification
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Order: | Carcharhiniformes |
| Family: | Carcharhinidae |
| Genus: | Carcharhinus |
| Species Name: |
Carcharhinus Amblyrhynchos |
Fact Sources & References
- “Coral Triangle”, World Wild Life.
- “Know about the habitat and mating behavior of grey reef shark”, Britannica.
- W. D. Robbins (Year), “Foraging mode of the grey reef shark, Carcharhinus amblyrhynchos, under two different scenarios”, Springer Link.
- Johann Mourier (2017), “Agonistic display Grey reef shark”, Vimeo.
- “Grey Reef Shark”, IUCN Red List.