I discovered my passion for sharks when I travelled around the world at the age of 19. I spent a lot of time scuba diving with a wide range of species, but nothing captivated me like the sharks that surrounded me on one amazing encounter in South Africa. (You can watch a video of my experience here).
Encountering these animals in the wild solidified my choice to study marine biology, and since then I have spent time learning about these animals via scuba diving, visiting aquariums, researching and writing articles about their biology, and talking about sharks with people worldwide.
I find it very interesting how sharks are often portrayed as large, voracious predators, when in reality most shark species are smaller fishes that are susceptible to predation.
There are approximately 500 species of sharks and only a small proportion of these are apex predators — animals at the top of the food chain. The majority of shark species are smaller mesopredators — animals that are predators, but are also often food for other species. The Vancouver Aquarium Marine Science Centre has four different species of sharks, the blacktip reef shark, zebra shark, white spotted bamboo shark and the epaulette shark, all of which are mesopredators.
In reality, all sharks are susceptible to predation during the smaller juvenile stages of their lifetime, while even larger species, such as whale sharks, tiger sharks and great whites may sometimes end up as a meal for other animals. Documented predators of sharks include larger sharks, marine mammals, bony fishes, crocodilians, octopuses and humans, and it is possible that more animals may include sharks in their diet from time to time. Nevertheless, it’s probably not easy to snack on a shark because these animals have evolved many strategies to ward off potential predators.
One common way sharks avoid becoming food is by hiding from their predators. Many mesopredator and juvenile sharks select habitats where larger predators are relatively rare or have difficulty entering. Often, they seek out the shelter of crevices, reefs, plant life or hang out in shallow water.
If you’ve seen sharks up close, you may have noticed that their undersides tend to be a much lighter colour than the backside; this is called countershading. Countershading helps a shark camouflage in its surroundings. The underside of the shark is often a light shade, close to white, so it creates less of a shadow against the sunlit waters when viewed from below. When viewed from above, the backside of the animal tends to resemble the environment where the shark commonly resides. Pelagic or neritic sharks — sharks that spend most of their lives swimming— often have dark blue or grey backsides that blend into the surrounding waters. Benthic sharks — sharks that spend most of their lives along the sea bottom, such as the zebra, white spotted bamboo shark and the epaulette shark at the Vancouver Aquarium — often have a pattern on their backsides that blend into the sea bottom.
The epaulette shark even goes as far as “walking” along the sea bottom to avoid being noticed. Using its fins to push off of the ground to move forward, walking is a strategy that allows the shark to stay close to the bottom where it can camouflage into its surroundings.
However, hiding from a threat does not guarantee safety. Many predators can track prey by sensing electrical impulses or smell, so sharks have other strategies to outwit predators.
To reduce the likelihood of being attacked by a predator, many shark species will travel in large, loose groups, a behaviour called shoaling. For example, in Kaneohe Bay, Oahu, groups of scalloped hammerhead juveniles can reach up to 10,000 individuals. In such a large group, the probability of a single individual being attacked by a predator is greatly reduced compared to encountering an attacker one-on-one. Therefore, although bigger groups may seem counterintuitive by revealing more prey to a predator, sharks can actually find safety in numbers.
In situations where an individual has to defend against an attack, sharks can perform escape manoeuvres called C-starts. These moves are defined by the muscles on one side of the body contracting to bend the shark’s body into a C-shape. This allows them to quickly change the direction they’re swimming. This agile move is then followed by a return flip of the tail, which will accelerate the shark away from the predator in the new direction.
Some sharks, for example spiny dogfish and horn sharks have even evolved sharp and poisonous spines in front of their dorsal fins, making these animals very dangerous to bite and swallow. Sharks may even react in self-defence with their own attack when exposed to threatening behaviours.
When I was younger, the word “shark” came with a great amount of intimidation and fear based on the way they are represented in the media. However, the more I take the time to learn about these animals, the more I come to realize the public tends to be misinformed about the reality of sharks. These animals show tremendous diversity in their shape, size, coloration, behaviour, and lifestyle. Researchers believe that the evolution of this great amount of diversity has been most likely fueled by millions of years of predator-prey interactions.
It’s my hope that by studying and writing about these animals, I can help people understand that sharks aren’t a threat to human safety, but an integral part of our oceans’ ecosystems.
Blog post by Scott Seamone, a PhD student at the University of Calgary