Whale shark and diver. Photo credit: Tongkan Worapanya.
Sharks are the most vilified and misunderstood creatures in our oceans. Danielle Crowley dives into their world to reveal some of their secrets, and their biggest threats.
When you think of sharks, what comes to mind? When sharks find themselves in the public eye, it is often for the wrong reasons. They are “man-eaters” and “public menaces”. But this isn’t entirely accurate.
Sharks are ancient having first evolved about 400 million years ago, long before the dinosaurs. Their body design hasn’t changed much, showcasing an evolutionary masterpiece that is perfectly suited to their environment. Sharks are able to detect changes in electrical and magnetic fields, changes in water pressure, low frequency sounds and, most famously, blood from up to a quarter of a mile away, even in quantities of one part per million of seawater. This allows them to hunt efficiently, even in darkness.
The world’s largest sharks prey only on plankton. These gentle giants include the whale shark and the basking shark, which is found in Ireland’s waters during the summer months. They can reach 12 meters in length.
In comparison the dwarf lanternshark, the smallest shark, can reach truly terrifying lengths of 20 centimetres. The larger velvet belly lanternshark, also a deep water species, has light producing photophores on its belly to avoid detection by both its prey and predators. Their bellies glow causing them to disappear against the paler surface when seen from below. They also have glowing spines on their dorsal fins like lightsabers. Researchers believe that these warn away predators.
The most feared shark, the great white, is the largest predatory fish at six meters long although most are smaller. They have a reputation as mindless killers, but this is more fiction than fact. It is now coming to light that these sharks have impeccable manners. They love to feast on dead whales, but form orderly queues leaving the largest sharks to eat first. When they encounter one another, they observe each other closely and the smaller will give way to the larger.
They even extend this courtesy to humans. Sharks will mostly ignore or keep their distance from humans, although some are curious and study humans just as much as we study them. When a human begins to overstay their welcome, the sharks will let them know using body language such as lowering their pectoral fins or arching their backs.
Sharks can be solitary, but whitetip reef sharks are social. During the day they rest together and once night falls they hunt together. Juvenile lemon sharks make friends. Their mothers swim into shallow waters near mangroves to give birth, since it gives their pups the greatest protection. Once born, the young sharks stay there for seven or eight years learning to hunt, often with one other particular shark.
Some species give birth to live young and others lay eggs. The mermaid’s purses found on beaches are the egg cases of dogfish. What is even more amazing is the fact that some of them can reproduce with no need for a male. This is called “virgin birth” and has been suggested as a survival strategy for isolated females.
Sharks have often been portrayed as dim witted animals but that simply isn’t true. Mother lemon sharks return to the same mangroves they were born in to give birth. Tiger sharks travel to areas where they know they’ll find food, such as the nesting sites of albatross and turtles. Their timing is uncanny, yet no one knows how they do it. Close relatives of sharks — manta rays — have the largest brains of any fish. They appear to have distinct personalities and have been reported to seek out divers to remove fishing line from their bodies. They are the largest rays, stretching eight meters from wingtip to wingtip.
Sharks are amazing, but endangered. Unlike “cute” animals such as pandas, sharks have such a bad reputation that no one seems to care about them. Each year, we kill 100 million sharks (the entire population of Spain, France and Austria) through by-catch, “revenge” culling and sport fishing. That’s three sharks every second. At most, sharks kill roughly five to seven people annually. Dogs kill 25,000.
The biggest culprit is “finning”, a practice where the shark is caught, its fins are removed, and it’s thrown back in the water to die. All for shark fin soup, which is toxic and has no nutritional value. Populations of oceanic whitetips have been decimated as a result, numbers are down by almost 99% in some places. They used to be one of the most numerous species.
Sharks are keystone species. If they are removed the ecosystem collapses, along with the wellbeing of the people who depend on it. We all depend on the oceans, therefore we all need to help protect sharks. As conservationist Ian Fergusson says: “Sharks are cool fish to have in the ocean, and wouldn’t it be a boring place without them?”